Electronic properties of isostructural molecular conductors (Ni (dddt) /sub 2/)/sub 3/ (HSO/sub 4/) /sub 2/ and (ET)/sub 3/ (HSO/sub 4/)/sub 2/. thermopower and tight binding calculations.

Summary form only given. The thermopower vs temperature dependence of molecular conductors (Ni(dddt)2)3(HS04)2 and (ET)3(HS04)2 have been investigated. Their crystal structures differ only by substituting of central C=C fragment for Ni atom. While both compounds possess similar temperature dependences of resistivity (metal-insulator transition at 25 K and 125 K respectively) , S(T) dependences demonstrate a drastic difference. A peak at 25 K in (Ni(dddt)2)3(HS04)2 was shown to be manifestation of metal to semimetal phase transition, and the abrupt decrease at 125 K in (ET)3(HS04)2 is concerned with metal to insulator phase transition. Tight binding band structure and Fermi surface for both compounds have been calculated. Semimetal band structure was found in both cases. Difference of thermopower behaviour is qualitatively explained on basis of band structure calculations.