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S. Wang et al. / CoordinationChemistryReviews256 (2012) 439464 441

Table 1

Some of thereported compounds and their magnetic coupling (J) values through thecyanide bridges.

Metal (MAMB) Cluster C NMB () g J(cm1)a Ref.

Cyano-bridged complexesbasedon [FeIII(L)(CN)2]/+ (L=bpb2 , salen2, s-bqdi2 , bpy)

[MnII(phen)2 Cl][FeIII(bpb)(CN)2]0.5CH3 CH2OH1.5H2O Fe

IIIMnII dimer 171.9(2) 2.01 1.34 [101]

[MnIII(saltn)(MeOH)][FeIII(bpb)(CN)2]3H2O FeIIIMnIII dimer 167.4(3) 1.93 3.2 [103]

{[FeIII(bpb)(CN)2][MnIII(TNPP)(H2 O)]}3H2O Fe

IIIMnIII dimer 158.4(4) 2.02 4.91 [102]

{[FeIII(bpb)(CN)2][MnIII(TClPP)(CH3OH)]}3CH3OH Fe

IIIMnIII dimer 159.9(3) 2.02 2.55 [102]

{[FeIII(bpb)(CN)2][MnIII(TMeOPP)(CH3CH2OH)]}2CH3 OHCH3CH2OHH2O Fe

IIIMnIII dimer 160.3(2) 2.00 1.72 [102]

[MnIII

(saltn)(H2O)FeIII

(bpmb)(CN)2]H2O FeIII

MnIII

dimer 1.97 2.06 [103][MnIII(saltn)(MeOH)Fe III(bpClb)(CN)2]2H2O Fe

IIIMnIII dimer 1.98 1.56 [103]

[NiIIL1][FeIII(bpb)(CN)2]2 H2 O

(L1 = 3,10-dimethyl-1,3,5,8,10,12-hexaazacyclotetradecane)

FeIIINiII trimer 160.2(7) 2.06 6.40 [104]

[NiIIL2][FeIII(bpb)(CN)2]2 6H2O

(L2 = 3,10-diethyl-1,3,5,8,10,12-hexaazacyclotetradecane)

FeIIINiII trimer 165.3(4) [104]


(L3 = 3,10-bis(2-hydroxyethyl)-1,3,5,8,10,12-hexaazacyclotetradecane)



(L4 = 3,10-bis(2-phenylethyl)-1,3,5,8,10,12-hexaazacyclotetradecane)


[NiIIL5][FeIII(bpb)(CN)2]2 (L5 = 3-methyl-1,3,5,8,12-pentaazacyclotetradecane) FeIIINiII trimer 157.0(2) 2.05 6.03 [104]

[CuIIL1][FeIII(bpb)(CN)2]24H2O

(L1 = 1,5,8,12-tetramethyl-1,3,6,8,10,13-hexaazacyclotetradecane)

FeIIICuII trimer 146.9(6) 2.09 0.59 [105]

{[FeIII(bpb)2]2[MnIII(TPP)]}[MnIII(TPP)(CH3 OH)2]xH2 OyCH3OH Fe

IIIMnIII trimer 159.4(2) 2.03 3.28 [102]

{[FeIII(bpmb)2]2[MnIII(TPP)]}[MnIII(TPP)(CH3OH)2]xH2OyCH3OH Fe

IIIMnIII trimer 159.9(2) 2.02 2.47 [102]

[MnIII 2(5-Br-saltn) 2(H2O)(EtOH)FeIII(bpb)(CN)2][Fe

III(bpb)(CN)2]6H2 O FeIIIMnIII trimer 166.6(13), 162.7(12) 2.00 2.61 [103]

[MnIII 2(5-Cl-

saltn)2(CH3OH)(EtOH)FeIII(bpb)(CN)2][Fe

III(bpb)(CN)2]5H2OMeCN

FeIIIMnIII trimer 166.7(6), 158.3(7) 2.03 3.72 [103]

[MnIII(5-Cl(salpn))] 2[FeIII(bpmb)(CN)2]23H2 OCH3CN FeIIIMnIII tetramer 147.2(3), 155.4(3) 2.0 2.15 [107]

[MnIII(salen)]6 [FeIII(bpmb)(CN)2]67H2O Fe

IIIMnIII dodecamer 140.8(4)163.3(5) 1.99 3.4 [107]

[MnIII(salen)]6 [FeIII(bpClb)(CN)2]64H2 O2CH3OH Fe


[MnIII(salen)]6 [FeIII(bpdmb)(CN)2]6 10H2O5CH3OH Fe


[MnIII(5-Br(salpn))] 6[FeIII(bpmb)(CN)2]624H2O8CH3 CN Fe


[MnIII(5-Cl(salpn))] 6[FeIII(bpmb)(CN)2]625H2 O5CH3CN Fe


[MnIII(5-Cl-salen)Fe III(bpClb)(CN)2]0.67MeCN0.5H2O FeIIIMnIII 1D 149.5(4)154.3(3) 2.05 3.61 [109]

[MnIII(5-Cl-salen)Fe III(bpb)(CN)2]0.5H2OMeOH FeIIIMnIII 1D 149.1(7)160.8(7) 1.99 4.30 [109]

[MnIII(5-Br-salen)Fe III(bpb)(CN)2]0.5H2OMeOH FeIIIMnIII 1D 149.0(3)161.3(2) 2.01 4.46 [109]

[MnIII(5-Me-salen)Fe III(bpb)(CN)2]0.5H2OMeOH FeIIIMnIII 1D 147.5(2)160.9(3) 2.00 0.49 [109]

[NiIIL6][FeIII(bpb)(CN)2]ClO4CH3OH(L6 = 1,9-diamino-3,7-diazanonane

(2,3,3-tet))

FeIIINiII 1D 168.8(2), 150.1(2) 2.06 7.1 [104]

[NiII(CH3)][FeIII(bpb)(CN)2]ClO4 H2O Fe

IIINiII 1D 173.9(10), 156.3(7) 2.08 6.1 [104]

[NiII(C6 H5CH2CH2)][FeIII(bpb)(CN)2]ClO42CH3CN Fe

IIINiII 1D 172.7(4), 166.7(4) 2.05 7.49 [104]

[MnII(L1)][FeIII(bpb)(CN)2]ClO40.5H2O (L1 =3 ,6- diazaoctan e- 1,8 -diamine ) FeIIIMnII 1D 162.2(4), 154.6(4) 2.0 1.16 [110]

[MnII(L2)][FeIII(bpb)(CN)2]ClO40.5H2O (L2 =3 ,6- dioxao ctan o- 1, 8-diamin e) FeIIIMnII 1D 159.1(4), 146.9(4) 2.0 3.10 [110]

[MnII(L1)][FeIII(bpClb)(CN)2]ClO4H2 O (L1 = 3 ,6-diazaoctane-1,8-di amine) FeIIIMnII 1D 163.3(7), 155.0(8) 2.0 1.10 [110]

[MnII(L2)][FeIII(bpClb)(CN)2]ClO40.5H2O (L2 = 3,6-dioxaoctano-1,8-diamine) FeIIIMnII 1D 148.1(5), 167.3(5) 2.0 1.99 [110][MnII(L1)][FeIII(bpdBrb)(CN)2 ]ClO4H2O (L

1 =3 ,6- diazaoctan e- 1,8- diamine ) FeIIIMnII 1D 166.8(8), 153.2(8) 2.0 1.23 [110]

{[CuIIMnII(L1)][FeIII(bpb)(CN)2]}n(ClO4)n(H2O)n FeIIICuII 1D 165.6(7), 2.03 6.92 [111]

{[FeIII(salen)(CN)2 ]2[MnII(bipy)2]}CH3OH2H2O Fe

IIIMnII trimer 164.3(4) 1.98 1.34 [133]

{[FeIII(salen)(CN)2 ]2[MnII(phen)2]}CH3OH FeIIIMnII trimer 159.9(3) 1.99 1.23 [133]

[FeIII(salen)(CN)2][MnII(L)]ClO4CH3 OH (L = 2,13-dimethyl-3,6,9,12,18-

pentaazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene)

FeIIIMnII 1D 151.5(5), 148.9(6) 1.99 3.25 [133]

[FeIII(salen)(CN)2][MnII(L)]ClO4CH3 OH (L = 2,13-dimethyl-6,9-dioxa-3,12,18-

triazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene)

FeIIIMnII 1D 154.3(3), 154.4(4) 2.01 2.675 [133]

K[CoII(s-bqdi)2][FeIII(s-bqdi)2(CN)2 ]10H2O Fe

IIICoII 1D gFe = 1.920,

gCo = 2.126

25.82 [80]

[FeIII2 CuII

2(-CN)4 (bpy)6](PF6)64CH3CN2CHCl3 FeIIICuII tetramer 176.3(3), 171.9(3) 2.077 6.3 [123]

Cyano-bridged complexesbasedon [RuIII(L)(CN)2] (L=acac, salen2)

{NiII(cyclam)[RuIII(acac)2(CN)2]2}2CH3 OH2H2O RuIIINiII trimer 168.0(8) 2.269 4.6 [82]

{MnII(CH3OH)4 [RuIII(salen)(CN)2]2}6CH3OH2H2O Ru

IIIMnII trimer 168.3(4) 2.117 1.8 [82]

[{MnIII(5,5-Me2salen)}2{RuIII(acac)2(CN)2}][RuIII(acac)2(CN)2]2CH3OH RuIIIMnIII trimer 168.1 (2) 1.96 0.87 [133]

[{RuIII(acac)2(CN)2}{NiII

2(L)(H2O)2}]{RuIII(acac)2 (CN)2}2H2O

(H2L = 11,23-dimethyl-3,7,15,19-tetrazatricyclo[19.3.1.1]hexacosa-2,7,9,11,13(26),14,19,21(25),22,24-decaene-25,26-diol)

RuIIINiII 1D 166.4(3) 2.12 6.6 [68]

[{RuIII(acac)2(CN)2}{NiII(dmphen)(NO3)}]H2O Ru

IIINiII 1D 170.1(7), 176.8(7) 2.20 3.2 [68]

{[{NiII(tren)}{RuIII(acac)2(CN)2}]ClO4CH3OH}n RuIIINiII 1D 178.8 (4), 173.6 (4) 2.20 1.92 [133]

{[{NiII(cyclen)}{RuIII(acac)2(CN)2}]ClO4CH3OH}n RuIIINiII 1D 167.8 (3), 171.1 (3) 2.24 0.85 [133]

[RuIII(salen)(CN)2][MnIII(L)] [L=N,N-(1-methylethylene)bis(2-

hydroxynaphthalene-1-carbaldehydene-iminate)

dianion]

RuIIIMnIII 1D 144.3(8), 143.1(8) gRu = 2.14,

gMn = 1.99

1.34 [135]

{[RuIII(acac)2(CN)2][MnIII(TPP)]}{[Ph3 (PhCH2)P]PF6}2CH3OH Ru

IIIMnIII 1D 152 gMn = 2.01,

gRu = 2.00

3.25 [136]

{[RuIII(acac)2(CN)2][MnIII(TPP)]}{[Ph3 (PhCH2)P]ClO4}2CH3OH Ru

IIIMnIII 1D 152 gMn = 2.02,

gRu = 2.01

3.43 [136]

{[{FeIII(salen)}{RuIII(acac)2(CN)2}]}n RuIIIFeIII 1D 166.98(23), 160.99(23) 2.08 0.62 [133]

Cyano-bridged complexesbasedon [OsIII(L)(CN)2] (L= salen2)

[OsIII(salen)(CN)2]2[CuII(Me3tacn)]CH3OH Os

IIICuII 1D 157.17(29)168.72(31) 2.19 1.56 [84]

[OsIII(salen)(CN)2][CuII(Me3tacn)]ClO4 Os

IIICuII 1D 178.62(14), 179.63(14) 2.11 2.03 [84]

Cyano-bridged complexesbasedon [CoII(L)(CN)2] (L= triphos)

{[CoII(triphos)(CN)2]2[MnII(MeOH)4]}(ClO4)2 Co

IIMnII trimer 146.7(3) 2.02 4.8 [144]

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442 S.Wang et al. / CoordinationChemistryReviews256 (2012) 439464

Table 1 (Continued )

Metal (MAMB) Cluster C NMB () g J(cm1)a Ref.

{[CoII(triphos)(CN) 2]2[FeII(MeOH)4]}(ClO4)2 Co

IIFeII trimer 148.4(4) 2.20 0.6 [144]

{[CoII(triphos)(CN) 2]2[CoII(MeOH)4]}(ClO4)2 CoIICoII trimer 152.2(13) 2.21 0.4 [144]

{[CoII(triphos)(CN) 2]2[NiII(MeOH)4]}(ClO4)2 Co

IINiII trimer 156.9(3) 2.22 3.0 [144]

{[CoII(triphos)(CN) 2]2[MnII(MeOH)4]2}(ClO4)4 Co

IIMnII tetramer 168.2(4) 2.05 6.8 [144]

{[CoII(triphos)(CN) 2]2[NiII(MeOH)4]2}(ClO4)4 Co

IINiII tetramer 167.9(4) 2.28 0.8 [144]

Cyano-bridged complexesbased on [CrIII(L)(CN)2] (L= salen2 , bpb2)

[Bu4N][{Cr(salen)CN}2CN]4H2O CrIIICrIII dimer 170(2)174(2) 1.96 5.7 [87]

[MnII

(phen)2 Cl][CrIII

(bpb)(CN)2]2H2O CrIII

MnII

dimer 166.4(7) 2.05 2.275 [101][CuIIL1][CrIII(bpb)(CN)2]24H2O

(L1 = 1,5,8,12-tetramethyl-1,3,6,8,10,13-hexaazacyclotetradecane)

CrIIICuII trimer 148.9(6) 1.98 0.18 [123]

[CrIII(salen)(CN)2]2 [MnII(phen)2]2H2O Cr

IIIMnII trimer 163.3(3) 1.99 2.02 [146]

{[CuIIMnII(L1)][CrIII(bpb)(CN)2]}n(ClO4 )n(H2O)n CrIIICuII 1D 157.2(8) 2.03 2.91 [111]

a The data were modeled with the Hamiltonian: such as for the dimer, H=2JS1S2 whereJis the exchange parameter between the two metal ions through the cyanide

bridges.

+1). In contrast to theneutral andpositively charged [MA(L)(CN)2]n

(n= 0,1), themonoanionic precursors arenegativelycharged which

help to alleviate the build-up of excessive charge in polynuclear

compounds and chains, making the synthesis of the target com-

pounds easier.

Previously, we have reviewed the structural topologies of

the tricyanometalate-based complexes and their related mag-

netic properties [70]. The main aim of this review is to provideinformation on the crystallochemistry of dicyanometalate-bearing

compounds and their related (e.g. magnetic/spectroscopic) prop-

erties if they have been studied. These results demonstrate that

the use of these dicyanometalate precursors as ligands is an open

field of research that provides a plethora of newextendedmagnetic

systems. Indeed, the use of blocking organic ligands results in a

number of polynuclear compoundscontainingdi-, tri-,tetra-,dode-

canuclear and various nD assemblies (n= 13). Some are promising

cyanide-bridged SMMs and SCMs, switchable molecular materials

or chemosensors with good light absorbing properties.

In the first part of our paper we will give a short descrip-

tion of the dicyanometalate precursors used for the preparation

of dicyanometalate-based complexes. This part is followed by a

concise description of discrete multinuclear complexes and nDassemblies(n= 13). The known magnetic or spectroscopic proper-

ties, which are interesting for the sake of comparison, are shown as

well. Important structural data (formula and the structural topolo-

gies) and magnetic exchange parameter between the metal ions

through the cyanide bridges along with references are presented

in Table 1. Throughout this paper and within the table we have

classified the dicyanometalate-based complexes following the cri-

teria: (i) the type of central metal atom; (ii) the type of blocking

organic ligands; and (iii) the structural topologies.

We hope the information presented will be helpful in under-

standing the magneto-structural correlation in this class of

compounds as well as being stimulating for both chemists and

physicists working in the field of metal-cyanide systems.

2. Dicyanometalate precursors

Concerning the cyanide-bearing precursor [MA(L)(CN)2]n, its

spin is determined by the nature and oxidation state of the cen-

tral metal ion MA and most of the research is focused on trivalent

paramagnetic transition metal ions such as Fe(III), Ru(III), Os(III)

and Cr(III) and bivalent diamagnetic transition metal ions such as

Fe(II), Ru(II) and Os(II). The unpaired electron of MA is defined bya

magnetic orbital whose symmetry is topologically dependent. The

local anisotropy of MA is also a factor to be taken into account

when aiming at preparing anisotropic high-spin (HS) molecules.

This is one of the crucial parameters needed to obtain SMMs. As

far as the peripheral ligand L is concerned, its nature is extremely

important because of the variety of roles that it can play. Firstly,

the charge of the precursor [MA(L)(CN)2]n depends not only on the

oxidation state of MA but also on L (in general, L is neutral but it

can be charged). Secondly, relative positions of the cyanide groups

bound to MA (stereochemical control of the coordinated cyanides)

arefixed by thedenticity andconformation of theperipheral ligand

L.Two cyanide groupsarein a cisposition when L is a neutral biden-

tate ligand(L = bpy orphen); if L is a charged bidentate ligandacac

or tetradentate ligand salen2, two cyanide groups adopt trans con-formations.In addition,whenL isnot only a terminalligand butmay

act as a bridge the complexing ability of the precursor is increased.

In the end, supramolecular interactions across the L ligand are pos-

sible: for instance, stacking involving the aromatic rings. In

the light of these considerations, one can easily understand the

potential richness of this synthetic route basedon dicyanometalate

precursors, as far as the rational design of nuclearity and dimen-

sionality controlled cyanide-bridged assemblies are concerned.

After the report on the first dicyanometalate precursor cis-

[FeII(bpy)2(CN)2] [71] interest in making different [MA(L)(CN)2]n

(n=2, 1, 0 or +1) building blocks having various ligands

and paramagnetic or diamagnetic metal centers has been long-

standing in a few groups and some dicyanometalate precursors

have been published: (i) [MA(L)(CN)2]2 (MA = FeII, L = TMP2[72], tn-OEP2 [73]); (ii) [MA(L)(CN)2]

(MA = FeIII, L = TPP2

[74], Pc2 [75], salen2, acacen2 [76], bpb2 [77], BQM2,

BenzBQM2 [78], TMP2 [79], s-bqdi2 [80]; MA = RuIII, L= salen2

[81], acac [82], N,N-bis(salicylidene)-o-cyclohexylenediamine

[83]; MA = OsIII, L = s alen2 [84]; MA = Co

III, L = bpb2 [77], Pc2

[85]; MA = CrIII, L = bpb2 [86], salen2 [87]); ( iii) [MA(L)(CN)2]

(MA = FeIII, L = OEOP [88]; MA = Fe

II, L = bpy [71], phen [89],

2,13-dimethyl-6,9-dioxa-3,12,18-triazabicyclo[12.3.1]-octadeca-

1(18),2,12,14,16-pentaene[90]; MA = RuII, L = DMPE [91], pyridine,

4-methylpyridine, 4-ethylpyridine [92]; MA = OsII, L = dpphen

[93], Ph2phen, bpy, phen, Ph2bpy,tBu2bpy, Br2phen, Clphen [94];

MA = CoII, L= triphos [95]); (iv) [MA(L)(CN)2]

+ (MA = FeIII, L = bpy

[96], dmbpy [97], phen [98]; MA = RuIII, L= 16-TMC [99]; MA = Cr

III,

L=cyclam [100]). In general, the preparation of these precursorscan be achieved by the reaction of [MAIII(L)Cl] (L= bpb2, salen2,

acac, etc.) and KCN (or NaCN) in a 1:2 stoichiometry to make the

corresponding [MA(L)(CN)2] (Scheme 1).

Crystallographic investigations have been reported for most of

the above mentioned complexes. The molecular structure consists

[FeIII(salen)Cl]2+2KCN K[FeIII(salen)(CN)2]

[FeIII(bpb)Cl(H2O)] H2O + 2NaCN Na[FeIII(bpb)(CN)2]

Ph4P[RuIII(acac)2Cl 2] + 2KCN Ph4P[RuIII(acac)2(CN)2]

Scheme 1. The synthetic routes of some dicyanometalate precursors, such as

Na[FeIII

(bpb)(CN)2] [77], K[Fe(salen)(CN)2] [76] andPh4P[RuIII

(acac)2(CN)2] [82].

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Fig. 1. View of the molecular structures of the dicyanometalate precursors trans-[MA(L)(CN)2]n (MA = Fe

III; L= bpb;n=1) (left) [77], cis-[MA(L)(CN)2]n (MA = Fe

III; L= phen;

n=1) (middle) [98] and[MA(L)(CN)2] (MA = CoII; L= triphos) (right) [95].

ofthe trans-[MA(L)(CN)2]n, cis-[MA(L)(CN)2]

n or [Co(triphos)(CN)2]

precursor (Fig. 1), sometimes the uncoordinated PPh4+ (or NEt4

+,

K+, ClO4, and SO4

2) counter ions and the crystallization solvent

molecules. Thechargeof the[MA(L)(CN)2]n precursorand thenum-

ber of counter ions are dependent on the central metal ion and the

blocking organic ligands L. Relative positions of the cyanide groups

(trans- or cis-) bound to MA are determined by the denticity and

conformation of the ligand L (Fig. 1). Generally, the Fe/Ru/Os/Cr

atom has a slightly distorted hexacoordinate octahedral coordina-

tion geometry while in [Co(triphos)(CN)2], Co is pentacoordinate

and has a square-pyramidal geometry.

The IR spectra of these precursors show a middle strong band

between 2000 and 2200cm1 that correspond to the terminal

cyanide stretching frequency. When coordinating to the metal

complex, the bridging cyanide groups usually absorb at a higher

frequency than do the terminal groups.

3. Dicyanometalate assemblies based on [MA(L)(CN)2]n

(MA=Fe; n=1, 0, 1)

3.1. [FeIII(L)(CN)2]/+ (L=bpb2, salen2, s-bqdi2, bpy)

3.1.1. [FeIII(L)(CN)2] (L=bpb2)

Since 1,2-bis-(pyridine-2-carboxamido)benzenate (bpb2) as a

tetradentate ligand had been discovered to coordinate to iron(III),

theamide analogs basedon bpb2 have beenemployedto construct

the building block [FeIII(L)(CN)2] (L=bpb2 and their deriva-

tives) [101]. Reactions of the dicyanometalate precursor, metal

ion and organic ligands have resulted in a number of polynuclear

compoundscontaining di-,tri-, tetra-, dodecanuclear and1D metal-

cyanide molecular architectures.

Two kinds of dinuclear cyanide-bridged complexes based

on the anionic dicyanometalate precursor [FeIII(bpb)(CN)2]have been reported: (i) FeIIIMnII dimers: [MnII(phen)2Cl]

[FeIII(bpb)(CN)2]0.5CH3CH2OH1.5H2O [101]; (ii) FeIIIMnIII

dimers: {[FeIII(bpb)(CN)2][MnIII(TNPP)(H2O)]}3H2O, {[Fe

III(bpb)

(CN)2][MnIII(TClPP)(CH3OH)]}3CH3OH, {[Fe

III(bpb)(CN)2][MnIII

(TMeOPP)(CH3CH2OH)]}2CH3OHCH3CH2OHH2O [102], [MnIII

(saltn)(H2O)FeIII(bpmb)(CN)2]H2O and [Mn

III(saltn)(MeOH)FeIII

(bpClb)(CN)2]2H2O [103].

The reaction of equimolar Mn(phen)2Cl2 with K[Fe(bpb)

(CN)2] affords a dimeric complex [MnII(phen)2Cl][Fe

III(bpb)

(CN)2]0.5CH3CH2OH1.5H2O [101]. [Fe(bpb)(CN)2] acts as a

monodentate ligand through one of its two cyanide groups toward

a [Mn(phen)2(Cl)]+ core (Fig. 2). The Fe(III) ion is coordinated

by four bpb2 nitrogen atoms and two cyanide carbon atoms,

in a slightly distorted octahedral geometry. The Mn(II) ions are

hexacoordinated with one chloride anion and one cyanide nitrogen

atom at cis positions and four nitrogen atoms from two cis-phen

ligands yielding a MnN5Cl octahedral surrounding. The formation

of a dimeric structure is understandable when one considers

that the presence of the bulky phen and bpb2 ligands hinders

the formation of trimeric or 1D complex. Magnetic susceptibility

measurements confirm the presence of overall antiferromagnetic

interactions between Fe(III) and Mn(II) withJFeMn =1.34cm1.

Self-assembly of the anionic building block [Fe(bpb)(CN)2]

and [Mn(saltn)]ClO4 has resulted in the formation of the FeIIIMnIII

dinuclear [MnIII(saltn)(MeOH)][FeIII(bpb)(CN)2]3H2O [103]. The

dinuclear unit is constructed from the anionic precursor trans-

[Fe(bpb)(CN)2] and the cationic [Mn(saltn)(MeOH)]+ part bridged

by the cyanide ligand. The Mn(III) ion exhibits an axially elongated

octahedral configuration, which is equatorially coordinated by two

nitrogen atoms and two phenoxo oxygen atoms of saltn2, and

axially linkedto onemethanoloxygen atom anda cyanide nitrogen

atom of [Fe(bpb)(CN)2] moiety. Four dinuclear units are linked

Fig. 2. View of the molecular structure of the dinuclear complex

[MnII(phen)2Cl][FeIII(bpb)(CN)2]0.5CH3CH2OH1.5H2O. The solvate molecules

have been removed forclarity [101].

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Fig. 3. Temperature dependence ofmTper MnFe for [Mn(saltn)(MeOH)][Fe(bpb)

(CN)2]3H2O. The line represents the best fit using the parameters discussed in

the text. Inset: out-of-phase AC magnetic susceptibilities measured under zero DC

magnetic field.

Reprinted with permission from Ref. [103]. Copyright 2009 The Royal Society of

Chemistry.

head-to-tail via hydrogen bonding between the non-bridging

cyanide nitrogen atoms and the coordinating methanol oxygen

atoms, giving rise to a metallo-supramolecular [MnFe]4 square.

Magnetic studies indicate the presence of global ferromagnetic

interaction with the cooperation of zero-field splitting (ZFS) of

Mn(III) and/or intermolecular magnetic coupling (Fig. 3). Using

the spin Hamiltonian H=2JSFeSMn, the best fits corresponded

to JFeMn =3.2cm1 and g= 1 .93. The ZFS parameter (DMn) value

of 1.25cm1 is normal for HS tetragonally elongated octahedral

Mn(III). Alternating-current (AC) magnetic susceptibility measure-

ments show obvious frequency-dependent

m signals at T< 3 K

(inset ofFig. 3), suggesting the presence of slow relaxation of mag-

netization. The absence of a maximum down to 1.8K precludesany

further characterization of the magnetizationrelaxation. FeIIIMnIII

ferromagnetic interactions (JFeMn = 1.564.91 cm1) have been

reported in the isostructural dinuclear complexes: {[FeIII(bpb)

(CN)2][MnIII(TNPP)(H2O)]}3H2O, {[Fe

III(bpb)(CN)2][MnIII(TClPP)

(CH3OH)]}3CH3OH, {[FeIII(bpb)(CN)2][Mn

III(TMeOPP)(CH3CH2OH)]}2CH3OHCH3CH2OHH2O [102], [Mn

III(saltn)(H2O)

FeIII(bpmb)(CN)2]H2O and [MnIII(saltn)(MeOH)FeIII(bpClb)(CN)2]

2H2O [103]. For {[FeIII(bpb)(CN)2][Mn

III(TNPP)(H2O)]}3H2O,

AC susceptibility measurements indicates the presence of slow

relaxation of magnetization.Five Fe(III)Ni(II)Fe(III) trimers have been obtained by

slow diffusing [NiL n](ClO4)2 into K[Fe(bpb)(CN)2] in the

methanol solution, namely [NiIIL1][FeIII(bpb)(CN)2]2H2O,

[NiIIL2][FeIII(bpb)(CN)2]26H2O, [NiIIL3][FeIII(bpb)(CN)2]27H2O,

[NiIIL4][FeIII(bpb)(CN)2]24H2O and [NiL 5][FeIII(bpb)(CN)2]2

(L1 = 3,10-dimethyl-1,3,5,8,10,12-hexaazacyclotetradecane; L2 =

3,10-diethyl-1,3,5,8,10,12-hexaazacyclotetradecane; L3 = 3,10-

bis(2-hydroxyethyl)-1,3,5,8,10,12-hexaazacyclotetradecane; L4 =

3,10-bis(2-phenylethyl)-1,3,5,8,10,12-hexaazacyclotetradecane;

L5 = 3-methyl-1,3,5,8,12-pentaazacyclotetradecane) [104]. These

complexes having similar sandwich-like molecular structures

are composed of neutral trinuclear entities of general formula

[NiLn][Fe(bpb)(CN)2]2 (n=15) (Fig. 4). Each [Fe(bpb)(CN)2] unit

acts as a monodentateligand through one of itstwo cyanide groups

toward the central Ni(II) ion. The variable-temperature magnetic

susceptibility studies revealed an intramolecular ferromagentic

interaction between the FeIII (S= 1 /2) and NiII (S=1) through the

cyanide bridges (JFeNi = 6.038.9cm1), giving anS= 2 ground state.

The study of the magneto-structural correlation shows that the

cyanide-bridging bond angle is related to the strength of magnetic

exchange coupling: the larger the NiN C bond angle, the stronger

the Fe Ni magnetic interaction.

Sandwich-like FeIIICuIIFeIII trinuclear compound

[CuIIL][FeIII(bpb)(CN)2]24H2O (L = 1,5,8,12-tetramethyl-

1,3,6,8,10,13-hexaazacyclotetradecane) [105] was prepared

by slow evaporation of equimolar mixtures of the Cu(II) precursors

and K[Fe(bpb)(CN)2]2 in the mixed solution (MeCNH2O). The

complex has a centrosymmetric trinuclear structure with the

copper ion situated at the inversion center. The coordination

Fig. 4. View of themolecular structure of thetrinuclear complex [NiL1

][Fe(bpb)(CN)2]2 H2O (L1

= CH3 ). Thesolvate watermolecules have been removed for clarity [104].

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geometry about Cu(II) is an axially elongated octahedron with

four secondary N atoms from the hexazamacrocycle occupying the

equatorial plane. The axial sites are occupied by two cyanide nitro-

gen atoms of [Fe(bpb)(CN)2], yielding a sandwich-like structure.

The CuN C bond angles deviate greatly from linearity (146.9(6)

and 148.9(6)). Magnetic susceptibility measurements confirm

the existence of weak antiferromagnetic coupling between LS

FeIII (S= 1/2) and CuII (S= 1/2) ions (JFeCu =0.59cm1), which

is supported by the isothermal magnetization measurements

at 2 K.

Attempts to extend this work to other ions such as Mn(III) and

Mn( II), afford a few FeIIIMnIIIFeIII and FeIIIMnIIFeIII polynu-

clear compounds: {[FeIII(bpb)(CN)2]2[MnIII(TPP)]}[Mn(TPP)

(CH3OH)2]xH2OyCH3O, {[FeIII(bpmb)(CN)2]2[Mn

III(TPP)]}[Mn

(TPP)(CH3OH)2]xH2OyCH3O [102], [MnIII

2(5-Br-saltn)2(H2O)(EtOH)Fe

III(bpb)(CN)2][FeIII(bpb)(CN)2]6H2O, [Mn

III2(5-

Cl-saltn)2(CH3OH)(EtOH)FeIII(bpb)(CN)2][Fe

III(bpb)(CN)2]5H2O

MeCN [103] and [MnII(CH3OH)2(H2O)2][FeIII(bpb)(CN)2]22H2O

[106].

In complexes {[FeIII(bpb)(CN)2]2[MnIII(TPP)]}[Mn(TPP)(CH3

OH)2]xH2OyCH3Oand{[FeIII(bpmb)(CN)2]2[Mn

III(TPP)]}[Mn(TPP)

(CH3OH)2]xH2OyCH3O [102], two trimers possess a similar

sandwich-like molecular structure. The magnetic suscepti-

bility data reveal the ferromagnetic interaction between FeIII

and MnIII magnetic centers with JFeMn = 2.473.28 cm1. AC

magnetic susceptibility measurements show obvious frequency-

dependent out-of-phase signals below 3.5K, along with clear

frequency-dependent in-phase signals. No maximum for

out-of-phase signals and hysteretic behavior were observed.

The [Mn2Fe]+[Fe] type complex [MnIII2(5-Br-

saltn)2(H2O)(EtOH)FeIII(bpb)(CN)2][Fe

III(bpb)(CN)2]6H2O [103]

was obtained by slow diffusion of equimolar [Mn(5-Br-saltn)]ClO4and K[Fe(bpb)(CN)2] in mixed solvent. The crystal structure

consists of a cyanide-bridged trinuclear cation [Mn2(5-Br-

saltn)2(EtOH)(H2O)(-CN)2Fe(bpb)]+ and a free [Fe(bpb)(CN)2]

anion. In the trinuclear cation, [Fe(bpb)(CN)2] uses two trans

cyanide ligands to connect two [Mn(5-Br-saltn)]+, resulting in

a linear MnFeMn arrangement. The benzene groups from the5-Br-saltn ligand deviate greatly from the N2O2 plane form-

ing a puckered configuration. The trinuclear cations and free

[Fe(bpb)(CN)2] anions are connected by Ncyanide HO hydrogen

bonding, resulting in a supramolecular macrocycle. Weak

interactions exist between the benzene rings of non-bridging

[Fe(bpb)(CN)2], yielding a 2D layered structure. Magnetic studies

indicate the antiferromagnetic interaction between LS Fe(III)

and Mn(III) through the cyanide bridges (JFeMn =2.61 cm1).

AC magnetic susceptibility measurements show the occurrence

of frequency-dependent out-of-phase signals. Due to the exis-

tence of intermolecular magnetic interaction (zJ =0.17cm1),

the complex displays an exchange-biased SMM behavior

below 0.5 K. Ferromagnetic interactions (JFeMn =3.72cm1)

were observed in the similar complex [MnIII2(5-Cl-saltn)2(CH3OH)(EtOH)Fe

III(bpb)(CN)2][FeIII(bpb)(CN)2]5H2OMeCN

[103]. AC susceptibility measurements are frequency-dependent,

suggesting the presence of slow magnetization relaxation.

Tetranuclear assembly[MnIII(5-Cl(salpn))]2[FeIII(bpmb)(CN)2]2

3H2OCH3CN, was reported by Kou in 2007 [107]. The reac-

tion of manganese(III) Schiff bases of the type salen2 with

[Fe(bpmb)(CN)2] produces cyanide-bridged molecular wheels,

from which the tetranuclear complex has been separated. The

compound possesses an arch-shaped neutral MnIII2FeIII

2 tetranu-

clear compound (Fig. 5). The axial positions of Mn(1) are occupied

by two cyanide nitrogen atoms while Mn(2) is axially coordinated

by one cyanide nitrogen atom and one water oxygen atom. Inter-

estingly, two Mn2Fe2 molecules are linked together by hydrogen

bonds between the nonbridging cyanide nitrogen atoms and the

Fig. 5. View of arch-like structure of the tetranuclear complex [Mn(5-

Cl(salpn))]2[Fe(bpmb)(CN) 2]23H2OCH3 CN. The solvate molecules have beenremoved for clarity [107].

coordinated water molecules, forming elliptical [Mn2Fe2]2 cyclic

structures. The dimeric cycles are further connected by hydrogen

bonds between coordinated water molecules and protonated

phenoxo oxygen atoms, yielding a 1D supramolecular structure.

Variable-temperature magnetic susceptibility data indicate

overall ferromagnetic interactions between Fe(III) and Mn(III) ions

(JFeMn =2.15cm1), giving an S=5 ground state. The decrease of

mTbelow 10K shows great sensitivity to theintermolecularinter-

action (hydrogen-bonding interactions) in contrast with the ZFS

parameter of the Mn(III) ion. AC magnetic susceptibilities are obvi-

ous frequency-dependent below 3.0K. Combination of the HS state

and a negative magnetic anisotropy (D=0.42cm1) results in the

observation of slow magnetization relaxation.The reaction of equimolar amounts of [Mn(salen)]ClO4

with K[Fe(bpmb)(CN)2] in MeOH/MeCN/H2O (6:3:1) affords the

first unique cyanide-bridged dodecanuclear nanosized molecular

wheel [{MnIII(salen)}6{FeIII(bpmb)(CN)2}6]7H2O [107,108]. X-ray

single-crystal structural analysis showed that the complex is

comprised of six MnIII and six FeIII ions alternately bridged by

cyanide ligands to give a centrosymmetrical, elliptical, dodecanu-

clear molecular wheel with a repeating [FeCNMnNC]6 unit,

which is the largest cyanide-bridged heterometallic metallamacro-

cycle (Fig. 6). The FeC N bond angles are approximately linear

(173.5(4)178.2(5)) except for N2 C2Fe1 (168.5(5)) while the

MnN C bond angles (151.8(3)158.6(3)) deviate significantly

from strict linearity. The largest intramolecular metalmetal dis-

tance is 2.178nm, which corresponds to the major axis of theellipse; the minor axis of the ellipse corresponds to a metalmetal

separation of 1.773nm, indicating that the complex is a nanosized

molecular wheel.

The mTvs Tdata show that the LS FeIII and anisotropic MnIII

centers are ferromagnetically coupled (Fig. 7a). Using a spin Hamil-

tonianH=2J(SFeiSMnj + SMn12SFe1) (i, odd;j, even), fitting of the

magnetic data gives J=3.4cm1 and g= 1.99. The high-field mag-

netization values are lower than calculated, which may be due to

the ZFS effect of MnIII. To explore whether the wheel-like complex

behaves as a SMM, single-crystal hysteresis loops and relaxation

measurements were performed. In the easy-axis direction, the

magnetization exhibits a rapid saturation and hysteresis loops of

classical magnet behavior below 0.8 K (Fig. 7b). The coercivities of

hysteresis loops were strongly temperature and time dependent,

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Fig. 6. View of the molecular structure of the dodecanuclear molecular wheel [{Mn(salen)}6{Fe(bpmb)(CN)2}6]7H2 O. The solvate water molecules have been omitted for

clarity [107,108].

Fig. 7. (a) Temperature dependence ofmTfor [{Mn(salen)}6{Fe(bpmb)(CN)2}6]7H2O at a field of 1000 Oe. Inset:the out-of-phase(

m) signals in theAC susceptibility. (b)

Hysteresis loop at differenttemperatures measured at a scan magnetic field speed of 0.14T s1. (c) Magnetization relaxation and relaxation time T1.

Reprinted with permission from Ref. [107]. Copyright 2007 American Chemical Society.

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Fig. 8. Viewof the chain [{MnIII(salen)}{FeIII(bpb)(CN)2}] [108].

increasing with decreasing temperature and increasing field sweep

rate, as expected fora SMM. Below 0.2K, thecoercivefield becomes

temperature independent, signifying QTM between MS =+15 and

MS =15.The blocking temperature (TB)isabout0.8K,abovewhich

hysteresis loops disappear. The hysteresis loop does not show the

steplike features that are indicative of resonant QTM between the

energy states of the molecules. The absence of QTM steps can be

rationalizedas thepresence of relativelymanifested intermolecular

interactions ( stacking and hydrogen bonds between the adja-

cent wheels). AC magnetic susceptibility measurements confirm it

is a SMM below 4 K. The relaxation time follows an Arrhenius law

with 0 =1.2107 s and the mean effective barrier to relaxation

Ueff= 7 .5 K(Fig. 7c). The relaxation barrier obtained is small, which

is consistent with the observation of the hysteresis loops only atlow temperatures.

Afterthe report on the above dodecanuclearcomplex,some sim-

ilar dodecanuclear FeIIIMnIII complexes with various ligands have

been reported: [MnIII(salen)]6[FeIII(bpClb)(CN)2]64H2O2CH3OH,

[MnIII(salen)]6[FeIII(bpdmb)(CN)2]610H2O5CH3OH, [Mn

III(5-

Br(salpn))]6[FeIII(bpmb)(CN)2]624H2O8CH3CN and

[MnIII(5-Cl(salpn))]6[FeIII(bpmb)(CN)2]625H2O5CH3CN [107].

Magnetic studies reveal HS ground state S= 1 5 is present in the

wheel compounds originated from a ferromagnetic interaction

between Fe(III) and Mn(III) through the cyanide bridges. The

magnetic coupling constantsJrange from 0.93 to 3.545 cm1. The

curve of reduced magnetization (M/NB) vs H/Tshows the isofield

lines do not superimpose, suggestive of significant magnetic

anisotropy in the ground state. All the complexes exhibit obviousAC frequency-dependent out-of-phase signals at T

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Fig. 9. View of the mixed cyano- and phenolate-bridged chain {[CuIIMnII(L1 )][FeIII(bpb)(CN)2 ]}n(ClO4)n(H2O)n. H2L1 is derived from 2,6-diformyl-4-methyl-phenol,

ethylenediamine and diethylenetriamine. The anions and solvate molecules have been removed for clarity [111].

interactions observed in the FeIIIMnIII chain discussed above, the

magnetic susceptibility measurements agree with ferromagnetic

coupling between FeIII and MnIII (JFeMn = 0.494.46 cm1) and

weak interchain antiferromagentic/ferromagnetic interactions in

these complexes. Magnetic studies demonstrate that a frequency-

dependent AC magnetic susceptibility typical of a SCM is observed

in [MnIII(5-Me-salen)FeIII(bpb)(CN)2]0.5H2OMeOH [109].

When extending this work to other ions such asnickel(II), Kou and coworkers reported the FeIIINiII chains:

[NiL1][Fe(bpb)(CN)2]ClO4H2O, [NiL 4][Fe(bpb)(CN)2]ClO42CH3CN

and [NiIIL6][FeIII(bpb)(CN)2]ClO4CH3OH (L 1 = 3,10-dimethyl-

1,3,5,8,10,12-hexaazacyclotetradecane; L4 = 3,10-bis(2-phe-

nylethyl)-1,3,5,8,10,12-hexaazacyclotetradecane; L6 = 1,9-dia-

mino-3,7-diazanonane (2,3,3-tet)) [104]. The structure consists

of alternating trans-bidentate [Fe(bpb)(CN)2] and [NiL]2+ units

generating a cyanide-bridged cationic polymeric chain with the

perchlorate as the counter anions. In the wave-like chain, two

trans CN groups in [Fe(bpb)(CN)2] are connected with two

[NiL]2+ groups, whereas each [NiL]2+ group is linked to two

[Fe(bpb)(CN)2] ions in trans positions. Magnetic studies indicate

ferromagnetic interaction between adjacent Fe(III) and Ni(II) ions.

Theinfinite chain canbe treated as alternating uniform FeNi dimerswith different intradimeric (Jd) and interdimeric exchange con-

stants (Jc). Fitting of the magnetic data givesJd = 6.17.49cm1 and

Jc = 0.5911.34 cm1. AC magnetic susceptibilities measurements

demonstrate that a long-range antiferromagnetic ordering is

observed below 3.5 K for [NiIIL6][FeIII(bpb)(CN)2]ClO4CH3OH,

while compounds [NiIIL1][Fe(bpb)(CN)2]ClO4H2O and

[NiIIL4][Fe(bpb)(CN)2]ClO42CH3CN show the absence of magnetic

ordering down to 2 K.

Jiang and co-workers have shown that the assem-

bly of the [Fe(L)(CN)2] building blocks and Mn(II)

1,8-diamine type complexes is an alternative synthetic

route for the design of cyanide-bridged FeIIIMnII chains:

[Mn(L1)][Fe(bpb)(CN)2]ClO40.5H2O, [Mn(L2)][Fe(bpb)(CN)2]ClO4

0.5H2O, [Mn(L 1

)][Fe(bpClb)(CN)2]ClO4H2O, [Mn(L 2

)][Fe(bpClb)

(CN)2]ClO40.5H2O and [Mn(L1)][Fe(bpdBrb)(CN)2]ClO4H2O [110].

In general, the structure is composed of alternating [Mn(L1)]2+

and [Fe(bpb)(CN)2] units in the cationic chain with free ClO4

as balanced anion. Magnetic measurements indicate that the

bridging cyanide ligands mediate antiferromagnetic interactions

between the Fe(III) and Mn(II) ions (JFeMn in the range of1.10 to

3.10 cm1). The nature of antiferromagnetic coupling between

Fe(III) and Mn(II) ions via the CN bridges is consistent with theFeIIIMnII systems made of Fe dicyanides [112114].

Recently, a 1D mixed cyanide- and phenolate-bridged

heterotrimetallic complex, {[CuIIMnII(L1)][FeIII(bpb)(CN)2]}n

(ClO4)n(H2O)n, was reported, in which H2L1 was derived

from 2,6-diformyl-4-methyl-phenol, ethylenediamine and

diethylenetriamine [111]. X-ray crystallography reveals that

two blocks [Fe(bpb)(CN)2] and [CuMn(L1)]2+ are connected

by the cyanide group binding to the Mn(II) ion. The repeated

[NCFe(bpb)CNMnCu(L1)] units extend along the b axis,

forming a infinite single chain structure (Fig. 9). The Cu(II), Fe(III)

and Mn(II) ions are tetra-, hexa-, and hepta-coordinated with

square planar, octahedral, and distorted pentagonal-bipyrimidal

coordination geometry, respectively. The neighboring chains are

connected via weak intermolecular hydrogen bond to form a2D supramolecular structure. Antiferromagnetic interaction was

observed in the complex (JCuMn =20.06 cm1, JMnFe =1.22cm

1

and g = 1.97). This represents the first 1D cyanide- and phenolate-

bridged compound containing three kinds of spin carriers

3d-3d-3d.

3.1.2. [FeIII(L)(CN)2] (L=salen2)

Using the trans-(dicyanide)iron(III) [FeIII(salen)(CN)2]

as a building block, two cyanide-bridged trinuclear com-

pounds, [FeIII(salen)(CN)2]2 [MnII(bpy)2]CH3OH2H2O and

[FeIII(salen)(CN)2]2[MnII(phen)2]CH3OH have been obtained

[115]. The neutral FeIIIMnIIFeIII compound is comprised of one

[Mn(L)2]2+ and two [Fe(salen)(CN)2]

units, in which the two

[Fe(salen)(CN)2]

units act as a monodentate ligand through

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Fig. 10. View of the molecular structure of the trinuclear complex

{[FeIII(salen)(CN)2]2 [MnII(bipy)2 ]}CH3OH2H2O. The solvate molecules have

been removed for clarity [115].

one of their trans cyanide groups to coordinate with the Mn(II)

ion in a cis manner (Fig. 10). The FeIII2MnII compounds show an

antiferromagnetic interaction between the FeIII and MnII through

the cyanide bridges (JFeMn =1.23 to1.34 cm1).

Attemptsto prepare differentcyanide-bridged assembliesbased

on the anionic dicyanometalate precursor, [Fe(salen)(CN)2], have

illustrated that the types of complexes to be formed are quite

dependent on the starting metal salts and the solvents used. In one

case, using [Mn(L)( H2O)Cl]ClO4 (L = 2,13-dimethyl-3,6,9,12,18-

pentaazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene and

2,13-dimethyl-6,9-dioxa-3,12,18-triazabicyclo[12.3.1] octadeca-

1(18),2,12,14,16-pentaene) instead of Mn(bipy)2Cl2 as starting

material have led to the isolation of the single chain complexes,

[FeIII(salen)(CN)2][MnII(L)]ClO4CH3OH [115]. The cationic chain

is consisted of repeating [NCFe(salen)CNMn(L)] units with

the positive charge balanced by ClO4 anions (Fig. 11). The

Mn(II) ion is seven-coordinated, forming a slightly distorted

pentagonal-bipyrimidal coordination geometry. It is worth noting

that cyanide-bridged FeIIIMnII complexes with perfect single

chain structures remain very rare despite the reports on several

examples with double zigzag chain structures [116122].

An antiferromagnetic interaction is found between the Fe(III)

and Mn(II) ions. This result is comparable to those of cyanide-

bridged FeIIIMnII 1D complexes based on [Fe(L)(CN)2] (L=bpb

derivatives) [110]. The infinite chain can be treated as alternat-

ing uniform FeIIIMnII dimers with different intradimeric (J1) and

intrachain (also interdimer) (J2) exchange constant. A best-fit to

the magnetic susceptibilities based on the alternating infinite sin-

gle chain model leads to J1 =3.25, J2 =0.785 cm1, g= 1.99 and

J1 =2.675, J2 =0.465 cm1, g= 2.01, respectively.

3.1.3. [FeIII(L)(CN)2] (L= s-bqdi2)

The design of extended architectures with novel spin-carrier

topologies starting from molecular precursors is an area of

immense interest. For instance, self-assembly of the anionic build-

ing block [Fe(s-bqdi)2(CN)2] with various metal ions and the

blocking ligand s-bqdi2 has resulted in the formation of a new

series of 1D heterobimetalllic polymers, K[MII(s-bqdi)2][FeIII(s-

bqdi)2(CN)2]10H2O (MII =Co, Ni and Cu) [80].

X-ray Powder diffraction studies reveal that these complexes

are isostructural and have primitive hexagonal unit lattice struc-

ture. Coordination of s-bqdi2 with transition metal ions gives

square planar geometry with molecular orbitals delocalized over

the entire system, further leading to the formation of infinite

chain networks. Duringcomplex formation, the free radical present

Fig.11. View of thechain{[FeIII(salen)(CN)2 ][MnII(L)]}ClO4 CH3OH (L = 2,13-dimethyl-3,6,9,12,18-pentaazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene). The anions

and solvate molecules have been removed for clarity [115].

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Fig.12. View of themolecular structureof thetetranuclear complex [FeIII2CuII

2(-

CN)4(bpy)6 ](PF6)64CH3CN2CHCl3. The anions and solvate molecules have been

removed for clarity [123].

on the s-bqdi2 ligands undergoes spin coupling. For K[CoII(s-

bqdi)2][FeIII(s-bqdi)2(CN)2]10H2O, magnetic susceptibility show a

strong antiferromagnetic coupling between the Fe(III) and Co(II)(JFeCo =25.82 cm

1,gFe = 1.920,gCo = 2.126). Significant spinorbit

coupling of the 2T2g ground term for LS octahedral FeIII ions and an

unquenched orbital contribution typical of the 4T1g ground state in

octahedral CoII complexes exist.

3.1.4. [FeIII(L)(CN)2]+ (L=bpy)

Self-assembly of the cationic building block, cis-

[FeIII(bpy)2(CN)2]+, with metal ions (CuII or NiII) and blocking

ligands have resulted in the formation of square-like tetranu-

clear compounds. The reaction of [FeIII(bpy)2(CN)2](PF6)

with [CuII(bpy)(CH3OH)2](PF6)2 in methanol produces the

cyanide-bridged cyclic tetranuclear complex [FeIII2CuII

2(-

CN)4(bpy)6](PF6)64CH3CN2CHCl3 [123]. X-ray crystal structure

analyses revealed that the complex cation having an inversion cen-ter is a tetranuclear macrocycle with the overall geometry being

nearlysquare. The Fe3+ and Cu2+ ions are alternately bridged by the

cyanide groups (Fig. 12). Magnetic susceptibility measurements

confirm that the adjacent FeIII and CuII ions are ferromagnetically

coupled through the cyanide bridges (JFeCu =+6.3cm1), giving

an S=2 ground state and weak antiferromagnetic interactions

between the diagonal FeIII FeIII and CuII CuII pairs are oper-

ative. The propagation of the ferromagnetic interaction can be

understood by the orthogonal magnetic orbitals of the LS Fe3+(d)

and Cu2+(d) ions.

A similar square-like structure has been reported for

[FeIII2CuII

2(-CN)4(dmbpy)4(impy)2](ClO4)64CH3OH4H2O [97],

magnetic data indicate that the Cu(II) ion and imino nitroxide

are ferromagnetically coupled with a fairly strong coupling

constant (JCu-radical > 300 K) and act as triplet species. In the square,

d(Fe(III)), d(Cu(II)) and p(imino nitroxide) spins are alter-

nately assembled, and this situation allowed the square to have

an S=3 ground state. The exchange coupling constant of Fe(III)

and the Cu(II)-radical moiety was estimated to beJFeCu =4.9cm1

(H=2JSFeSCu-radical ).

3.2. [FeII(L)(CN)2] (L= bpy, phen)

3.2.1. [FeII(L)(CN)2] (L= bpy)

Self-assembly of the neutral diamagnetic building block cis-

[FeII(bpy)2(CN)2] with metal ions and blocking ligands have

resulted in the formation of square-like tetranuclear compounds:

( i) FeII2CuII

2: [FeII

2CuII

2(-CN)4(bpy)6](PF6)42H2O4CHCl3 [123],

[FeII2CuII

2(-CN)4(dmbpy)4(impy)2](ClO4)44CH3OHC6H6 [97]

and [FeII2CuII

2(bpy)6(-CN)4(NCS)2]2[FeII(CN)5(NO)](NCS)25H2O

[124]; (ii) FeII2CoII/III

2: [FeII

2CoII

2(-CN)4(bpy)8](PF6)43CHCl3

2CH3CN and [FeII

2Co2III(-CN)4(bpy)8](PF6)62CHCl3 4CH3NO2

[125]; (iii) FeII2RuII

2: [RuII

2FeII

2(-CN)4(bpy)8](PF6)4CHCl3H2O

[126]; (iv) FeII4: [FeII

4(-CN)4(bpy)8](PF6)44H2O

[125], [FeII4(-CN)4(bpy)4(tpa)4](PF6)4 [127] and

[FeII4(CN)4(bpy)4(bpym)4](PF6)46MeOH4H2O [128]; (v)

FeII2MnII

2: [(bipy)2FeII(CN)2Mn

II(bipy)2]2(ClO4)4 and

[(bipy)2FeII(CN)2MnII(DMF)3(H2O)]2(ClO4)4 [119]; (vi) FeII2NiII2:

[{NiII(rac-CTH)}2{FeII(CN)2(bpy)2}2](ClO4)4H2O [129]. X-ray

crystallographic studies have revealed that they possess similar

square-like structures. In the square unit, Fe(II) and the metal

ion are located at alternating corners of the rectangle and each

[Fe(bpy)2(CN)2] unit uses its two cis cyanide groups to connect the

metal ions.

In the FeII2CuII

2 tetranuclear compounds,

[FeII2CuII

2(-CN)4(bpy)6](PF6)42H2O4CHCl3 [123] and

[FeII2CuII

2(-CN)4(dmbpy)4(impy)2](ClO4)44CH3OHC6H6 [97],

Cu(II) ions adopt a square pyramidal geometry, in which the

equatorial coordination sites are occupied by four nitrogen

atoms from the auxiliary ligands and two cyanide groups and

the apical position is completed by solvent molecule. The

magnetic data of [FeII2CuII2(-CN)4(bpy)6](PF6)42H2O4CHCl3show that magnetic interactions between CuII ions through

the LS FeII ions are negligibly small. However, in [FeII2CuII

2(-

CN)4(dmbpy)4(impy)2](ClO4)44CH3OHC6H6, the orthogonal

arrangement of the Cu(II) magnetic orbital (dx2y2) and imino

nitroxide magnetic orbitals (p*) leads to a fairly strong ferro-

magnetic interaction. The Cu(II)-radical moieties are magnetically

separated by the Fe(II) ions.

The crystal structure of [FeII2CuII

2(bpy)6(-CN)4(NCS)2]2[FeII(CN)5(NO)](NCS)25H2O [124] consists of unsymmet-

rical tetranuclear [FeII2CuII

2(bpy)6(-CN)4(NCS)2]+ cations,

[FeII(CN)5(NO)]2 and NCS anions and water molecules of crys-

tallization. The overall geometry of the tetranuclear cationic core

is almost square. Magnetic susceptibility data indicate that the

Fe(II) ions in the Fe2Cu2 tetranuclear cation and the nitroprussideanion are diamagnetic. They present a LS S= 0 d6 configuration

and do not contribute to the total magnetic moment. A very weak

antiferromagnetic coupling was found between the Cu(II) ions

through the NCFeCN bridges (JFeCu =0.185 cm1).

For [Fe2IICo2

II(-CN)4(bpy)8](PF6)43CHCl32CH3CN [125],

X-ray crystallography has revealed that individual squares are chi-

ral,but the crystal as a whole is racemic. Each metal ion has either a

or a configuration. The -back bonding donation

character of a FeII ion is stronger than that of a CoII/III ion. The FeII

ions are coordinated to the cyanide carbon atoms, and as a result

the FeIIC(cyanide) bonds are shorter than the CoN(cyanide)

bonds. The HS CoII ions are antiferromagnetically coupled through

the diamagnetic FeII ions (JCoCo =2.7cm1). However, com-

plex [FeII

2Co2III

(-CN)4(bpy)8](PF6)62CHCl34CH3NO2 [125]

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has the absolute configurations of either or .

Magnetic susceptibility measurements revealed that the com-

plex is diamagnetic, which implies the FeII and CoIII ions are

in the LS state. Electrochemical measurements are performed.

At present it is unclear whether the iron sites in [FeII2Co2III(-

CN)4(bpy)8](PF6)62CHCl34CH3NO2 showed two-step electron

transfer process in comparison to the one-step two electron trans-

fer process in [Fe2IICo2

II(-CN)4(bpy)8](PF6)43CHCl32CH3CN,

although the electronic interaction between the iron cen-

ters through the CNCoIIINC groups are weak for both. A

photo-irradiation experiment on the mixed-valent square of

[FeII2Co2III(-CN)4(bpy)8](PF6)62CHCl34CH3NO2 has been car-

ried out. UV/Vis spectra indicate that the electron transfer did

not take place or the back electron transfer process was too rapid

to be detected at 7K, confirming the absence of photo-induced

magnetic ordering due to the light-induced electron transfer

between FeIIICoII and FeIICoIII ions.

The reaction of [Fe(bpy)2(CN)2] with [Ru(bpy)2(solvent)2]2+

in ethanol produces a tetranuclear compound [RuII2FeII

2(-

CN)4(bpy)8](PF6)4CHCl3H2O [126]. The [RuII

2FeII

2]4+ cation is

nearly a square macrocycle with alternating RuII and FeII ions at

the corners of the square. The cyanide groups are arranged in

an anti-parallel fashion in order to link neighboring metal ions

and have flipped during the course of the reaction. Individual

squares are chiral, with the metal ions having either or

configurations. Both metal ions are diamagnetic. The elec-

trochemically generated mixed-valence states have been studied

by spectroelectrochemical methods. The IVCT interaction between

cyanide-bridged ruthenium and iron ions is stronger than that

between iron ions, due to the asymmetric bridging cyanide lig-

and. Cyanide ions have the potential to assemble metal ions and

propagate not only magnetic but also electronic interactions.

Reactions of the starting metal salt, the auxiliary lig-

ands (bpy, tpa and bpym) and [Fe(bpy)2(CN)2]H2O in

methanol resulted in the formation of three cyanide-bridged

FeII4 square-like polynuclear compounds: [Fe4II(-

CN)4(bpy)8](PF6)44H2O [125], [FeII

4(-CN)4(bpy)4(tpa)4](PF6)4

[127] and [FeII4(CN)4(bpy)4(bpym)4](PF6)46MeOH4H2O [128].Magnetic measurements indicate that the bridging cyanide lig-

ands mediate diamagnetic interaction between Fe(II) ions in

[Fe4II(-CN)4(bpy)8](PF6)44H2O [125].

For [FeII4(-CN)4(bpy)4(tpa)4](PF6)4, variable-temperature X-

ray crystal structure analyses show that four FeII ions in the

square are in the LS states below 100K [127]. In the square, two

{Fe(bpy)2}2+ centers and two {Fe(tpa)}2+ centers are alternately

bridged by four CN groups (Fig. 13). The two remaining cis posi-

tions are coordinated by either carbon or nitrogen atoms from the

cyanide groups. The carbon and nitrogen atoms of the cyanide lig-

andsactas acceptorsanddonors, respectively. The coordination

bond lengths of FeII ions are different between the LS and HS states

(d = 0.20.3 A) and the average bond lengths are related to the

spin state of the FeII ions. Magnetic susceptibility and Mssbauermeasurementsdemonstratethe occurrence of a two-step spin con-

version with the first step occurring on the Fe2 ion at Tsc =160K

and the second step starting to occur on Fe4 at 300K. No hysteresis

was observed in temperature range measured (Fig. 14). However,

thermally induced one-step reversible spin crossover was found in

[FeII4(CN)4(bpy)4(bpym)4](PF6)46MeOH4H2O [128].

The first complete characterization of a cyanide-bridged

FeII2MnII

2 molecular square based on the dicyanometalate precur-

sor [FeIII(bipy)2(CN)2]ClO4, [(bipy)2FeII(CN)2Mn

II(bipy)2]2(ClO4)4was reported by Gao [119]. The Fe(III) ions are reduced to Fe(II)

ions during the reactions. This is a common phenomenon found

in the synthesis of the FeII2M2 polynuclear compounds. There

are weak intermolecular interactions between two adja-

cent bipy molecules coordinated to Mn(II), resulting in an infinite

Fig.13. Viewof thestructure of molecularsquare[FeII 4(-CN)4(bpy)4(tpa)4](PF6 )4.

The anions andsolvate moleculeshave been removed forclarity [127].

chain-like structure. For the Fe2IIMn2

II compound, weak inter-

molecular interactions between twoadjacent bipy molecules

coordinated to Fe(II) generate a 2D sheet. The 2D sheets are fur-

ther connected through the intermolecular hydrogen bonds. The

FeII2MnII

2 compound show very weak ferromagnetic interactions

between the Mn(II) ions through the bent NCFe(II)CN bridges

(J= 0.0380.040cm1).

In the FeII2NiII

2 compound, [{NiII(rac-CTH)}2{Fe

II(CN)2(bpy)2}2](ClO4)4H2O [129], the Fe

II and NiII ions have a dis-

torted octahedral coordination environment and are alternatelyplaced at the square corners. mT vs T data indicate that the

decrease ofmTin the high-temperature region (350200K) is due

to the end of a transition from the HS to the LS state of the octahe-

dral FeII ion (Fig. 15). At 200K, the mTvalue (2.05cm3 mol1 K)is

close to the calculated value for a magnetically uncoupled system

with two LS FeII ions (S= 0 ) and two NiII ions (S= 1). The decrease

ofmT from 50 K to 2 K is due to the local anisotropy of the NiII

ions (|D|=2.65cm1 andg= 2.012).

Fig. 14. The mTvs Tplot for[FeII

4(-CN)4 (bpy)4(tpa)4 ](PF6)4.

Reprinted with permission from Ref. [127]. Copyright 2005 Wiley.

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Fig. 15. Temperature dependence of the mT product for [{NiII(rac-

CTH)}2{FeII(CN)2(bpy)2}2](ClO4)4H2 O. The inset is an expansion of the

low-temperature region. The solid line is the best-fit curve to the theoretical

equation for two isolated NiII ions with axial zero-field splitting.

Reprinted withpermissionfromRef. [129]. Copyright2006AmericanChemicalSoci-

ety.

3.2.2. [FeII(L)(CN)2] (L= phen)

Four cyanide-bridged FeII4 square-like polynuclear compounds,

namely (i) [FeII4(-CN)4(phen)4(TPMA)2](PF6)4, [FeII

4(-

CN)4(phen)4(MeTPMA)2](PF6)4, and [FeII

4(-CN)4(phen)4(Me2TPMA)2](PF6)4NH4PF6 [130]; (ii) [(phen)2Fe

II(CN)2FeII(bpqa)]2(PF4)4H2O(CH3OH)2 [131] have been obtained

through the reaction of the Fe(II) salts, the blocking ligands and

the cis-[FeII(phen)2(CN)2] precursor.

X-ray crystal structure analyses revealed that the three

compounds crystallize in the C2/c space group and con-

sist of [FeII4(-CN)4(phen)4(L)2]4+ square-shaped cations with

two distinct iron(II) sites [130]. The iron(II) sites, associated

with [FeII(phen)2(CN)2] and [FeII(L)(CN)2] (L = TPMA, MeTPMA,

Me2TPMA and bpcq) moieties, are connected by cyanide bridg-

ing ligands and reside in different [FeN4C2] and [FeN6] ligand-field

environments. For [FeII4(-CN)4(phen)4(TPMA)2](PF6)4, the struc-

tural features of both sites at 100 and 293 K are those of an iron(II)

atom in the LS state, according to the magnetic properties. At 370K

the structure of the [FeN6] site is consistent with a quite complete

change of spin state from the LS state to the HS state, a behavior

confirmed by the magnetic study. Introduction of a methyl sub-

stituent in the sixth position of one or two pyridine groups to get

the MeTPMA and Me2TPMA derivatives, induce notable steric con-

straint in the [FeN6] site making longer the average FeN bonddistances thereby weakening the ligand-field strength and stabi-

lizing the HS state. The [FeN4C2] site remains in the LS state in the

three compounds.

In the centrosymmetric positive-charged FeII4 square

[(phen)2FeII(CN)2Fe

II(bpqa)]2(PF4)4H2O(CH3OH)2, FeII ions

capped by two phen ligands are linked to FeII(bpqa) unit through

two cyanide bridges [131]. The combined X-ray crystal structure

analyses and magnetic studies unambiguously show the existence

of pure [LS2HS2] entities in the whole temperature measured.

The spin alignment in the [LS2HS2] entities gave a trans structure,

namely, [LSHSLSHS], a typical checkboard pattern.

Two zigzag chain-1ike compounds [FeII(phen)2(CN)2NiII

(cyclam)](ClO4)2DMF2H2O and [FeII(phen)2(CN)2Ni(cyclam)]

(PF6)2CH3CN [132] were prepared by self-assembling a cis-

[Fe(phen)2(CN)2] precursor and M(cyclam)2+ (M= Ni, Zn). Both

complexes are centrosymmetric and the geometry around each

metal atom is an octahedron (Fig. 16).

4. Dicyanometalate assemblies based on [MA(L)(CN)2]n

(MA=Ru and Os; n=1, 0)

4.1. [RuIII(L)(CN)2] (L=acac, salen2)

Dicyanometalate precursors, trans-[Ru(acac)2(CN)2] and

trans-[Ru(salen)(CN)2], with electron configuration t2g

5 and

S = 1/2, exhibit the magnetic behavior expected for a LS distorted

octahedral ruthenium (III) system with significant spinorbit

coupling of the 2T2g ground term. Self-assembly of these anionic

building blocks with metal ions in the presence (or absence)

of blocking ligands have resulted in the formation of cyanide-

bridged trinuclear complexes, 1D compounds with different

topologies, 2D and 3D coordination polymers (details seen in

Fig. 16. View of thezigzag chain [FeII

(phen)2(CN)2NiII

(Cyclam)](ClO4)2DMF2H2O. Theanions and solvate moleculeshave been removed forclarity [132].

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Fig. 17. (a) Temperature dependence ofmT (squares) and m1 (circles) for [{MnIII(5,5-Me2salen)}2{Ru

III(acac)2(CN)2}][RuIII(acac)2(CN)2]2CH3OH. The inset is plots of

ZFC and FC magnetization at 20Oe. (b) Hysteresis loop at 0.5K. Inset: field dependence of the magnetization. (c) Temperature dependence of the real (m) and imaginary

(

m) partsof theAC susceptibility measured under various oscillating frequencies (101000Hz) with zero field. (d) Theplot of ln versus T1.


Table 1): (i) trinuclear compounds RuIIINiIIRuIII, RuIIIMnIIRuIII

and RuIIIMnIIIRuIII [82,133]; (ii) RuIIINiII linear/zigzag chains

[68,133,134]; (iii) RuIIICoII linear chain [68]; (iv) RuIIIMnIIIlinear chains [135,136]; (v) RuIIIFeIII linear chain [133]; (vi) 2D

coordination polymers [82,137]; (vii) 3D polymers [68,82,138].

The X-ray structure of{Ni(cyclam)[Ru(acac)2(CN)2]2}2CH3OH

2H2Oshowsthatthetrinuclearcomplexconsistsofa[Ni(cyclam)]2+

unit bonded to two [Ru(acac)2(CN)2] ions through the cyanide

nitrogen atoms [82]. The NiII center has a distorted octahedral

environment and is coordinated to the four nitrogen atoms of

the cyclam ligand and to two [Ru(acac)2(CN)2] units through the

cyanide nitrogen atoms in a trans configuration. The compound

shows ferromagnetic coupling between RuIII and NiII through the

cyanide bridge (JRuNi =4.6cm1, zJ =0.02, g= 2.269). AC magnetic

susceptibilities studies indicate that no magnetic ordering occurs

down to2 K.

Magnetic studies for a similar trinuclear complex,{MnII(CH3OH)4[Ru

III(salen)(CN)2]2}6CH3OH2H2O, are con-

sistent with intratrimer antiferromagnetic interaction between

RuIII and MnII centers and intertrimer ferromagnetic coupling

(JRuMn =1.8cm1,zJ =0.87,g= 2.117), which is in agreement with

the field dependence of magnetization [82]. The ferrimagnetic-like

character arises from the competition between intratrimer and

intertrimer magnetic interactions.

A similar structure has been reported for complex [{MnIII(5,5-

Me2salen)}2{RuIII(acac)2(CN)2}][Ru

III(acac)2(CN)2]2CH3OH [133],

in which two MnIII ions are coordinated to trans-[Ru(acac)2(CN)2]

to form linear trinuclear RuMn2 units. The RuMn2 units are linked

together through stacking and weak Mn O* (phenolate

oxygen of the adjacent [MnIII(5,5-Me2salen)]+ unit) interac-

tions to form a infinite chain. The increase ofmTon lowering the

temperature (Fig. 17a) and the rapid rise inMwithH(Fig. 17b) con-

firms the RuIIIMnIII ferromagnetic coupling through the cyanide

bridges (JRuMn =0.87cm1) and the intertrimer ferromagneticcoupling (JMnMn =0.24cm

1). No long-range ordering occurs above

2 K. AC susceptibility measurements reveal the slow relaxation of

the magnetization below 3.0K with= (Tp/Tp)/ logf=0.25(TP,

the shift of peak temperature of the in phase signal ), charac-

teristic of a superparamagnetic behavior (Fig. 17c). The relaxation

time follows an Arrhenius law with an energy gap of 16.4K and

0 =3.04107 s (Fig. 17d). The magnetic behavior is attributed

to the unique 1D supramolecular organization through the

stacking. The free [Ru(acac)2(CN)2] ions separate the polymeric

chains and thus weaken the interchain interaction. The slow

magnetic relaxation reflects that the contributions to the energy

barrier come from both the anisotropy of isolated cluster and

intercluster interactions. The compound behaves as an unusual

SCM rather than as a SMM due to the strong magnetic interactionbetween the clusters in the chain through noncovalent stacking.

The first 1D linear network based on the anionic precur-

sor trans-[Ru(acac)2(CN)2], [{Ru(acac)2(CN)2}{Ni2(L)(H2O)2}]

{Ru(acac)2(CN)2}2H2O (H2L = 11,23-dimethyl-3,7,15,19-tetraza-

tricyclo[19.3.1.1] hexacosa-2,7,9,11,13(26),14,19,21(25),22,24-

decaene-25,26-diol), was reported by Julve and co-workers

in 2006 [68]. The reaction of trans-PPh4[Ru(acac)2(CN)2] and

NiII2L(H2O)2(ClO4)2 in methanol leads to the formation of a

1D cationic polymer [{Ru(acac)2(CN)2}{Ni2(L)(H2O)2}]+, with

free [Ru(acac)2(CN)2] as counter ions. The chain is made up of

centrosymmetric [Ni2(L)(H2O)2]2+ dinuclear motifs connected

through the two trans cyanide groups of the {Ru(acac)2(CN)2}

units, affording a bimetallic RuIIINiIINiIIRuIII chain (Fig. 18).

Chains are further held together by hydrogen bonds and van

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Fig. 18. Viewof the chain [{Ru(acac)2(CN)2}{Ni2 (L)(H2O)2}] {Ru(acac)2(CN)2}2H2O. Theanions andsolvate moleculeshave been removed forclarity [68].

der Waals forces. The magnetic susceptibility data exhibit an

overall intrachain antiferromagnetic behavior (JNiNi =50.0cm1,

JRuNi =+6.6cm1 andg= 2.12).

X-ray crystallographic analyses reveal that complexes

[{RuIII(acac)2(CN)2}{NiII(dmphen)(NO3)}]H2O [68] and

[RuIII(salen)(CN)2][NiII(cyclam)]ClO4 [134] are neutral lin-

ear chains and consist of repeating RuIII-NiII units through

the cyanide bridges. Ferromagnetic RuIII-NiII interactionswere found in both chains. The difference in the mag-

nitude of the two ferromagnetic coupling (+6.6 cm1 in

[{Ru(acac)2(CN)2}{Ni2(L)(H2O)2}]{Ru(acac)2(CN)2}2H2O vs

+3.2 cm1 in [{RuIII(acac)2(CN)2}{NiII(dmphen)(NO3)}]H2O

[68]) is due to subtle structural differences such as the dif-

ferent chromophore around the nickel atom (NiO4N2 in

the former case vs NiO2N4 in the later complex) and the

greater distortion of the environment of the nickel atom in

[{RuIII(acac)2(CN)2}{NiII(dmphen)(NO3)}]H2O (the coordination

of the nitrate group as an asymmetrical bidentateligand). For com-

plex [RuIII(salen)(CN)2][NiII(cyclam)]ClO4 [134], no long-range

magnetic ordering or slow relaxation of the magnetization was

observed above 3 K and it displays negligible hysteresis at 2 K.

The zigzag chain {[{NiII

(cyclen)}{RuIII

(acac)2(CN)2}]ClO4CH3OH}n (cyclen = 1,4,7,10-tetra-azacyclododecane) [133] is formed

by assembly of the [Ru( acac)2(CN)2] and [Ni(cyclen)]2+ ions

through the trans cyanide groups. The perchlorate anions and

methanol solvates are situated between the polymeric chains.

Each NiII center is octahedrally coordinated to the four nitro-

gen atoms of cyclen and two nitrogen atoms of cyanide groups

in a cis configuration, resulting in a zigzag pattern (Fig. 19).

The NiN C bond angles (167.8(3)171.1(3)) deviate from strict

linearity. The closest intrachain Ni Ru distance is 5.225(5) A

and the closest interchain Ru Ru and Ni Ni separations are

7.574(4) A and 8.4493(7) A, respectively. The mT vs T data

indicate that the RuIII and NiII centers are ferromagnetically

coupled with very weak interchain antiferromagnetic inter-

actions (JRuNi =+0.85cm

1

, zJ

=0.16cm

1

, g = 2 .24). A slightly

stronger ferromagnetic interaction was observed in the isostruc-

tural zigzag chain {[{NiII(tren)}{RuIII(acac)2(CN)2}]ClO4CH3OH}nwithJRuNi = +1.92cm

1,zJ =1.37cm1, g= 2.20 [133].

A RuIIICoII linear chain, [{RuIII(acac)2(CN)2}{CoII(dmphen)

(NO3)}]H2O [68], was prepared by self-assembling trans-

PPh4[Ru(acac)2(CN)2] and CoII(dmphen)(NO3)2. Two crystallo-

graphically independent ruthenium atoms [Ru(1) and Ru(2)] are

situated at centers of symmetry.The chain consists of regular alter-nating Co(II) and Ru(III) ions bridged by single cyanide groups

(Fig. 20). The Co atom has a compressed cis-distorted octahe-

dral coordination geometry. Parallel neighboring chains are loosely

linked into sheets through hydrogen bonds and overlaps

between dmphen ligands. Magnetic studies indicate the presence

of an intrachain ferromagnetic interaction between the Ru(III) and

Co(II) centers and significant spinorbit coupling effects of both

metal ions. No magnetic ordering is detected above 1.9K, indicating

that the ferromagnetic chains are well isolated from each other.

The stoichiometric reactions of trans-[Ru(salen)2(CN)2]

or trans-[Ru(acac)2(CN)2] and Mn(III) salts afford

three cyanide-linked RuIIIMnIII linear chains:

[RuIII(salen)(CN)2][MnIII(L)] [L =N,N-(1-methylethylene)bis(2-

hydroxynaphthalene-1-carbaldehydene-iminate)dianion] [135],{[RuIII(acac)2(CN)2][Mn

III(TPP)]}{[Ph3(PhCH2)P]PF6}2CH3OH and

{[RuIII(acac)2(CN)2][MnIII(TPP)]}{[Ph3(PhCH2)P]ClO4}2CH3OH

[136]. The neutral linear chain of [RuIII(salen)(CN)2][MnIII( L)] is

formed by assembly of the [Ru(acac)2(CN)2] and the [Mn(L)]+

cation in which the CN groups act as bridges to link two neigh-

boring MnIII centers in a trans mode [135]. Two adjacent chains

are correlated with extensive stacking forces between naph-

thalene rings. The intrachain ferromagnetic coupling between

RuIII and MnIII are established through the cyanide bridges

(JRuMn =1.34cm1), whereas the interchain antiferromagnetic

interactions subsist, leading to an antiferromagnet and accom-

panying the occurrence of a long-range antiferromagnetic order

with TN = 2.5K. AC magnetic susceptibility is slightly frequency

dependent on both in-phase and out-of-phase components, which

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Fig. 19. View of thezigzag chain {[{NiII(cyclen)} {RuIII(acac)2(CN)2}][ClO4]CH3OH}n. Theanions and solvate moleculeshave been removed forclarity [133].

is a signature of a glassy magnetized state probably reminiscent of

SCM-like behavior or spin canting. Because the antiferromagnetic

order arises from the interchain antiferromagnetic interactions,

spin canting, which is in conjunction with single-ion anisotropy of

RuIII and MnIII, may be more feasible. A field-induced spin-flop or

metamagnetic transition occurs at Hc =3.5kG.

Single-crystal XRD analyses reveal that complexes,

{[RuIII(acac)2(CN)2][MnIII(TPP)]}{[Ph3(PhCH2)P]PF6}2CH3OHand

{[RuIII(acac)2(CN)2][MnIII(TPP)]}{[Ph3(PhCH2)P]ClO4}2CH3OH

[136], exist as neutral linear single chains consisting of alternating

[Ru(acac)2(CN)2] anions and [Mn(TPP)]+ cations. Interestingly,

[Ph3(PhCH2)P]PF6 and [Ph3(PhCH2)P]ClO4, act as co-crystallized

molecules filling in the space of the inter-chains. The magnetic

susceptibility data indicate the occurrence of the ferromag-netic ordering about 50 K . In contrast to the above complex

[RuIII(salen)(CN)2][MnIII(L)] [L =N,N-(1-methylethylene)bis(2-

hydroxynaphthalene-1-carbaldehydene-iminate)dianion] [135],

in which thereexist interchain interactions, the chainsin these

two complexes were well separated by the large steric hindrance

arising from the porphyrin ligand at the equatorial plane and

the co-crystallized bulk anions and cations between the chains.

DC magnetic studies show ferromagnetic coupling between

the spin orbitals of RuIII and MnIII (JRuMn = 3.253.43 cm1) in

both complexes, resulting in S=5/2 ground state. For complex

{[RuIII(acac)2(CN)2][MnIII(TPP)]}{[Ph3(PhCH2)P]PF6}2CH3OH,

the AC magnetic susceptibilities are strongly frequency-dependent

below 3.5K, suggestive of the slow magnetization relaxation of

SCMs. Hysteresis loops characteristic of classical magnetic behav-

ior were observed below 1.6 K. The ColeCole plot indicates the

presence of a single relaxation process (= 0.059). The best sets of

parameters of Arrhenius plots are 0 = 1.09109

s, Ueff=26.1Kand 0 =8.9510

10 s, Ueff= 25.88 K, respectively. The relatively

small barrier obtained is consistent with the observation of the

hysteresis loops only at low temperatures.

Fig. 20. Viewof the linearchain [{RuIII

(acac)2(CN)2}{CoII

(dmphen)(NO3)}]H2O. Thesolvate molecules have been removed forclarity [68].

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Fig.21. View ofthe 2Dnetworkstructureof Ph4P{Tb(NO3)2[Ru(acac)2 (CN)2]2}. The

ligands, anionsand solvate molecules have been removed for clarity [137].

In the RuIIIFeIII linear chain {[{FeIII(salen)}{RuIII(acac)2(CN)2}]}n [133], each [Ru(acac)2(CN)2]

unit is connected to two

[Fe(salen)]+ units through the trans cyanide groups. Magnetic sus-

ceptibility measurements reveal ferromagnetic coupling between

RuIII and FeIII through the cyanide bridge. The plots of the ZFC

and FC m(T) at 20Oe are clearly suggestive of a transition from

ferromagnetic to antiferromagnetic behavior at about 2.6 K. The

double-S shape ofthe magnetization curve is indicative of a meta-

magnet, which switches from an antiferromagnetic ground state to

a ferromagnetic-like state upon the application of a large enough

field. The magnetic phase transition is further confirmed by the

temperature dependenceof the AC magneticsusceptibility. The real

part (m) has a maximum at 2.6 K and the imaginary part (m) isnegligibly small, suggesting an antiferromagnetic ordering below

2.6K.

Thereactionof Mn(ClO4)26H2O withtrans-[Ru(salen)(CN)2]in

methanol results in the formation of a 2D cyanide-bridged

complex {MnII(H2O)2[RuIII(salen)(CN)2]2H2O}n [82]. The Mn cen-

ters having distorted octahedral environment are linked by

[Ru(salen)(CN)2] to produce a 2D sheet structure. Magnetic stud-

ies show antiferromagnetic coupling between RuIII and MnII,

leading to a ferrimagnetic-like behavior, which arises from the

competition between intralayer antiferromagnetic and interlayer

ferromagnetic coupling. A high magnetic field might remove the

anomaly around 36K.

When extendingthiswork tothe lanthanide ions Ln(III),Gao and

co-workers reported a new series of 2D cyanide-bridged RuIII2LnIIIcoordination polymers: Ph4P{Ln(NO3)2[Ru(acac)2(CN)2]2}

(Ln= Tb, Dy, Er, Gd) [137]. X-ray crystallographic determination

reveals that these compounds are isostructural and have a wavy

(4,4) layer structure. In Ph4P{Tb(NO3)2[Ru(acac)2(CN)2]2}, each

Tb3+ ion is eight coordinated by four oxygen atoms of two nitrate

ionsand fourcyanide nitrogen atoms of four[Ru(acac)2(CN)2] ions

(Fig. 21). Tb atoms are connected by linear [NCRu(acac)2CN]

ions to produce a wavy (4,4) 2D layer structure. The Tb(III) and the

[Ru(acac)2(CN)2] units form 24-member Tb4Ru4(CN)8 squares

with the Tb atoms occupying the vertexes and the Ru atoms resid-

ing in the middle of the four sides of the squares. Magnetic studies

show that the magnetic coupling between the Ru(III) and Ln(III)

ions through the cyanide bridges is negligibly weak, although the

4d orbitals of Ru(III) are more diffuse than the 3d orbitals of Fe(III).

Self-assembly of the building block [Ru(acac)2(CN)2] and

metal ions have resulted in the formation of 3D polymers,

{MnII[Ru(acac)2(CN)2]2}n [138] and {CoII[Ru(acac)2(CN)2]2}n [82].

The structure of {MnII[Ru(acac)2(CN)2]2}n was determined by

X-ray crystallography[138]. Each Mn centeris tetrahedrallycoordi-

nated to four [Ru(acac)2(CN)2] ions through the cyanide nitrogen

atoms to produce a 3D polymer with a diamond-like structure

(Fig. 22a). Ferromagnetic coupling is observed between the RuIII

and MnII ions (Fig. 22b). The onset of a long-range magnetic phase

transition is evidenced by the low-field temperature dependence

of the magnetization (Fig. 22c), which increases abruptly below

4 K, characteristic of a long-range magnetic ordering (TC =3.6K)

(Fig. 22d). A characteristic hysteresis loop is observed at 1.85K

but with negligible remnant magnetization (0.06NB) and coer-

cive field (6Oe). AC susceptibility studies showed no evidence for

glassy behavior.

A 3D 2-fold penetrating diamond-like structure has been

reported for {Co[Ru(acac)2(CN)2]2}n [82]. It is isostructural with

{MnII[Ru(acac)2(CN)2]2}n [138]. Each CoII center is tetrahedrally

coordinated to four [Ru(acac)2(CN)2] through the cyanide nitro-

genatomsto produce a 3Dstructure. ThemTvsTdataindicatethat

the Ru and Co centers are ferromagnetically coupled (Fig. 23a). A

long-range ferromagnetic ordering is observed below 4.6K. AC sus-

ceptibility measurements show no frequency dependence and this

rules out the presence of glassy behavior (Fig. 23b). However, a

small shoulder around 5.6K was observed in low-field DC and AC

mTcurves, and it disappears above 300 Oe (Fig. 23c). This might

be another ferromagnetic transition or just due to trace impurities.

A characteristic hysteresis loop is observed at 1.8K with a coer-

cive field of ca. 17 Oe (Fig. 23d), which is slightly larger than that

in the Mn analog (ca. 6 Oe) [138], presumably due to the stronger

anisotropy of the CoII ion.

4.2. [OsIII(L)(CN)2] (L=salen2)

Recently, Lau and co-workers demonstrated that

trans-[Os(salen)(CN)2] is a good building block for

the construction of low-dimensional 3d-5d magneticmaterials. The reaction of trans-[Os(salen)(CN)2]

and

[Cu(Me3tacn)(H2O)2](ClO4)2 in the mixture of water and DMF

solution resulted in the formation of 1D complexes with dif-

ferent topologies: [Os(salen)(CN)2]2[Cu(Me3tacn)]CH3OH and

[Os(salen)(CN)2][Cu(Me3tacn)]ClO4 [84].

X-ray crystallographic analysis revealed that the asym-

metric unit of [Os(salen)(CN)2]2[Cu(Me3tacn)]CH3OH consists

of one [Cu(Me3tacn)]2+ and two [Os(salen)(CN)2]

ions. The

[Os(salen)(CN)2] ions are in two different coordination environ-

ments (Fig. 24). One type of [Os(salen)(CN)2] is connected to two

[Cu(Me3tacn)]2+ units using its trans cyanide groups to form a

zigzag chain. The other type of [Os(salen)(CN)2] ion is connected

to [Cu(Me3tacn)]2+ using only one of its cyanide group. The CuII is

hexa-coordinated to six nitrogen atoms, three from the Me3tacnligand and three from bridging cyanide ligands, in a slightly dis-

torted octahedral geometry.

For [Os(salen)(CN)2][Cu(Me3tacn)]ClO4, each [Os(salen)(CN)2]

unit is connected to two [Cu(Me3tacn)]2+ units using its trans

cyanidegroupstoformazigzagchain.TheOsIII isinadistortedocta-

hedral geometry: the salen ligand occupies the equatorialpositions

and the two cyanide ligands are at the axial sites. Each Cu is penta-

coordinated to five nitrogen atoms in a distorted square-pyramidal

geometry.

The magnetic susceptibility data confirm typical intrachain fer-

romagnetic coupling between OsIII and CuII through the cyanide

bridge (JOsCu =+1.56 to +2.03cm1) and weak antiferromagnetic

interaction between the neighboring chains. No long-range order-

ing was detected down to 2K in both complexes. The exchange

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Fig. 22. (a) View of the 3D structure of{MnII[Ru(acac)2(CN)2 ]2}n. (b) Temperature dependence ofmTat 10kOe. (c) Temperature dependence of magnetization at 100Oe.

(d) Temperature dependence of AC susceptibility measuredat zeroexternal magnetic field andHac = 2Oe with differentfrequency111Hz (),199Hz(),355Hz (),633Hz

(), and 1111Hz();in phase m (filled symbols) and out-of-phase

m (open symbols).


Fig.23. (a) Temperature dependenceofm1 () andmT(O)for {Co[Ru(acac)2(CN)2]2}n at10 kOe. (b) Magnetizationvsfieldup toH= 70kOeat 1.8K.Inset:hysteresisloopin

the0.5kOerange at1.8K, with a coercivefieldHc of about 17Oe. (c) Temperaturedependenceof magneticsusceptibility measuredat lowfield. (d)Temperaturedependence

ofAC susceptibilitymeasured at zeroexternal magnetic field andHac = 2Oe with differentfrequency111Hz (),199Hz(),355Hz(),633Hz(), and 1111Hz(); in phase

m (filled symbols) and out-of-phase

m (open symbols).


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Fig. 24. View of the chain [Os(salen)(CN)2]2[Cu(Me3tacn)]CH3OH. The solvate moleculeshave been removed forclarity [84].

interaction between OsIII and CuII in these twocompounds is weak,

which may be partially due to the Cu(II) ions having only S= 1/2.

It is expected that the magnetic coupling would be stronger if

the CuII ions were replaced by metal ions with larger spins (e.g.,

MnIII or FeIII), owing to greater radial extension of d orbitals and

higher degree of electron density delocalization over the bridging

cyanides.

4.3. [RuII(L)(CN)2] (L= bpy, phen, py)

4.3.1. [RuII(L)(CN)2] (L= bpy/phen)

The design of new heterometallic complexes for photoinduced

atomtransferreactionshas received current interest. One approach

is to link a low-valent metalpolypyridine to a high-valent metal-

oxo fragment via self-assembly reactions. The former would serve

as a good light absorber while the latter functions as an oxygen

atom transfer agent.

Self-assembly of the d6 [Ru(bpy)2(CN)2] precursor and d2

[OsO2(mes)2] has resulted in the formation of a dinuclear com-

plex [OsVIO2(mes)2(NC)RuII(bpy)2(CN)] [139]. The osmium atom

adopts a distorted square-pyramidal geometry. Although the mea-

sured N CRu angle (177.7(4)) is close to180, the OsN C angleof 160.5(4) reveals that the RuC NOs array is not quite lin-

ear. The excited state which localizes at the ruthenium center

should be MLCT in nature. However, this excited state is rapidly

quenched by intramolecular energy and/or electron transfer path-

ways.This heterometalliccomplex in the solidstate is non-emissive

suggesting that the long-lived emissive low-energy MLCT state of

the Ru(bpy)2(CN)2 chromophore is completely quenched by the

OsO2(mes)2 unit via the bridging cyanide group.

A competitive indicator displacement assay has been suc-

cessfully developed for the ratiometric determination of

sulfhydryl-containing amino acids and peptides using heter-

obimetallic donoracceptor complexes as chemodosimetric

ensembles. Chromotropic cis-[M(L)2(CN)2] (M = FeII, RuII, OsII;

L= diimine) are used as signaling indicators and PtII

(DMSO)Cl2

acceptor moiety is used as the receptor for the sulfhydryl-

containing analytes. Two heterobimetallic donoracceptor

complexes, cis-RuII(phen)2[CNPtII(DMSO)Cl2]2 [140] and cis-

RuII(bpy)2[CNPtII(DMSO)Cl2]2 [141], have been reported by Lam

and co-workers.

In cis-RuII(phen)2[CNPtII(DMSO)Cl2]2 [140], the three metal

centers adopt a V-shaped configuration with two Pt(DMSO)Cl2

moieties bridged to a Ru(II) center via cyanide bridges (Fig. 25).Thecoordination geometry of thetwo Pt(II) centers is square planar

withtwochloro ligands trans toeach otherand a coordinatedDMSO

Fig. 25. View of the molecular structure of the trinuclear complex cis-

RuII

(phen)2[CNPtII

(DMSO)Cl2]2 [140].

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Fig. 26. Luminescent responses ofcis-RuII(phen)2[CNPtII(DMSO)Cl2]2 toward amino acids and peptides: (a) enhancement of luminescent intensity at 621nm in a typical

spectrofluorimetrictitrationby cysteine.(b) Resultsof spectrofluorimetric titrationsby common amino acids/GSHmonitoredas a functionof theincrease in emissionintensity

(I/IO) at621nm. (c) Photographs of the chemosensing responses: (a) Cys; (b) Met; (c) Hcys; (d) GSH; (ev) l-alanine, l-arginine, l-asparagine, l-aspartic acid, l-glutamine,

l-glutamic acid, glycine, l-histidine, l-isoleucine, l-leucine, l-lysine, l-phenylalanine, l-proline, l-serine, l-threonine, l-tryptophan, l-tyrosine, and l-valine, respectively;

(w) the trimeralone. All titrations were carried outin aqueous DMF (1:1,v/v) at pH 7. Excitation was 467 nm.


trans to the cyanide bridge. Upon coordination of the Pt(DMSO)Cl2acceptors, the Ru(d)phen(*) MLCT transition of the Ru(II)-

diimine chromophore shifts from 452 to 384nm, and the MLCT

emission shifts from 621 to 595nm with a drastic reduction in

luminescent intensity (Fig. 26). The concomitant blue-shift of the

MLCT transitions and the decrease of the MLCT emission intensity

are consistent with the coordination of good electron acceptors tothe cyanide donors of [Ru(phen)2(CN)2]. The close resemblance of

theluminescentresponses tothoseofcis-[Ru(phen)2(CN)2]andthe

subsequent observation of [Ru(phen)2(CN)2] in the electrospray-

MS amino acid mixtures mean that the cyanide bridges between

Ru(II) and Pt(II) of the trinuclear complex are cleaved after the

binding of sulfhydryl-containing amino acids/peptides to the Pt(II)

centers. Notably, the complex is the first luminescent chemo-

dosimeter selective for sulfhydryl-containing amino acids and

peptides. Fluorimetric responses of the ensembles can be tuned by

using different polypyridyl ligands on the chromotropic donor.The

use of bpy instead of phen leads to a similar luminescent complex

cis-RuII(bpy)2[CNPtII(DMSO)Cl2]2 [141]. The chromophore ligand

shifts the MLCT emission of the donor from 621 to 632 nm.

4.3.2. [RuII(L)(CN)2] (L= py)

The complex trans-Ru(py)4(CN)2 can be used as

a starting precursor for the stepwise construction of

nonchromophoric Ru(II) trans assemblies by addition of

trans-{RuCl(py)4}+ units: (i) asymmetrical bimetallic complex

trans-[Cl(py)4Ru(NC)Ru(py)4(CN)]PF6; (ii) symmetrical trimetallic

complexes trans-[Cl(py)4Ru(NC)Ru(py)4(CN)Ru(py)4Cl](PF6)2 and

trans-[(MeCN)(py)4Ru(NC)Ru(py)4(CN)Ru(py)4(MeCN)](PF6)4[142]. X-ray crystallography reveals that they have an

almost perfectly linear geometry. The bond lengths indicate

d(RuII)*(CN) back-bonding from both C- and N-bonded

Ru centers. All metal centers display the characteristic trans-

[Ru(py)4]2+ propeller geometry, with typical pitches and adopt an

almost completely eclipsed configuration.

For the cyanide-bridged salts, the RuII py MLCT bands are

similar in shape, and have maximaat almost the same wavelength,

as that of trans-Ru(py)4(CN)2. There is an expected increase in

extinction on binding first one (in trans-[Cl(py)4Ru(NC)Ru(py)4(CN)](PF6)) and then two (in trans-[Cl(py)4Ru(NC)Ru(py)4(CN)

Ru(py)4Cl](PF6)2) trans-{Ru(py)4Cl}+ moieties to the cyanide

nitrogen atoms because of the increased number of pyridine lig-ands. This is accompanied by an intensifying yellow coloration due

to increased tailing of the MLCT band into the visible. The complex

trans-[(MeCN)(py)4Ru(NC)Ru(py)4(CN)Ru(py)4(MeCN)](PF6)4 is

almost colorless and has a very intense d(RuII)*(py)

MLCT absorption at 346 nm, blue shifted by 2160 c m1 with

respect to that of its chloro precursor trans-[Cl(py)4Ru(NC)

Ru(py)4(CN)Ru(py)4Cl](PF6)2. This is indicative of a raising

in energy of the * LUMO of the pyridine ligands or, more

likely, stabilization of the Ru d orbitals upon replacement

of the chlorides by acetonitrile. The bimetallic complex trans-

[Cl(py)4Ru(NC)Ru(py)4(CN)](PF6) shows two well separated,

reversible RuIII/II oxidation waves. For the trimetallic complex

trans-[Cl(py)4Ru(NC)Ru(py)4(CN)Ru(py)4Cl](PF6)2, the outer Ru

centers give two closely spaced one-electron oxidation waves at0.64and0.54VvsSCE.TheEl/2 value ofca.100mV for these Ru

III/II

couples indicates a significant electronic coupling between the

two metal centers, occurring via the bridging trans-Ru(py)4(CN)2ligand. Substitution of the chlorides by acetonitrile to give

trans-[(MeCN)(py)4Ru(NC)Ru(py)4(CN)Ru(py)4(MeCN)](PF6)4 has

a dramatic effect on the electrochemical behavior of the linear

trimetallic cyanide-bridged unit. The RuIII/II oxidat

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