Crystal structure and physical properties of molecular metal (DI-DCNQI)2Cu (DI-DCNQI=2,5-Diiodo-N,N′-Dicyanoquinonediimine)

(DI-DCNQI)2Cu belongs to a new category in a series of exotic mixed-valence copper complexes (R1, R2-DCNQI)2Cu. This salt is metallic down to 4.2 K. Anisotropy of the resistivity is small (ϱ//c:ϱ⊥c = 1:3). In the DCNQI-Cu system, pressure induces the metal-insulator transition and the distortion of the coordination tetrahedron around Cu (∠ NCuN angle; α) is correlated to the stability of the metallic state. (DI-DCNQI)2Cu has the smallest α value (122.3•) 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 magnetic susceptibility and T2-dependence of the resistivity suggest an existence of the strong electron-electron interaction.