Synthesis, X‐ray Structure, Thermal and Magnetic Behavior of [(bipy)2Ni2(μ‐Cl)2Cl2(H2O)2]: The First Neutral Ferromagnetically Coupled Six‐Coordinate Dichlorido‐Bridged Nickel(II) Dimer

NiCl2·6H2O and 2,2′-bipyridine (bipy) (1:1) were allowed to react under ambient conditions in dimethyl sulfoxide in the presence of acetylacetone (Hacac). The resulting green solution was concentrated in vacuo, and a green solid was isolated by precipitation with cold acetone. X-ray quality crystals of [(bipy)2Ni2(μ-Cl)2(Cl)2(H2O)2] (1) were grown by subsequent vapor/liquid diffusion of acetonitrile into a methanolic solution for one week. The structure of 1 consists of a dimeric nickel system with each metal atom in an octahedral geometry. Both equatorial bridging and axial chlorine atoms are present in this neutral species. The nickel–nickel distance (3.441 A) is the shortest reported to date for this class of complexes and the bridging chlorido angles at 91.5° are the most acute. Variable-temperature magnetic susceptibility measurements reveal the complex to have the strongest ferromagnetic interaction reported to date (J = +16.8 cm–1, the Hamiltonian being defined as H = –JSA·SB) for this family of complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

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