Synthesis, Crystal Structures and Intermolecular Magnetic Coupling Mechanism of the Mononuclear Radical Complex [1-N-methyl-1,10-phenanthrolium][Ni(dmit)(2)]

The mononuclear radical anionic complex [1-N-methyl-1,10-phenanthrolium][Ni(dmit)(2)] (dmit = 1,3-dithiole-2-thione-4,5-dithiolate) with a new countercation has been prepared and its crystal structure was determined by X-ray crystallography at 298 and 80 K. In the mononuclear radical anionic complex, the nickel ion assumes a slightly distorted square-planar geometry. There are two and three kinds of intermolecular interactions between adjacent mononuclear radical anionic complexes in the crystal at 298 and 80 K, respectively (i.e., Models A and B at 298 K; and Models C, D and E at 80 K). The variable-temperature magnetic moments indicate a strong antiferromagnetic interaction between the adjacent mononuclear radical anionic complexes, and the theoretical calculations reveal that the stronger antiferromagnetic coupling strength at lower temperature should be contributed to the larger overlap integrals between the short contact atoms. This study is the first to reveal the mechanism of stronger magnetic coupling strength at lower temperature for a mononuclear radical anionic nickel complex with dmit as the ligand.