Chemical Control of the Electronic States in the pπ-d System

Substituent effects in the pπ-d system (DCNQI)2Cu are described. Electrical and magnetic properties of (R1, R2-DCNQI)2Cu are quite sensitive to the substituents R1 and R2. Especially, when R1 = R2 = CH3, the system at low temperature changes from a metal to an insulator according to the isotope substitution. A variety of substituent effects would be generally understood in terms of the amount of charge transfer from Cu to DCNQI which is sensitive to the N-Cu-N coordination angle.