A neutral bis(diethylthiotetrathiafulvalenyldiselenolato)nickel complex: a superior organic conductor to the corresponding dithiolato derivative

Abstract

The tetra-n-hexylammonium salt of the bis(diethylthiotetrathiafulvalenyldiselenolato)nickelate complex monoanion (1b) was obtained by the reaction of bis(tetra-n-hexylammonium) diethylthiotetrathiafulvalenyldiselenolate with nickel(II) acetylacetonate. X-Ray structure analysis of 1b showed that the molecular skeleton, except for the four ethyl groups, is almost planar, with the six sulfur and two selenium atoms on each ligand being essentially located in the same plane and with the geometry around the nickel atom being square-planar. From the SQUID and EPR measurements, the unpaired spin in 1b is located primarily on the nickel atom, which is best described as a Ni(III) (S = 1/2) metal center. Iodine oxidation of 1b gave the corresponding neutral complex 1a as microcrystals. A compressed pellet of 1a exhibited a room-temperature electrical conductivity of 2.8 S cm^–1, which is higher by ca. 60 times, than that for the corresponding dithiolato complex 2a (5.0 × 10^–2 S cm^–1) obtained by iodine oxidation of tetra-n-hexylammonium bis(diethylthiotetrathiafulvalenyldithiolato)nickelate 2b. The temperature dependence of the electrical conductivity was as expected for a semiconductor, but the activation energy was very low (0.014 eV).