Ferromagnetic ordering in bis(benzene)chromium(+) bis(4,5-dimethoxybenzene-1,2-dithiolato)nickel(-)

The compound bis(benzene)chromium(+) bis(4,5-dimethoxy-1,2-benzenedithiolato)nickel(-), [Cr(bz)(2)](+)[Ni(dmox)(2)](-), was prepared as well-defined crystals by a metathesis reaction. X-ray single-crystal structure confirms the expected symmetries of the cations (D-6h) and anions (D-2h). The Ni-S bond length is typical for a monoanionic bis(arene)-1,2-dithiolato nickel complex thus confirming the ascribed charges. The structure reveals interpenetrating cation and anion sublattices where all ions are well separated from other ions of the same charge and with almost perpendicular symmetry planes of cations and anions. Above ca. 10 K the compound is paramagnetic and follows the Curie-Weiss law for S = 1/2 on each ion with a Weiss temperature of 8.5 K. Magnetic susceptibility and magnetization studies reveal the transition to a ferromagnetically ordered phase at 3.4 K. The ferromagnetic interaction is likely to occur through short contacts between anion heteroatoms (O and Ni) and cation H atoms, forming a 2-D network. A third dimension is possible through somewhat longer interionic S-H contacts. The Curie-Weiss law behavior can be modeled for 1-D chains with a ferromagnetic interaction of J = 11.6 K.