Giant Metal-Insulator-Metal Transition Induced by Selective Deuteration of the Molecular Conductor, (DMe-DCNQI)2Cu (DMe-DCNQI = 2,5-dimethyl-N,N′-dicyanoquinonediimine)

The Cu salts of selectively deuterated DMe-DCNQI’s were prepared, and the electrical conductivities were examined. By deuteration of two hydrogens of the methyl groups, a drastic metal-insulator-metal transition was induced for the first time in a non-alloy system at ambient pressure. On the other hand, deuteration of two ring hydrogens or one methyl hydrogen did not affect the stability of a metallic state down to 4.2 K. These phenomena are discussed in terms of the “chemical pressure” effect.