Comparative study of BEDT TTF and Ni(dddt)(2) electroconducting salts withthe HXO4 (X = Se, S) anions

Isostructural bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) and Ni(dddt) (2) radical cation salts with the HSeO4 anion as well as mixed salts {(BEDT -TTF)(1-x)[Ni(dddt)(2)](x)}(3)(HSO4)(2) have been synthesized. Their conduc tivities as well as the crystal and electronic structure of the (BEDT-TTF)( 3)(HSeO4)(2) salt have been studied and compared with those of the already known salts with the HSO4 anion. Replacement of the HSO4 anion by the large r HSeO4 lead to different effects on the conducting properties of the isost ructural BEDT-TTF and Ni(dddt)(2) salts: the metal-insulator transition tem perature is raised in the case of the BEDT-TTF salt (180 versus 130 K) but it is left unaltered in the case of the Ni(dddt)(2) one (30 K). Possible re asons for such behavior are discussed. (C) 2001 Elsevier Science B.V. All r ights reserved.