Abstract
Three new charge-transfer salts of tetrathiafulvalene (TTF)-based donors with thiocyanato- or selenocyanato-metal complex anions have been synthesised. The salts isolated were [BMDT-TTF][Cr(NCS)] (1), [TM-TTF][Cr(NCS)]·2CHCN (2) and [TM-TTF][Cr(NCSe)]·2CHCN (3) [BMDT-TTF = bis-(methylenedithio)tetrathiafulvalene and TM-TTF = tetramethyltetrathiafulvalene]. Single crystals of compound 1 crystallise in the monoclinic C2/c space group with a = 37.286(3), b= 10.0539(6), c= 21.069(2) Å, β = 124.348(4)°, V = 6520.9(9) Å and Z = 4. Compound 3 was also suitable for an X-ray diffraction study, however the anionic part, [Cr(NCSe)] was highly disordered and the best solution gave a final R factor of 16.4%. A solution was found for the monoclinic space groupo C2/m with a = 113.787(3), b= 19.507(3), c = 14.735(5) Å, β = 102.90(3)°, V = 3862.9(17) Å and Z = 2. For compound 1 there are several S ⋯ S close atomic contacts between the donors and acceptors, but there is no discernible magnetic exchange between ions. Such an interaction was previously observed in related salts such as [TTF][Cr(NCS)(phenanthroline)] and [donor] [M(NCS)(isoquinoline)] [M = Cr, Fe and donor = TTF, BEDT-TTF or TM-TTF (tetramethyltetrathiafulvalene)]. Compounds 1 to 3 are all paramagnetic semiconductors in which the magnetic susceptibility is dominated by the Cr-containing anions. The structure-function relationship, along with a comparison with related compounds, indicates that there is no long-range magnetic order because there are no π-stacking interactions between donor and acceptor; these types of interactions are seen in all of the bulk magnets of this type in which the donor spin is magnetically coupled to the anion. © Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.