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The role of the bridging group in exchange coupling in dinuclear homo- and heterometallic Ni(II) and Co(II) complexes with oxalate, oxamidate and dithiooxamidate bridges
Journal article

The role of the bridging group in exchange coupling in dinuclear homo- and heterometallic Ni(II) and Co(II) complexes with oxalate, oxamidate and dithiooxamidate bridges

Elena A. Mikhalyova, Sergey V. Kolotilov, Olivier Cador, Matthias Zeller, Swiatoslaw Trofimenko, Lahcene Ouahab, Anthony W. Addison, Vitaly V. Pavlishchuk and Allen D. Hunter
Dalton transactions : an international journal of inorganic chemistry, v 41(37), pp 11319-11329
01 Jan 2012
PMID: 22885878

Abstract

Chemistry Chemistry, Inorganic & Nuclear Physical Sciences Science & Technology
Six homodinuclear and two heteronuclear complexes Tp(Np)Co-C2O4-CoTp(Np) (1), Tp(Np)Co-C2O4-NiTp(Cy) (2), Tp(Cy)Ni-C2O4-NiTp(Cy) (3), Tp(Np)Co-C2O2(NH)(2)-CoTp(Np) (4), Tp(Cy)Ni-C2O2(NH)(2)-NiTp(Cy) (5), Tp(Np)Co-C2S2(NH)(2)-CoTp(Np) (6), Tp(Np)Co-C2S2(NH)(2)-NiTp(Cy) (7), Tp(Cy)Ni-C2S2(NH)(2)-NiTp(Cy) (8) (Tp(Np) = tris(3-neopentylpyrazolyl)borate, Tp(Cy) = tris(3-cyclohexylpyrazolyl)borate), were synthesized and characterized by mass spectrometry, electronic spectroscopy and X-ray crystallography. These compounds possess similar molecular structures, with the metal ions linked by bridging oxalate (1-3), oxamidate (4 and 5) or dithiooxamidate (6-8) ions. The heteronuclear nature of compounds 2 and 7 was additionally confirmed by high-resolution mass spectrometry. The magnetic properties of the Co2+ complexes were modelled taking into account zero-field splitting of this ion, yielding D-values for Co2+ in the range -17(1) to -50(1) cm(-1). All the metal ion pairs in compounds 1-8 are antiferromagnetically-coupled, with J values between -10.0(1) and -45.0(2) cm(-1) (via the exchange Hamiltonian (H) over cap (ex) = -2J (S) over cap (1)(S) over cap (2)) and vertical bar J vertical bar increasing in the order oxalate < oxamidate < dithiooxamidate. This tendency can be attributed to greater M-S bond covalency compared to M-N or M-O bonds (M = Co2+ and Ni2+). It was found that this antiferromagnetic coupling of Co2+ and Ni2+ ions through oxalate is more efficient for these tris(pyrazolyl) borate complexes than for similar oxalate-bridged systems with neutral aliphatic amine ligands.

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Chemistry, Inorganic & Nuclear
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