SYNTHESIS, MOLECULAR-STRUCTURE, CRYSTAL PACKING, AND DYNAMIC BEHAVIOR IN THE SOLID-STATE OF [FE-2(ETA-5-C5H5)2-(MU-CO)(CO)2(MU-CR(CN))] (R=H OR CN)

The dinuclear complexes [Fe2(eta5-C5H5)2(mu-CO)(CO)2{mu-CH(CN)}] 1 and [Fe2(eta5-C5H5)2(mu-CO)(CO)2{mu-C(CN)2}] 2 have been obtained from the sulfonium cation [Fe2(eta5-C5H5)2(mu-CO)(CO)2{mu-C(SMe2)(CN)}]+ via SMe2 displacement with H- and CN- respectively. Complex 1 is present in solution and in the solid state as a mixture of isomers, the relative composition depending on the solvent. The structures of the cis isomers of 1 (cis-1a) and 2 (cis-2) have been determined by single-crystal X-ray diffraction: cis-1a, monoclinic, space group P2(1)/m, a = 6.408(1), b = 13.58(1), c = 8.004(1) angstrom, beta = 93.1 7(2)-degrees, Z = 2, 2225 measured, 1392 unique observed reflections [l > 2.0sigma(l)], R = 0.035, R' = 0.036; cis-2, orthorhombic, space group Pnma, a = 10.346(3), b = 12.313(4), c = 12.590(3) angstrom, Z = 4, 1645 measured, 1115 unique observed reflections [l > 2.0sigma(l)], R = 0.027, R' = 0.029. The dynamic behaviour of the two complexes in the solid state has been investigated by variable-temperature H-1 spin-lattice relaxation time measurements and C-13 magic angle spinning NMR spectroscopy. The activation energies for the reorientational processes have been estimated. The separate intra- and intermolecular contributions to the total reorientational barriers have been evaluated by means of potential-energy barrier calculations within the pairwise atom-atom approach.