doi.org/10.26434/chemrxiv.11911383.v1

An Iron Pyridyl-Carbene Catalyst for Low Overpotential CO2 reduction toCO: Mechanistic Comparisons with the Ruthenium Analogue andPhotochemical PromotionSergio Gonell, Julio Lloret, Alexander Miller

Submitted date: 02/03/2020 • Posted date: 02/03/2020Licence: CC BY-NC-ND 4.0Citation information: Gonell, Sergio; Lloret, Julio; Miller, Alexander (2020): An Iron Pyridyl-Carbene Catalystfor Low Overpotential CO2 reduction to CO: Mechanistic Comparisons with the Ruthenium Analogue andPhotochemical Promotion. ChemRxiv. Preprint. https://doi.org/10.26434/chemrxiv.11911383.v1

Electrocatalysts for CO2 reduction based on first row transition metal ions have attracted attention asabundant and affordable candidates for energy conversion applications. We hypothesized that a successfulstrategy in ruthenium electrocatalyst design, featuring two chelating ligands that can be individually tuned toadjust the overpotential and catalytic activity, could be equally applicable in the analogous iron complexes.New iron complexes supported by a redox-active 2,2':6',2''-terpyridine (tpy) ligand and strong trans effectpyridyl- N-heterocyclic carbene ligand (1-methyl-benzimidazol-2-ylidene-3-(2-pyridine)) were synthesized,and these isostructural analogues to leading ruthenium catalysts were also found to be active CO2 reductionelectrocatalysts. Electrochemical and computational studies reveal completely distinct mechanisms for theiron and ruthenium complexes, with hemilability in the iron system enabling electrocatalysis at overpotentialsas low as 150 mV (ca. 500 mV lower than the ruthenium analogue). Cyclic voltammetry studies elucidated themechanism of the net 4e–/2H+ process that occurs within the single reductive feature, with an iron solventocomplex undergoing reduction, CO2 activation, and further reduction to an iron carbonyl. The mechanisticinsight guided development of photoelectrocatalytic conditions under a continuous flow of CO2 that exhibitedimproved performance, with Faradaic efficiency up to 99%.

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An Iron Pyridyl-Carbene Catalyst for Low Overpotential CO2 reduction to CO:

Mechanistic Comparisons with the Ruthenium Analogue and Photochemical Promotion

Sergio Gonell,a,b,* Julio Lloret-Fillol,b,c,* and Alexander J. M. Millera,*

a University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3290 United States

b Institute of Chemical Research of Catalonia (ICIQ), The Barcelona Institute of Science and

Technology, Avinguda Països Catalans 16, 43007 Tarragona, Spain

c Catalan Institution for Research and Advanced Studies (ICREA), Passeig Lluïs Companys,

23, 08010 Barcelona, Spain

Corresponding Author E-mail Addresses:

sgonell@iciq.es (S.G.)

jlloret@iciq.es (J.L.)

ajmm@email.unc.edu (A.J.M.M.)

Abstract

Electrocatalysts for CO2 reduction based on first row transition metal ions have attracted

attention as abundant and affordable candidates for energy conversion applications. We

hypothesized that a successful strategy in ruthenium electrocatalyst design, featuring two

chelating ligands that can be individually tuned to adjust the overpotential and catalytic

activity, could be equally applicable in the analogous iron complexes. New iron complexes

supported by a redox-active 2,2':6',2''-terpyridine (tpy) ligand and strong trans effect pyridyl-

N-heterocyclic carbene ligand (1-methyl-benzimidazol-2-ylidene-3-(2-pyridine)) were

synthesized, and these isostructural analogues to leading ruthenium catalysts were also found

to be active CO2 reduction electrocatalysts. Electrochemical and computational studies reveal

completely distinct mechanisms for the iron and ruthenium complexes, with hemilability in

the iron system enabling electrocatalysis at overpotentials as low as 150 mV (ca. 500 mV

lower than the ruthenium analogue). Cyclic voltammetry studies elucidated the mechanism of

the net 4e–/2H+ process that occurs within the single reductive feature, with an iron solvento

complex undergoing reduction, CO2 activation, and further reduction to an iron carbonyl. The

mechanistic insight guided development of photoelectrocatalytic conditions under a

continuous flow of CO2 that exhibited improved performance, with Faradaic efficiency up to

99%.

TOC Graphic

Introduction

Carbon dioxide (CO2) is an ideal carbon source for the sustainable synthesis of fuels and

chemicals. CO2 utilization by electrochemical reduction holds promise, despite inherent

challenges in achieving selective conversion to a particular carbon-containing product (while

avoiding H2 production) with high activity at low overpotential. Molecular electrocatalysts

have attracted widespread attention for overcoming some of these challenges to achieve high

activity and high selectivity, often through a mechanism-guided development approach.1,2

An emerging design motif in molecular electrocatalysts for CO2 reduction involves pairing a

redox-active supporting ligand with a strongly donating, but redox-inactive supporting

ligand.3–5 The prototypical catalysts following this design are ruthenium complexes supported

by 2,2':6',2''-terpyridine (tpy) and pyridyl-N-heterocyclic carbene (pyridyl-NHC) ligands. The

complex C-trans-[Ru(tpy)(Mebim-py)(MeCN)]2+ (Mebim-py = 1-methyl-benzimidazol-2-

ylidene-3-(2-pyridine)),6 where C-trans denotes the isomer with the NHC carbon sitting trans

to the monodentate ligand, can achieve high activity without sacrificing overpotential.

Mechanistic studies of isolated isomeric C-trans and N-trans (isomer with the N atom of the

Mebim-py trans to the monodentate ligand) Ru complexes indicate that the high activity is a

direct result of the strong trans effect of the NHC ligand.6 This phenomenon,7 commonly

invoked in organometallic chemistry but rarely connected to electrocatalyst performance, can

explain the dramatic acceleration of CO ligand dissociation when the strongly s-donating

NHC sits trans to the active site. The overpotential is separately controlled by the redox-

active tpy ligand in these complexes, leading to a situation where the kinetics of key chemical

steps and the reduction potential that initiates electrocatalysis are decoupled.

To date, this approach of independently tunable reduction potentials and chemical kinetics in

CO2 electroreduction has only been explored for ruthenium complexes. Yet we hypothesized

Mechanistically-guided performance optimization

Eo(CO2/CO)

that these design features should be equally applicable to first row transition metal complexes.

For example, both Mn8–10 and Re11,12 complexes that are supported by redox-active bpy

ligands have proven to be active electrocatalysts for CO2 reduction.

Herein we report the synthesis of new iron complexes supported by tpy and Mebim-py and

show that these direct isostructural analogues to a leading Ru catalyst are active and efficient

CO2 reduction electrocatalysts at mild potentials. A single electrochemical feature is observed

under CO2, prompting a mechanistic study that elucidated a rapid 4e–/2H+ transformation

from an iron solvento complex to an iron carbonyl. These studies reveal important differences

between the isostructural iron and ruthenium catalysts, with rapid ligand substitution kinetics

at iron enabling low overpotential electrocatalysis and access to a distinct resting state. The

mechanistic insight guided development of photoelectrocatalytic conditions under a constant

flow of CO2 that show improved activity and Faradaic efficiency.

Results and Discussion

The desired iron complex was synthesized by treating Fe(tpy)Cl213 with the free NHC Mebim-

py (generated in situ, see SI for details) at –78 ºC in THF, followed by addition of KPF6 in

MeCN (Scheme 1). Analytically pure dark-red needles were obtained from a concentrated

CH2Cl2 solution of the complex layered with Et2O. X-ray diffraction studies confirmed the

composition of the product as C-trans-[Fe(tpy)(Mebim-py)(MeCN)][PF6]2 (C-Fe-MeCN2+,

Figure 1), with an octahedral geometry in which the NHC is positioned trans to the

monodentate ligand, MeCN. The sharp, well-resolved 1H NMR signals of C-Fe-MeCN2+

confirm that the complex is diamagnetic with a low-spin d6 configuration. The chemical shift

of the N-methyl resonance is diagnostic of complex geometry in Mebim-py complexes, with

the upfield resonance at 2.78 ppm indicating a C-trans geometry (Figure S1 in the SI).6 13C

NMR spectroscopy shows the characteristic resonance of the metallated carbene carbon at

215.9 ppm (Figure S2 in the SI).

Scheme 1. Synthesis of C-Fe-MeCN2+.

Figure 1. Structural representation of C-Fe-MeCN2+ with ellipsoids drawn at the 50% level. Hydrogen atoms, two PF6 counterions, and dichloromethane solvent are omitted for clarity. Selected distances (Å) and angles (deg): Fe(1)–C(1) 1.922(5), Fe(1)–N(1) 1.997(4), Fe(1)–N(2) 1.978(4), Fe(1)–N(3) 1.985(4), Fe(1)–N(4) 1.870(4), Fe(1)–N(5) 1.985(4); C(1)–Fe(1)–N(2) 171.79(18), N(4)–Fe(1)–N(1) 176.64(16), N(5)–Fe(1)–N(3) 162.30(16).

The C-trans isomer C-Fe-MeCN2+ was the only species detected in spectroscopic studies,

with no evidence for formation of the corresponding N-trans species. Density functional

theory (DFT) computational studies using the B3LYP functional,14 6-311+g** basis set, and

implicit SMD acetonitrile solvation predicted C-Fe-MeCN2+ to be slightly stable than the N-

Fe-MeCN2+ (DGº = 0.5 kcal·mol-1; all computations are reported as free energies).

Cyclic voltammograms (CVs) of C-Fe-MeCN2+ under N2 revealed two reversible features,

one oxidation (E1/2 = 0.63 V vs. Fc+/Fc, ∆Ep = 59 mV, Figure S12 and S13 in the SI) and one

reduction (E1/2 = –1.66 V vs. Fc+/Fc, Figure 2). The peak current of the reduction feature was

twice that of the oxidation wave and the peak-to-peak separation (∆Ep) was only 42 mV,

consistent with a 2e– process.10,15 Multi-segment CVs (Figure S14) over a wide range of scan

rates showed little variation, as expected for an EEC mechanism involving two electron

transfers at the same potential followed by acetonitrile dissociation. DFT computations are

also consistent with an EEC mechanism. The C-Fe-MeCN2+/C-Fe-MeCN+ reduction

potential and the C-Fe-MeCN+/C-Fe0 reduction potential (with concurrent acetonitrile

dissociation) are computed to occur at the same potential (–1.90 V vs Fc+/Fc). The singly

reduced complex C-Fe-MeCN+ is also predicted to be more stable than the N-trans isomer N-

Fe-MeCN+. Further reduction of either species is computationally predicted to produce only a

single isomer, C-trans-Fe(tpy)(Mebim-py) (C-Fe0): all attempts to optimize an N-trans isomer

of the doubly reduced complex resulted in rearrangement to C-Fe0 in a square pyramidal C-

trans geometry.

Figure 2. CV of C-Fe-MeCN2+ in MeCN under N2 atmosphere (black) and under CO2 atmosphere with 5 % H2O. Conditions: [Fe] = 1 mM, [TBAPF6] = 100 mM, 3 mm glassy carbon disc working electrode, Pt wire counter electrode, Ag wire pseudo-reference electrode, 100 mV/s.

The initial reduction of C-Fe-MeCN2+ is proposed to be centered on the tpy ligand, based on

DFT computations showing the highest occupied molecular orbital (HOMO) of C-Fe-MeCN+

predominantly located on tpy (Figure 3, top and Section 6 in the SI). The similarity of the first

reduction potentials of C-Fe-MeCN2+ (E1/2 = –1.66 V) and the Ru analogue C-Ru-MeCN2+

(E1/2 = -1.69 V)3,6 provide further evidence for a ligand-centered reduction in each case. The

species formed after 2e– reduction and acetonitrile dissociation, C-Fe0, features a HOMO with

a high degree of metal character along with some tpy character (Figure 2, bottom). While the

HOMO in the analogous Ru complex C-Ru0 has similar orbital character, it is only accessed

at much more negative potentials (E1/2 = -1.94 V vs. Fc+/Fc).3,6 The higher electronegativity

and less destabilized d-orbitals in iron complexes can help explain the milder reduction

second potential.16

Figure 3. HOMO of C-Fe-MeCN+ (top) and C-Fe0 (bottom).

Water was chosen as the proton source for CO2 reduction to enable comparisons with the Ru

analogues.6 Under N2, CVs in 95/5 MeCN/H2O were essentially identical to those collected in

pure MeCN (Figure S15 in the SI). With no indication of metal hydride formation or H2

evolution catalysis upon reduction of C-Fe-MeCN2+ in the presence of water, there was a

clear opportunity for selective reduction of CO2.

Under 1 atm CO2, the CVs underwent striking changes. The reduction feature became

irreversible, with the cathodic peak potential shifting anodically and the cathodic peak current

(ip,c) doubling (Figure 2 and Figure S16 in the SI). This behavior is consistent a rapid

chemical reaction with CO2 upon reduction of C-Fe-MeCN2+, followed by additional

electrochemical reactions to give a total of 4e– transferred in the single reduction feature.

Controlled potential electrolysis (CPE) of CO2-saturated 95/5 MeCN/H2O solutions of C-Fe-

MeCN2+ at -1.68 V vs Fc+/Fc passed sustained current during 1 h (passing 450 mC of charge

at a 3 mm GC working electrode, Scheme 2 and Figure S17 in the SI). The only product

detected in the gas phase (by gas chromatography) or liquid phase (NMR and ion

chromatography) was CO, produced in 33% Faradaic efficiency (FE). Monitoring the reaction

by UV-vis spectroelectrochemistry (SEC) in CO2-saturated 95/5 MeCN/H2O revealed the

formation of a new species featuring a broad absorption extending beyond 900 nm (Figure

S18 in the SI), while infrared SEC revealed the growth of a new strong band at 1831 cm-1

(Figure 4) indicative of a low-valent Fe carbonyl complex. The resting state during

electrocatalysis is therefore a low-valent carbonyl complex, providing a plausible explanation

for the low FE (which measures gas-phase CO, and does not account for catalyst-bound CO).

The new iron complex C-Fe-MeCN2+ thus facilitates the reduction of CO2 to CO with

excellent selectivity relative to H2 and other carbon-containing products and at only 240 mV

overpotential (under the utilized conditions, EºCO2/CO = -1.44 V vs Fc+/Fc).17

Scheme 2. Catalytic performance of C-Fe-MeCN2+

Figure 4. IR-SEC monitoring reduction of C-Fe-MeCN2+ with applied potential (vs. Ag wire pseudoreference) stepped from –950 mV to –1150 mV. Conditions: CO2 atmosphere, [Fe] = 3 mM, [TBAPF6] = 100 mM, MeCN + 5 % H2O, Au working electrode, Pt wire counter-electrode, Ag wire pseudo-reference electrode.

A detailed study of the mechanism of CO2 reduction mediated by C-Fe-MeCN2+ was

undertaken, motivated by the very low overpotential, the unusual voltammetric response

consistent with a single and rapid 4e–/2H+ reduction, and the promise of directly comparing

reaction pathways with the previously studied Ru analogue C-Ru-MeCN2+. A key

observation was the appearance of a new reduction feature in multi-segment CVs of solutions

of C-Fe-MeCN2+ in 95/5 MeCN/H2O under 1 atm CO2 (Figure 5a). This new feature is

attributed to the reduction of an intermediate iron complex formed during electrochemical

CO2 reduction. The appearance of a new feature anodic of C-Fe-MeCN2+, along with the

decrease in cathodic peak current (ip,c) for the initially observed reduction, is precisely the

scenario expected for an ECE-type mechanism, wherein the intermediate is easier to reduce

than the initial complex C-Fe-MeCN2+.18–22

Figure 5. (a) Multi-segment CV of C-Fe-MeCN2+ in MeCN under CO2 atmosphere with 5 % H2O. (b) CV of N-Fe-CO2+ in MeCN under N2 atmosphere. Conditions: [Fe] = 1 mM, [TBAPF6] = 100 mM, 3 mm glassy carbon disc working electrode, Pt wire counter electrode, Ag wire pseudo-reference electrode, 40 V/s.

Hypothesizing that the redox-active intermediate detected in CV studies was a carbonyl

complex, an iron(II) carbonyl derivative was independently synthesized. Treatment of C-Fe-

MeCN2+ with CO in CH2Cl2 at room temperature resulted in precipitation of an orange solid.

The strong IR band at 2023 cm–1 in the isolated product confirmed the presence of a carbonyl

ligand (Scheme 3). The 1H NMR spectrum displays a singlet at 4.77 ppm for the N-methyl

protons (Figure S4 in the SI), with a far downfield shift relative to C-Fe-MeCN2+ announcing

isomerization to an N-trans geometry.6 An X-ray diffraction study confirmed the constitution

of N-trans-[Fe(tpy)(Mebim-py)(CO)][PF6]2, N-Fe-CO2+ (Figure 6). The geometric

isomerization during ligand substitution was unexpected, considering that the Ru analogue C-

Ru-MeCN2+ was readily converted to C-Ru-CO2+ without rearrangement.6 A plausible

mechanism supported by DFT computations involves Mebim-py hemilability (see Section 6

in the SI). Initial MeCN dissociation is followed by a “windshield wiper” rotation that

converts the five-coordinate intermediate C-Fe2+ to N-Fe2+ before CO binding produces N-

Fe-CO2+ (Figure S39 in the SI). All the complexes bearing a CO ligand showed

thermodynamic preference for the N-trans geometry.

Scheme 3. Synthesis of N-Fe-CO2+

Figure 6. Structural representation of N-Fe-CO2+ with ellipsoids drawn at the 50% level. Hydrogen atoms, two PF6 counterions, and dichloromethane solvent are omitted for clarity. Selected distances (Å) and angles (deg): Fe(1)–C(1) 1.921(5), Fe(1)–N(1) 2.015(4), Fe(1)–N(2) 1.991(4), Fe(1)–N(3) 1.919(4), Fe(1)–N(4) 1.979(4), Fe(1)–C(2) 1.774(5), C(2)–O(1) 1.144(6); C(1)–Fe(1)–N(3) 172.64(18), N(1)–Fe(1)–C(2) 173.30(19), N(2)–Fe(1)–N(4) 161.43(17).

CVs of N-Fe-CO2+ at 40 V/s reveal an initial reduction with a very similar Ep,c value to the

feature observed in multi-segment CVs of C-Fe-MeCN2+ under CO2, and a return oxidation

that also aligns almost perfectly with the oxidation feature in catalytic conditions (Figure 5b).

While the details of the reduction of N-Fe-CO2+ will be examined later, these comparative

CVs clearly pointed to the intermediacy of N-Fe-CO2+ during catalysis.

The reduction of N-Fe-CO2+ was monitored in SEC experiments. Applying progressively

more negative potentials in an IR-SEC study of N-Fe-CO2+ under N2 led to the disappearance

of the band associated with the starting complex (2023 cm–1), before eventually reaching

potentials at which the characteristic 1831 cm-1 stretch of the catalytic intermediate appeared

(Figure 7). UV-vis-SEC experiments also confirm that reduction of N-Fe-CO2+ forms the

species present during catalysis (Figure S19 in the SI).

Figure 7. IR-SEC monitoring reduction of N-Fe-CO2+ with applied potentials (vs. Ag wire pseudoreference) from –750 mV to –1150 mV. Conditions: N2 atmosphere, [Fe] = 3 mM, [TBAPF6] = 100 mM, MeCN, Au working electrode, Pt wire counter-electrode, Ag wire pseudo-reference electrode.

To gain additional insight into the structure of the low-valent Fe carbonyl species, an

authentic synthesis was designed. Treating N-Fe-CO2+ with two equivalents of Cp*2Co (Eº' =

-1.91 V vs. Fc+/Fc)23 in THF-d8 led to a color change from pale orange to dark red. The

resulting 1H NMR spectrum revealed clean conversion to a single new diamagnetic species

(Figure S7 in the SI). The 13C{1H} NMR spectrum confirmed the presence of a carbonyl

ligand and a metallated carbene carbon (Figure S8 in the SI). The pyridine resonances in the 1H NMR spectrum have distinct chemical shifts compared to the other complexes in the

family, and these resonances were quite broad at room temperature. On the basis of the

combined spectroscopic data, the structure is assigned as a five-coordinate neutral carbonyl

complex in which the Mebim-py ligand is bound in a monodentate fashion through the NHC

carbon (with the pyridine arm dissociated, Scheme 4). Variable temperature NMR studies are

consistent with a fluxional process involving the free pyridyl arm, such as rotation about the

M–CNHC bond, with two energetically similar conformers observed at low temperatures

(Figures S9 and S10 in the SI).

Scheme 4. Relative energy (298 K) differences between doubly-reduced carbonyl complexes.

DFT computations support the proposed structure and conformational dynamics. Efforts to

find an energy minimum for the six-coordinate neutral carbonyl complex N-Fe-CO0 were

unsuccessful, with the computations always providing 5-coordinate structures. Two

energetically similar conformational isomers with trigonal bipyramidal geometries were

optimized, differing in the position of the dangling pyridine group (isomerization DG = -1.21

kcal/mol, Scheme 4). The computed IR stretches (1816 cm-1 for k1N-Fe-CO0 and 1830 cm-1

for k1C-Fe-CO0) are very similar to the band observed experimentally (1831 cm-1). The six-

coordinate isomer C-Fe-CO0 has a computed CO stretching frequency of 1963 cm–1, and is

predicted to be almost 20 kcal/mol higher in energy than the five-coordinate isomers (Scheme

4).

The combined experimental and computational data point to a CO2 electroreduction

mechanism involving 2e– reduction of C-Fe-MeCN2+ followed by nucleophilic attack of CO2

and hydrolysis to produce the carbonyl complex of opposite geometry N-Fe-CO2+ (Scheme

5). The carbonyl complex is easier to reduce than the original acetonitrile complex, leading to

another 2e– reduction to form a low-valent five-coordinate iron complex k1-Fe-CO0. This

sequence is noteworthy for the extremely rapid ligand dissociation and isomerization events,

which may contribute to the ability to access CO at mild applied potentials. The hemilability

of pyridine is also a defining feature, leading to a stable 18-electron carbonyl species that may

inhibit CO release during catalysis.

Scheme 5. Proposed mechanism of CO2 electroreduction starting from C-Fe-MeCN2+.

To further probe the remarkable 4e–/2H+ transformation that converts CO2 to CO, the

elementary steps involved in the reduction of N-Fe-CO2+ were examined in a series of scan

rate dependence cyclic voltammetry studies. The following conditions were compared: (a) C-

Fe-MeCN2+ under N2, (b) C-Fe-MeCN2+ under CO, (c) N-Fe-CO2+ under N2, and (d) N-Fe-

CO2+ under CO. Distinct behavior was observed at fast scan rates (above 1 V/s, Figure 8) and

slow scan rates (0.05 to 1 V/s, Figure 9), reflecting the interplay of several chemical and

electrochemical steps.

CVs in the fast scan rate regime (between 2 and 30 V/s) are shown in Figure 8. The

acetonitrile complex C-Fe-MeCN2+ exhibits a reduction event that has the same scan rate

dependent cathodic peak potential under either N2 or CO (Figure 8a, 8b and S20 in the SI),

which suggests that CO binding is not involved (with acetonitrile dissociation presumably

limiting the chemical kinetics). Whereas the 2e– reduction is completely reversible under N2,

the CV becomes irreversible under CO. On the basis of the location of the return oxidation,

we assign the process as 2e– reduction followed by CO binding and pyridine loss to give k1-

Fe-CO0, which is reoxidized to N-Fe-CO2+ during the return sweep. This process was

confirmed by multi-segment CVs of solutions of C-Fe-MeCN2+ under 1 atm CO (Figure S21

in the SI, compare it with Figure 5), which revealed the presence of a new reduction feature

attributed to the reduction of N-Fe-CO2+ generated at the surroundings of the electrode.

Figure 8. Normalized CVs of C-Fe-MeCN2+ under N2 atmosphere (a) and under CO atmosphere (b) and of N-Fe-CO2+ under N2 atmosphere (c) and under CO atmosphere (d) from 2 to 30 V/s. Conditions: N2, [Fe] = 1 mM, [TBAPF6] = 100 mM, MeCN, GC working disc electrode (3 mm), Pt wire counter-electrode, Ag wire pseudo-reference electrode.

CVs of N-Fe-CO2+ under N2 above 1 V/s display two reduction waves in the forward scan

and two oxidation features in the return sweep, suggesting two reversible reduction events

(Figure 8c and S22 in the SI). The first reduction is anodically shifted relative to C-Fe-

MeCN2+ by about 200 mV, as is typical for carbonyl complexes.6 Reversing the sweep such

that only the first feature is present gives a peak-to-peak separation consistent with a 1e–

reduction (Figure S23 in the SI). The second reduction appears at the almost the same

potential as seen for C-Fe-MeCN2+ under N2 (Figure 8a). CVs of N-Fe-CO2+ under CO

above 1 V/s are qualitatively similar to those under N2, but the second reduction feature

exhibits a substantial anodic shift at all scan rates under CO (Figure 8d). The CO-dependent

potential of the second reduction indicates that CO binding is kinetically relevant to the

electrochemical response. This situation contrasts the behavior of C-Fe-MeCN2+ under N2

and CO, suggesting that despite similar potentials, the second reduction feature in Figures 8c

and 8d is not simply reduction of C-Fe-MeCN2+. Instead, the data suggest a reaction sequence

in which 1e– reduction of N-Fe-CO2+ is followed by CO dissociation and isomerization to

form C-Fe-MeCN+, which then undergoes 1e– reduction at more negative potentials. C-Fe-

MeCN+ and C-Fe-MeCN2+ have almost the same E1/2 values, as discussed earlier, but distinct

dependence on CO pressure and scan rate. The broader features in CVs of N-Fe-CO2+ under

N2 are attributed to partial CO dissociation, as reflected in the small return oxidation

associated with oxidation of C-Fe0 to C-Fe-MeCN2+ (Figures 8c and S22 in the SI).

CVs in the slow scan rate regime are shown in Figure 9. The voltammograms are remarkably

different from those collected at fast scan rates. In CVs of N-Fe-CO2+ under N2 (Figure 9c),

the first reduction feature is essentially absent, having decreased into the baseline. Instead, the

CV looks quite similar to that of C-Fe-MeCN2+ under CO (Figure 9b). The disappearance of

the first reduction wave is attributed to a chemical redox-catalyzed ligand substitution process

that consumes N-Fe-CO2+. The initial reduction product N-Fe-CO+ dissociates CO and

isomerizes to form C-Fe-MeCN+, which reduces another equivalent of N-Fe-CO2+, initiating

a chain reaction that converts all of N-Fe-CO2+ to C-Fe-MeCN2+ while only passing tiny

amounts of current. Such electron-transfer chain catalysis is well known in other contexts,

including a Re CO2 reduction catalyst 24–26

Figure 9. Normalized CVs of C-Fe-MeCN2+ under N2 atmosphere (a) and under CO atmosphere (b) and of N-Fe-CO2+ under N2 atmosphere (c) and under CO atmosphere (d) from 0.05 to 1 V/s. Conditions: N2, [Fe] = 1 mM, [TBAPF6] = 100 mM, MeCN, GC working disc electrode (3 mm), Pt wire counter-electrode, Ag wire pseudo-reference electrode.

The viability of a redox catalysis mechanism of ligand substitution was probed by treating N-

Fe-CO2+ with a catalytic amount of the chemical reductant Cp*2Co in CD3CN. Upon addition

of Cp*2Co, the solution immediately changed color from pale orange to dark red, and the 1H

NMR spectrum revealed complete conversion of N-Fe-CO2+ to C-Fe-MeCN2+ (Figure S11 in

the SI). IR-SEC experiments provide further support for redox catalytic CO release. Holding

the potential of the cell only capable of effecting the first reduction process (-820 mV vs. Ag

wire pseudoreference) led to the disappearance of the CO stretch of N-Fe-CO2+ without the

appearance of a new stretch (Figure S24 in the SI), attributed to loss of redox-catalyzed loss

of CO and formation of C-Fe-MeCN2+. Applying more negative potentials, capable of

reducing the newly formed solvento complex (-950 mV vs. Ag pseudoreference) led to the

appearance of the band corresponding to the low valent iron carbonyl species.

Under CO, CVs of N-Fe-CO2+ show two features at 1 V/s (Figure 9d), which merge into a

single wave as the scan rate is decreased to 50 mV/s. This behavior is attributed to somewhat

slower CO dissociation inhibiting the redox catalysis, in conjunction with a significant anodic

shift in the reduction of the generated C-Fe-MeCN2+ under CO in this scan rate range. Thus,

the reduction feature of C-Fe-MeCN2+ shifts anodically with decreasing scan rates until it is

overlapping with the reduction feature of N-Fe-CO2+. The same anodic shift is also apparent

in CVs of C-Fe-MeCN2+ itself under CO (Figure 9b).

A unified mechanism for reduction of the carbonyl complex that is consistent with both the

slow and fast scan rate regimes is shown in Scheme 6. The reduction of N-Fe-CO2+ is

remarkably complex, featuring CO dissociation and re-association as well as geometric

isomerizations. Initial reduction of N-Fe-CO2+ generates N-Fe-CO+, which undergoes rapid

MeCN substitution for the CO ligand and isomerization to generate C-Fe-MeCN+. At slow

scan rates, C-Fe-MeCN+ builds up to sufficient concentrations to initiate a chemical redox-

catalyzed substitution process that converts all unreduced N-Fe-CO2+ near the electrode

surface to the solvento isomer C-Fe-MeCN2+. Thus, at slow scan rates, the CVs look

essentially identical to those of C-Fe-MeCN2+ itself under N2. Under 1 atm CO, however, the

redox-catalyzed process is somewhat slower. At fast scan rates, the singly-reduced

intermediate C-Fe-MeCN+ is electrochemically reduced at a rate that outcompetes the

chemical redox-catalyzed substitution reaction. In both cases, CO release is observed initially,

but reduction of C-Fe-MeCN+ triggers re-binding of CO along with dissociation of the NHC

pyridine ligand to form the five-coordinate complex k1-Fe-CO0. Whereas C-Fe-MeCN2+ is

more stable than N-Fe-CO2+ complex under 1 atm of N2, while k1-Fe-CO0 is more stable than

C-Fe0 under 1 atm N2. The high affinity of k1-Fe-CO0 for CO helps explain the strong anodic

shifts in the reduction of C-Fe-MeCN+, which is followed by highly favorable CO

association.

Scheme 6. Competing pathways proposed to operate during reduction of N-Fe-CO2+.

The mechanistic pathways of Scheme 6 suggest that the pyridine-dissociated complex k1-Fe-

CO0 has an extraordinarily high CO binding affinity. Even when only one equivalent of CO is

present in the system, after dissociation from N-Fe-CO2+, the stable product k1-Fe-CO0 is

formed in nearly quantitative yield. We therefore considered CO dissociation from the

carbonyl complex k1-Fe-CO0 likely to be a limiting process in the overall catalytic process.

This is further supported by the observation of this species by IR under during catalysis (vida

supra).

On the basis of many examples of photochemical CO dissociation,27–29 we carried out

electrocatalysis under simultaneous visible light illumination in an attempt to trigger CO

dissociation from k1-Fe-CO0. CVs under illumination slowed a slight current enhancement,

indicating increased catalytic activity (Figure S25 in the SI). Bulk electrolysis of C-Fe-

MeCN2+ under identical conditions than before (Scheme 2), but under visible light irradiation

led to an increase of the Faradaic efficiency for the generation of CO (55 % FE). CO was the

only product detected the headspace (by gas chromatography) or in the liquid phase (by

NMR). This improvement in the generation of CO leads to a TOF of 14 s-1 at an overpotential

of just 240 mV.

Electrolysis under a continuous flow of CO2 was also explored as an alternative strategy for

promoting CO release from the low valent iron species, keeping the conditions depicted in

Scheme 2. Under applied potentials of –1.68 V vs. Fc+/Fc and with a constant CO2 flow,

NC

CH3

N

N

N

FeN

NN

+

N

N

N

FeN

NN

OC

N

N

N

FeN

NN

CO

E1/2 = –1.66 V

NC

CH3

N

N

N

FeN

NN

2+

+ e–

– e–

2+

N

N

N

FeN

NN

CO Ep,c = –1.45 V

+ e–

– e–

E1/2 = –1.66 V

+ e–

– e–

+

C-Fe-MeCN+

redox-catalyzed substitution

Path A — fast scan rates

Path B slow scan rates

NC

CH3

N

N

N

FeN

NN

– CO+ MeCN

+ CO– MeCN

C-Fe-MeCN+– CO+ MeCN

+ CO– MeCN

– CO+ MeCN

substitution / isomerization

sustained current was passed during more than 1 h (amounting to 7.24 C of charge passed at

the GC rod working electrode, Figure S26). As shown in Figure 10, these conditions led to a

striking increase in the Faradaic efficiency for the production of CO (average 80%, as

compared to only 33% under analogous conditions with a static CO2 atmosphere).

Conditions of flowing CO2 open the possibility to reach high efficiencies at low

overpotentials. High surface area reticulated vitreous carbon (RVC) was utilized as working

electrode for this purpose. Electrocatalytic CO generation was observed at applied potentials

as mild as -1.59 V vs Fc+/Fc, representing an overpotential of only 150 mV.17 An average

Faradaic efficiency of 80% was maintained during the 3 h experiment (Figure S27 and S28 in

the SI). The total CO generated in this experiment corresponds to a TON of 10 TON (with

respect the total amount of catalyst in solution, representing a gross underestimate due to the

large amount of catalyst idling away from the electrode surface at any moment). This

overpotential is among the smallest reported to date for a molecular electrocatalyst for CO

production.29–35

The charge passed during the controlled potential electrolyses under CO2 flow started to

decrease after 1.5 h (Figures S26, S27 and S29), with concomitant decrease in CO generation.

The color of the solution change from dark-red to pink, characteristic of the homoleptic

complex [Fe(tpy)2]2+.36 A CV recorded at the end of the experiment revealed two reversible

1e– features (Figure S30 in the SI) at -1.60 V and -1.84 V vs Fc+/Fc, in close agreement with

an authentic sample of [Fe(tpy)2]2+. Long-term stability represents a focus area for future

catalyst development.

Figure 10. Faradaic efficiency for the generation of CO with respect time, under dark (black dots) and light irradiation (red dots). Conditions: MeCN + 5% H2O, CO2 atmosphere, [Fe] = 1 mM, [TBAPF6] = 100 mM, glassy carbon disc working electrode (122.5 mm2), Pt wire counter

electrode, Ag/AgNO3 reference electrode, applied potential –1.68 V vs Fc+/Fc, constant flow of CO2 (30 mL/min).

The combination of a constant CO2 flow and visible light illumination finally provided

quantitative Faradaic efficiency. When the working compartment of the cell was irradiated

with a mercury arc lamp under a constant flow of CO2 during electrolysis at –1.68 V vs Fc+/Fc

(Figure S29), CO was produced at an average Faradaic efficiency > 99 % (Figure 10).

Comparing the photoelectrochemical conditions of under constant CO2 flow and under a static

atmosphere of CO2 (Faradaic efficiency >99% and 55%, respectively) reveals the importance

of both photodissociation and the mass transport of CO removal.

Conclusions

A new iron complex supported by tpy and pyridyl-carbene ligands was synthesized and found

to catalyze electrochemical CO2 reduction to CO with high selectivity at low overpotentials.

Mechanistic studies based on cyclic voltammetry, in situ spectroelectrochemistry, authentic

syntheses, and DFT computations elucidate the reaction pathway that completes a 4e–/2H+

reduction of CO2 to CO in a single voltammetric wave. Each trip through the catalytic cycle

involves geometric isomerization between structures with the carbene trans to the active site

and pyridine trans to the active site. Furthermore, the pyridine connected to the NHC was

found to be hemilabile, leading to a relatively stable carbonyl complex. The lability of the

pyridine of the Mebim-py ligand, enhanced by the strong trans effect of CO.7 Recognizing

that CO release from the pyridine-dissociated intermediate to be a key step,

photoelectrocatalysis was undertaken and found to significantly improve the activity and

Faradaic efficiency while maintaining the same selectivity and low overpotential.

Comparisons between the new iron catalyst and the previously studied ruthenium catalyst are

instructive.6 Despite having identical supporting ligands, the behavior between the two

systems is strikingly different in most respects. Under N2, MeCN solutions of C-Ru-MeCN2+

display two sequential 1e– reductions, while C-Fe-MeCN2+ features a single 2e– reduction.

The ca. 500 mV difference in the potential of the second reduction results in the iron system

having a dramatically lower overpotential for electrocatalytic CO2 reduction to CO (ca. 150

mV for Fe, ca. 650 mV for Ru). This low overpotential comes at the expense of activity, as

the ruthenium system boasts substantially higher rates (ca. 14 s–1 for Fe, ca. 2000 s–1 for Ru).

The difference in activity stems in part from the ruthenium system enjoying turnover free

from CO inhibition (with high activity and Faradaic efficiency under batch conditions in the

dark);3,4,6 the iron system is inhibited by CO, but the use of a constant CO2 flow and visible

light illumination greatly increase efficiency. The mechanistic studies suggest that the

differences in activity stem from the dramatically increased ligand lability in the iron system

relative to the ruthenium system. During electrocatalysis, C-Ru-MeCN2+ maintains a

geometry with the NHC trans to the active site, and the pyridine remains bound throughout

the cycle. In contrast, C-Fe-MeCN2+ isomerizes to N-Fe-CO2+ rapidly, and upon reduction of

this species the pyridine ligand dissociates. This behavior is attributed to the strong trans

effect of the CO ligand, which in the Ru system is always trans to another strong trans effect

NHC ligand, but in the Fe system lies across from the more labile pyridine ligand. Thus, CO

dissociation is extremely rapid in the Ru catalyst, but slow in the Fe catalyst. Nonetheless,

illumination and perform the electrolysis under constant flow can promote CO dissociation

and accelerate catalysis in the Fe system.

This study shows that Fe and Ru are both viable electrocatalysts supported by tpy and pyridyl-

carbene ligands, once the Fe congener can be synthetized. The characteristics of each system

are distinct, with different strengths and weaknesses as catalysts. Through careful mechanistic

studies, we now understand how ligand lability and isomerization lead to different reaction

pathways for Fe relative to Ru. This knowledge will guide the development of new first-row

transition metal electrocatalysts.

Supporting information

Experimental details, NMR spectra, electrochemical methods, crystallographic methods, and

computational methods (PDF)

Coordinates of computational output files (PDF)

Crystallographic data (CIF)

Acknowledgements

This material is based upon work supported as part of the Alliance for Molecular

PhotoElectrode Design for Solar Fuels (AMPED), an Energy Frontier Research Center

(EFRC) funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy

Sciences under Award Number DE-SC0001011. Quinton J. Bruch and Josh Chen assisted

with crystallographic data collection. Brandie M. Ehrmann assisted with mass spectrometry.

The mass spectrometry work was supported by the National Science Foundation under Grant

No. (CHE-1726291). We would like to thank the European Commission for the ERC-CG-

2014-648304 project and the Spanish Ministry of Science for the project CTQ2016-80038-R

(J.Ll.-F). S.G. thanks the EU for Horizon 2020 Marie Skłodowska-Curie Fellowship (grant

no.794119, Fe-RedOx-Cat).

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download fileview on ChemRxivFeBimpy_Manuscript_Submission.pdf (1.92 MiB)

S1

Supporting information for:

An Iron Pyridyl-Carbene Catalyst for Low Overpotential CO2 reduction to CO:

Mechanistic Comparisons with the Ruthenium Analogue and Photochemical Promotion

Sergio Gonell,* Julio Lloret-Fillol* and Alexander J. M. Miller*

1. Experimental Details S3

1.1. General Considerations S3

1.2. Synthesis of C-Fe-MeCN2+ S4

1.3. Synthesis of N-Fe-CO2+ S5

1.4. Synthesis of k1-Fe-CO0 S5

1.5. Redox-catalyzed CO loss from N-Fe-CO2+ S5

2. NMR spectra S6

2.1. 1H, 13C and HSQC NMR spectra of C-Fe-MeCN2+ S6

2.2. 1H, 13C and HSQC NMR spectra of N-Fe-CO2+ S7

2.3. 1H and 13C NMR NMR spectra of k1Fe-CO0 S9

2.4. CO loss studies S11

3. Electrochemical methods S12

3.1. Electrochemical measurements S12

3.2. Spectroelectrochemical measurements S13

3.3. Electrochemical kinetic analysis S14

3.4. CPE under light irradiation S25

3.5. Turnover frequency determination S25

4. Crystallographic methods S27

5. Computational methods S34

S2

5.1 Overview of computational methods S34

5.2 Computed Gibbs free energies of different complexes S34

5.3 Molecular orbital representations of MeCN complexes S36

5.4. Molecular representation of the computed five coordinate complexes S37

5.5. Infrared vibrational computations S38

5.6. Reaction free energies of different transformations S39

5.7. Computed reduction potentials S42

6. References S43

S3

1. Experimental Details

1.1. General considerations. All operations were carried out by using standard Schlenk

techniques under nitrogen atmosphere or in a nitrogen filled glovebox. MeCN, THF and

CH2Cl2 were dried and degassed with argon using a Pure Process Technology solvent system.

CD3CN and THF-d8 were purchased from Cambridge Isotope Laboratories Inc., degassed by

freeze-pump-thaw (three times), dried by passage through a small column of activated

alumina, and stored over molecular sieves (3 Å). [Mebim-pyH][PF6]1, Fe(tpy)Cl22 and

[Fe(tpy)2][PF6]23 were synthesized according to reported procedures, dried overnight under

vacuum and stored in a nitrogen filled glovebox. All other materials were commercially

available and used as received, unless otherwise noted. NMR spectra were recorded on either

a 400 or 600 MHz spectrometer at 25 °C. Chemical shifts are reported with respect to residual

organic solvents.4 Infrared spectroscopy was carried out with a Thermo Scientific Nicolet iS5

FT-IR equipped with a iD1 Transmission Accessory (Thermo Scientific) for solution

measurements in a demountable liquid cell with CaF2 windows (0.05 mm path length, Pike

Technologies Inc.). UV−vis spectra were collected with an Ocean Optics USB2000+

spectrometer with a DT-MINI-2GS deuterium/tungsten halogen light source. Single-crystal

X-ray diffraction data were collected on a Bruker APEX II diffractometer at 100 K with Cu

Ka radiation (l = 1.54175 Å). The structures were solved by direct methods using SHELXS,

and refined with SHELXL5 with least squares minimization using the Olex2 software

package.6 Data were corrected for absorption effects using the Multi-Scan method

(SADABS). The calculated minimum and maximum transmission coefficients are 0.583 and

0.726. Non-hydrogen atoms were refined anisotropically. The hydrogen atoms were placed in

geometrically calculated positions with Uiso = 1.2Uequiv of the parent atom (Uiso =

1.5Uequiv for methyl). See the Section 7 for additional crystallographic details for each

complex. High Resolution Mass Spectrometry (HRMS) was performed in a Q Exactive HF-X

(ThermoFisher, Bremen, Germany) mass spectrometer. Samples in MeCN were introduced

via a heated electrospray source (HESI) at a flow rate of 10 µL/min. Xcalibur (ThermoFisher,

Bremen, Germany) was used to analyze the data. Molecular formula assignments were

determined with Molecular Formula Calculator (v 1.2.3). Elemental analyses were performed

by Robertson Microlit Laboratories of Ledgewood, NJ.

S4

1.2. Synthesis of C-Fe-MeCN2+. Inside a glovebox, [Mebim-pyH][PF6] (147.9 mg, 0.42

mmol), LiHMDS (71.9 mg, 0.42 mmol) and Fe(tpy)Cl2 (100 mg, 0.28 mmol) were introduced

in three different Schlenk flasks and THF was added (15 mL, 5 mL and 10 mL, respectively).

The flasks were sealed, brought outside the glovebox and connected to a Schlenk line. The

Schlenk flask containing [Mebim-pyH][PF6] was cooled at -78 ºC and the solution

containing LiHMDS was added dropwise via syringe. The mixture was stirred at -78 ºC for

30 min. This solution was transferred via an oven dried cannula to the Schlenk flask

containing Fe(tpy)Cl2. The mixture was stirred at -78 ºC for 30 min, then the mixture was

allowed to warm up and stirred to room temperature during 24 h in the absence of light. Inside

of a glovebox, the dark blue solid generated was collected by filtration and washed with THF

(5 mL). The residue was extracted with CH2Cl2 (10 mL) and the volatiles were removed

under vacuum. The solid was dissolved in MeCN (15 mL), then KPF6 (154.6 mg, 0.84 mmol)

was added and the mixture was stirred during 12 h in the absence of light. The solvent was

removed under vacuum. The residue was extracted with cold CH2Cl2. The first 2 mL were

discarded and the other fractions (3x10 mL) were layered with diethyl ether and kept at -30

ºC during 48 h. The analytically pure desired product crystalized as dark red needles (suitable

for X-ray analysis), which were collected by filtration, washed with diethyl ether and dried

under vacuum (79.6 mg, 34% yield). 1H NMR (400 MHz, CD3CN): δ 9.47 (d, 3JH–H = 6.8 Hz,

1H, CHarom), 8.61 (d, 3JH–H = 8.6 Hz, 1H, CHarom), 8.51 (m, 2H, CHarom), 8.48 (m, 1H,

CHarom), 8.40 (m, 1H, CHarom), 8.35 (d, 3JH–H = 8.4 Hz, 2H, CHarom), 8.23 (d, 3JH–H = 8.4 Hz,

1H, CHarom), 7.97 (m, 2H, CHarom), 7.81 (m, 1H, CHarom), 7.46 (m, 1H, CHarom), 7.38 (m, 1H,

CHarom), 7.30 (m, 1H, CHarom), 7.22 (m, 2H, CHarom), 7.18 (m, 2H, CHarom), 2.78 (s, 3H, CH3). 13C {1H} NMR (151 MHz, CD3CN): δ 215.9 (Fe–Ccarbene), 161.3 (Cq), 158.6 (Cq), 157.4 (Cq),

156.0 (CHarom), 154.3 (CHarom), 141.7 (CHarom), 139.2 (CHarom), 139.0 (CHarom), 132.6 (Cq),

131.7 (Cq), 128.1 (CHarom), 125.3 (CHarom), 124.9 (CHarom), 124.2 (CHarom), 123.5 (CHarom),

123.4 (CHarom), 114.3 (CHarom), 112.2 (CHarom), 110.9 (CHarom), 31.9 (CH3). Anal. Calcd for

FeC30H25N7P2F12: C, 43.44; H, 3.04; N, 11.82. Found: C, 43.13; H, 2.83; N, 11.65. HRMS

(ESI, m/z): 269.57568 [M]2+ (calculated 269.57603).

1.3. Synthesis of N-Fe-CO2+. Inside a glovebox, C-Fe-MeCN2+ (50 mg, 0.06 mmol) was

introduced in a Schlenk flasks and dissolved in CH2Cl2 (15 mL). Outside the glovebox, the

solution was degassed by three freeze-pump-thaw cycles. A CO atmosphere was introduced at

ambient temperature, the Schenk flask was sealed, and the mixture was stirred while protected

from light at room temperature for 24 hours. During the course of the reaction, an orange

S5

solid precipitated. Inside a glovebox, the reaction mixture was cooled at -30 ºC, the solid was

collected by filtration and washed with cold CH2Cl2 (-30 ºC) and diethyl ether, providing the

analytically pure product (35.5 mg, 72% yield). 1H NMR (400 MHz, CD3CN): δ 8.70 (m, 3H,

CHarom), 8.41 (d, 3JH–H = 8.5 Hz, 1H, CHarom), 8.36 (m, 3H, CHarom), 8.14 (m, 1H, CHarom),

8.01 (m, 3H, CHarom), 7.74 (m, 2H, CHarom), 7.36 (d, 3JH–H = 5.6 Hz, 2H, CHarom), 7.16 (m,

3H, CHarom), 7.07 (d, 3JH–H = 5.0 Hz, 1H, CHarom), 4.77 (s, 3H, CH3). 13C {1H} NMR (151

MHz, CD3CN): δ 213.8 (Fe–Ccarbene), 212.5 (Fe–CO), 157.9 (CHarom), 157.4 (Cq), 157.3 (Cq),

155.1 (Cq), 148.9 (CHarom), 143.4 (CHarom), 142.3 (CHarom), 141.1 (CHarom), 139.8 (Cq), 133.0

(Cq), 129.3 (CHarom), 126.5 (CHarom), 126.4 (CHarom), 125.5 (CHarom), 125.5 (CHarom), 124.6

(CHarom), 114.8 (CHarom), 113.5 (CHarom), 112.9 (CHarom), 36.6 (CH3). Anal. Calcd for

FeC29H22N6OP2F12: C, 42.67; H, 2.72; N, 10.30. Found: C, 42.49; H, 2.65; N, 10.56. HRMS

(ESI, m/z): 263.05990 [M]2+ (calculated 263.06021).

1.4. Synthesis of k1-Fe-CO0. Inside a glovebox, Cp*2Co (17.1 mg, 0.052 mmol) was

dissolved in THF (4 mL) in a scintillation vial. This solution was added to another

scintillation vial containing N-Fe-CO2+ (21 mg, 0.026 mmol). The solution changed color

immediately from dark red to dark brown. The mixture was stirred for 5 min and the insoluble

materials were removed by filtration. The solvent was removed under vacuum affording k1-

Fe-CO0 quantitatively (20 mg, 94% yield). 1H NMR (600 MHz, THF-d8) δ 8.89 (d, 3JH–H =

5.9 Hz, 2H, CHarom), 8.44 (d, 3JH–H = 7.5 Hz, 2H, CHarom), 8.16 (d, 3JH–H = 7.5 Hz, 2H,

CHarom), 8.04 (bs, 1H, CHarom), 7.33 (m, 2H, CHarom), 7.23 (t, 3JH–H = 7.4 Hz, 2H, CHarom),

7.12 (t, 3JH–H = 7.6 Hz, 1H, CHarom), 7.05-6.75 (m, 4H, CHarom), 6.62 (t, 3JH–H = 6.2 Hz, 2H,

CHarom), 5.90 (bs, 1H, CHarom), 4.09 (bs, 3H, CH3). 13C {1H} NMR (151 MHz, THF-d8): δ

224.0 (Fe–Ccarbene), 219.4 (Fe–CO), 154.7 (CHarom), 149.3 (CHarom), 149.0 (CHarom), 147.5

(CHarom), 140.2 (CHarom), 128.7 (CHarom), 128.0 (CHarom), 123.6 (CHarom), 123.3 (CHarom),

121.8 (CHarom), 121.7 (CHarom), 121.5 (CHarom), 120.6 (CHarom), 120.4 (CHarom), 119.7

(CHarom), 116.1 (CHarom), 116.0 (CHarom), 110.6 (CHarom), 109.5 (CHarom), 34.1 (CH3).

1.5. Redox-catalyzed CO loss from N-Fe-CO2+. Inside a glovebox, N-Fe-CO2+ (4 mg,

4.9·10-3 0.0049 mmol) and mesitylene as internal standard (one drop) were dissolved in

CD3CN (0.6 mL) and introduced in a Young NMR tube. A 1H NMR spectrum was recorded.

Inside a glovebox, Cp*2Co (0.2 mg, 6.125·10-4 mmol) was dissolved in the mixture of the

Young NMR tube. The solution changed color immediately from orange to dark-red. The

solution was introduced again in a Young NMR tube. A 1H NMR spectrum was recorded

immediately showing quantitative formation of C-Fe-MeCN2+ (Figure S11).

S6

2. NMR spectra

2.1 1H, 13C and HSQC NMR spectra of C-Fe-MeCN2+

Figure S1. 1H NMR spectrum of C-Fe-MeCN2+ in CD3CN, 400 MHz

Figure S2. 13C{1H} NMR spectrum of C-Fe-MeCN2+ in CD3CN, 151 MHz

S7

Figure S3. 1H-13C HSQC NMR spectrum of C-Fe-MeCN2+ in CD3CN, 400 MHz.

2.2 1H, 13C and HSQC NMR spectra of N-Fe-CO2+

Figure S4. 1H NMR spectrum of N-Fe-CO2+ in CD3CN, 400 MHz.

S8

Figure S5. 13C{1H} NMR spectrum of N-Fe-CO2+ in CD3CN, 151 MHz.

Figure S6. 1H-13C HSQC NMR spectrum of N-Fe-CO2+ in CD3CN, 400 MHz.

S9

2.3 1H and 13C of k1Fe-CO0

Figure S7. 1H NMR spectrum of k1Fe-CO0 in THF-d8 at 298 K, 600 MHz.

Figure S8. 13C{1H} NMR spectrum of k1Fe-CO0 in THF-d8 at 298 K, 151 MHz.

S10

Figure S9. 1H NMR spectrum of k1Fe-CO0 in THF-d8 from 253 to 273 K, 600 MHz.

Figure S10. 1H NMR spectrum of k1Fe-CO0 in THF-d8 from 213 to 243 K, 600 MHz.

S11

2.4 CO loss studies

Figure S11. 1H NMR spectrum of N-Fe-CO2+ in CD3CN, 400 MHz, before (a) and after (b) the addition of a catalytic amount of (Cp*)2Co in the presence of mesitylene as internal standard.

S12

3. Electrochemical methods

3.1 Electrochemical measurements

Electrochemical studies were performed using a WaveDriver bipotentiostat controlled with

Aftermath software (Pine Research) or a CHI601 E potentiostat station (CH Instruments,

Inc.). All the solutions were deoxygenated by sparging with N2 for at least 20 min. In the case

of electrocatalytic CO2 reduction experiments, the solutions were first sparged with N2 for 20

min, and then saturated with CO2 by sparging for at least 20 min. Tetrabutylammonium

hexafluorophosphate (TBAPF6, Sigma Aldrich, electrochemical grade) was used as

electrolyte (100 mM) in all experiments. TBAPF6 was purified by crystallization in EtOH

twice, then dried under vacuum overnight at 70 ºC and stored in a nitrogen-filled glovebox.

Cyclic voltammetry was performed in an undivided three-electrode cell with a 3 mm diameter

disk glassy carbon working electrode, platinum counter electrode, and a silver wire pseudo-

reference electrode. The glassy carbon working electrode (CH Instruments) was polished

between scans with 0.05-µm alumina powder (CH Instruments, contained no agglomeration

agents) before rinsing with deionized water and acetone. All scans were referenced to the

ferrocenium/ferrocene (Fc+/Fc) couple at 0 V. Ferrocene was present in each scan unless

otherwise noted. Ohmic drop was minimized by minimizing the distance between the working

and reference electrodes. The residual ohmic drop was compensated using the method

developed by Pine Research Instrumentation for the WaveDriver potentiostat.

The normalized scan rate dependent CVs were built taking into account Randles−Sevcik

equation, dividing the current of the sweep by the square root of the scan rate. The

Randles−Sevcik equation describes how the peak current ip (A) increases linearly with the

square root of the scan rate u (V s-1), for an electrochemically reversible electron transfer

process involving freely diffusing species. n is the number of electrons transferred in the

redox event, A (cm2) is the electrode surface area, D0 (cm2 s-1) is the diffusion coefficient of

the analyte, and C0 (mol cm-3) is the bulk concentration of analyte.

𝑖" = 0.446𝑛𝐹𝐴𝐶, -𝑛𝐹𝜐𝐷,𝑅𝑇 2

3/5

(𝐸𝑞𝑆1)

Controlled potential electrolysis studies under batch conditions were performed in a two-

compartment custom-made gastight electrochemical cell (see ref 7 for the details of the cell).

The cathodic compartment was fitted with a glassy carbon disk (3 mm diameter) as a working

electrode and a Ag/AgNO3 reference electrode (silver wire in a glass tube containing 100 mM

S13

TBAPF6/CH3CN solution and 10 mM of AgNO3, separated from the rest of the cell with a

porous glass Vycor tip;8 Eº = –89 mV vs. Fc+/Fc).9 A platinum coil was used as counter

electrode in the anodic compartment. The residual ohmic drop was compensated using the

method developed by Pine Research Instrumentation for the WaveDriver potentiostat. The

solutions of both compartments were sparged with N2 (20 min) and then with CO2 (20 min).

The cell was sealed under CO2 and the bulk electrolysis was performed applying the desired

potential, with a vigorous stirring (ca. 1000 rpm). At the end of the electrolysis, headspace

samples were taken by using a gastight syringe and analyzed by gas chromatography.

Analysis of the liquid phase by 1H NMR spectroscopy and ion chromatography did not reveal

the generation of any additional product than CO.

Controlled potential electrolysis under constant flow of CO2 was performed in a similar cell

than under batch conditions, but the headspace of both compartments was connected. For this

experiments a reticulated vitreous carbon electrode or a glassy carbon rod were used as

working electrode. On-line analysis of the gas evolution during electrolysis was performed

using an Agilent 490 micro gas chromatograph equipped with a thermal conductivity detector

and a Molesieve 5Å column was calibrated with different H2/He/CO/CH4 mixtures of known

composition (for details about the set up see the SI of ref 10).

Controlled potential electrolysis under light irradiation was performed using an Arc light Hg

lamp (LSB610 100 W Hg, wavelength range 220-600 nm), for details about the setup see

Figure S32.

3.2. Spectroelectrochemical measurements

Infrared spectroelectrochemistry (IR-SEC) measurements were performed using a gastight,

optically transparent thin-layer solution IR cell fabricated by Prof. Hartl at the University of

Reading (Reading, U.K.), as described previously.11 The IR-SEC cell contained a masked Au-

minigrid working electrode (32 wires/cm), a Pt-gauze auxiliary electrode, and an Ag-wire

pseudo-reference electrode and had CaF2 windows. In each experiment, electrochemical

reduction of the species of interest ([Fe] = 3 mM, [TBAPF6] = 100 mM in MeCN) was

monitored by IR spectroscopy for a period of 2−5 min. First the potential of the cell was

swept negatively recording a thin-layer cyclic voltammogram (5 mV/s) to identify the

potential window of interest. Then, fresh analyte solution was introduced in the cell and the

potential was varied within range of interest in 50 mV steps. The electrolysis step did not

exceed 30 s. After each step an IR spectrum was collected. Diffusion and mixing of the redox

products generated at the working and auxiliary electrodes in the IR cell were reasonably

S14

suppressed within the total experimental time (no more than 5 min for one complete

measurement). Samples saturated with the desired gas (CO2 or N2) were loaded directly into

the IR-SEC inside a nitrogen filled glovebox. Then the cell was brought outside the glovebox

to perform the experiment.

UV-vis spectroelectrochemistry (UV-vis-SEC) measurements were performed inside a

nitrogen filled glovebox, in a short path (0.2 cm) cuvette containing a MeCN solution of the

iron complex under study (0.5 mM) and TBAPF6 (100 mM). The solution was saturated with

the desired gas (N2 or CO2) before being introduced in the glovebox. The cuvette was

equipped with a Au honeycomb working electrode, Au counter electrode, and a Ag wire

pseudoreference electrode. A CV was recorded to determine the potential of the reduction

feature. The solution was replaced with a fresh solution of the desired complex and a CV was

taken (5 mV/s), with collection of UV-vis spectra every 5 sec (Figure S18 and S19).

3.3 Electrochemical kinetic analysis.

Figure S12. Anodic part of the CV of C-Fe-MeCN2+ under N2 atmosphere in the presence of Fc. Conditions: N2 atmosphere, MeCN, [Fe] = 1 mM, [TBAPF6] = 100 mM, 3 mm glassy carbon disc working electrode, Pt wire counter electrode, Ag wire pseudo-reference electrode, 100 mV/s.

S15

Figure S13. Normalized CVs of the oxidation of C-Fe-MeCN2+. Conditions: N2 atmosphere, MeCN, [Ru] = 1 mM, [TBAPF6] = 100 mM, 3 mm glassy carbon disc working electrode, Pt wire counter electrode, Ag wirepseudo-reference electrode.

Figure S14. Multi-segment CV of C-Fe-MeCN2+ in MeCN under N2 atmosphere. Conditions: [Fe] = 1 mM, [TBAPF6] = 100 mM, 3 mm glassy carbon disc working electrode, Pt wire counter electrode, Ag wire pseudo-reference electrode, 40 V/s.

S16

Figure S15. CV of C-Fe-MeCN2+ under N2 in anhydrous conditions (black) and with 5 % added H2O. Conditions: N2 atmosphere, MeCN or MeCN + 5 % H2O, [Fe] = 1 mM, [TBAPF6] = 100 mM, 3 mm glassy carbon disc working electrode, Pt wire counter electrode, Ag wire pseudo-reference electrode, 100 mV/s.

Figure S16. Normalized CVs of C-Fe-MeCN2+ under CO2 atmosphere and 5 % H2O from 50 to 1000 mV/s. Conditions: CO2 atmosphere, MeCN + 5% H2O, [Ru] = 1 mM, [TBAPF6] = 100 mM, 3 mm glassy carbon disc working electrode, Pt wire counter electrode, Ag wirepseudo-reference electrode.

S17

Figure S17. CPE of C-Fe-MeCN2+ under batch conditions (for details about the cell and set up see the SI of ref 7) Conditions: MeCN + 5% H2O, CO2 atmosphere, [Fe] = 1 mM, [TBAPF6] = 100 mM, 3 mm glassy carbon disc working electrode, Pt wire counter electrode, Ag/AgNO3 reference electrode, applied potential –1.68 V vs Fc+/Fc.

Figure S18. UV-vis-SEC of C-Fe-MeCN2+ (red), showing the conversion (grey) to the new product (blue) upon reduction. Conditions: CO2 atmosphere, [Fe] = 0.25 mM, [TBAPF6] = 100 mM, MeCN + 5 % H2O, Ag wire pseudoreference electrode, Au working and counter electrodes in a “honeycomb” cell arrangement. A CV was taken between -0.8 to -1.4 V vs

S18

Ag wire pseudorefence at 5 mV/s, during this time a UV spectra was taken every 5 s (only selected spectra shown).

Figure S19. UV-vis-SEC of N-Fe-CO2+ (red), showing the conversion (grey) to the new product (blue) upon reduction. Conditions: N2 atmosphere, [Fe] = 0.25 mM, [TBAPF6] = 100 mM, MeCN, Ag wire pseudoreference electrode, Au working and counter electrodes in a “honeycomb” cell arrangement. A CV was taken between -0.8 to -1.4 V vs Ag wire pseudorefence at 5 mV/s, during this time a UV spectra was taken every 5 s (only selected spectra shown).

S19

Figure S20. Normalized CVs of C-Fe-MeCN2+ under CO from 40 to 90 V/s. Conditions: CO atmosphere, [Fe] = 1 mM, [TBAPF6] = 100 mM, MeCN, GC working disc electrode (1 mm), Pt wire counter-electrode, Ag wire pseudo-reference electrode.

Figure S21. Multi-segment CV of C-Fe-MeCN2+ in MeCN under CO atmosphere. Conditions: CO atmosphere, [Fe] = 1 mM, [TBAPF6] = 100 mM, 3 mm glassy carbon disc working electrode, Pt wire counter electrode, Ag wire pseudo-reference electrode, 40 V/s.

S20

Figure S22. Normalized CVs of N-Fe-CO2+ under N2 from 40 to 90 V/s. Conditions: N2, [Fe] = 1 mM, [TBAPF6] = 100 mM, MeCN, GC working disc electrode (1 mm), Pt wire counter-electrode, Ag wire pseudo-reference electrode.

Figure S23. CV of N-Fe-CO2+ under N2 atmosphere. Conditions: N2 atmosphere, MeCN, [Fe] = 1 mM, [TBAPF6] = 100 mM, 3 mm glassy carbon disc working electrode, Pt wire counter electrode, Ag wire pseudo-reference electrode, 40 V/s.

S21

Figure S24. IR-SEC of N-Fe-CO2+. Conditions: N2 atmosphere, [Fe] = 3 mM, [TBAPF6] = 100 mM, MeCN, Au working electrode, Pt wire counter-electrode, Ag wire pseudo-reference electrode. -820 V vs. Ag wire.

Figure S25. CV of C-Fe-MeCN2+ under CO2 atmosphere with 5 % H2O in the dark (black) and under visible light irradiation (red). Conditions: CO2 atmosphere, MeCN + 5% H2O, [Fe] = 1 mM, [TBAPF6] = 100 mM, 3 mm glassy carbon disc working electrode, Pt wire counter electrode, Ag wire pseudo-reference electrode, 100 mV/s.

S22

Figure S26. CPE of C-Fe-MeCN2+ under constant flow of CO2 (30 mL/min). Conditions: MeCN + 5% H2O, CO2 atmosphere, [Fe] = 1 mM, [TBAPF6] = 100 mM, glassy carbon disc working electrode (122.5 mm2), Pt wire counter electrode, Ag/AgNO3 reference electrode, applied potential –1.68 V vs Fc+/Fc.

Figure S27. CPE of C-Fe-MeCN2+ with constant flow of CO2 (30 mL/min). Conditions: MeCN + 5% H2O, CO2 atmosphere, [Fe] = 1 mM, [TBAPF6] = 100 mM, reticulated vitreous carbon working electrode, Pt wire counter electrode, Ag/AgNO3 reference electrode, applied potential –1.68 V vs Fc+/Fc.

S23

Figure S28. Faradaic efficiency for the generation of CO with respect time. Conditions: MeCN + 5% H2O, CO2 atmosphere, [Fe] = 1 mM, [TBAPF6] = 100 mM, reticulated vitreous carbon working electrode (122.5 mm2), Pt wire counter electrode, Ag/AgNO3 reference electrode, applied potential –1.59 V vs Fc+/Fc, constant flow of CO2 (30 ml/min).

Figure S29. CPE of C-Fe-MeCN2+ under constant flow of CO2 (30 mL/min) and light irradiation. Conditions: MeCN + 5% H2O, CO2 atmosphere, [Fe] = 1 mM, [TBAPF6] = 100 mM, glassy carbon disc working electrode (122.5 mm2), Pt wire counter electrode, Ag/AgNO3 reference electrode, applied potential –1.68 V vs Fc+/Fc.

S24

Figure S30. CV of C-Fe-MeCN2+ before (black) and after (red) CPE (for conditions of the CPE see Figure S26). Conditions: CO2 atmosphere, MeCN + 5% H2O, [Fe] = 1 mM, [TBAPF6] = 100 mM, 3 mm glassy carbon disc working electrode, Pt wire counter electrode, Ag wire pseudo-reference electrode, 100 mV/s.

Figure S31. CV of [Fe(tpy)2][PF6]2 recorded under different conditions. Conditions: N2 or CO2 atmosphere, MeCN or MeCN + 5% H2O, [Fe] = 1 mM, [TBAPF6] = 100 mM, 3 mm glassy carbon disc working electrode, Pt wire counter electrode, Ag wire pseudo-reference electrode, 100 mV/s.

S25

3.4 Bulk electrolysis under light irradiation

The CPE under light irradiation was performed according to the setup depicted in Figure S32.

The lamp was directed towards the cathodic compartment of the cell. The reference electrode

(Ag/AgNO3) was covered with aluminum foil to avoid shifting of the potential. A fan was

pointed between the cell and the lamp to avoid increase of temperature. Temperature of the

cell was monitored to be constant and kept at room temperature during the course of the

experimented by thermometer located between the lamp and the cell.

Figure S32. Setup to perform CPE under light irradiation.

3.5 Turnover frequency determination

Under the assumption that electron transfer of the catalyst is fast and follows the Nerst law,

the TOF can be estimated as:12,13

𝑇𝑂𝐹 =𝑖>?@𝑘BCD𝐹𝐴√𝐷[𝑅𝑢]

(𝐸𝑞𝑆2)

S26

𝑇𝑂𝐹 =𝑘BCD

1 + 𝑒𝑥𝑝 N 𝐹𝑅𝑇 -𝐸O""–𝐸352Q(𝐸𝑞𝑆3)

Combination of these two equations gives:

𝑇𝑂𝐹 =STUV W3X>Y"Z [\]W^_``–^aV

bcb

dVeVf[gh]V(𝐸𝑞𝑆4)

with, 𝑖>? =i·d^k

In which Q is the charge passed during the CPE in coulombs, FE is the faradaic efficiency of

the experiment, t is the time of the electrolysis (3600 s−1), Eapp is the applied potential (−1.68

vs Fc+/Fc), E1/2 is the half-wave potential of the catalytic wave (−1.60 vs Fc+/Fc), F is the

Faraday constant (96485 C/mol), A is the area of the electrode (7.1·10−2 cm2), D is the

diffusion coefficient of the iron complex (it is assumed to be the same than the Ru analogue,

5.2·10−6 cm2/s),14 and [Fe] is the concentration of catalyst in the bulk solution (1·10−6

mol/cm3). This gives TOF(C-Fe-MeCN2+) = 8 s−1 in the dark, and equal to 14 s−1and in the

presence of light.

S27

4. Crystallographic methods

Table S1. Crystal data and structure refinement for C-Fe-MeCN2+.

Empirical formula C31H27Cl2F12.43FeN7P2 Formula weight 922.41 Temperature/K 100.15 Crystal system monoclinic Space group P21/n a/Å 13.7127(2) b/Å 17.4292(3) c/Å 16.0993(2) α/° 90 β/° 107.9380(10) γ/° 90 Volume/Å3 3660.72(10) Z 4 ρcalcg/cm3 1.674 µ/mm-1 6.386 F(000) 1855.0 Crystal size/mm3 0.225 × 0.107 × 0.07 Radiation CuKα (λ = 1.54178) 2Θ range for data collection/° 7.426 to 136.55 Index ranges ? ≤ h ≤ ?, ? ≤ k ≤ ?, ? ≤ l ≤ ? Reflections collected 6701 Independent reflections 6701 [Rint = ?, Rsigma = 0.0402] Data/restraints/parameters 6701/0/548 Goodness-of-fit on F2 1.028 Final R indexes [I>=2σ (I)] R1 = 0.0661, wR2 = 0.1542 Final R indexes [all data] R1 = 0.0860, wR2 = 0.1662 Largest diff. peak/hole / e Å-3 0.64/-0.68

Table S2. Bond lengths [Å] for C-Fe-MeCN2+.

Atom Atom Length/Å Atom Atom Length/Å Fe1 N5 1.985(4) C17 C16 1.380(7) Fe1 N4 1.870(4) C25 C24 1.393(7) Fe1 N3 1.985(4) C25 C26 1.388(7) Fe1 N1 1.997(4) C16 C15 1.378(7) Fe1 N2 1.978(4) C9 C10 1.385(7) Fe1 C1 1.922(5) C13 C12 1.380(7) Cl1 C31 1.750(6) C29 C30 1.446(8) N5 C28 1.345(6) C14 C15 1.377(7) N5 C24 1.363(6) C5 C6 1.369(7) N4 C19 1.354(6) C20 C21 1.383(7) N4 C23 1.350(6) C21 C22 1.397(7) N3 C18 1.371(6) C10 C11 1.397(7)

S28

N3 C14 1.336(6) C12 C11 1.385(7) N7 C3 1.402(6) P1 F6 1.591(4) N7 C1 1.379(6) P1 F4 1.595(3) N7 C9 1.408(6) P1 F5 1.598(3) N1 C7 1.344(6) P1 F1 1.586(4) N1 C3 1.355(6) P1 F3 1.590(4) N6 C8 1.402(6) P1 F2 1.575(3) N6 C1 1.334(6) P2 F7 1.571(4) N6 C2 1.459(6) P2 F8 1.568(4) C18 C19 1.476(7) P2 F14 1.601(5) C18 C17 1.377(6) P2 F10 1.552(6) C19 C20 1.369(7) P2 F16 1.528(16) N2 C29 1.148(6) P2 F12 1.626(6) C7 C6 1.372(7) P2 F15 1.548(15) C27 C28 1.382(7) P2 F9 1.596(13) C27 C26 1.374(8) P2 F11 1.557(15) C3 C4 1.385(6) P2 F13 1.442(17) C8 C9 1.388(7) F8 F13 1.61(3) C8 C13 1.388(7) F14 F15 1.74(2) C23 C24 1.464(6) F14 F13 1.198(17) C23 C22 1.389(7) C31 Cl3 1.705(12) C4 C5 1.393(7) C31 Cl2 1.814(9)

Table S3. Angles [°] for C-Fe-MeCN2+.

Atom Atom Atom Angle/˚ Atom Atom Atom Angle/˚ N5 Fe1 N3 162.30(16) C6 C5 C4 119.6(5) N5 Fe1 N1 95.97(15) C19 C20 C21 118.9(5) N4 Fe1 N5 81.35(16) C20 C21 C22 120.2(5) N4 Fe1 N3 81.20(16) C23 C22 C21 118.3(5) N4 Fe1 N1 176.64(16) C5 C6 C7 119.1(5) N4 Fe1 N2 90.91(16) C9 C10 C11 117.3(5) N4 Fe1 C1 97.21(17) C14 C15 C16 119.3(5) N3 Fe1 N1 101.56(16) C13 C12 C11 121.7(5) N2 Fe1 N5 91.22(16) C12 C11 C10 121.1(5) N2 Fe1 N3 86.09(16) C27 C26 C25 119.4(5) N2 Fe1 N1 91.19(16) F6 P1 F4 89.2(2) C1 Fe1 N5 91.22(17) F6 P1 F5 178.9(2) C1 Fe1 N3 93.91(17) F4 P1 F5 90.71(19) C1 Fe1 N1 80.76(17) F1 P1 F6 90.0(2) C1 Fe1 N2 171.79(18) F1 P1 F4 88.81(19) C28 N5 Fe1 128.4(3) F1 P1 F5 88.9(2) C28 N5 C24 117.8(4) F1 P1 F3 177.7(2) C24 N5 Fe1 113.8(3) F3 P1 F6 90.8(2) C19 N4 Fe1 120.2(3) F3 P1 F4 89.0(2) C23 N4 Fe1 119.2(3) F3 P1 F5 90.3(2)

S29

C23 N4 C19 120.6(4) F2 P1 F6 90.5(2) C18 N3 Fe1 114.0(3) F2 P1 F4 178.8(2) C14 N3 Fe1 128.1(3) F2 P1 F5 89.6(2) C14 N3 C18 117.8(4) F2 P1 F1 92.4(2) C3 N7 C9 131.2(4) F2 P1 F3 89.8(2) C1 N7 C3 117.5(4) F7 P2 F14 88.1(3) C1 N7 C9 111.3(4) F7 P2 F12 83.4(3) C7 N1 Fe1 127.5(3) F7 P2 F9 73.3(8) C7 N1 C3 116.5(4) F8 P2 F7 172.7(3) C3 N1 Fe1 115.6(3) F8 P2 F14 89.9(3) C8 N6 C2 121.6(4) F8 P2 F12 89.6(3) C1 N6 C8 111.3(4) F8 P2 F9 112.9(9) C1 N6 C2 127.1(4) F14 P2 F12 87.5(4) N3 C18 C19 113.6(4) F10 P2 F7 95.1(3) N3 C18 C17 122.0(4) F10 P2 F8 86.4(3) C17 C18 C19 124.4(4) F10 P2 F14 174.5(6) N4 C19 C18 111.0(4) F10 P2 F12 88.4(7) N4 C19 C20 121.2(5) F16 P2 F7 106.7(17) C20 C19 C18 127.7(4) F16 P2 F8 80.3(16) C29 N2 Fe1 171.2(4) F16 P2 F14 92.3(8) N1 C7 C6 123.6(5) F16 P2 F10 91.1(11) C26 C27 C28 119.4(5) F16 P2 F12 169.9(16) N1 C3 N7 111.6(4) F15 P2 F7 88.2(5) N1 C3 C4 123.7(4) F15 P2 F8 97.5(5) C4 C3 N7 124.7(4) F15 P2 F14 67.0(11) C9 C8 N6 107.3(4) F15 P2 F9 70.5(12) C9 C8 C13 121.9(4) F15 P2 F11 160.7(13) C13 C8 N6 130.8(4) F9 P2 F14 133.8(8) N4 C23 C24 112.0(4) F11 P2 F7 87.9(6) N4 C23 C22 120.7(4) F11 P2 F8 88.2(6) C22 C23 C24 127.3(4) F11 P2 F14 131.7(9) N7 C1 Fe1 114.0(3) F11 P2 F9 90.3(11) N6 C1 Fe1 140.5(3) F13 P2 F7 109.5(12) N6 C1 N7 105.5(4) F13 P2 F8 64.5(12) C3 C4 C5 117.5(5) F13 P2 F14 46.0(7) N5 C28 C27 122.6(5) F13 P2 F15 108.1(14) C18 C17 C16 119.0(5) F13 P2 F9 177.0(16) C26 C25 C24 118.5(5) F13 P2 F11 91.0(13) C15 C16 C17 119.2(5) P2 F8 F13 54.0(8) C8 C9 N7 104.6(4) P2 F14 F15 55.1(7) C10 C9 N7 134.5(5) F13 F14 P2 59.9(9) C10 C9 C8 120.9(5) F13 F14 F15 109.7(12) C12 C13 C8 117.0(5) Cl1 C31 Cl2 113.9(4) N2 C29 C30 176.9(6) Cl3 C31 Cl1 107.6(5) N3 C14 C15 122.6(5) P2 F15 F14 58.0(7)

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N5 C24 C23 113.5(4) P2 F13 F8 61.6(8) N5 C24 C25 122.2(4) F14 F13 P2 74.0(9) C25 C24 C23 124.3(5) F14 F13 F8 104.9(18)

Table S4. Crystal data and structure refinement for N-Fe-CO2+.

Empirical formula C29.50 H23Cl1F12Fe1N6O1P2 Formula weight 858.77 Crystal color, shape, size yellow plate, 0.150 x 0.150 x 0.050 mm3 Temperature 150 K Wavelength 1.54180 Å Crystal system, space group Monoclinic, C2/c Unit cell dimensions a = 20.0016(5) Å a= 90°. b = 18.5063(5) Å b= 105.9805(18)°. c = 18.5977(5) Å g = 90°. Volume 6618.0(3) Å3 Z 8 Density (calculated) 1.724 Mg/m3 Absorption coefficient 6.284 mm-1 F(000) 3448 Data collection Diffractometer Bruker Apex Kappa Duo, Bruker Theta range for data collection 3.314 to 66.672°. Index ranges -23<=h<=20, -20<=k<=19, -21<=l<=21 Reflections collected 39044 Independent reflections 5688 [R(int) = 0.088] Observed Reflections 4298 Completeness to theta = 43.337° 99.5 % Solution and Refinement Absorption correction Semi-empirical from equivalents Max. and min. transmission 0.73 and 0.39 Solution Direct methods Refinement method Full-matrix least-squares on F2 Weighting scheme w = [s2Fo2+ AP2+ BP]-1, with P = (Fo2+ 2 Fc2)/3, A = 0.060, B = 47.150 Data / restraints / parameters 5659 / 2 / 476 Goodness-of-fit on F2 1.0189 Final R indices [I>2sigma(I)] R1 = 0.0626, wR2 = 0.1449 R indices (all data) R1 = 0.0856, wR2 = 0.1586 Largest diff. peak and hole 1.71 and -0.82 e.Å-3

S31

Table S5. Bond lengths [Å] for N-Fe-CO2+ ___________________________________________________________________________ Fe1-N1 1.979(4) Fe1-N2 1.919(4) Fe1-N3 1.991(4) Fe1-N4 2.015(4) Fe1-C21 1.921(5) Fe1-C29 1.774(5) Cl1-C30 1.748(6) P1-F1 1.594(3) P1-F2 1.588(3) P1-F3 1.593(3) P1-F4 1.587(4) P1-F5 1.611(3) P1-F6 1.601(3) P2-F7 1.598(3) P2-F8 1.601(3) P2-F9 1.604(3) P2-F10 1.582(4) P2-F11 1.605(3) P2-F12 1.599(3) O1-C29 1.144(6) N1-C1 1.330(6) N1-C5 1.370(6) N2-C6 1.353(6) N2-C10 1.333(6) N3-C11 1.383(6) N3-C15 1.341(7) N4-C16 1.340(6) N4-C20 1.360(6) N5-C20 1.406(6) N5-C21 1.385(6) N5-C22 1.410(6) N6-C21 1.340(6) N6-C27 1.403(6) N6-C28 1.467(6) C1-C2 1.376(7) C1-H11 0.950 C2-C3 1.362(8) C2-H21 0.950 C3-C4 1.388(8) C3-H31 0.950 C4-C5 1.387(7) C4-H41 0.950 C5-C6 1.465(7) C6-C7 1.383(7) C7-C8 1.387(8) C7-H71 0.950 C8-C9 1.385(8) C8-H81 0.950 C9-C10 1.393(7) C9-H91 0.950 C10-C11 1.470(7) C11-C12 1.376(7) C12-C13 1.388(8) C12-H121 0.950 C13-C14 1.382(9) C13-H131 0.950 C14-C15 1.385(8) C14-H141 0.950 C15-H151 0.950 C16-C17 1.380(7) C16-H161 0.950 C17-C18 1.381(7) C17-H171 0.950 C18-C19 1.382(7) C18-H181 0.950 C19-C20 1.374(7) C19-H191 0.950 C22-C23 1.384(7) C22-C27 1.389(7) C23-C24 1.401(7) C23-H231 0.950 C24-C25 1.380(8) C24-H241 0.950 C25-C26 1.382(7) C25-H251 0.950 C26-C27 1.382(7) C26-H261 0.950 C28-H281 0.950 C28-H282 0.950 C28-H283 0.950 C30-H301#1 0.950 C30-H301 0.950

S32

Table S6. Angles [°] for N-Fe-CO2+ N1-Fe1-N2 81.15(17) N1-Fe1-N3 161.43(17) N2-Fe1-N3 80.49(17) N1-Fe1-N4 90.29(16) N2-Fe1-N4 92.70(16) N3-Fe1-N4 87.80(16) N1-Fe1-C21 96.76(17) N2-Fe1-C21 172.64(18) N3-Fe1-C21 101.10(17) N4-Fe1-C21 80.21(18) N1-Fe1-C29 94.7(2) N2-Fe1-C29 92.45(19) N3-Fe1-C29 88.8(2) N4-Fe1-C29 173.31(19) C21-Fe1-C29 94.8(2) F1-P1-F2 90.26(19) F1-P1-F3 89.51(19) F2-P1-F3 91.24(18) F1-P1-F4 179.3(2) F2-P1-F4 90.33(19) F3-P1-F4 90.8(2) F1-P1-F5 89.37(19) F2-P1-F5 179.08(19) F3-P1-F5 89.60(17) F4-P1-F5 90.0(2) F1-P1-F6 89.7(2) F2-P1-F6 89.55(18) F3-P1-F6 178.9(2) F4-P1-F6 90.0(2) F5-P1-F6 89.60(17) F7-P2-F8 89.37(19) F7-P2-F9 89.23(19) F8-P2-F9 90.6(2) F7-P2-F10 178.8(2) F8-P2-F10 89.7(2) F9-P2-F10 90.0(2) F7-P2-F11 89.7(2) F8-P2-F11 179.0(2) F9-P2-F11 89.83(19) F10-P2-F11 91.2(2) F7-P2-F12 90.02(18) F8-P2-F12 89.85(19) F9-P2-F12 179.1(2) F10-P2-F12 90.8(2) F11-P2-F12 89.71(18) Fe1-N1-C1 127.9(3) Fe1-N1-C5 114.2(3) C1-N1-C5 117.9(4) Fe1-N2-C6 118.3(3) Fe1-N2-C10 119.5(3) C6-N2-C10 122.2(4) Fe1-N3-C11 114.2(3) Fe1-N3-C15 127.4(4) C11-N3-C15 118.4(4) Fe1-N4-C16 127.1(3) Fe1-N4-C20 115.4(3) C16-N4-C20 117.3(4) C20-N5-C21 116.7(4) C20-N5-C22 132.0(4) C21-N5-C22 111.0(4) C21-N6-C27 110.9(4) C21-N6-C28 126.1(4) C27-N6-C28 123.0(4) N1-C1-C2 123.7(5) N1-C1-H11 117.9 C2-C1-H11 118.5 C1-C2-C3 118.7(5) C1-C2-H21 120.6 C3-C2-H21 120.7 C2-C3-C4 119.5(5) C2-C3-H31 119.9 C4-C3-H31 120.6 C3-C4-C5 119.3(5) C3-C4-H41 120.4 C5-C4-H41 120.3 C4-C5-N1 120.9(5) C4-C5-C6 124.8(5) N1-C5-C6 114.3(4) C5-C6-N2 111.9(4) C5-C6-C7 127.5(5) N2-C6-C7 120.6(5) C6-C7-C8 117.6(5) C6-C7-H71 120.9 C8-C7-H71 121.5 C7-C8-C9 121.4(5) C7-C8-H81 119.4

S33

C9-C8-H81 119.2 C8-C9-C10 118.3(5) C8-C9-H91 121.3 C10-C9-H91 120.5 C9-C10-N2 119.9(5) C9-C10-C11 127.9(5) N2-C10-C11 112.2(4) C10-C11-N3 113.5(4) C10-C11-C12 125.1(5) N3-C11-C12 121.4(5) C11-C12-C13 119.5(5) C11-C12-H121 119.8 C13-C12-H121 120.7 C12-C13-C14 119.1(5) C12-C13-H131 120.4 C14-C13-H131 120.5 C13-C14-C15 119.5(5) C13-C14-H141 120.1 C15-C14-H141 120.4 C14-C15-N3 122.1(5) C14-C15-H151 119.2 N3-C15-H151 118.7 N4-C16-C17 123.3(5) N4-C16-H161 118.1 C17-C16-H161 118.6 C16-C17-C18 118.3(5) C16-C17-H171 121.0 C18-C17-H171 120.7 C17-C18-C19 119.6(5) C17-C18-H181 120.2 C19-C18-H181 120.2 C18-C19-C20 118.7(5) C18-C19-H191 121.0 C20-C19-H191 120.4 N5-C20-C19 125.4(4) N5-C20-N4 111.9(4) C19-C20-N4 122.7(5) N5-C21-N6 105.7(4) N5-C21-Fe1 115.1(3) N6-C21-Fe1 139.1(4) N5-C22-C23 134.3(5) N5-C22-C27 104.7(4) C23-C22-C27 121.0(4) C22-C23-C24 116.7(5) C22-C23-H231 121.4 C24-C23-H231 121.9 C23-C24-C25 121.7(5) C23-C24-H241 119.1 C25-C24-H241 119.1 C24-C25-C26 121.4(5) C24-C25-H251 119.1 C26-C25-H251 119.5 C25-C26-C27 117.1(5) C25-C26-H261 121.9 C27-C26-H261 121.1 N6-C27-C22 107.6(4) N6-C27-C26 130.2(5) C22-C27-C26 122.1(4) N6-C28-H281 109.4 N6-C28-H282 109.5 H281-C28-H282 109.5 N6-C28-H283 109.6 H281-C28-H283 109.5 H282-C28-H283 109.5 O1-C29-Fe1 176.9(5) Cl1-C30-Cl1#1 113.3(5) Cl1-C30-H301#1 108.5 Cl1#1-C30-H301#1 108.5 Cl1-C30-H301 108.5 Cl1#1-C30-H301 108.5 H301#1-C30-H301 109.5 ___________________________________________________________________________

S34

5. Computational methods

5.1 Overview of computational methods.

The DFT calculations have been performed with the Gaussian09 software package15 using the

B3LYP density functional.16 Geometry optimizations and subsequent frequency calculations

have been performed at the B3LYP/6-31+g** level of theory. The effect of the solvent

(acetonitrile) and London interactions are considered through the SMD model17 and Grimme-

D3 dispersion correction,18 respectively.

The redox potentials (E°) have been evaluated through the Nernst equation in standard state

conditions and using the Standard Hydrogen Electrode (𝑆𝐻𝐸) as the reference (Eq. S5). To

compare with the experimental values, the potentials are reported versus the Fc+/Fc reference.

𝐸,(𝑉) = −W∆𝐺,

𝑛𝐹 −∆𝐺qr^,

𝐹 b(𝐸𝑞𝑆5)

where n is the number of electrons involved in the reduction step, F is the Faraday constant,

∆𝐺qr^, = -4.28 eV.

Scaling factor employed for the theoretical IR data was 0.967. The conversion factor used from Hartrees to kcal/mol was 627.5.

5.2 Computed Gibbs free energies of different complexes

Table S7. Calculated Gibbs free energy of different intermediates in MeCN

C-trans compound G (kcal/mol) N-trans compound G kcal/mol

-1760241.36

-1760240.862

-1760310.657

-1760310.538

S35

-1676913.382

-1676910.63

-1676992.286

-1676990.357

-1677054.882

-

-

-1795432,727

-1795432,205

-1748054.532

-1748057.948

-1748127.156

-1748131.48

-1748128.362

-1748130.083

S36

-1748181.636

-

-

-1748200,715

-1748201,924

5.3 Molecular orbital representations of MeCN complexes

Figure S33. HOMO (a) and LUMO (b) of C-Fe-MeCN2+

Figure S34. HOMO (a) and LUMO (b) of C-Fe-MeCN+

S37

Figure S35. Spin density plot of C-Fe-MeCN+

Figure S36. HOMO (a) and LUMO (b) of C-Fe0

5.4 Molecular representations of the computed five coordinate complexes

Figure S37. DFT computed structures of k1C-Fe-CO+ (a) and k1N-Fe-CO+ (b).

S38

Figure S38. DFT computed structures of k1C-Fe-CO0 (a) and k1N-Fe-CO0 (b).

5.5. Infrared vibrational computations.

Table S8. Computed infrared CO stretching frequencies (nCO).

Complex nCO (cm–1) C-Fe-CO2+ 2022 N-Fe-CO2+ 2009 C-Fe-CO+ 1992 N-Fe-CO+ 1975 k1C-Fe-CO+ 1883 k1N-Fe-CO+ 1876 C-Fe-CO0 1962 k1C-Fe-CO0 1830 k1N-Fe-CO0 1816

S39

5.6. Reaction free energies of different transformations

Table S9. Calculated change in Gibbs free energy of different reactions

Reaction DG (kcal/mol)

0.5

0.12

2.75

1.93

-0.5

-3.42

S40

-4.32

-1.21

-1.72

-1.41

-20.29

-19.08

-1.21

S41

Figure S39. Relative energy of the intermediates in the carbonylation of C-Fe-MeCN2+ to N-Fe-CO2+

Figure S40. Relative energies of carbonyl complexes at the charge state +1

S42

Figure S41. Relative energies of doubly reduced carbonyl complexes.

5.7. Computed reduction potentials

Figure S42. DFT computed reduction potentials of C-Fe-MeCN2+ (all potentials vs Fc+/Fc).

S43

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download fileview on ChemRxiv20200302_FeBimpy_SI.pdf (7.95 MiB)

1

Coordinates for Optimized Geometries in MeCN

1. C-trans complexes 2

1.1 C-Fe-MeCN2+ 2

1.2 C-Fe-MeCN+ 3

1.3 C-Fe2+ 5

1.4 C-Fe+ 6

1.5 C-Fe0 8

1.6 C-Fe-CO20 9

1.7 C-Fe-CO2+ 11

1.8 C-Fe-CO+ 12

1.9 k1C-Fe-CO+ 14

1.10 C-Fe-CO0 15

1.11 k1C-Fe-CO0 17

2. N-trans complexes 19

2.1 N-Fe-MeCN2+ 19

2.2 N-Fe-MeCN+ 20

2.3 N-Fe2+ 22

2.4 N-Fe+ 23

2.5 N-Fe-CO20 25

2.6 N-Fe-CO2+ 26

2.7 N-Fe-CO+ 28

2.8 k1N-Fe-CO+ 29

2.9 k1N-Fe-CO0 31

2

1. C-trans complexes

1.1 C-Fe-MeCN2+

Fe -0.594111000000 0.353652000000 0.293664000000 N -0.466132000000 -1.076036000000 1.698829000000 N -1.769291000000 -0.929952000000 -0.479791000000 N -1.147795000000 1.382359000000 -1.340151000000 N 2.196359000000 0.415830000000 -0.040820000000 N 0.677545000000 1.702307000000 1.089715000000 N 1.546374000000 -1.262069000000 -1.266098000000 C -2.035784000000 0.715573000000 -2.128568000000 C -2.407910000000 -0.617677000000 -1.621409000000 N -2.162451000000 1.103410000000 1.258213000000 C 0.339006000000 2.748782000000 1.864684000000 H -0.711524000000 2.846365000000 2.094249000000 C 0.272586000000 -2.099898000000 3.730157000000 H 0.869356000000 -2.023795000000 4.630035000000 C 1.979150000000 1.539464000000 0.769983000000 C 2.945621000000 -1.256326000000 -1.303258000000 C -1.981211000000 -2.088594000000 0.167805000000 C 1.078711000000 -0.271386000000 -0.487107000000 C 2.971941000000 2.417915000000 1.194045000000 H 3.998833000000 2.288367000000 0.897271000000 C 0.250381000000 -1.041574000000 2.828536000000 H 0.817641000000 -0.138048000000 3.007460000000 C -2.531800000000 1.276380000000 -3.302214000000 H -3.233319000000 0.724584000000 -3.913689000000 C -1.232835000000 -3.277259000000 2.280644000000 H -1.831965000000 -4.145212000000 2.039946000000 C -2.114183000000 2.550662000000 -3.672815000000 H -2.488458000000 3.003893000000 -4.582739000000 C 3.378943000000 -0.180066000000 -0.514993000000 C 0.757241000000 -2.275339000000 -1.962450000000 H 1.192018000000 -2.445134000000 -2.947068000000 H -0.258224000000 -1.923745000000 -2.087714000000 H 0.763345000000 -3.208376000000 -1.396880000000 C 3.833571000000 -2.114161000000 -1.942286000000 H 3.482470000000 -2.944519000000 -2.541205000000

3

C -3.125510000000 1.459577000000 1.775341000000 C -0.755905000000 2.610260000000 -1.700546000000 H -0.056060000000 3.101761000000 -1.038158000000 C -1.212140000000 -2.181298000000 1.422563000000 C 2.603786000000 3.490567000000 1.996305000000 H 3.358781000000 4.187855000000 2.338627000000 C -3.295811000000 -1.524693000000 -2.197327000000 H -3.809832000000 -1.287340000000 -3.118937000000 C -3.506556000000 -2.745118000000 -1.558179000000 H -4.188026000000 -3.467767000000 -1.989912000000 C -2.853266000000 -3.037948000000 -0.362636000000 H -3.023436000000 -3.978507000000 0.143603000000 C 1.266340000000 3.659521000000 2.344330000000 H 0.940011000000 4.482175000000 2.966893000000 C 4.740296000000 0.059656000000 -0.332923000000 H 5.118457000000 0.859419000000 0.284357000000 C -1.214063000000 3.230379000000 -2.857905000000 H -0.865794000000 4.224791000000 -3.106047000000 C 5.193157000000 -1.864946000000 -1.768090000000 H 5.918797000000 -2.511062000000 -2.247749000000 C 5.634403000000 -0.798221000000 -0.973969000000 H 6.697658000000 -0.632728000000 -0.846093000000 C -0.478138000000 -3.236957000000 3.448822000000 H -0.480614000000 -4.080366000000 4.128693000000 C -4.330083000000 1.920629000000 2.432470000000 H -4.784354000000 1.096912000000 2.987453000000 H -5.037863000000 2.287252000000 1.685674000000 H -4.082907000000 2.729916000000 3.123324000000

1.2 C-Fe-MeCN+

Fe -0.568628000000 0.382022000000 0.254004000000 N -0.650124000000 -0.893767000000 1.796346000000 N -1.786332000000 -0.883023000000 -0.490464000000 N -0.941448000000 1.274069000000 -1.510685000000 N 2.230377000000 0.287956000000 0.070701000000 N 0.726649000000 1.714083000000 1.039687000000 N 1.548529000000 -1.439906000000 -1.067109000000

4

C -1.829560000000 0.599772000000 -2.297279000000 C -2.344351000000 -0.642952000000 -1.693500000000 N -2.173727000000 1.333890000000 1.008321000000 C 0.407589000000 2.810336000000 1.751465000000 H -0.648318000000 2.989811000000 1.890548000000 C -0.122853000000 -1.768649000000 3.972303000000 H 0.426004000000 -1.651572000000 4.897858000000 C 2.034745000000 1.446196000000 0.835833000000 C 2.945374000000 -1.459864000000 -1.106696000000 C -2.152068000000 -1.957735000000 0.293043000000 C 1.093427000000 -0.390463000000 -0.355903000000 C 3.053668000000 2.251797000000 1.338806000000 H 4.090601000000 2.015314000000 1.171213000000 C -0.000653000000 -0.823168000000 2.968185000000 H 0.643624000000 0.039314000000 3.094179000000 C -2.192373000000 1.082707000000 -3.554643000000 H -2.896402000000 0.530536000000 -4.163261000000 C -1.654717000000 -2.976950000000 2.554251000000 H -2.309894000000 -3.818337000000 2.362073000000 C -1.643677000000 2.274289000000 -4.013493000000 H -1.916017000000 2.661431000000 -4.988144000000 C 3.400451000000 -0.348816000000 -0.380389000000 C 0.744965000000 -2.467660000000 -1.721149000000 H 1.052931000000 -2.555179000000 -2.764016000000 H -0.298302000000 -2.186593000000 -1.672813000000 H 0.891951000000 -3.425466000000 -1.218677000000 C 3.813291000000 -2.354818000000 -1.720364000000 H 3.441781000000 -3.207275000000 -2.274371000000 C -3.157412000000 1.801586000000 1.377885000000 C -0.420519000000 2.425941000000 -1.960581000000 H 0.270844000000 2.924520000000 -1.294168000000 C -1.500335000000 -1.976877000000 1.560514000000 C 2.703675000000 3.377950000000 2.072870000000 H 3.479281000000 4.019082000000 2.474049000000 C -3.276349000000 -1.511281000000 -2.240184000000 H -3.720857000000 -1.323590000000 -3.207861000000 C -3.637855000000 -2.656093000000 -1.482019000000 H -4.359760000000 -3.356891000000 -1.884955000000 C -3.091276000000 -2.875477000000 -0.232770000000 H -3.386167000000 -3.740973000000 0.348307000000 C 1.357748000000 3.667350000000 2.283224000000 H 1.044181000000 4.535234000000 2.848477000000 C 4.766694000000 -0.101677000000 -0.256113000000 H 5.163599000000 0.741720000000 0.286276000000 C -0.741572000000 2.960743000000 -3.200542000000 H -0.292033000000 3.893876000000 -3.515764000000 C 5.178910000000 -2.106369000000 -1.590844000000 H 5.889953000000 -2.780234000000 -2.054012000000 C 5.642757000000 -0.997875000000 -0.871387000000 H 6.709131000000 -0.824483000000 -0.786899000000

5

C -0.977565000000 -2.877456000000 3.747525000000 H -1.095781000000 -3.641667000000 4.507606000000 C -4.392530000000 2.399216000000 1.843294000000 H -4.908681000000 1.705849000000 2.511034000000 H -5.036424000000 2.624314000000 0.990164000000 H -4.174168000000 3.323338000000 2.383433000000

1.3 C-Fe2+

Fe -0.600099000000 0.123480000000 0.804517000000 N -0.804024000000 -1.875724000000 0.997964000000 N -2.250515000000 -0.109484000000 -0.134062000000 N -1.013333000000 2.046921000000 0.409666000000 N 2.029521000000 0.083289000000 -0.113333000000 N 1.039034000000 0.387343000000 1.910604000000 N 0.796935000000 -0.274070000000 -1.879536000000 C -2.168465000000 2.231269000000 -0.292245000000 C -2.902822000000 0.982294000000 -0.577914000000 C 1.029179000000 0.623022000000 3.232224000000 H 0.050339000000 0.646175000000 3.695791000000 C -0.184711000000 -4.091972000000 1.652516000000 H 0.519843000000 -4.732282000000 2.167406000000 C 2.214211000000 0.342221000000 1.253587000000 C 2.130911000000 -0.338462000000 -2.297610000000 C -2.766043000000 -1.348122000000 -0.247867000000 C 0.718306000000 -0.034485000000 -0.560708000000 C 3.430270000000 0.544151000000 1.898429000000 H 4.364674000000 0.518815000000 1.362723000000 C 0.030803000000 -2.718358000000 1.619153000000 H 0.891975000000 -2.270103000000 2.096220000000 C -2.583356000000 3.498427000000 -0.686900000000 H -3.499572000000 3.623102000000 -1.248369000000 C -2.182903000000 -3.739816000000 0.369622000000 H -3.063449000000 -4.117768000000 -0.132537000000 C -1.802559000000 4.601865000000 -0.351998000000 H -2.109189000000 5.596302000000 -0.652870000000 C 2.934656000000 -0.106076000000 -1.171003000000 C -0.325362000000 -0.485426000000 -2.789108000000 H -0.154153000000 0.083000000000 -3.703143000000

6

H -1.234716000000 -0.136971000000 -2.316546000000 H -0.414999000000 -1.546363000000 -3.028464000000 C 2.669201000000 -0.583793000000 -3.555130000000 H 2.034588000000 -0.767016000000 -4.412631000000 C -0.269944000000 3.114338000000 0.729182000000 H 0.636621000000 2.915251000000 1.284868000000 C -1.910954000000 -2.376279000000 0.378565000000 C 3.409612000000 0.786319000000 3.268098000000 H 4.342844000000 0.945895000000 3.794577000000 C -4.128100000000 0.850550000000 -1.227379000000 H -4.658111000000 1.718799000000 -1.594596000000 C -4.659450000000 -0.428026000000 -1.388435000000 H -5.608403000000 -0.555498000000 -1.894702000000 C -3.986664000000 -1.542449000000 -0.890196000000 H -4.407199000000 -2.533175000000 -0.994382000000 C 2.195646000000 0.825485000000 3.952334000000 H 2.150121000000 1.012327000000 5.016987000000 C 4.323560000000 -0.111682000000 -1.278057000000 H 4.973949000000 0.059298000000 -0.434295000000 C -0.629326000000 4.408480000000 0.368805000000 H 0.005769000000 5.238542000000 0.650165000000 C 4.058840000000 -0.588209000000 -3.659602000000 H 4.520007000000 -0.776156000000 -4.621888000000 C 4.867897000000 -0.355728000000 -2.539214000000 H 5.945831000000 -0.366601000000 -2.648848000000 C -1.306692000000 -4.609388000000 1.014459000000 H -1.501949000000 -5.674889000000 1.016320000000

1.4 C-Fe+

Fe -0.609227000000 -0.006559000000 0.738225000000 N -0.962445000000 -1.974210000000 0.696781000000 N -2.261888000000 -0.002203000000 -0.156109000000 N -0.967922000000 1.959978000000 0.726747000000 N 2.071542000000 -0.002791000000 -0.074995000000 N 1.005722000000 -0.015272000000 1.937262000000 N 0.899444000000 0.020352000000 -1.916585000000 C -2.093302000000 2.324323000000 0.020449000000 C -2.863523000000 1.193242000000 -0.464006000000

7

C 0.964271000000 -0.024682000000 3.279669000000 H -0.027666000000 -0.025515000000 3.714748000000 C -0.457634000000 -4.300707000000 1.020514000000 H 0.203389000000 -5.044057000000 1.448060000000 C 2.206047000000 -0.013851000000 1.319704000000 C 2.244185000000 0.023945000000 -2.296464000000 C -2.861016000000 -1.194489000000 -0.480793000000 C 0.770096000000 0.005107000000 -0.575764000000 C 3.405507000000 -0.021634000000 2.026326000000 H 4.355505000000 -0.020710000000 1.518764000000 C -0.182372000000 -2.957801000000 1.195058000000 H 0.687373000000 -2.630618000000 1.749472000000 C -2.418508000000 3.673090000000 -0.177552000000 H -3.301555000000 3.932596000000 -0.747671000000 C -2.409396000000 -3.677032000000 -0.232535000000 H -3.292373000000 -3.929970000000 -0.805692000000 C -1.608159000000 4.659573000000 0.356621000000 H -1.849835000000 5.705762000000 0.211587000000 C 3.011514000000 0.009201000000 -1.119094000000 C -0.204249000000 0.049357000000 -2.868363000000 H -0.170045000000 0.974538000000 -3.446462000000 H -1.134800000000 -0.001629000000 -2.313286000000 H -0.130098000000 -0.803605000000 -3.544697000000 C 2.823471000000 0.038677000000 -3.558993000000 H 2.215486000000 0.050202000000 -4.454827000000 C -0.191664000000 2.937637000000 1.242234000000 H 0.677636000000 2.603830000000 1.793451000000 C -2.087535000000 -2.330662000000 -0.013893000000 C 3.347408000000 -0.031174000000 3.415445000000 H 4.266947000000 -0.037326000000 3.988198000000 C -4.072720000000 1.214353000000 -1.148654000000 H -4.546435000000 2.156789000000 -1.392803000000 C -4.677897000000 0.004707000000 -1.507952000000 H -5.621122000000 0.007467000000 -2.039913000000 C -4.070316000000 -1.208588000000 -1.165501000000 H -4.542195000000 -2.148515000000 -1.422512000000 C 2.110508000000 -0.032709000000 4.058992000000 H 2.032211000000 -0.039856000000 5.138183000000 C 4.402917000000 0.008867000000 -1.182543000000 H 5.028629000000 -0.001974000000 -0.303118000000 C -0.470507000000 4.282354000000 1.088543000000 H 0.187459000000 5.020759000000 1.529171000000 C 4.217140000000 0.038295000000 -3.619071000000 H 4.708740000000 0.049673000000 -4.584707000000 C 4.988911000000 0.023793000000 -2.450439000000 H 6.070029000000 0.024077000000 -2.525106000000 C -1.595525000000 -4.669584000000 0.284740000000 H -1.834456000000 -5.714024000000 0.123516000000

8

1.5 C-Fe0

Fe 0.604124000000 -0.003157000000 0.614887000000 N 0.956526000000 1.938980000000 0.660933000000 N 2.296855000000 0.027342000000 -0.176953000000 N 1.020444000000 -1.932065000000 0.648499000000 N -2.119919000000 -0.022504000000 -0.023799000000 N -0.950277000000 -0.025544000000 1.925797000000 N -1.013579000000 -0.018514000000 -1.913047000000 C 2.180798000000 -2.298422000000 -0.041020000000 C 2.936176000000 -1.169216000000 -0.495330000000 C -0.850852000000 -0.030380000000 3.265665000000 H 0.159941000000 -0.029250000000 3.654430000000 C 0.395158000000 4.261352000000 1.014516000000 H -0.294713000000 4.981186000000 1.438416000000 C -2.185828000000 -0.026850000000 1.372080000000 C -2.368546000000 -0.020217000000 -2.240210000000 C 2.896082000000 1.246227000000 -0.487998000000 C -0.826963000000 -0.017276000000 -0.568903000000 C -3.350967000000 -0.031359000000 2.136390000000 H -4.324176000000 -0.031226000000 1.673232000000 C 0.143102000000 2.916539000000 1.151062000000 H -0.740505000000 2.565234000000 1.669166000000 C 2.515342000000 -3.654260000000 -0.226511000000 H 3.416063000000 -3.903055000000 -0.775693000000 C 2.395485000000 3.714429000000 -0.200784000000 H 3.287768000000 3.995695000000 -0.748041000000 C 1.706345000000 -4.648592000000 0.280552000000 H 1.959440000000 -5.693184000000 0.142389000000 C -3.094696000000 -0.023918000000 -1.033105000000 C 0.065716000000 -0.005564000000 -2.890380000000 H -0.031614000000 -0.857964000000 -3.565338000000 H 1.005798000000 -0.069994000000 -2.347467000000 H 0.037940000000 0.919401000000 -3.470463000000 C -2.998062000000 -0.019730000000 -3.478457000000 H -2.425132000000 -0.016395000000 -4.397266000000 C 0.239006000000 -2.938903000000 1.131299000000 H -0.654203000000 -2.619574000000 1.653319000000 C 2.104305000000 2.347333000000 -0.025833000000 C -3.226413000000 -0.035838000000 3.520858000000

9

H -4.116521000000 -0.039300000000 4.138638000000 C 4.162644000000 -1.153885000000 -1.146639000000 H 4.661028000000 -2.085713000000 -1.387864000000 C 4.762170000000 0.072000000000 -1.476854000000 H 5.721409000000 0.089537000000 -1.980009000000 C 4.122203000000 1.275407000000 -1.139305000000 H 4.589389000000 2.224657000000 -1.375053000000 C -1.957952000000 -0.035851000000 4.101109000000 H -1.825599000000 -0.039472000000 5.175190000000 C -4.486381000000 -0.028159000000 -1.045752000000 H -5.075656000000 -0.031321000000 -0.141041000000 C 0.533301000000 -4.273868000000 0.983894000000 H -0.133331000000 -5.018444000000 1.402194000000 C -4.394969000000 -0.023623000000 -3.486895000000 H -4.921361000000 -0.023154000000 -4.434281000000 C -5.122510000000 -0.027747000000 -2.291660000000 H -6.205830000000 -0.030536000000 -2.325142000000 C 1.555704000000 4.678602000000 0.314623000000 H 1.775915000000 5.731724000000 0.185152000000

1.6 C-FeCO20

N -2.199831000 0.285805000 -0.109056000 C -3.293270000 -0.214614000 -0.838981000 C -2.719144000 -1.019995000 -1.837120000 N -1.334540000 -0.964964000 -1.666977000 C -0.995534000 -0.189523000 -0.613108000 C -3.486496000 -1.707808000 -2.769589000 C -4.871773000 -1.570942000 -2.681673000 C -5.453314000 -0.775064000 -1.687232000 C -4.678492000 -0.086499000 -0.750692000 Fe 0.596005000 0.272413000 0.421620000 C 2.108537000 0.851870000 1.816978000 C -0.406804000 -1.686889000 -2.529492000 C -2.121713000 1.171521000 0.975677000 C -3.214752000 1.841484000 1.521787000 C -2.993282000 2.716926000 2.577267000 C -1.696976000 2.893932000 3.051911000 C -0.667139000 2.180240000 2.455983000

10

N -0.858359000 1.325482000 1.432823000 N 1.947002000 -0.647817000 -0.459408000 C 2.705417000 0.020657000 -1.366196000 C 3.758827000 -0.624513000 -2.013660000 C 4.031397000 -1.956035000 -1.704710000 C 3.261718000 -2.621269000 -0.745933000 C 2.221674000 -1.936255000 -0.127151000 C 2.253990000 1.396171000 -1.546490000 C 2.815933000 2.310800000 -2.443895000 C 2.292476000 3.591300000 -2.530913000 C 1.202081000 3.929646000 -1.721736000 C 0.684157000 2.974767000 -0.861941000 N 1.187349000 1.731549000 -0.758754000 C 1.340981000 -2.411548000 0.938948000 C 1.359894000 -3.694469000 1.489373000 C 0.497573000 -3.999159000 2.534333000 C -0.362638000 -3.005233000 3.007899000 C -0.333953000 -1.751764000 2.415002000 N 0.487964000 -1.447423000 1.396799000 H 4.845451000 -2.471958000 -2.199002000 H 4.359126000 -0.097017000 -2.743626000 H 3.477763000 -3.648389000 -0.481409000 H 3.655197000 2.015540000 -3.060703000 H 2.718815000 4.313599000 -3.216952000 H -0.160521000 3.196024000 -0.223102000 H 0.758080000 4.916768000 -1.756253000 H 2.045614000 -4.437636000 1.103343000 H 0.496844000 -4.989106000 2.974628000 H -0.980302000 -0.953443000 2.752549000 H -1.046628000 -3.195197000 3.825846000 H -6.532440000 -0.689310000 -1.635091000 H -5.505175000 -2.091619000 -3.390321000 H -3.024516000 -2.327263000 -3.527849000 H -5.164781000 0.507823000 0.007063000 H -0.434549000 -2.755240000 -2.305236000 H -0.689157000 -1.530615000 -3.571472000 H 0.594025000 -1.304017000 -2.369452000 H -4.208123000 1.704270000 1.130280000 H -3.826790000 3.253015000 3.015397000 H 0.350579000 2.251985000 2.806098000 H -1.479138000 3.567117000 3.871194000 O 3.172540000 1.330178000 1.349732000 O 1.853855000 0.661958000 3.037278000

11

1.7 C-Fe-CO2+

Fe -0.643457000000 0.385081000000 0.660374000000 N -0.487498000000 -1.426772000000 1.523322000000 N -2.060997000000 -0.511935000000 -0.261679000000 N -1.238618000000 1.885031000000 -0.542055000000 N 2.061385000000 0.247167000000 -0.202225000000 N 0.949962000000 1.286926000000 1.517042000000 N 0.988731000000 -0.927581000000 -1.686208000000 C -2.292607000000 1.558193000000 -1.341137000000 C -2.774620000000 0.175637000000 -1.170510000000 C -1.841734000000 0.902151000000 1.963947000000 C 0.911408000000 2.079643000000 2.605864000000 H -0.057013000000 2.227588000000 3.060773000000 C 0.416119000000 -3.086319000000 2.983833000000 H 1.141760000000 -3.339838000000 3.745682000000 C 2.144614000000 1.087029000000 0.919017000000 C 2.351231000000 -1.044874000000 -1.991921000000 C -2.307370000000 -1.799917000000 0.031913000000 C 0.807061000000 -0.166918000000 -0.598594000000 C 3.319263000000 1.673205000000 1.379931000000 H 4.255583000000 1.520973000000 0.872256000000 C 0.386133000000 -1.796118000000 2.466781000000 H 1.072965000000 -1.033216000000 2.807538000000 C -2.833914000000 2.475331000000 -2.236630000000 H -3.669891000000 2.196286000000 -2.863818000000 C -1.410065000000 -3.641712000000 1.529069000000 H -2.131335000000 -4.349549000000 1.143907000000 C -2.285942000000 3.751947000000 -2.312600000000 H -2.693412000000 4.478610000000 -3.004878000000 C 3.055464000000 -0.290217000000 -1.042277000000 C -0.053538000000 -1.619786000000 -2.445697000000 H 0.291539000000 -1.756664000000 -3.468086000000 H -0.952333000000 -1.015678000000 -2.468841000000 H -0.260366000000 -2.592016000000 -1.998092000000 C 2.994167000000 -1.752108000000 -3.002678000000 H 2.440717000000 -2.337416000000 -3.724874000000 O -2.626685000000 1.163373000000 2.744889000000 C -0.721044000000 3.116708000000 -0.614817000000

12

H 0.107440000000 3.328392000000 0.047002000000 C -1.389359000000 -2.333856000000 1.054997000000 C 3.258852000000 2.483595000000 2.505608000000 H 4.162008000000 2.949697000000 2.880104000000 C -3.814386000000 -0.450279000000 -1.855015000000 H -4.394774000000 0.086453000000 -2.592690000000 C -4.084645000000 -1.787815000000 -1.572474000000 H -4.885536000000 -2.295481000000 -2.095583000000 C -3.332251000000 -2.478518000000 -0.625166000000 H -3.538546000000 -3.517664000000 -0.408314000000 C 2.035251000000 2.690411000000 3.134859000000 H 1.943122000000 3.314627000000 4.013577000000 C 4.448649000000 -0.229767000000 -1.078578000000 H 5.033145000000 0.321889000000 -0.359547000000 C -1.213815000000 4.078771000000 -1.489217000000 H -0.759017000000 5.060560000000 -1.513837000000 C 4.383668000000 -1.682516000000 -3.040585000000 H 4.922276000000 -2.219827000000 -3.811986000000 C 5.095013000000 -0.935152000000 -2.091920000000 H 6.177095000000 -0.904750000000 -2.139318000000 C -0.494409000000 -4.022622000000 2.505176000000 H -0.495971000000 -5.036689000000 2.885759000000

1.8 C-Fe-CO+

Fe -0.634069000000 0.320336000000 0.707470000000 N -0.633920000000 -1.584595000000 1.375784000000 N -2.076615000000 -0.386246000000 -0.334238000000 N -1.085866000000 1.973202000000 -0.341273000000 N 2.083468000000 0.142564000000 -0.127728000000 N 0.989466000000 1.020681000000 1.691291000000 N 0.990286000000 -0.783711000000 -1.763570000000 C -2.154054000000 1.781808000000 -1.220005000000 C -2.715658000000 0.473123000000 -1.204274000000 C -1.855146000000 0.805472000000 1.979214000000 C 0.970346000000 1.680128000000 2.865640000000 H 0.001066000000 1.819091000000 3.321512000000

13

C 0.114566000000 -3.443725000000 2.680977000000 H 0.801961000000 -3.824626000000 3.425421000000 C 2.184131000000 0.830123000000 1.092094000000 C 2.349727000000 -0.901810000000 -2.074143000000 C -2.432320000000 -1.677061000000 -0.187622000000 C 0.815729000000 -0.168961000000 -0.584712000000 C 3.378832000000 1.294333000000 1.636313000000 H 4.317555000000 1.143956000000 1.132281000000 C 0.188162000000 -2.112898000000 2.294173000000 H 0.920715000000 -1.440802000000 2.721241000000 C -2.585431000000 2.858162000000 -2.037197000000 H -3.409764000000 2.704353000000 -2.722941000000 C -1.711303000000 -3.717407000000 1.147129000000 H -2.472323000000 -4.327211000000 0.678480000000 C -1.960849000000 4.080604000000 -1.957152000000 H -2.289544000000 4.902405000000 -2.583246000000 C 3.068981000000 -0.305770000000 -1.028491000000 C -0.050280000000 -1.308713000000 -2.645484000000 H 0.188942000000 -1.034904000000 -3.672971000000 H -1.002775000000 -0.874084000000 -2.376030000000 H -0.095211000000 -2.395572000000 -2.560386000000 C 2.973101000000 -1.483295000000 -3.172357000000 H 2.399735000000 -1.943336000000 -3.966753000000 O -2.685142000000 1.086751000000 2.710387000000 C -0.499555000000 3.178167000000 -0.275158000000 H 0.314413000000 3.265212000000 0.434543000000 C -1.586497000000 -2.372782000000 0.799718000000 C 3.337005000000 1.971063000000 2.847793000000 H 4.254830000000 2.341786000000 3.287622000000 C -3.784664000000 -0.044234000000 -1.975339000000 H -4.308096000000 0.598769000000 -2.672089000000 C -4.148729000000 -1.368144000000 -1.839129000000 H -4.964103000000 -1.765466000000 -2.432082000000 C -3.467297000000 -2.220940000000 -0.929408000000 H -3.750174000000 -3.258742000000 -0.822349000000 C 2.112009000000 2.168042000000 3.478449000000 H 2.033371000000 2.690773000000 4.422446000000 C 4.463196000000 -0.279829000000 -1.059409000000 H 5.061690000000 0.157984000000 -0.276529000000 C -0.886019000000 4.257340000000 -1.049899000000 H -0.371979000000 5.204776000000 -0.953541000000 C 4.364972000000 -1.452889000000 -3.200649000000 H 4.891002000000 -1.896519000000 -4.037569000000 C 5.092935000000 -0.861250000000 -2.159617000000 H 6.175696000000 -0.854377000000 -2.203031000000 C -0.852626000000 -4.259709000000 2.095591000000 H -0.937391000000 -5.303178000000 2.374503000000

14

1.9 k1C-Fe-CO+

Fe 0.797466000000 0.032486000000 0.112406000000 O 0.488026000000 0.825006000000 2.924403000000 N 0.976101000000 -1.927506000000 0.515206000000 N 2.686723000000 -0.171595000000 -0.071786000000 N 1.259216000000 1.821647000000 -0.663761000000 N -2.120253000000 2.095090000000 1.261231000000 N -2.301164000000 0.153410000000 -0.040183000000 N -1.322141000000 -0.727528000000 -1.764476000000 C -0.017096000000 -2.777406000000 0.836778000000 C 0.210732000000 -4.089839000000 1.217620000000 C 1.525817000000 -4.555601000000 1.281788000000 C 2.561155000000 -3.689604000000 0.959673000000 C 2.265312000000 -2.380204000000 0.574657000000 C 3.258045000000 -1.371798000000 0.200551000000 C 4.635945000000 -1.539059000000 0.089284000000 C 5.414404000000 -0.457550000000 -0.324253000000 C 4.809501000000 0.758986000000 -0.641324000000 C 3.427756000000 0.874880000000 -0.514610000000 C 2.599072000000 2.036857000000 -0.836998000000 C 3.089563000000 3.263107000000 -1.289334000000 C 2.199479000000 4.288676000000 -1.575166000000 C 0.832815000000 4.065618000000 -1.394482000000 C 0.407653000000 2.827931000000 -0.937575000000 C -2.312557000000 2.746787000000 2.414886000000 C -2.923031000000 2.167525000000 3.524542000000 C -3.345362000000 0.843223000000 3.435868000000 C -3.137149000000 0.149521000000 2.247658000000 C -2.522388000000 0.829561000000 1.200424000000 C -1.067142000000 -0.114580000000 -0.575541000000 C -3.327196000000 -0.306587000000 -0.872879000000 C -4.714619000000 -0.265752000000 -0.770127000000 C -5.441419000000 -0.829002000000 -1.818392000000 C -4.801712000000 -1.408030000000 -2.927582000000 C -3.411809000000 -1.440288000000 -3.029590000000 C -2.688904000000 -0.875467000000 -1.981507000000 C -0.303167000000 -1.231504000000 -2.679913000000 C 0.564334000000 0.536929000000 1.807203000000

15

H -1.019032000000 -2.373915000000 0.785262000000 H -0.628397000000 -4.729498000000 1.459978000000 H 1.738165000000 -5.575229000000 1.579843000000 H 3.590217000000 -4.020698000000 1.004784000000 H 5.095136000000 -2.493245000000 0.311534000000 H 6.487919000000 -0.567953000000 -0.415282000000 H 5.402546000000 1.594817000000 -0.988538000000 H 4.155058000000 3.405562000000 -1.413275000000 H 2.562730000000 5.245612000000 -1.930119000000 H 0.102742000000 4.837594000000 -1.602460000000 H -0.637422000000 2.617837000000 -0.758181000000 H -1.967073000000 3.775048000000 2.447302000000 H -3.060604000000 2.742335000000 4.432067000000 H -3.819251000000 0.353688000000 4.278447000000 H -3.431175000000 -0.885529000000 2.129725000000 H -5.205649000000 0.179663000000 0.085575000000 H -6.524319000000 -0.820123000000 -1.775034000000 H -5.401261000000 -1.838718000000 -3.721159000000 H -2.915273000000 -1.884516000000 -3.882953000000 H -0.568280000000 -0.957665000000 -3.701861000000 H -0.227782000000 -2.317874000000 -2.601623000000 H 0.655126000000 -0.780473000000 -2.425379000000

1.10 C-Fe-CO0

Fe -0.622001000000 0.115247000000 0.769043000000 N -0.904698000000 -1.883263000000 0.861525000000 N -2.088385000000 -0.082270000000 -0.454969000000 N -0.789616000000 2.041467000000 0.223804000000 N 2.107518000000 -0.031203000000 -0.058322000000 N 1.021005000000 0.288927000000 1.938955000000 N 0.997493000000 -0.340412000000 -1.902257000000 C -1.873189000000 2.246572000000 -0.697310000000 C -2.583340000000 1.108800000000 -1.043948000000 C -1.852170000000 0.431401000000 2.062975000000 C 1.011623000000 0.515919000000 3.266520000000 H 0.039539000000 0.555425000000 3.736343000000 C -0.451766000000 -4.125259000000 1.577336000000

16

H 0.157243000000 -4.792427000000 2.174506000000 C 2.218383000000 0.224051000000 1.317282000000 C 2.353182000000 -0.421172000000 -2.235891000000 C -2.639283000000 -1.284463000000 -0.661929000000 C 0.831693000000 -0.121000000000 -0.589077000000 C 3.424068000000 0.415539000000 1.988511000000 H 4.365439000000 0.391128000000 1.467305000000 C -0.187423000000 -2.764547000000 1.582914000000 H 0.617258000000 -2.347955000000 2.174974000000 C -2.107755000000 3.591780000000 -1.165406000000 H -2.920422000000 3.762996000000 -1.863949000000 C -2.252025000000 -3.698385000000 0.046651000000 H -3.072972000000 -4.036919000000 -0.571739000000 C -1.326557000000 4.629545000000 -0.747156000000 H -1.517460000000 5.633861000000 -1.112877000000 C 3.084022000000 -0.223199000000 -1.054317000000 C -0.064103000000 -0.526026000000 -2.888284000000 H 0.170834000000 0.057198000000 -3.778864000000 H -0.998302000000 -0.182446000000 -2.462740000000 H -0.141109000000 -1.581911000000 -3.155556000000 C 2.966342000000 -0.661923000000 -3.459647000000 H 2.383921000000 -0.817297000000 -4.358685000000 O -2.702395000000 0.668607000000 2.792481000000 C -0.054294000000 3.091510000000 0.610792000000 H 0.742000000000 2.863731000000 1.313662000000 C -1.936004000000 -2.340645000000 0.090974000000 C 3.391081000000 0.652988000000 3.356373000000 H 4.317162000000 0.804276000000 3.897691000000 C -3.704790000000 0.947710000000 -1.927418000000 H -4.124215000000 1.820071000000 -2.417665000000 C -4.247794000000 -0.290957000000 -2.154063000000 H -5.094043000000 -0.389306000000 -2.825972000000 C -3.719374000000 -1.469951000000 -1.511732000000 H -4.150101000000 -2.446064000000 -1.683989000000 C 2.164156000000 0.696804000000 4.012861000000 H 2.093033000000 0.876034000000 5.077632000000 C 4.477435000000 -0.271725000000 -1.073099000000 H 5.081438000000 -0.143226000000 -0.189129000000 C -0.249707000000 4.392429000000 0.180649000000 H 0.386720000000 5.191406000000 0.538602000000 C 4.359116000000 -0.701166000000 -3.475566000000 H 4.877298000000 -0.886367000000 -4.409084000000 C 5.097410000000 -0.510670000000 -2.300139000000 H 6.179716000000 -0.552483000000 -2.337143000000 C -1.506343000000 -4.603425000000 0.794920000000 H -1.740581000000 -5.660934000000 0.767905000000

17

1.11 k1C-Fe-CO0

Fe -0.799720000000 -0.206607000000 0.467115000000 O 0.105958000000 -1.267095000000 3.015018000000 N -0.939873000000 1.682578000000 1.027771000000 N -2.577185000000 0.119926000000 0.037059000000 N -1.265593000000 -1.931398000000 -0.391727000000 N 2.575045000000 -2.110923000000 0.792728000000 N 2.173840000000 -0.064394000000 -0.290665000000 N 0.845475000000 0.899750000000 -1.710199000000 C 0.055870000000 2.444997000000 1.547281000000 C -0.117246000000 3.755229000000 1.932675000000 C -1.392090000000 4.345828000000 1.793343000000 C -2.420184000000 3.591858000000 1.269176000000 C -2.188199000000 2.257671000000 0.880225000000 C -3.150152000000 1.360562000000 0.307683000000 C -4.486456000000 1.604982000000 0.018194000000 C -5.270295000000 0.601509000000 -0.565027000000 C -4.689207000000 -0.639403000000 -0.861307000000 C -3.353186000000 -0.867708000000 -0.563320000000 C -2.579950000000 -2.054014000000 -0.801159000000 C -3.051320000000 -3.248440000000 -1.380115000000 C -2.193338000000 -4.312946000000 -1.557955000000 C -0.850309000000 -4.177630000000 -1.147762000000 C -0.439469000000 -2.992329000000 -0.577859000000 C 3.051301000000 -2.802159000000 1.836143000000 C 3.662117000000 -2.200521000000 2.933527000000 C 3.777421000000 -0.812835000000 2.952549000000 C 3.273517000000 -0.082962000000 1.880528000000 C 2.682500000000 -0.786972000000 0.835804000000 C 0.842250000000 0.159411000000 -0.560227000000 C 3.000070000000 0.541975000000 -1.240045000000 C 4.382980000000 0.601319000000 -1.383607000000 C 4.874505000000 1.315322000000 -2.476682000000 C 4.010722000000 1.943603000000 -3.389515000000 C 2.625093000000 1.878522000000 -3.242269000000 C 2.137882000000 1.163159000000 -2.150792000000 C -0.336384000000 1.435692000000 -2.375024000000 C -0.162324000000 -0.845140000000 1.961282000000

18

H 1.013675000000 1.949616000000 1.643934000000 H 0.719971000000 4.310777000000 2.336689000000 H -1.559546000000 5.374084000000 2.091727000000 H -3.409482000000 4.015141000000 1.146500000000 H -4.918262000000 2.573803000000 0.239981000000 H -6.312110000000 0.786126000000 -0.795761000000 H -5.278993000000 -1.419476000000 -1.328023000000 H -4.088967000000 -3.317548000000 -1.682620000000 H -2.545400000000 -5.235831000000 -2.003853000000 H -0.140431000000 -4.986613000000 -1.269544000000 H 0.579396000000 -2.846202000000 -0.241549000000 H 2.940604000000 -3.880689000000 1.786847000000 H 4.034372000000 -2.807841000000 3.749447000000 H 4.242310000000 -0.305557000000 3.789712000000 H 3.323532000000 0.997718000000 1.849498000000 H 5.045184000000 0.119562000000 -0.675158000000 H 5.946008000000 1.387019000000 -2.623158000000 H 4.429493000000 2.491274000000 -4.225894000000 H 1.956919000000 2.363362000000 -3.942976000000 H -0.269832000000 1.238758000000 -3.446203000000 H -0.404559000000 2.512779000000 -2.208204000000 H -1.217486000000 0.948028000000 -1.965760000000

19

2. N-trans complexes

2.1 N-Fe-MeCN2+

Fe 0.443331000000 -0.060740000000 0.273488000000 C 1.361060000000 -0.122858000000 3.225393000000 N 0.906469000000 -2.005992000000 0.056547000000 N 2.324933000000 0.103482000000 -0.138015000000 N 0.628576000000 1.949709000000 0.332581000000 N -0.152195000000 0.071672000000 -1.642688000000 N -2.215268000000 -0.018524000000 -0.651327000000 N -2.388966000000 -0.352814000000 1.494008000000 C 0.075859000000 -3.050255000000 0.166398000000 C 0.495313000000 -4.363306000000 -0.018530000000 C 1.829291000000 -4.603520000000 -0.330021000000 C 2.701685000000 -3.525267000000 -0.442149000000 C 2.215795000000 -2.236263000000 -0.242326000000 C 3.041305000000 -1.015410000000 -0.330632000000 C 4.409627000000 -0.935713000000 -0.586203000000 C 5.001355000000 0.325209000000 -0.631731000000 C 4.240137000000 1.473411000000 -0.420428000000 C 2.876735000000 1.326429000000 -0.167997000000 C 1.891952000000 2.396656000000 0.086337000000 C 2.197118000000 3.754621000000 0.085863000000 C 1.187264000000 4.676926000000 0.342736000000 C -0.099945000000 4.215303000000 0.595480000000 C -0.335359000000 2.844641000000 0.581699000000 C 0.657742000000 0.164320000000 -2.711147000000 C 0.181876000000 0.310434000000 -4.004204000000 C -1.194902000000 0.364605000000 -4.200743000000 C -2.046665000000 0.264460000000 -3.108125000000 C -1.486832000000 0.113580000000 -1.842392000000 C -1.483158000000 -0.190524000000 0.513580000000 C -3.596771000000 -0.047281000000 -0.387440000000 C -4.746575000000 0.090949000000 -1.164040000000 C -5.977364000000 0.015070000000 -0.512143000000 C -6.066269000000 -0.191218000000 0.870625000000 C -4.920246000000 -0.329808000000 1.650236000000 C -3.693982000000 -0.257090000000 0.998325000000 C -2.066526000000 -0.575041000000 2.902411000000

20

N 0.947425000000 -0.129661000000 2.153183000000 H -0.952222000000 -2.818379000000 0.409630000000 H -0.217999000000 -5.171464000000 0.080766000000 H 2.188705000000 -5.613863000000 -0.483483000000 H 3.744592000000 -3.682750000000 -0.683296000000 H 4.998850000000 -1.828502000000 -0.744651000000 H 6.062455000000 0.413482000000 -0.830587000000 H 4.698876000000 2.452188000000 -0.451280000000 H 3.207981000000 4.085490000000 -0.111380000000 H 1.406183000000 5.737863000000 0.345666000000 H -0.915764000000 4.895870000000 0.802430000000 H -1.321557000000 2.444910000000 0.776072000000 H 1.718150000000 0.121956000000 -2.511578000000 H 0.878852000000 0.380433000000 -4.828837000000 H -1.609698000000 0.481337000000 -5.194590000000 H -3.113388000000 0.298497000000 -3.246902000000 H -4.718801000000 0.258012000000 -2.229384000000 H -6.884281000000 0.123034000000 -1.095259000000 H -7.039985000000 -0.240325000000 1.343437000000 H -4.983085000000 -0.483124000000 2.719518000000 H -2.912958000000 -1.054102000000 3.389892000000 H -1.852212000000 0.373952000000 3.395961000000 H -1.204931000000 -1.231706000000 2.970862000000 C 1.852137000000 -0.116893000000 4.587197000000 H 1.335825000000 0.657278000000 5.159393000000 H 1.667805000000 -1.089800000000 5.048587000000 H 2.925224000000 0.086869000000 4.592116000000

2.2 N-Fe-MeCN+

Fe 0.443331000000 -0.060740000000 0.273488000000 C 1.361060000000 -0.122858000000 3.225393000000 N 0.906469000000 -2.005992000000 0.056547000000 N 2.324933000000 0.103482000000 -0.138015000000 N 0.628576000000 1.949709000000 0.332581000000 N -0.152195000000 0.071672000000 -1.642688000000 N -2.215268000000 -0.018524000000 -0.651327000000 N -2.388966000000 -0.352814000000 1.494008000000 C 0.075859000000 -3.050255000000 0.166398000000

21

C 0.495313000000 -4.363306000000 -0.018530000000 C 1.829291000000 -4.603520000000 -0.330021000000 C 2.701685000000 -3.525267000000 -0.442149000000 C 2.215795000000 -2.236263000000 -0.242326000000 C 3.041305000000 -1.015410000000 -0.330632000000 C 4.409627000000 -0.935713000000 -0.586203000000 C 5.001355000000 0.325209000000 -0.631731000000 C 4.240137000000 1.473411000000 -0.420428000000 C 2.876735000000 1.326429000000 -0.167997000000 C 1.891952000000 2.396656000000 0.086337000000 C 2.197118000000 3.754621000000 0.085863000000 C 1.187264000000 4.676926000000 0.342736000000 C -0.099945000000 4.215303000000 0.595480000000 C -0.335359000000 2.844641000000 0.581699000000 C 0.657742000000 0.164320000000 -2.711147000000 C 0.181876000000 0.310434000000 -4.004204000000 C -1.194902000000 0.364605000000 -4.200743000000 C -2.046665000000 0.264460000000 -3.108125000000 C -1.486832000000 0.113580000000 -1.842392000000 C -1.483158000000 -0.190524000000 0.513580000000 C -3.596771000000 -0.047281000000 -0.387440000000 C -4.746575000000 0.090949000000 -1.164040000000 C -5.977364000000 0.015070000000 -0.512143000000 C -6.066269000000 -0.191218000000 0.870625000000 C -4.920246000000 -0.329808000000 1.650236000000 C -3.693982000000 -0.257090000000 0.998325000000 C -2.066526000000 -0.575041000000 2.902411000000 N 0.947425000000 -0.129661000000 2.153183000000 H -0.952222000000 -2.818379000000 0.409630000000 H -0.217999000000 -5.171464000000 0.080766000000 H 2.188705000000 -5.613863000000 -0.483483000000 H 3.744592000000 -3.682750000000 -0.683296000000 H 4.998850000000 -1.828502000000 -0.744651000000 H 6.062455000000 0.413482000000 -0.830587000000 H 4.698876000000 2.452188000000 -0.451280000000 H 3.207981000000 4.085490000000 -0.111380000000 H 1.406183000000 5.737863000000 0.345666000000 H -0.915764000000 4.895870000000 0.802430000000 H -1.321557000000 2.444910000000 0.776072000000 H 1.718150000000 0.121956000000 -2.511578000000 H 0.878852000000 0.380433000000 -4.828837000000 H -1.609698000000 0.481337000000 -5.194590000000 H -3.113388000000 0.298497000000 -3.246902000000 H -4.718801000000 0.258012000000 -2.229384000000 H -6.884281000000 0.123034000000 -1.095259000000 H -7.039985000000 -0.240325000000 1.343437000000 H -4.983085000000 -0.483124000000 2.719518000000 H -2.912958000000 -1.054102000000 3.389892000000 H -1.852212000000 0.373952000000 3.395961000000 H -1.204931000000 -1.231706000000 2.970862000000

22

C 1.852137000000 -0.116893000000 4.587197000000 H 1.335825000000 0.657278000000 5.159393000000 H 1.667805000000 -1.089800000000 5.048587000000 H 2.925224000000 0.086869000000 4.592116000000

2.3 N-Fe2+

Fe 0.500061000000 0.000011000000 -0.541547000000 N 0.840462000000 1.987098000000 -0.532121000000 N 2.432437000000 -0.000050000000 -0.364728000000 N 0.840343000000 -1.987109000000 -0.532073000000 N 0.057004000000 0.000037000000 1.379764000000 N -2.075553000000 0.000070000000 0.545430000000 N -2.360625000000 0.000040000000 -1.615493000000 C -0.075821000000 2.961527000000 -0.610078000000 C 0.260581000000 4.310309000000 -0.566674000000 C 1.599039000000 4.663134000000 -0.437006000000 C 2.559636000000 3.658548000000 -0.353562000000 C 2.155272000000 2.328962000000 -0.404959000000 C 3.077788000000 1.177298000000 -0.331220000000 C 4.467685000000 1.211015000000 -0.237017000000 C 5.156121000000 -0.000127000000 -0.187017000000 C 4.467614000000 -1.211230000000 -0.236988000000 C 3.077718000000 -1.177434000000 -0.331195000000 C 2.155135000000 -2.329046000000 -0.404920000000 C 2.559423000000 -3.658655000000 -0.353532000000 C 1.598770000000 -4.663188000000 -0.436978000000 C 0.260331000000 -4.310288000000 -0.566638000000 C -0.075995000000 -2.961486000000 -0.610032000000 C 0.951289000000 0.000022000000 2.383049000000 C 0.575915000000 0.000024000000 3.716597000000 C -0.781773000000 0.000044000000 4.025154000000 C -1.719369000000 0.000063000000 2.999488000000 C -1.262173000000 0.000057000000 1.686072000000 C -1.414103000000 0.000056000000 -0.668272000000 C -3.468845000000 0.000058000000 0.350681000000 C -4.575205000000 0.000063000000 1.196374000000 C -5.837740000000 0.000049000000 0.600777000000 C -5.997699000000 0.000032000000 -0.791304000000

23

C -4.892649000000 0.000029000000 -1.641282000000 C -3.637753000000 0.000041000000 -1.045998000000 C -2.078662000000 0.000005000000 -3.046020000000 H -1.104748000000 2.642004000000 -0.707644000000 H -0.518804000000 5.058400000000 -0.633966000000 H 1.895722000000 5.704274000000 -0.399196000000 H 3.607742000000 3.906209000000 -0.251133000000 H 5.001396000000 2.150903000000 -0.207089000000 H 6.236793000000 -0.000158000000 -0.113723000000 H 5.001271000000 -2.151147000000 -0.207035000000 H 3.607516000000 -3.906379000000 -0.251113000000 H 1.895395000000 -5.704344000000 -0.399179000000 H -0.519096000000 -5.058334000000 -0.633934000000 H -1.104904000000 -2.641904000000 -0.707592000000 H 1.991068000000 0.000005000000 2.092046000000 H 1.335086000000 0.000010000000 4.487576000000 H -1.115050000000 0.000047000000 5.055773000000 H -2.773666000000 0.000080000000 3.221285000000 H -4.485855000000 0.000077000000 2.272257000000 H -6.714446000000 0.000051000000 1.237618000000 H -6.995103000000 0.000022000000 -1.214473000000 H -5.000816000000 0.000016000000 -2.718581000000 H -2.504672000000 0.891532000000 -3.508725000000 H -2.504680000000 -0.891540000000 -3.508682000000 H -0.997381000000 -0.000004000000 -3.174714000000

2.4 N-Fe+

Fe 0.537754000000 0.000026000000 -0.441638000000 N 0.874990000000 1.964649000000 -0.530683000000 N 2.430162000000 0.000399000000 -0.380292000000 N 0.875741000000 -1.964425000000 -0.531126000000 N -0.022066000000 -0.000470000000 1.489001000000 N -2.104731000000 -0.000073000000 0.540387000000 N -2.297275000000 -0.000299000000 -1.632089000000 C -0.046749000000 2.949435000000 -0.611522000000 C 0.276624000000 4.293247000000 -0.582864000000 C 1.624176000000 4.663613000000 -0.460021000000 C 2.584852000000 3.671150000000 -0.369134000000

24

C 2.198698000000 2.325196000000 -0.406620000000 C 3.105022000000 1.191757000000 -0.331468000000 C 4.491804000000 1.212301000000 -0.236807000000 C 5.191130000000 0.000882000000 -0.189934000000 C 4.492230000000 -1.210789000000 -0.236885000000 C 3.105449000000 -1.190700000000 -0.331559000000 C 2.199537000000 -2.324488000000 -0.406866000000 C 2.586189000000 -3.670295000000 -0.369316000000 C 1.625880000000 -4.663105000000 -0.460362000000 C 0.278217000000 -4.293224000000 -0.583441000000 C -0.045643000000 -2.949531000000 -0.612143000000 C 0.822604000000 -0.000827000000 2.532490000000 C 0.383537000000 -0.000939000000 3.847552000000 C -0.989149000000 -0.000667000000 4.087155000000 C -1.876296000000 -0.000343000000 3.016183000000 C -1.352068000000 -0.000296000000 1.726368000000 C -1.384079000000 -0.000226000000 -0.646667000000 C -3.487518000000 -0.000148000000 0.283775000000 C -4.632282000000 -0.000026000000 1.077498000000 C -5.868345000000 -0.000050000000 0.427018000000 C -5.966655000000 -0.000178000000 -0.970149000000 C -4.823647000000 -0.000274000000 -1.769383000000 C -3.596084000000 -0.000264000000 -1.119389000000 C -1.961285000000 -0.000723000000 -3.049866000000 H -1.074884000000 2.623875000000 -0.702581000000 H -0.508516000000 5.035237000000 -0.656308000000 H 1.910404000000 5.708277000000 -0.434313000000 H 3.632390000000 3.925609000000 -0.269290000000 H 5.024844000000 2.153946000000 -0.203086000000 H 6.271754000000 0.001074000000 -0.118868000000 H 5.025580000000 -2.152258000000 -0.203226000000 H 3.633804000000 -3.924361000000 -0.269272000000 H 1.912473000000 -5.707667000000 -0.434591000000 H -0.506643000000 -5.035497000000 -0.657014000000 H -1.073874000000 -2.624311000000 -0.703361000000 H 1.875332000000 -0.001003000000 2.281599000000 H 1.101776000000 -0.001215000000 4.657134000000 H -1.373490000000 -0.000709000000 5.099969000000 H -2.939355000000 -0.000130000000 3.190464000000 H -4.594007000000 0.000074000000 2.156107000000 H -6.772115000000 0.000037000000 1.025032000000 H -6.944125000000 -0.000189000000 -1.437861000000 H -4.884513000000 -0.000370000000 -2.850426000000 H -2.368817000000 0.890434000000 -3.530365000000 H -2.368498000000 -0.892359000000 -3.529754000000 H -0.875754000000 -0.000565000000 -3.135658000000

25

2.5 N-Fe-CO20

N -0.103579000 0.467380000 1.554889000 C -1.415157000 0.731415000 1.699164000 C -1.939920000 1.304494000 2.857765000 C -1.072500000 1.572331000 3.910453000 C 0.282290000 1.273147000 3.778911000 C 0.721681000 0.732735000 2.579464000 N -2.159907000 0.380776000 0.564219000 C -1.451409000 -0.038227000 -0.572417000 N -2.416319000 -0.384979000 -1.459868000 C -3.695859000 -0.225278000 -0.926971000 C -3.546814000 0.266855000 0.379102000 C -4.942918000 -0.487639000 -1.483378000 C -6.062306000 -0.241189000 -0.688666000 C -5.922637000 0.241811000 0.618096000 C -4.667952000 0.501708000 1.174236000 Fe 0.486043000 -0.092292000 -0.347196000 N 0.626969000 -2.008839000 0.154806000 C 1.899415000 -2.418250000 0.430703000 C 2.184306000 -3.733661000 0.802329000 C 1.151839000 -4.658432000 0.883000000 C -0.147970000 -4.238062000 0.599004000 C -0.361750000 -2.912460000 0.246139000 C 2.900712000 -1.354208000 0.321415000 N 2.343615000 -0.166001000 -0.004278000 C 3.095755000 0.952602000 -0.117543000 C 4.472788000 0.908501000 0.083323000 C 5.064105000 -0.314932000 0.404644000 C 4.276363000 -1.458123000 0.528825000 C 2.279795000 2.118136000 -0.478909000 N 0.963552000 1.820502000 -0.669336000 C 0.131614000 2.812589000 -1.018989000 C 0.551351000 4.125411000 -1.188686000 C 1.897124000 4.433958000 -0.992158000 C 2.771038000 3.415023000 -0.633265000 C -2.203601000 -0.948807000 -2.788431000 C 0.959516000 -0.512853000 -2.302159000 H 6.134448000 -0.374845000 0.559885000 H 4.725537000 -2.409508000 0.781892000

26

H 5.073946000 1.802906000 -0.014318000 H 3.202826000 -4.024770000 1.024279000 H 1.354850000 -5.684804000 1.164888000 H -1.356062000 -2.552630000 0.018104000 H -0.986741000 -4.921269000 0.647797000 H 3.821799000 3.619047000 -0.474073000 H 2.257934000 5.448109000 -1.115915000 H -0.902470000 2.532689000 -1.165943000 H -0.166496000 4.885417000 -1.471214000 H -6.806604000 0.418440000 1.219803000 H -7.051993000 -0.431942000 -1.086895000 H -5.038501000 -0.872008000 -2.490722000 H -4.600190000 0.861672000 2.188932000 H -2.406455000 -2.022491000 -2.772976000 H -2.883930000 -0.468104000 -3.493589000 H -1.180493000 -0.754950000 -3.091156000 H -2.983852000 1.557741000 2.938796000 H -1.456553000 2.016573000 4.820985000 H 1.766172000 0.502048000 2.415074000 H 0.986499000 1.462564000 4.578769000 O 0.730048000 0.375134000 -3.177383000 O 1.498141000 -1.630600000 -2.543662000

2.6 N-Fe-CO2+

Fe -0.477415000000 -0.032966000000 -0.517611000000 O -1.019537000000 -0.062066000000 -3.403118000000 N -0.881236000000 -1.999474000000 -0.366504000000 N -2.384907000000 0.055777000000 -0.191933000000 N -0.720245000000 1.968523000000 -0.481823000000 N -0.037960000000 0.031830000000 1.481077000000 N 2.097617000000 -0.013085000000 0.649895000000 N 2.446735000000 -0.189848000000 -1.493369000000 C -0.006506000000 -3.007374000000 -0.470277000000 C -0.386498000000 -4.338185000000 -0.336912000000 C -1.722449000000 -4.633540000000 -0.089463000000 C -2.638892000000 -3.591385000000 0.013579000000 C -2.193812000000 -2.281254000000 -0.132111000000

27

C -3.064209000000 -1.092951000000 -0.043416000000 C -4.437879000000 -1.063348000000 0.190093000000 C -5.068605000000 0.176626000000 0.269978000000 C -4.340314000000 1.355737000000 0.123105000000 C -2.970079000000 1.261737000000 -0.114918000000 C -2.007849000000 2.368242000000 -0.280419000000 C -2.348328000000 3.716037000000 -0.233757000000 C -1.351151000000 4.673712000000 -0.391747000000 C -0.040016000000 4.258005000000 -0.593789000000 C 0.233350000000 2.895302000000 -0.635432000000 C -0.929123000000 0.077522000000 2.484982000000 C -0.556269000000 0.141228000000 3.817621000000 C 0.800402000000 0.161589000000 4.124010000000 C 1.735492000000 0.115301000000 3.097792000000 C 1.275884000000 0.048958000000 1.786053000000 C 1.470343000000 -0.104905000000 -0.577181000000 C 3.496478000000 -0.024292000000 0.496636000000 C 4.577886000000 0.050963000000 1.374161000000 C 5.856995000000 0.018134000000 0.822086000000 C 6.060266000000 -0.085971000000 -0.560686000000 C 4.984239000000 -0.163347000000 -1.440000000000 C 3.707827000000 -0.133449000000 -0.887511000000 C 2.229432000000 -0.320427000000 -2.934549000000 C -0.758780000000 -0.060763000000 -2.293336000000 H 1.021068000000 -2.732131000000 -0.665106000000 H 0.359171000000 -5.117435000000 -0.427676000000 H -2.050651000000 -5.659933000000 0.020646000000 H -3.684471000000 -3.792493000000 0.204914000000 H -5.000288000000 -1.978779000000 0.311034000000 H -6.134817000000 0.224662000000 0.454170000000 H -4.828605000000 2.317877000000 0.195362000000 H -3.376737000000 4.011850000000 -0.077097000000 H -1.598678000000 5.727681000000 -0.357308000000 H 0.766737000000 4.968150000000 -0.720916000000 H 1.238585000000 2.529948000000 -0.795629000000 H -1.971306000000 0.062010000000 2.205860000000 H -1.316081000000 0.174209000000 4.587141000000 H 1.136551000000 0.212088000000 5.152482000000 H 2.787299000000 0.130335000000 3.324222000000 H 4.460925000000 0.134073000000 2.442983000000 H 6.712426000000 0.076869000000 1.484453000000 H 7.069788000000 -0.104694000000 -0.953476000000 H 5.137714000000 -0.239378000000 -2.508271000000 H 3.178759000000 -0.530428000000 -3.420049000000 H 1.821699000000 0.606598000000 -3.337245000000 H 1.552958000000 -1.150903000000 -3.126600000000

28

2.7 N-Fe-CO+

Fe -0.476415000000 -0.053690000000 -0.533317000000 O -1.048149000000 -0.060147000000 -3.394352000000 N -0.922959000000 -2.012481000000 -0.337862000000 N -2.367903000000 0.066658000000 -0.180772000000 N -0.675215000000 1.944742000000 -0.516809000000 N -0.032060000000 0.047774000000 1.488851000000 N 2.098858000000 -0.025728000000 0.654047000000 N 2.447846000000 -0.269140000000 -1.482806000000 C -0.066623000000 -3.042708000000 -0.435712000000 C -0.465171000000 -4.362614000000 -0.288078000000 C -1.810605000000 -4.633517000000 -0.032178000000 C -2.705271000000 -3.576206000000 0.062695000000 C -2.243271000000 -2.268736000000 -0.095047000000 C -3.087287000000 -1.066970000000 -0.015656000000 C -4.448259000000 -1.015511000000 0.221481000000 C -5.066682000000 0.259700000000 0.282603000000 C -4.321820000000 1.413048000000 0.113239000000 C -2.935612000000 1.319334000000 -0.125497000000 C -1.986517000000 2.371673000000 -0.307548000000 C -2.280179000000 3.755512000000 -0.289201000000 C -1.276212000000 4.678789000000 -0.469906000000 C 0.050247000000 4.228451000000 -0.679592000000 C 0.287439000000 2.867647000000 -0.698566000000 C -0.925234000000 0.133473000000 2.485479000000 C -0.553747000000 0.245003000000 3.816722000000 C 0.803371000000 0.270075000000 4.123132000000 C 1.740772000000 0.183550000000 3.100722000000 C 1.279637000000 0.072747000000 1.791482000000 C 1.467067000000 -0.151530000000 -0.571204000000 C 3.497140000000 -0.043718000000 0.500327000000 C 4.579417000000 0.058781000000 1.373845000000 C 5.859249000000 0.007423000000 0.822835000000 C 6.061851000000 -0.141248000000 -0.555593000000 C 4.984445000000 -0.245005000000 -1.431628000000 C 3.708341000000 -0.196118000000 -0.880399000000 C 2.228772000000 -0.430228000000 -2.919266000000 C -0.770147000000 -0.079697000000 -2.284263000000

29

H 0.964479000000 -2.785935000000 -0.638788000000 H 0.266674000000 -5.155747000000 -0.372988000000 H -2.155386000000 -5.653366000000 0.089587000000 H -3.754191000000 -3.756274000000 0.258668000000 H -5.026174000000 -1.918661000000 0.361538000000 H -6.131968000000 0.328016000000 0.467659000000 H -4.799182000000 2.383857000000 0.165634000000 H -3.302316000000 4.076760000000 -0.130466000000 H -1.499794000000 5.739297000000 -0.453342000000 H 0.868875000000 4.921156000000 -0.825452000000 H 1.286000000000 2.480850000000 -0.861733000000 H -1.964381000000 0.110801000000 2.192722000000 H -1.312617000000 0.310278000000 4.585320000000 H 1.138559000000 0.356280000000 5.149714000000 H 2.792520000000 0.201760000000 3.328173000000 H 4.462946000000 0.177526000000 2.439443000000 H 6.714902000000 0.087302000000 1.482793000000 H 7.071172000000 -0.173535000000 -0.948255000000 H 5.136586000000 -0.355077000000 -2.497260000000 H 3.167722000000 -0.702816000000 -3.394615000000 H 1.866389000000 0.503033000000 -3.351089000000 H 1.510501000000 -1.229554000000 -3.090132000000

2.8 k1N-Fe-CO+

Fe 0.589805000000 0.471913000000 -0.724674000000 O 0.849783000000 1.287230000000 -3.538771000000 N 1.166722000000 2.167523000000 0.196071000000 N 2.362390000000 -0.024601000000 -0.193932000000 N 0.550130000000 -1.486601000000 -1.173045000000 N -0.263826000000 -0.576257000000 2.149068000000 N -1.974250000000 -0.185629000000 0.592229000000 N -2.377617000000 1.302177000000 -0.938377000000 C 0.441710000000 3.287406000000 0.368279000000 C 0.962895000000 4.444306000000 0.926659000000 C 2.298729000000 4.456742000000 1.330480000000 C 3.057585000000 3.305957000000 1.169672000000

30

C 2.470557000000 2.170964000000 0.607624000000 C 3.152263000000 0.888221000000 0.420482000000 C 4.435903000000 0.545652000000 0.838307000000 C 4.882445000000 -0.760102000000 0.636041000000 C 4.042245000000 -1.702408000000 0.043560000000 C 2.770201000000 -1.305958000000 -0.361372000000 C 1.729325000000 -2.143558000000 -0.960500000000 C 1.885441000000 -3.489463000000 -1.295017000000 C 0.821595000000 -4.178279000000 -1.860950000000 C -0.376550000000 -3.499908000000 -2.089427000000 C -0.467372000000 -2.163100000000 -1.736422000000 C 0.461035000000 -1.416320000000 2.899696000000 C 0.194555000000 -2.779753000000 2.988150000000 C -0.876908000000 -3.295264000000 2.261579000000 C -1.627472000000 -2.436497000000 1.465342000000 C -1.268268000000 -1.090724000000 1.444768000000 C -1.365856000000 0.601155000000 -0.365148000000 C -3.359518000000 0.003554000000 0.599033000000 C -4.385378000000 -0.539281000000 1.368143000000 C -5.679497000000 -0.096435000000 1.098062000000 C -5.935720000000 0.857407000000 0.098834000000 C -4.904567000000 1.406265000000 -0.661759000000 C -3.613081000000 0.962201000000 -0.388718000000 C -2.241332000000 2.247100000000 -2.041304000000 C 0.732892000000 1.004950000000 -2.422236000000 H -0.588804000000 3.238498000000 0.047622000000 H 0.328951000000 5.314163000000 1.042753000000 H 2.737955000000 5.345774000000 1.766704000000 H 4.094541000000 3.282220000000 1.477475000000 H 5.070178000000 1.274268000000 1.325315000000 H 5.875820000000 -1.047647000000 0.957707000000 H 4.368603000000 -2.725394000000 -0.088818000000 H 2.830625000000 -3.984667000000 -1.115087000000 H 0.924649000000 -5.224180000000 -2.123717000000 H -1.231610000000 -3.995134000000 -2.531583000000 H -1.376696000000 -1.600139000000 -1.897684000000 H 1.284286000000 -0.974429000000 3.451335000000 H 0.811903000000 -3.416367000000 3.609757000000 H -1.115152000000 -4.351702000000 2.297584000000 H -2.447781000000 -2.794338000000 0.857538000000 H -4.189268000000 -1.273717000000 2.138245000000 H -6.505641000000 -0.498901000000 1.672610000000 H -6.955849000000 1.174234000000 -0.084228000000 H -5.097557000000 2.144013000000 -1.430216000000 H -2.867969000000 3.117660000000 -1.845653000000 H -2.550384000000 1.779688000000 -2.978517000000 H -1.205990000000 2.563245000000 -2.112705000000

31

2.9 k1N-Fe-CO0

Fe 0.435669000000 0.329773000000 -1.219293000000 O 0.158284000000 0.835798000000 -4.069781000000 N 0.701818000000 2.188591000000 -0.594421000000 N 2.013311000000 0.117101000000 -0.260048000000 N 0.677445000000 -1.622008000000 -1.394638000000 N -0.093146000000 0.428130000000 2.438578000000 N -1.599301000000 -0.272418000000 0.779758000000 N -2.649504000000 0.431339000000 -0.981553000000 C -0.113327000000 3.244887000000 -0.836316000000 C 0.138125000000 4.516092000000 -0.368939000000 C 1.300578000000 4.744157000000 0.396428000000 C 2.143231000000 3.684259000000 0.658714000000 C 1.835334000000 2.402399000000 0.164498000000 C 2.606090000000 1.206209000000 0.368571000000 C 3.782399000000 1.056489000000 1.089292000000 C 4.383582000000 -0.205160000000 1.190445000000 C 3.785478000000 -1.304501000000 0.562863000000 C 2.606484000000 -1.136156000000 -0.149600000000 C 1.820680000000 -2.136657000000 -0.814341000000 C 2.108898000000 -3.513206000000 -0.881739000000 C 1.235927000000 -4.369335000000 -1.518473000000 C 0.063251000000 -3.838991000000 -2.097950000000 C -0.165798000000 -2.483606000000 -2.017082000000 C 0.892603000000 0.163791000000 3.304807000000 C 1.447593000000 -1.104191000000 3.466379000000 C 0.950295000000 -2.151036000000 2.693360000000 C -0.072922000000 -1.890574000000 1.788170000000 C -0.538777000000 -0.583430000000 1.695695000000 C -1.396355000000 0.187108000000 -0.499119000000 C -2.953664000000 -0.326383000000 1.102930000000 C -3.632518000000 -0.711918000000 2.254597000000 C -5.025141000000 -0.639673000000 2.219752000000 C -5.706566000000 -0.197407000000 1.073325000000 C -5.019926000000 0.191152000000 -0.077484000000 C -3.629215000000 0.120681000000 -0.039248000000 C -2.975829000000 0.923031000000 -2.313269000000 C 0.185782000000 0.651219000000 -2.916542000000

32

H -0.991047000000 3.024203000000 -1.430328000000 H -0.553738000000 5.317943000000 -0.595131000000 H 1.527519000000 5.734407000000 0.773639000000 H 3.042512000000 3.825588000000 1.245564000000 H 4.228781000000 1.913758000000 1.578954000000 H 5.299708000000 -0.329704000000 1.754364000000 H 4.231387000000 -2.288593000000 0.644340000000 H 3.014753000000 -3.888069000000 -0.421506000000 H 1.445199000000 -5.431350000000 -1.570134000000 H -0.652975000000 -4.475230000000 -2.602973000000 H -1.048556000000 -2.030438000000 -2.450860000000 H 1.253382000000 1.002685000000 3.891199000000 H 2.249596000000 -1.260075000000 4.177058000000 H 1.356962000000 -3.151252000000 2.784253000000 H -0.485119000000 -2.660830000000 1.150310000000 H -3.100714000000 -1.051708000000 3.134652000000 H -5.592865000000 -0.931121000000 3.095927000000 H -6.789703000000 -0.157120000000 1.082150000000 H -5.545252000000 0.531316000000 -0.961096000000 H -3.763726000000 1.673338000000 -2.235866000000 H -3.318958000000 0.103815000000 -2.949285000000 H -2.092924000000 1.377318000000 -2.747444000000

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