Enhanced charge localization in the organic alloys [(TMTSF${)}_{1\mathrm{-}\mathit{x}}$(TMTTF${)}_{\mathit{x}}$${]}_2$${\mathrm{ReO}}_4$

Structural, electrical, and magnetic studies of [(TMTSF${)}_{1\mathrm{-}\mathit{x}}$(TMTTF${)}_{\mathit{x}}$ ${]}_2$ ${\mathrm{ReO}}_4$ alloys are reported. They exhibit around x∼0.5 an enhanced charge localization and a strong decrease of the (1/2,1/2,1/2) anion-ordering (AO) transition temperature. The localization enhancement is attributed to a 4${\mathit{k}}_{\mathit{F}}$ order of charge on the sites due to the alternate order of TMTSF and TMTTF molecules. This heteropolar charge distribution is suggested to weaken the 2${\mathit{k}}_{\mathit{F}}$ bond response and thus to depress the AO transition. These properties contrast with those exhibited by the hybrid salt (TMDTDSF${)}_2$ ${\mathrm{ReO}}_4$.