Chemical pressure effect by selective deuteriation in the molecular-based conductor, 2,5-dimethyl-N,N′-dicyano-p-benzoquinone immine-copper salt, (DMe-DCNQI) 2 Cu

The mixed-valence copper salt of DMe-DCNQI (1, where DMe-DCNQI = 2,5-dimethyl-N,N′-dicyano-p-benzoquinone diimine) is a molecular conductor whose electrical and magnetic properties are quite sensitive to pressure. We have performed selective deuteriation of the molecule 1. By control of the position and number of deuterium atoms, the low-pressure region (≲500 bar) in the pressure-temperature phase diagram of (1)2Cu was reproduced at ambient pressure. The equivalency of the deuteriation and pressure effects is explained from steric origins; ‘contraction’ aroused by the slightly shorter C–D bond (steric isotope effect) and ‘constriction’ by pressure.