(~nBu_4N)[Ni(dmstfdt)_2]:A Planar Nickel Coordination Complex with an Extended-TTF Ligand Exhibiting Metallic Conduction,Metal-Insulator Transition,and Weak Ferromagnetism

摘要

The 1:1 tetrabutylammonium salt of a nickel complex with an extended-TTF ligand,("Bu4N)[Ni-(dmstfdt)2] (dmstfdt = dimethyldiselenadithiafulvalenedithiolate) (1) is a unique ambivalent molecular system exhibiting weakly metallic conduction above room temperature and a weak ferromagnetism at low temperature.Its X-ray structure consists of two independent [Ni(dmstfdt)2]- (A and B) and two ~nBU4N~+ in the unit cell.The pseudo-planar anions are arranged in a zigzag -ABA'B'- manner along the molecular side-by-side direction with a dihedral angle of the molecular planes of 42.6°.The tight-binding band structure calculation,based on transfer integrals estimated by the extended Hiickel approximation,presents both three-dimensional electron and hole Fermi surfaces,which is consistent with the observed weakly metallic conduction around room-temperature despite the 1:1 stoichiometry of the complex.At 147 K,1 shows a sharp insulating transition associated with the localization of one electron on each nickel complex below 160 K.The chi T values of 1 increase linearly from 0.129 to 0.383 emu K mol-1 with decreasing temperature (160-340 K),suggesting a gradual electron localization with lowering the temperature.In the range of temperature of 80-150 K,chi follows the Curie-Weiss law:chi = C/(T - theta);C = 0.383 emu K mol-1;and theta = - 4 K.Weak ferromagnetism sets in below 20 K.The coercive field is +-1.3 kOe at 2.0 K.