TRIPLET EXCITON ACTIVATION IN MODERATELY COUPLED (0.21 EV), DISCRETE TETRAKIS(METHYLTHIO)-TTF(- A MANIFESTATION OF THE WEAKENING OF THE INTRADIMER INTERACTION UPON BINDING OF THE OUTER METHYLTHIO AND THIOCYANATE FUNCTIONALITIES IN [(MES)4TTF(+)]2[MO6CL8(NCS)6(2-)], COMPLETED BY THE SYNTHESIS AND STRUCTURE OF THE TETRABUTYLAMMONIUM SALT OF THE CLUSTER DIANION, (BU4N)2[MO6CL8(NCS)6]() DIMERS )

Reaction of MoCl2 with NaOH followed by the addition of Bu4N(NCS) and HBF4 in methanol affords (Bu4N)2[Mo6-Cl8(NCS)6] (1), whose crystal str ucture is reported: space group P2(1)/c, Z = 2, a = 10.443(6) angstrom , b = 19.568(3) angstrom, c = 15.654(2) angstrom, beta = 94.20(2)degre es, V = 3190(3) angstrom3. Single crystals of [(MeS)4TTF]2[Mo6Cl8(NCS) 6] (2) were grown by oxidation of tetrakis(methylthio)tetrathiafulvale ne, (MeS)4TTF, in the presence of the tetrabutylammonium salt 1, and t he structure of 2 was determined: space group P1BAR, Z = 1, a = 11.568 (1) angstrom, b = 13.931(1) angstrom, c = 11.299 (2) angstrom, alpha = 93.52(1)degrees, beta = 110.71(1)degrees, gamma = 64.03(1)degrees, V = 1521.7(4) angstrom3. The structure of 2 consists of discrete [(MeS)4 TTF.+]2 dimers with a slipped pattern of overlap of the planar molecul ar cation radicals. The binding of the dimers and the inorganic cluste r anion framework occurs via S...S and C-H...S contacts. The ESR spect rum observed at room temperature is characteristic of mobile triplet F renkel excitations whose features are thoroughly analyzed. The experim ental determination of the fine structure tensor principal values and axes affords the zero-field splitting (ZFS) parameters D = -315 G and E = 35 G and the tensor orientation, leading to the conclusion that th e unpaired electrons in the triplet state (observed and calculated mag netic gaps of 0.211 and 0.215 eV, respectively) remain adjacent within the cation radical dimer. A manifestation of this correlation is foun d in the close proximity between the fine structure tensor axes and di mer molecular symmetry axes, thereby allowing a unique correlation to be made between the molecular dimer spin density and configuration and the effect of organic-inorganic chalcogen binding in the solid state.