Isotope Effect on Metal-Insulator Transition of (EDO-TTF)2XF6(X=P,As) with Multi-Instability of Metallic State

The partially deuterated 4,5-ethylenedioxy-tetrathiafulvalene-d2 (EDO-TTF-d2) was synthesized from the undeuterated EDO-TTF-d0. The single crystals of (EDO-TTF-d2)2XF6 (X = P, As) were prepared by the conventional electrocrystallization technique. The deuterium contents of EDO-TTF-d2 itself and the radical cation salts were 99% D by mass spectral analysis. The magnetic susceptibility measurement revealed that (EDO-TTF-d2)2XF6 undergoes a metal–insulator transition at 2–3 K higher temperature than the undeuterated salts. In infrared and Raman spectra, significant isotope shifts were observed not only on C–H vibrational modes but also on TTF-skeletal modes. The assignment of experimental bands was performed on the basis of normal-mode analysis at B3LYP/6-31G(d,p) level of theory