SYNTHESIS, STRUCTURES AND PHYSICAL-PROPERTIES OF BIS(ETHYLENEDITHIO)TETRATHIAFULVALENIUM SALTS OF PARAMAGNETIC METALLACARBORANE ANIONS

Single phases of the bis(ethylenedithio)tetrathiafulvalenium (et(.+)) salts [et](2)[Cr(1,2-C2B9H11)(2)] 1 and [et](2)[Fe{1-SC4H3-1,2-C2B9H10}(2)] 2 (SC4H3 = thiophen-2-yl) were synthesised via chemical and electrochemical routes, respectively. The crystal structures of both salts feature alternating. layers of et units and metallacarborane anions. The packing motif of 1 is very similar to that of the beta'-[et](2)X salts {X = [ICl2](-) or [BrICl](-)}, with the rod-shaped [Cr(C2B9H11)(2)](-) anions functioning as paramagnetic analogues of the trihalide anions and the et units being linked by short intermolecular S ... S interactions (3.4-3.6 Angstrom) to form one-dimensional 'tapes' extending in the (1 0 0) direction. The et units,in 2 are packed more evenly. resulting in a two-dimensional honeycomb network of short intermolecular S ... S interactions (3.4-3.6 Angstrom) within each et layer. The [Fe(C2B9H10C4H3S)(2)](-) anions in 2 pack to form unusual double-layers in which the thiophene groups are oriented towards each other and away from the et layers, indicating that inter-et S ... S interactions are favoured over et-thiophene S ... S interactions. Both compounds 1 and 2 are semiconductors with complex temperature-dependent conductivities between ca. 75 and 280 K. Their conductivities at room temperature are ca. 2 x 10(-3) S cm(-1) (1, compressed pellet) and 5 x 10(-1) S cm(-1) (2, single crystals). The absence of metallic behaviour in 1;and 2 may be attributed in part to the loose packing of the et molecules. due to the large,size of the anions, in these compounds. The magnetic susceptibilities of 1 and 2 were fitted by the Curie-Weiss law between 25 and 300 K to give Weiss constants of -1.1 and +1.6 K respectively.