Ground states of DCNQI-metal complexes, (R(1),R(2)-DCNQI)(2)M; (R(1), R(2)=CH3,I,M=Ag,Cu,Li1-xCux)

The electrical resistance, magnetic susceptibility, H-1- and C-13-NMR measurements have been performed to investigate the ground states of the metal complexes of DCNQI, (R(1),R(2)-DCNQI)(2)M, where R(1)(R(2)) is CH3 (Me) or iodine (I) and M is Ag, Cu or Li1-xCux. A new member of DCNQI-M complexes, (DI-DCNQI)(2)Ag, is nonmetallic below room temperature and shows a Bonner-Fisher type of susceptibility, of which the value is nealy the same as that of (DI-DCNQI)(2)Cu at room temperature. An antiferromagnetic ordering was found at 5.5K in contrast to the spin-Peierls ground state in the isostructural (DMe-DCNQI)(2)Ag. The alloy systems, (DMe-DCNQI)(2)Li1-xCux, have been studied with an aim at control of the electronic state by the doping of Cu into the insulator, (DMe-DCNQI)(2)Li. For the Cu doping up to x=30%, the systems show the spin-Peierls transition while the system with x>50% are metallic down to low temperatures. The (T1T)(-1) of C-13-NMR shows systematic change with doping.