Structures and UV-visible absorption properties of unsymmetrical bisdithiolene nickel complexes

A new unsymmetrical bisdithiolene nickel complex Ni(Et(2)dazdt)(mnt) was synthesized and structurally characterized, where Et2dazdt and mnt denote 1,4-diethy-1-perhydrodiazepine-2,3-d thione and maleonitrildithiolate, respectively. Its crystal structure and absorption spectrum were determined and compared to those of Ni(Et(2)pipdt)(mnt), where Et(2)pipdt is 1,4-diethyl-piperazine-2,3-dithione. X-ray diffraction analysis reveals that the Ni(S2C2)(2) moiety of Ni(Et(2)dazdt)(mnt) is not planar due to the twist conformation of a seven-member ring of Et(2)dazdt ligand. The twisting of Et(2)pipdt is less severe and NiS4 center of Ni(Et(2)pipdt)(mnt) possesses a closer to planar conformation than that of Ni(Et(2)dazdt)(mnt). Unlike Ni(Et(2)pipdt)(mnt), Ni(dazdt)(mnt) shows two major separated absorption bands in the visible and near-IR region, although both absorption bands show negative solvatochromism similar to that of Ni(Et(2)pipdt)(mnt).