SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF METALLACARBORANE SANDWICH SALTS WITH TETRATHIAFULVALENE (TTF) [M(C2B9H11)2][TTF] (M=CR, FE, NI)

Tetrathiafulvalenium (ttf.+) salts of the metallacarborane anions commo-[3,3'-M(1,2-C2B9H11)2]- (1, M = Cr; 2, M = Fe; 3, M = Ni) were synthesized for a study of their magnetic properties. They are complementary to the magnetic charge-transfer salts based on decamethylmetallocenes previously studied by others. X-Ray crystallographic analysis revealed that the molecular packing in 1 consists of alternating layers of ttf.+ radical cations and [Cr(C2B9H11)2]- anions. In contrast, the crystal structures of 2 and 3, which are isomorphous, comprise three-dimensional herring-bone networks of the corresponding metallacarborane anions, with stacked dimers of ttf.+ cations occupying cavities in the network. The interplanar separation between the fully eclipsed ttf.+ radical cations in each dimer is 3.4 angstrom, indicating significant bonding interactions between the radical cations. There are otherwise no intermolecular distances shorter than van der Waals contacts in any of the salts 1-3. Variable-temperature magnetic susceptibility measurements were performed on the title compounds down to 6 K. The susceptibility data fit the Curie-Weiss law for systems containing non-interacting unpaired spins, with small values of theta (theta = -2.5 K for 1; theta = 2.0 K for 2 and theta = +1.5 K for 3).