Unusual magnetic property associated with dimerization within a nickel tetramer.

A new ion-pair complex, 1-benzyl-4-aminopyridinium bis(maleonitriledithiolato)nickelate(III) (1), has been synthesized. The variable magnetic susceptibility results of 1 show a discontinuity around 184 K, which is phenomenologically similar to that observed for first-row transition metal complexes undergoing a spin crossover transition. The crystal structure analyses of 1 at high and low temperatures indicate that this unusual magnetic property is associated with a packing structure that changes from tetrameric spin clusters to dimers between neighboring spin carriers.