CRYSTAL-STRUCTURE AND PHYSICAL-PROPERTIES OF MOLECULAR-METAL (DI-DCNQI)(2)CU (DI-DCNQI=2,5-DIIODO-N, N'-DICYANOQUINONEDIIMINE)

(DI-DCNQI)(2)Cu belongs to a new category in a series of exotic mixed- valence copper complexes (R(1),R(2)-DCNQI)(2)Cu. This salt is metallic down to 4.2 K. Anisotropy of the resistivity is small (rho(//c) : rho (perpendicular to c) =1:3). In the DCNQI-Cu system, pressure induces t he metal-insulator transition and the distortion of the coordination t etrahedron around Cu (angle N-Cu-N angle; alpha) is correlated to the stability of the metallic state. (DI-DCNQI)(2)Cu has the smallest a va lue (122.3 degrees) and the highest critical pressure (ca 15 kbar). It is remarkable that the pressure induced metal-insulator transition is suppressed above ca 20 kbar. Enhanced and temperature-dependent magne tic susceptibility and T-2-dependence of the resistivity suggest an ex istence of the strong electron-electron interaction.