This article is published as part of the Dalton Transactions themed issue entitled: Molecular Magnets Guest Editor Euan Brechin University of Edinburgh, UK Published in issue 20, 2010 of Dalton Transactions Image reproduced with permission of Jürgen Schnack Articles in the issue include: PERSPECTIVES: Magnetic quantum tunneling: insights from simple molecule-based magnets Stephen Hill, Saiti Datta, Junjie Liu, Ross Inglis, Constantinos J. Milios, Patrick L. Feng, John J. Henderson, Enrique del Barco, Euan K. Brechin and David N. Hendrickson, Dalton Trans., 2010, DOI: 10.1039/c002750b Effects of frustration on magnetic molecules: a survey from Olivier Kahn until today Jürgen Schnack, Dalton Trans., 2010, DOI: 10.1039/b925358k COMMUNICATIONS: Pressure effect on the three-dimensional charge-transfer ferromagnet [{Ru2(m- FPhCO2)4}2(BTDA-TCNQ)] Natsuko Motokawa, Hitoshi Miyasaka and Masahiro Yamashita, Dalton Trans., 2010, DOI: 10.1039/b925685g Slow magnetic relaxation in a 3D network of cobalt(II) citrate cubanes Kyle W. Galloway, Marc Schmidtmann, Javier Sanchez-Benitez, Konstantin V. Kamenev, Wolfgang Wernsdorfer and Mark Murrie, Dalton Trans., 2010, DOI: 10.1039/b924803j Visit the Dalton Transactions website for more cutting-edge inorganic and organometallic research www.rsc.org/dalton Downloaded by North Carolina State University on 20 March 2013 Published on 20 April 2010 on http://pubs.rsc.org | doi:10.1039/B927522C View Article Online / Journal Homepage / Table of Contents for this issue
Transcript
This article is published as part of the Dalton Transactions themed issue entitled:
Molecular Magnets
Guest Editor Euan Brechin University of Edinburgh, UK
Published in issue 20, 2010 of Dalton Transactions
Image reproduced with permission of Jürgen Schnack
Articles in the issue include: PERSPECTIVES: Magnetic quantum tunneling: insights from simple molecule-based magnets Stephen Hill, Saiti Datta, Junjie Liu, Ross Inglis, Constantinos J. Milios, Patrick L. Feng, John J. Henderson, Enrique del Barco, Euan K. Brechin and David N. Hendrickson, Dalton Trans., 2010, DOI: 10.1039/c002750b Effects of frustration on magnetic molecules: a survey from Olivier Kahn until today Jürgen Schnack, Dalton Trans., 2010, DOI: 10.1039/b925358k COMMUNICATIONS: Pressure effect on the three-dimensional charge-transfer ferromagnet [{Ru2(m-FPhCO2)4}2(BTDA-TCNQ)]Natsuko Motokawa, Hitoshi Miyasaka and Masahiro Yamashita, Dalton Trans., 2010, DOI: 10.1039/b925685g Slow magnetic relaxation in a 3D network of cobalt(II) citrate cubanes Kyle W. Galloway, Marc Schmidtmann, Javier Sanchez-Benitez, Konstantin V. Kamenev, Wolfgang Wernsdorfer and Mark Murrie, Dalton Trans., 2010, DOI: 10.1039/b924803j Visit the Dalton Transactions website for more cutting-edge inorganic and organometallic research
www.rsc.org/dalton
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Heterocyclic amine directed synthesis of metal(II)-oxalates: investigating themagnetic properties of two complete series of chains with S = 5/2 to S = 1/2†
Tony D. Keene,*‡a,b,c Iwan Zimmermann,a Antonia Neels,d Olha Sereda,d Jurg Hauser,a Michel Bonin,a
Michael B. Hursthouse,b Daniel J. Price*c and Silvio Decurtins*a
Received 5th January 2010, Accepted 27th March 2010First published as an Advance Article on the web 20th April 2010DOI: 10.1039/b927522c
We report here two series of coordination polymer chains: the first being [M(II)(ox)(bnz)2]n (M = Mn 1,Fe 2, Co 3, Ni 4, Cu 5 and Zn 6; ox = oxalate C2O4
2-; bnz = benzimidazole) and the second[M(II)(ox)(btz)2]n (M = Mn 7, Fe 8, Co 9, Ni 10, Cu 11 and Zn 12; btz = benzotriazole). The first seriesdisplays an unusual homometallic [–Mi–Mii–Mii–]n chain topology and the second series is isostructuralto [Fe(II)(ox)(btz)2]n, originally reported by Jia et al. (Collect. Czech. Chem. Commun., 2002, 67,1609–1615). These two series allow us to make comparisons between the spin state of each metal andthe magnetic coupling interaction within an isostructural series spanning the full range of spin statesavailable in 3d metals and to investigate which models are the best to use in each case. Compound 8 is asingle-chain magnet, the behaviour through spin-canting arising from a Dzyaloshinskii-Moriyainteraction. Additionally, we have synthesised a two-dimensional coordination polymer{[Zn(II)(bnz)4][Zn(II)2(ox)3]}n (13), in which distorted hexagonal [Zn(II)2(ox)3]n
2n- layers are hydrogenbonded by [Zn(II)(bnz)4]2+ cations to give an interlayer separation of 12.001(2) A.
Introduction
Oxalate has proved to be one of the most useful bridging ligandsavailable for the design and synthesis of coordination polymersdue to its marked preference for chelating and bridging 3d metalsin a range of structural topologies and dimensionalities.1 Inaddition to its useful structural properties, oxalate has the abilityto carry significant magnetic interactions between spin carrierswith a degree of predictability as to the magnitude and sign ofthe interaction for a given metal combination.1a,b,d,e Despite themany years that one-dimensional magnetism has been studiedby physicists and chemists, new models are continually emergingfor describing the magnetic properties of such chains.2 Magneticmaterials based on chains are also of interest in the field of single
aDepartement fur Chemie und Biochemie, Universtat Bern, Freiestrasse 3,CH-3012, Bern, Switzerland. E-mail: [email protected] of Chemistry, University of Southampton, University Road, High-field, Southampton, SO17 1BJ, UKcWestCHEM, Department of Chemistry, University of Glasgow, UniversityAvenue, Glasgow, G12 8QQ, Scotland, UK. E-mail: [email protected] Suisse d’Electronique et de Microtechnique SA, Jaquet-Droz 1, CasePostale, CH-2002, Neuchatel, Switzerland† Electronic supplementary information (ESI) available: Asymmetric unitdiagrams for 2, 4–5, 9, 11–12, powder plots with Le Bail fits for 3, 6 and10, asymmetric unit diagram from PXD for 10, hydrogen bond tablesfor 2, 4–5, 9 and 11–12 p–H interaction diagram for 4, bond-valencesum calculations for 1–2 and 7–9, plot of average cis-angles against metaltype, magnetic susceptibility plots for 7–10, susceptibility, magnetisation,hysteresis, Arrhenius and in-phase AC plots for 8, magnetisation plotsfor 5 and 11, a full structural description for 14 and CIF information for1–2, 4–5, 7, 9, and 11–14. CCDC reference numbers 760875–760884. ForESI and crystallographic data in CIF or other electronic format see DOI:10.1039/b927522c‡ Current address: School of Chemistry, The University of Sydney, NSW2006, Australia. E-mail: [email protected]
chain magnets (SCMs): one-dimensional materials analogous tosingle-molecule magnets in displaying slow magnetic relaxation.3
In this study, we have synthesised two series of [M(II)(ox)(L)2]n
chains where ox is the oxalate dianion and L is benzimidazole(bnz; M = Mn 1, Fe 2, Co 3, Ni 4, Cu 5, Zn 6) or benzotriazole(btz, M = Mn 7, Fe 8, Co 9, Ni 10, Cu 11 and Zn 12). Of the btzseries, the Fe(II) congener was previously reported by Jia et al.,4
and we present here a detailed analysis of its magnetic properties.The synthesis of these compounds has required us to utilise
a wide range of synthetic techniques from ambient benchtopreactions to hydrothermal synthesis. Fe(II) salts present oxidationproblems when added to basic solutions, so this was overcome bythe use of iron oxalate dihydrate, the insolubility of which keeps theFe(II) ions stable in hydrothermal reactions until high temperatureand pressure, at which point the reaction conditions are reducing,thus allowing us to access Fe(II) compounds. Additionally, theuse of a microwave synthesiser enabled us to shorten many ofthe reaction times and increase the purity of the products dueto the even heating of the reaction solution when compared tomore traditional hydrothermal methods. Nevertheless, standardhydrothermal synthesis was employed to obtain single crystalssuitable for X-ray analysis.
A related compound, {[Zn(II)(bnz)4][Zn(II)2(ox)3]}n (13) wasalso formed from similar synthetic conditions and shows furtherflexibility in the use of these types of ligands.
Experimental
Experimental methods
All starting materials were used as received from commercialsources without further purification. Hydrothermal synthesis wascarried out in 23 ml Teflon-lined steel autoclaves. Microwavesynthesis was carried out using a Biotage Initiator 2.0 microwave
synthesiser. IR measurements were made using a Perkin-ElmerSpectrum One spectrometer and peaks are reported as strong (s),medium (m) and weak (w). Elemental analysis was performed ona Carlo Erba Instruments EA 1110 elemental analyser.
Single crystal X-ray diffraction measurements for 1–2, 5, 7, 9and 12–13 (Tables 1 and 2) were carried out on a Stoe Mark-IIImaging Plate Diffractometer System equipped with a graphitemonochromator. Data collection was at -100 ◦C using Mo-Karadiation (l = 0.71073 A). Absorption corrections were madeusing MULscanABS.5 Compound 4 was measured on an EnrafNonius Kappa CCD area detector at -100 ◦C using Mo-Karadiation. Data collection and unit cell refinement were managedby DENZO6 and absorption corrections were applied usingSORTAV .7 Compound 11 was measured on a Bruker Smart
Apex II area detector diffractometer equipped with a graphitemonochromator. Data collection was at -100 ◦C using Mo-Ka radiation (l = 0.71073 A). Absorption corrections weremade using SADABS.8 Structure solutions were carried out bySHELXS-979 (1–2, 4–5) or SIR9210 (7, 9, 11–13 and 14) andthe refinement by SHELXL-979 in the WINGX 11 environment.Hydrogen atom positions were generated in calculated positionsand refined in riding mode on the parent atom using the defaultparameters in SHELXL-97. All non-hydrogen atoms were refinedanisotropically. Crystallographic diagrams were prepared usingDiamond 2.1a.12 Powder X-ray measurements were made on aStoe StadiP diffractometer in transmission mode using Cu-Ka1
radiation (l = 1.54056 A) using a position-sensitive device, exceptfor 3, which was double monochromated due to fluorescence from
Table 1 Single-crystal X-ray crystallographic parameters for bnz compounds
Compound 1 2 4 5 13
Formula MnC16H12N4O4 FeC16H12N4O4 NiC16H12N4O4 CuC16H12N4O4 Zn3C34H24N8O12
the Co atoms. Unit cell refinements for 3, 6 and 10 (Table 3)were obtained using the Le Bail method13 in Rietica.14 Structuralrefinement of 10 from powder X-ray measurements was carriedout using Jana.15
Magnetic susceptibility measurements were made in a QuantumDesigns MPMS-XL SQUID magnetometer under applied fieldsof 1000 G between 300–1.8 K. Samples were prepared in Saranfilm bags and held in plastic straws for insertion in to themagnetometer. Diamagnetic corrections were applied for thesample holder using Pascal’s constants16 and for the samplesusing the approximation 0.45 ¥ formula weight (per M(II) ion) ¥10-6 cm3 mol-1. Magnetisation measurements were carried outbetween 0–5 T at 1.9 K. Hysteresis measurements were also carriedout at 1.9 K. Zero-field cooled and field cooled magnetisationmeasurements were made between 2–15 K in an applied field of500 G. AC susceptibility measurements were carried out between1.8–15 K with a driving field of 3 G with frequencies in the rangeof 1–1488 Hz.
Synthesis of [Mn(II)(ox)(bnz)2]n, 1. Mn(II) acetate tetrahydrate(1.00 mmol, 245 mg), oxalic acid dihydrate (1.00 mmol, 126 mg),benzimidazole (6.00 mmol, 708 mg) and distilled water (10 ml)were heated in a microwave synthesiser at 150 ◦C for 15 min beforebeing allowed to cool, after which the finely divided white powderproduct was filtered, washed with distilled water and acetone anddried under suction.
Single crystals of 1 were formed by heating the same reactantsto 165 ◦C in a Teflon-lined autoclave for 72 h.
C16H12MnN4O4 (379.23 g mol-1): expected: C 50.67; H 3.19; N14.77. Found C 50.20; H 3.13; N 14.20.
Synthesis of [Fe(II)(ox)(bnz)2]n, 2. Fe(II) oxalate dihydrate(1.00 mmol, 180 mg), benzimidazole (6.00 mmol, 708 mg) anddistilled water (10 ml) were heated at 95 ◦C for 72 h in a Teflon-lined steel autoclave to give single crystals of the yellow product.
C16H12FeN4O4 (380.14 g mol-1): expected: C 50.55; H 3.18; N14.74. Found C 49.83; H 2.91; N 14.63.
Co(II) acetate tetrahydrate (1.00 mmol, 249 mg), oxalic aciddihydrate (1.00 mmol, 126 mg), benzimidazole (5.00 mmol,590 mg) and distilled water (10 ml) were heated in a microwavesynthesiser at 165 ◦C for 15 min before being allowed to cool, afterwhich the finely divided red-pink powder product was filtered,washed with distilled water and acetone and dried under suction.
C16H12CoN4O4 (383.23 g mol-1): expected: C 50.15; H 3.16; N14.62. Found C 49.61; H 3.13; N 14.17.
Ni(II) acetate tetrahydrate (1.00 mmol, 249 mg), oxalic aciddihydrate (1.00 mmol, 126 mg), benzimidazole (5.00 mmol,590 mg) and distilled water (10 ml) were heated in a microwavesynthesiser at 165 ◦C for 15 min before being allowed to cool, afterwhich the finely divided blue-green powder product was filtered,washed with distilled water and acetone and dried under suction.
Single crystals of 4 were formed by hydrothermal reactionof nickel(II) hydroxide (1.00 mmol), oxalic acid (4.00 mmol), o-phenylenediamine (4.00 mmol) and distilled water (10 ml) whichwas heated to 180 ◦C for 72 h.
C16H12N4NiO4 (383.00 g mol-1): expected: C 50.18; H 3.16; N14.63. Found C 49.77; H 3.12; N 14.12.
Synthesis of [Cu(II)(ox)(bnz)2]n, 5. Cu(II) sulfate pentahydrate(1.00 mmol, 250 mg), oxalic acid dihydrate (6.00 mmol, 756 mg),benzimidazole (6.00 mmol, 708 mg) and distilled water (10 ml)were heated at 95 ◦C for 72 h in a Teflon-lined steel autoclaveto give single crystals of the pale green product 5 and purplecrystals of [Cu(SO4)(benz)4]. The two components were separatedfrom an insoluble white product by adding the mixture to acetoneand placing in a sonic bath. Compound 5 was then separatedby suspending the mixture in a 1 : 1 mixture of chloroform anddibromoethane and removing each component as it floated orsank.
C16H12CuN4O4 (387.84 g mol-1): expected: C 49.55; H 3.12; N14.45. Found C 49.69; H 3.18; N 14.12.
Synthesis of [Zn(II)(ox)(bnz)2]n, 6. Zn(II) chloride (1.00 mmol,136 mg) was dissolved in DMSO (10 ml) and added to a solutionof benzimidazole (6.00 mmol, 708 mg) and oxalic acid (6.00 mmol,756 mg) in 20 ml DMSO. Precipitation occurred after a fewminutes to give a fine white powder.
Synthesis of [M(II)(ox)(btz)2]n, 7–12. A 1 M aqueous solutionof M(II)Cl2.nH2O (n: Mn 4, Fe 4, Co 7, Ni 6, Cu 2, Zn 0) waslayered over an equal volume of a 2 M DMSO solution of oxalicacid and benzotriazole. Single crystals suitable for X-ray analysisformed from as little as 30 min (11) to two days (9), while for 10,only powders could be formed, despite various synthetic methodsbeing used.
[Mn(II)(ox)(btz)2]n, 7. C14H10MnN6O4 (381.21 g mol-1): ex-pected: C 44.11; H 2.64; N 22.05. Found C 44.23; H 2.41; N21.83.
Synthesis of {[Zn(II)(bnz)4][Zn(II)2(ox)3]}n, 13. Zn(II) chloride(1.00 mmol, 136 mg), oxalic acid dihydrate (1.00 mmol, 126 mg),benzimidazole (6.00 mmol, 708 mg) and distilled water (10 ml)were heated at 180 ◦C in a Teflon-lined steel autoclave to givecolourless single crystals of the product which were then filtered,washed with water and acetone and left to dry under suction.
C34H24N8O12Zn3 (932.75 g mol-1): expected: C 43.78; H 2.59; N12.01. Found C 43.44; H 2.50; N 11.88.
Compound 1 crystallises in the monoclinic space group C2/c.The asymmetric unit (Fig. 1) contains two Mn(II) ions, one anda half oxalate dianions and three benzimidazole molecules. TheMn(II) ions are approximately octahedrally coordinated in a cis-N2O4 coordination sphere by two oxalates and two benzimidazoles(Tables 4 and 5). The Mn–O bond distances are between 2.160(3)and 2.240(3) A and Mn–N distances of 2.199(3) and 2.219(4) A.The oxalates chelate and bridge the Mn(II) ions to give a one-dimensional zigzag [Mn(ox)]n chain in the 101 direction with theMn(II) centres displaying alternate D–K chiralities with Mn–Mndistances of 5.708(1) and 5.730(1) A. The arrangement of theMn(II) ions within the chain is [–Mn1–Mn2–Mn2–]n due to theinversion centre in the Mn2–Mn2 oxalate bridge and Mn1 lyingon a two-fold rotation axis. The remaining two coordinationsites are occupied by the benzimidazole molecules (benzimidazolemolecule labels are indicated by the atom number prefix, e.g.
Fig. 1 Asymmetric unit and selected symmetry equivalents of 1. Hydro-gen atoms omitted for clarity. Thermal ellipsoids are at the 50% level.Symmetry operators: i) 1-x, y, 1
a Values in brackets are for the M–L distances in the dx2 -y2 orbital only.
Table 5 L–M–L angles (◦) for 1–2 and 4–5
CompoundMetal atomlabel
averagetrans-angle
cis-anglerange
average cis-angledifferencea
1 1 168.89 21.51 5.502 164.17 26.60 7.41
2 1 168.92 18.93 5.062 165.07 24.22 6.97
4 1 170.71 14.30 3.992 167.94 20.74 5.23
5 1 170.13 17.40 4.622 164.74 28.08 6.12
a Calculated as |90◦ - cis-angle|.
benzimidazole 2 has N2x, C2x, H2x) and, with the exception ofbenzimidazole 3, these take part in hydrogen bonding betweenthe well-separated chains (Fig. 2 and Table 6) to determine themolecular packing (Fig. 3a). There are several C–H ◊ ◊ ◊ O shortcontacts within the chains between the benzimidazoles and theoxalates. Benzimidazoles 1 and 3 take part in a p ◊ ◊ ◊ H interactionwith the C35–H35 bond pointing into the centre of the benzenering of benzimidazole 2 with an average H ◊ ◊ ◊ C distance of 3.11 A.(Fig. S1, ESI†).
Fig. 2 Intra- and interchain hydrogen bonding and short C–H ◊ ◊ ◊ Ointeractions in 1.
Asymmetric units for 2, 4 and 5 are shown in Fig. S2–S4 in theESI.† Compounds 2 and 4 are isostructural to 1 with decreasinglengths in the M–L bonds (Table 4), as expected for the decreasing
Table 6 Hydrogen bond distances (A) and angles (◦) for 1
X-ray diffraction shows they are isostructural (Table 3 and Fig.S5†). The unit cell of 6 is closer to that of 1, which is expectedgiven the longer M–L bond lengths of the Mn(II) and Zn(II) ionsdue to their respective half- and fully filled d-shells. Compound5 is also isostructural despite the expected Jahn–Teller distortionabout the Cu(II) ions.
The hydrogen bonding system of this series changes subtly asit progresses from Mn to Cu in that N32–H32 ◊ ◊ ◊ O6ii and C13–H13 ◊ ◊ ◊ O2iv increase until they are effectively non-connected andN12–H12 ◊ ◊ ◊ O3ii starts to appear when M = Ni (see Tables 6,S1–S3†).
Compounds 7–12 are isostructural to that reported for[Fe(II)(ox)(btz)2]n (compound 8) by Jia et al.4 and crystallise in thepolar space group Cc. In 7, the asymmetric unit (Fig. 4) consistsof one Mn(II) ion, one oxalate dianion and two benzotriazolemolecules. The Mn(II) ion is chelated and bridged by two oxalateanions in a cis-fashion and the remaining two coordinationsites are filled by benzotriazole molecules (Tables 7 and 8),with Mn–O bonds of 2.176(5)–2.214(4) A and Mn–N bonds of2.212(5) and 2.221(5) A to give an approximately octahedral cis-N2O4 coordination sphere. The Mn–Mn distance in the chain is5.668(2) A and the Mn atoms display alternate D–K chiralities.The benzotriazole molecules take part in hydrogen bonding toneighbouring chains as well as one C–H ◊ ◊ ◊ O short contact todetermine the crystal packing (Fig. 3b and Table 9). No intrachainhydrogen bonding or p–H interactions are seen.
Fig. 4 Asymmetric unit and selected symmetry equivalents of 7. Hydro-gen atoms omitted for clarity. Thermal ellipsoids are at the 50% level.Symmetry operators: i) x, -y, 1
2+z.
We see the same trend for decreasing bond lengths across theseries 7–12 (Table 7) as well as the small distortion to the structurein 11 from the Jahn–Teller axis on the Cu(II) ion. The hydrogenbonding system is more or less unchanged across the series (TablesS4–S6†). Asymmetric units are shown in Fig. S6–S8 in the ESI.†These compounds crystallise in a polar space group, Cc, and aremerohedrally twinned by a pseudo-inversion centre (see Flackparameters in Table 2). Compound 10 occurs only as a powder(Fig. S9† and Table 3), but powder X-ray data of sufficient qualityfor a provisional structural refinement was obtained. Initially, a
rigid group model was used and structural parameters were slowlyreleased as the refinement progressed to give a structure that wasconsistent with the other members of the series (Fig. S10†).
Compound 13 crystallises in the orthorhombic space groupPbcn. The asymmetric unit (Fig. 6) consists of two Zn(II) ions,two benzimidazole molecules and one and a half oxalate dianions.The oxalate anions chelate Zn1 so that the coordination sphereis approximately octahedral and bridge the Zn1 ions to form ahexagonal 63 [Zn2(ox)3]n
2n- layer in the ab-plane (Fig. 7a). TheZn–O distances range from 2.063(1)–2.162(1) A. The separationbetween the mean plane of the layers is half the c-parameter at12.001(2) A. The Zn–Zn separations in the layer are 5.452(1) and5.369(1) A through the C15/16 and C17 oxalates, respectively.The angles in the hexagonal layer are also deviated from a regularstructure value of 120◦ with 109.33(1), 109.64(1) and 141.00(1)◦,which gives elongated hexagonal rings within the layer. Theremaining Zn(II) ion, Zn2, is tetrahedrally coordinated by fourbenzimidazole molecules to give a [Zn(II)(bnz)4]2+ cation. Thiscation then hydrogen bonds to the [Zn2(ox)3]n
2n- layers throughthe N–H groups of all four of the benzimidazole molecules
Fig. 5 Interchain hydrogen bonding and short C–H ◊ ◊ ◊ O interactions in7. Symmetry codes: ii: 1
2+x, 1
2-y, 1
2+z; iii: 1
2+x, 1
2+y, z; iv: - 1
2+x, 1
2+y, z.
Fig. 6 Asymmetric unit and selected symmetry equivalents of 13 withthermal ellipsoids at the 70% level. Hydrogen atoms omitted for clarity.Symmetry codes: i) -x, 1-y, -z; ii) 1
2-x, 1
2+y, z; iii) 1-x, y, 1
2-z.
Fig. 7 a) View of the hexagonal [Zn2(ox)3]n2n- layer in compound 13 in
the ab-plane, looking down the c-axis. b) View of the layer separation andhydrogen bonding network, looking down the b-axis.
with H ◊ ◊ ◊ O distances of 1.903(1) and 2.019(1) A (Fig. 7b andTable 10). Two C–H ◊ ◊ ◊ O short contacts also bind the cation tothe anionic layers with distances of 2.324 and 2.355 A. Given
Table 10 Hydrogen bond distances (A) and angles (◦) for 13
that no C–H bonds point clearly to any of the aromatic rings onneighbouring benzimidazole molecules, the packing is most likelyto be determined by the hydrogen bonding and C–H ◊ ◊ ◊ O shortcontacts (Table 10).
Discussion
To the best of our knowledge, the [–Mi–Mii–Mii–]n oxalate chainmotif has only been reported in the literature once,17 despite thediscovery of other [M(II)(ox)(L)x]n chains with similar ligands tobnz and btz.18 A search of the literature shows that these two seriesof compounds span the widest continuous range of 3d metalsin isostructural [M(II)(ox)(L)x]n chains: the a-[M(II)(ox)(H2O)2]n
series is broken by the lack of a Cu(II) compound (reaction ofCu(II) salts and oxalate produces a-Cu(ox),19 most likely due tothe weak Cu–OH2 bond in the Jahn–Teller axis breaking and thechains combining to form the three-dimensional solid). Having anisostructural series of chains across all the spin states from S = 5/2to S = 0 should provide an interesting comparison of magneticbehaviour, which we have investigated below.
Aside from the direct synthesis of compounds 1–6 from benz-imidazole, we also experimented with the hydrothermal reactionof o-phenylenediamine with oxalic acid. In the case of reactionwith a Ni(II) salt, the formation of benzimidazole resulted, givingcompound 4, while in the presence of Co(II), a Schiff basecompound, 1,4-dihydro-2,3-quinoxalinedione, is formed, but 3 isnot. The formation of 1,4-dihydro-2,3-quinoxalinedione from o-phenylenediamine and oxalic acid is also accomplished by a hy-drothermal reaction in the presence of Cu(II).20 Another exampleof a Schiff base reaction occurring under hydrothermal conditionsto give oxalate chains with imidazole-based ligands is that ofHao and Zhang21 where acetonitrile and ethylenediamine reactto give 2-methylimidazole, which acts as a ligand in [M(II)(ox)(2-methylimidazole)2]n (M = Co, Zn).
As mentioned above, 7 and 9–12 are isostructural to[Fe(ox)(btz)2]n, which we have also synthesised here to investigateits magnetic properties. An interesting point is that despite the highdegree of similarity between benzimidazole and benzotriazole, thechain structures formed have subtle, but important, differences.The likely explanation for this is the role of the C–H ◊ ◊ ◊ Ointeraction in determining the local structure, which in turn affectsthe crystal packing of the chains. Several solvent systems can beused for producing 7–10 and 12 in good yield, but 11 is sensitive tothe solvent present. In MeOH, a different monomeric compoundforms: [Cu(ox)(bnz)2(H2O) 1
2(MeOH) 1
2] (14 – see ESI†), while in
DMF and DMSO, other compounds form as powders that wehave not yet fully characterised, but can be seen from the IR tocontain the respective solvents.
In the two series, we see a contraction of the M–L distancesfrom Mn(II) to Ni(II) (Tables 4 and 7), which is consistent withthe decreasing ionic radii of the respective metal atoms as theatomic number increases (Fig. 8).22 This is due to the incompleteshielding of the 3d orbital from the nuclear charge. The Cu(II) andZn(II) radii are larger in size than Ni and this is also reflected inthe M–L distances. We also see that the coordination sphere of themetal(II) ions becomes more octahedral as we move from Mn(II) toNi(II), as predicted by ligand-field theory. The d5 configuration hasno crystal-field stabilisation energy and as such the arrangementof ligands around the metal centre is more heavily dictated bythe crystal packing. As electrons are added to the 3d orbital, theCFSE decreases, reaching a minimum at d8 with a value of -6/5Doct and then increasing in d9 before becoming zero in the case ofd10. It can be seen that in the plot of the difference in cis-anglefrom 90◦ (Tables 5 and 8 and Fig. S11†) that the difference followsthis, although Zn(II) is not quite as irregular as expected. Thisimplies that steric hindrance around the metal atom also plays apart in the configuration of the coordination sphere as the smallerionic radius of Zn(II) may not allow larger changes away from theoctahedral as in Mn(II).
Fig. 8 Plots of normalised crystal radii and normalised M–L distances.Note that Ni(btz)2(ox), 10, data is from room temperature PXD data,whereas all other points are SXD at 173 K.
As an additional check on the oxidation state of the Mn, Feand Co atoms in these compounds, bond-valence sums23 werecalculated and all metal atoms were found to be in the 2+ state(Table S7†).
The hexagonal {[A][M2(ox)3]}n layer structure is well-known incoordination chemistry, but usually occurs for mixed metal types,often with Cr(III),1d-f while homometallic layers are not so com-mon. These compounds are usually templated by organic cations,but a few cases of organometallic cations templating this structureare known.24 There are several reported {[A]2+[Zn2(ox)3]2-}n com-pounds with the same hexagonal layer structure,1c,25 but compound13 is first to have a metal-based cation to template the structure.The separation between the layers of 12.001(5) A is the smallestfound in this type of compound, with ref. 25a-d and 1c rangingfrom 12.415–17.798 A. Compound 13 is also one of only two ofthis class of {[A][Zn2(ox)3]}n networks where water does not playa role in hydrogen bonding the layers.
Magnetism
A magnetic susceptibility plot, c(T), for 1 (Fig. 9) shows a broadmaximum at 12 K with cmax = 0.1074 cm3 mol-1. An inversesusceptibility plot, c-1(T), shows linear behaviour above 60 K andfitting the data above 100 K with the Curie–Weiss equation, weobtain C = 4.376(3) cm3 K mol-1 and q = -18.6(2) K from whichwe derive a g-value of 2.00. A cT(T) plot shows a decreasingproduct upon cooling with a value of 4.112 cm3 K mol-1 at 300 K.
Fig. 9 Plot of c(T) and cT(T) for 1 with fits from the S = 5/2 Fishermodel (eqn (2)) giving g = 2.002(2) and J/kB = -2.82(1) K.
The chain topology in 1–7 is not a regular chain (Scheme 1),i.e. that there is more than one spin centre and more than oneintrachain coupling pathway, however, the intrachain metal–metaldistances are very similar in compound 1 (5.70 and 5.73 A) and as
g-values for Mn(II) are usually very close to 2.00, we can treat thischain as being approximately regular.
Given the large value of S, the negative Weiss constant anddecreasing cT value on cooling, we can apply the Fisherclassical model for antiferromagnetically-coupled one-dimensional Heisenberg chains26 (eqn (2)). The large number ofms states of the Mn(II) ion and the Heisenberg-like nature of thed5 electronic configuration make the classical equation a goodapproximation to this system.
H J S Si i
i
= − ⋅ +∑ 1 (1)
cm
=+( )
⋅−+
=+( )
−+( )Ng S S
k T
u
uu
T
JS S k
JS S kB
B
B2 2 1
3
1
1 1
1where
B/coth
/
TT
(2)
Fitting the data above 8 K, we obtain g = 2.002(2) and J/kB =-2.82(1) K. Below 8 K, the susceptibility is overestimated by themodel, most likely due to either a small magnetic anisotropyor weak interchain interactions. Compound 7 shows similarbehaviour with a maximum at 12 K, C = 4.364(7) cm3 K mol-1, q =-16.6(4) K and cT = 4.136 cm3 K mol-1 at 300 K. A fit to the datawith the Fisher model gave g = 2.019(4) and J/kB = -2.86(1) K(Fig. S12†). In 7–12, there is only one coupling pathway and onespin centre, so the Fisher equation can be used without making anapproximation regarding the chain topology.
Comparison with other [Mn(II)(ox)]n chains shows the valuesobtained are within the expected range of -1.2 to -3.2 K.18a,27
The couplings in 1 and 7 are at the higher end of this range,which is consistent with the findings of Castillo et al.28 that theless-electronegative N2O4 coordination sphere of the Mn(II) allowsmore electron density to be involved in the orbital overlap betweenthe metal and oxalate, thus increasing the coupling strength whencompared to the more electronegative O6 coordination sphere.
The magnetic susceptibility of 2 (Fig. 10) shows a broadmaximum at 26 K with cmax = 7.86 ¥ 10-2 cm3 mol-1. An inversesusceptibility plot, c-1(T), shows linear behaviour above 150 Kand fitting the data above 150 K with the Curie–Weiss equation,we obtain C = 4.71(1) cm3 K mol-1 and q = -10.8(6) K from whichwe can derive an average g-value of 2.51. A cT(T) plot shows adecreasing product upon cooling with a value of 4.531 cm3 K mol-1
at 300 K.Fe(II) is affected by a strong spin–orbit coupling and a large
orbital contribution, which can make data modelling difficult. Tomodel the data, we used the equation from Drillon et al.:29
c m= ⋅
24
2 2Ng
k TJ k TB
BBexp( / ) (3)
From this, we obtain a good fit to the data over almost the wholetemperature range with g = 2.65(1) and J/kB = -6.08(2) K.
Fig. 10 Plot of c(T) and cT(T) for 2 with fits from the S = 2 Ising chainmodel (eqn (3)) giving g = 2.65(1) and J/kB = -6.08(2) K.
Compound 8 shows similar behaviour in the high-temperatureregion (Fig. S13†) with C = 5.59(2) cm3 K mol-1 and q = -19(1) K,but below 10 K, we see a sharp increase in the susceptibility (Fig.S13 inset†). The value of the maximum in the molar temperature-dependent magnetisation (1849 cm3 G mol-1 at 1.9 K) is wellbelow that of an ordered S = 2 ferromagnet. The field dependentmagnetisation curve (Fig. S14†) shows an abrupt increase inmoment until 500 G and hysteresis is observed (Fig. S15†) with acoercive field of 98 G and a remnant magnetisation of 0.193 mB.
The transition temperature does not correspond with any likelyimpurity or side product from this reaction and three samplesmade in slightly different ways show the same sized signal,suggesting that it is intrinsic to the sample. As there is only oneFe(II) ion in the asymmetric unit, it is not possible that this momentis caused by ferrimagnetism. It is possible that spin canting canoccur in certain cases where there is only one spin carrier in theasymmetric unit, which is the case here. The lack of an inversioncentre in the coupling pathway between adjacent Fe(II) centres,due to the non-centrosymmetric Cc space group, can allow aDzyaloshinskii–Moriya interaction, which can in turn lead to aspin canting through antisymmetric spin-exchange.30
The value of c in the area where we would expect cmax to occuris affected by the increasing susceptibility due to the spin canting,thus making a fit with eqn (3) unreliable. However, modelling cTat higher temperatures (> 50 K, Fig. S16†) gives g = 2.78(1) andJ/kB = -6.7(1) K, similar to compound 2.
Taking the intercept of the gradient of the magnetisation above1000 G (1767 cm3 G mol-1), we can calculate a spin-cantingangle of 3.3◦ for a compound with an average g-value of 2.73 (ascalculated from the Curie constant). The remnant magnetisationmeasurement (Fig. S17†) shows that the moment falls off rapidlyon warming from 1.8 K, indicating that the material is a softmagnet, as also shown by the small remnant magnetisation andcoercive field from the hysteresis measurement. This is consistentwith a material with a small spin canting and a good spatialseparation between the chains.
AC susceptibility measurements show a marked frequencydependence in the in-phase, c¢, and (Fig. S18†) out-of-phasecomponent, c”, (Fig. 11) and also a maximum at each frequency.
Fig. 11 Out-of-phase AC susceptibility plot, c”(T), for 8 from 1 Hz to1488 Hz.
This behaviour is characteristic of a blocking temperature. Giventhat it is likely we are seeing well-separated chains with a netmoment, the frequency dependence indicates that we are seeingsingle-chain magnetic behaviour. Plotting the maximum of thec”(T) plots at each frequency, we can model the data using anArrhenius plot (eqn (4), Fig. S19†)
t = t 0 exp-Ea /kB T (4)
from which we obtain a reorientation energy barrier, Ea/kB, of62(1) K and a pre-exponential factor, t 0, of 2(1) ¥ 10-14 s. Bothparameters are consistent with other SCMs,31 although t 0 is atthe smaller end of this range, indicating that the relaxation timesare comparatively short in 8 (at 2 K (the lowest measuredtemperature), the relaxation time is in the region of 0.6 s). ACole–Cole plot (Fig. 12) shows semi-circular curves, indicative
Fig. 12 Cole–Cole plot for 8 with fit to c”(T) data from the generalisedDebye model (eqn (5)), giving a = 0.682(3).
also of the formation of an SCM phase. Fitting the out-of-phaseAC data at each frequency with the generalised Debye expressionfor a distribution of single relaxation pathways32 using a commonalpha parameter:
c w c c c wt apwt ap wt
a
a a"( )( )( ) cos
( ) sin ( ) ( )=
−+ +
−
− −sT S
1 12
1 12
2 11 2(5)
where cT is the isothermal susceptibility, cS is the adiabaticsusceptibility, w is the frequency and a is the distribution of singlerelaxation pathways.
We obtain a = 0.682(3), indicating that there is a widedistribution of single relaxation pathways (a = 0 for an infinitelynarrow distribution of single relaxation pathways).
Compound 8 is only the second SCM system based on oxalate,the other being a series of bimetallic chains33 and has the importantadvantages that the coupling constant is comparatively high whilethe interchain coupling is low, which are important factors in thedesign of SCMs.31a It is also one of a small group of spin-cantedSCMs,34 which provides a useful design pathway in addition tothe use of bimetallic systems. Additionally, it is only the secondreported SCM utilising solely Fe(II).31c
Apart from [Fe(II)(ox)(H2O)2]n35 there is little magnetic work
on [Fe(II)(ox)]n chains, only three of which appear to show one-dimensional behaviour27f,36 with the remaining two showing three-dimensional order at low temperatures.37
The magnetic susceptibility of 3 (Fig. 13) shows a broadmaximum at 19 K with cmax = 38.4 ¥ 10-3 cm3 mol-1. An inversesusceptibility plot, c-1(T), shows linear behaviour above 100 K andfitting the data above 120 K with the Curie–Weiss equation, weobtain C = 3.224(2) cm3 K mol-1 and q = -50.3(2) K from whichwe can derive a g-value of 2.62. A cT(T) plot shows a decreasingproduct upon cooling with a value of 2.761 cm3 K mol-1 at 300 K.
Fig. 13 Plot of c(T) and cT(T) for 3 with fits from the modified Rueffmodel (eqn (6)) giving g = 2.59(1), D/kB = 68(1) K, a = 1.82(2) andJ/kB = -15.2(2) K.
The Co(II) ion is also heavily affected by spin–orbit coupling,which gives rise to a large zero-field splitting parameter and aneffective S’ = 1/2 ground state at low temperatures. As such,the high temperature region can be modelled as for an S = 3/2Heisenberg spin and the low temperature as an S = 1/2 Ising spin.However, as the sample is polycrystalline, this approach does notwork well in the Ising case as the number of parameters to refine is
high. Currently, the best approach to modelling this type of chainis to use the model of Rueff et al.38 which we have modified toallow refinement of the average g-parameter39 (eqn (6)).
c m a a= ⋅ −( ) −( )+ ( )Ng
k TD k T J k TB
BB B
2 2
33 75. exp / exp / (6)
where D is the zero-field splitting parameter, and a is a dummyparameter to give a ratio between the component parts of theequation, although it seems to bear an inverse relationship to theelectronegativity of the coordination sphere.
Fitting the data from 12–300 K gives a good fit and g = 2.59(1),D/kB = 68(1) K, a = 1.82(2) and J/kB = -15.2(2) K. Comparisonwith other [Co(ox)]n chains shows that these values are well withinthe expected and quite narrow range for such compounds.39
Compound 9 shows very similar behaviour with C =3.224(2) cm3 K mol-1 and q = -50.3(2) K and a fit to the data givesg = 2.54(1), D/kB = 87(2) K, a = 1.78(2) and J/kB = -19.3(2) K(Fig. S20†).
The susceptibility of 4 (Fig. 14) shows a broad maximum at46 K with cmax = 8.24 ¥ 10-3 cm3 mol-1. An inverse susceptibilityplot, c-1(T), shows linear behaviour above 160 K and fitting thedata above 160 K with the Curie–Weiss equation, we obtain C =1.348(3) cm3 K mol-1 and q = -88.8(8) K from which we can derivea g-value of 2.32. A cT(T) plot shows a decreasing product uponcooling with a value of 1.039 cm3 K mol-1 at 300 K.
Fig. 14 Plot of c(T) and cT(T) for 4 with fits from the Souletie model(eqn (7)) giving g = 2.15(1) and J/kB = -39.2(2) K.
To model the susceptibility data of 4, we have used the model ofSouletie et al.40 (eqn (7)), which is accurate to low temperatures andalso takes account of the Haldane gap—an energy gap betweenthe ground and first excited spin states of an infinite integer-spinchain.
c m= −( ) −⎛
⎝⎜⎜⎜⎜
⎞
⎠⎟⎟⎟⎟+
−1 0 125
0 4510 564
12 2
pNg
k T
J
k TB
B B
. exp.
. exp.7793
31
2 2
J
k T
pNg
k TS S
B
B
B
⎛
⎝⎜⎜⎜⎜
⎞
⎠⎟⎟⎟⎟
⎡
⎣⎢⎢⎢
⎤
⎦⎥⎥⎥
+ +( )⎛
⎝⎜⎜⎜⎜
⎞
⎠⎟⎟m⎟⎟⎟
(7)
where p is the percentage paramagnetic impurity.
From this fit to the data, we obtain g = 2.15(1), J/kB =-39.2(2) K and a small paramagnetic impurity, p, of 1.2(1)%.From the work of Souletie et al., the value of the Haldane gap asa function of J can be obtained as 0.421 ¥ |J/kB| = 16.5 K.The formation of a Haldane gap requires that the zero-fieldsplitting parameter to be in the range -0.2 < D < 1, in unitsof J, and that there is a very low ratio of interchain to intrachaincoupling.2 D values for Ni(II) are usually in the range of -30 to+6 K41 and there is a large separation of the chains in 4 (~9 A),so it is quite likely we are seeing the formation of a Haldanestate.
The susceptibility data for 10 shows a large paramagnetic tailin the low-temperature region, most likely due to monomericimpurities or superparamagnetic particles, resulting from the smallparticle size obtained. Similar results to 4 are obtained for 10with C = 1.325(3) cm3 K mol-1 and q = -94.7(7) K and acT value of 1.007 cm3 K mol-1 at 300 K. We can derive g-values of 2.30 and 2.01 from C and cT 300 K, respectively. Thesusceptibility data was modelled as for 4, except we use the termfor an S = 1 paramagnetic impurity to approximate the low-temperature tail. From this fit, we obtain g = 2.11(1), J/kB =-41.1(5) K and p = 4.9(2)% (Fig. S21†). While we expect a Haldanegap, the paramagnetic impurity precludes our observation of thisstate.
The susceptibility of 5 (Fig. 15) shows a continuous increase oncooling, with cmax = 190.4 ¥ 10-3 cm3 mol-1 at 1.8 K. An inversesusceptibility plot, c-1(T), shows linear behaviour above 10 Kand fitting the data above 50 K with the Curie–Weiss equation,we obtain C = 0.428(1) cm3 K mol-1 and q = -1.8(3) K fromwhich we can derive a g-value of 2.14. A cT(T) plot shows linearbehaviour upon cooling down to 20 K upon which there is asmall increase in the value before decreasing sharply. The valueof cT at 300 K is 0.418 cm3 K mol-1, which gives a g-valueof 2.12.
Fig. 15 Plot of c(T) and cT(T) for 5 with calculated data for g = 2.14,J1/kB = +2.5 K and J2/kB = -2.8 K. Inset: Coupling diagram for 5.
The data was modelled with the Feyerherm polynomial foran S = 1/2 antiferromagnetically-coupled Heisenberg chain42
and gave g = 2.14(1) and J/kB = -0.54(1) K. This fit did
not model the low temperature data well. The small rise inthe value of cT indicates a ferromagnetic component. We thenused full-matrix diagonalisation techniques43 to model the datausing the arrangement in Fig. 15 where the Cu1–Cu2 couplingis ferromagnetic to give ferromagnetically-coupled trimers whichare then antiferromagnetically-coupled through the Cu2–Cu2couplings. The best fit was obtained if J1/kB = +2.50(5) K, J2/kB =-2.75(5) K and g = 2.14(1).
There is a wide variation of magnetic behaviours for[Cu(II)(ox)]• chains in the literature, usually depending on thecoordination mode of the oxalate and through which orbitals itligates to the metal (Fig. 16). The range of couplings depends verystrongly on this: if the oxalate bridges solely through the dx2 -y2
orbitals (Fig. 16a; e.g. in b-Cu(ox)–strictly a 3-D coordinationcompound, but the predominant magnetic interaction is that ofa linear chain), the coupling can be as high as -419 K,16 butif the bridging mode occurs through the dz2 on one of the Cuatoms, (Fig. 16b and c) then the couplings are substantially weaker,usually in the range of J/kB = -20 to -45 K,44 while with both Cuatoms bridged through the dz2 results in an even weaker couplingthat can also become ferromagnetic, with |J/kB| = 0–5 K.17,18b,45
Similar couplings can be seen in [Cu(II)2(ox)] dimers.1b Castilloet al. state that if the Cu–O–C angle in the dz
2 axis is less than109.5◦, then the coupling through the oxalate is ferromagnetic.27f
Given that in square planar, square pyramidal and tetragonally-elongated octahedral coordination, the eg is split so that the dz2
orbital is lower in energy than the dx2 -y2 , it is possible to assignthe orbitals involved in ligand bonding. As the dx2 -y2 is only half-full, the interelectron repulsion towards the ligands will be lessthan in the fully-occupied dz2 , leading to shorter Cu–L bonds.Between the Cu2 atoms, the Cu–O–C angle is 108.2(7)◦, (with theJahn–Teller axis, O3–Cu2–O5, defining the dz2 axis) indicative ofa small ferromagnetic interaction, as is seen above, while in theCu1–Cu2 oxalate, the Cu–O–C angles (with O2–Cu1–O2 definingthe dz
2 axis) are 111.0(8) and 106.4(8)◦, giving an average angleof 108.7(8)◦, which would still indicate ferromagnetism, but giventhe size of the measurement errors on this angle and that the sizeof the critical angle was based on a relatively small number ofcompounds along with the cT(T) data, it is likely that we do seean antiferromagnetic coupling through this bridge. We have alsomodelled the magnetisation curve43 for this system (Fig. S22†)which shows a fair agreement with the data and both the data and
Fig. 16 Schematic of the relative alignments of the SOMOs (singularlyoccupied magnetic orbitals) in oxalate-bridged Cu chains.
the simulation lie under the Brillouin curve for an S = 1/2 ionwith g = 2.14.
Compound 11 shows an increasing magnetic susceptibility oncooling (from 1.40 ¥ 10-3 cm3 mol-1 at 300 K to 0.315 cm3 mol-1
at 1.85 K) and an increasing value of cT on cooling (Fig. 17).A Curie–Weiss fit to the inverse susceptibility data gave C =0.424(1) cm3 K mol-1 and q = +0.12(4) K. From the value ofcT at 300 K (0.421 cm3 K mol-1) and C, we can derive g-valuesof 2.12 and 2.13, respectively. Given the positive Weiss constantand increasing value of cT , we expect to see a ferromagneticcoupling within the chain. To model this data, we used the modelof Baker et al.46 which, while not modelling antiferromagneticchains as accurately as later models,47 fits ferromagnetic chainswell.
c m= ⋅
⎛⎝⎜⎜⎜
⎞⎠⎟⎟⎟⎟
Ng
k T
N
DB
B
2 2 23
4(8)
Fig. 17 Plot of c(T) and cT(T) for 11 with fits from the Baker model(eqn (8)) with g = 2.113(1) and J/kB = +1.49(1) K.
where N = 1 + 5.7979916a + 16.902653a2 + 29.376885a3 +29.832959a4 + 14.036918a5, D = 1 + 2.7979916a + 7.008678a2 +8.6538644a3 + 4.5743114a4 and a = J/4kBT
Fitting to the whole data set gave a good fit with g = 2.113(1) andJ/kB = +1.49(1) K. This ferromagnetic interaction is consistentwith the findings of Castillo et al. as the average Cu–O–C angleis 109.2◦ (the dz2 axis being O1–Cu1–O4).27f As an additionalcheck, we simulated the magnetisation data at 1.9 K using aferromagnetically coupled n = 16 ring with g and J/kB valuesfrom the Baker fit and obtained a good fit to the experimentaldata (Fig. S23†) with both the model and the data lying above theBrillouin curve for S = 1/2 and g = 2.113.
With the exception of the ferromagnetic couplings in 5 and11, the coupling values in the chains correspond excellentlywith the values obtained for [M(II)2(ox)]n dimers by Glerupet al.1a
We have synthesised the first fully isostructural series of[M(II)(ox)(L)2]n chains spanning from Mn to Zn, thus allowingus to compare magnetic interactions across a series from S = 5/2to 1/2, the analysis of which also allows us to investigate whichare the most appropriate models for such a series. The single-chain magnetic properties of 8 are interesting for the combinationof crystallographic and physical effects that give rise to thebehaviour.
Additionally, we have found a distorted two-dimensional 63
net with an interesting [Zn(II)(bnz)4]2+ complex cation and acomparatively small inter-layer spacing of 12.001(1) A.
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