Issue 37, 2012

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

Abstract

Six homodinuclear and two heteronuclear complexes TpNpCo–C2O4–CoTpNp (1), TpNpCo–C2O4–NiTpCy (2), TpCyNi–C2O4–NiTpCy (3), TpNpCo–C2O2(NH)2–CoTpNp (4), TpCyNi–C2O2(NH)2–NiTpCy (5), TpNpCo–C2S2(NH)2–CoTpNp (6), TpNpCo–C2S2(NH)2–NiTpCy (7), TpCyNi–C2S2(NH)2–NiTpCy (8) (TpNp = tris(3-neopentylpyrazolyl)borate, TpCy = 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 Ĥex. = −21Ŝ2) and |J| 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.

Graphical abstract: 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

Supplementary files

Article information

Article type
Paper
Submitted
24 May 2012
Accepted
09 Jul 2012
First published
10 Aug 2012

Dalton Trans., 2012,41, 11319-11329

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

E. A. Mikhalyova, S. V. Kolotilov, O. Cador, M. Zeller, S. Trofimenko, L. Ouahab, A. W. Addison, V. V. Pavlishchuk and A. D. Hunter, Dalton Trans., 2012, 41, 11319 DOI: 10.1039/C2DT31121F

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