Synthesis, molecular structure, crystal packing, and dynamic behaviour in the solid state of [Fe2(η5-C5H5)2(µ-CO)(CO)2{µ-CR(CN)}](R = H or CN)

Abstract

The dinuclear complexes [Fe₂(η⁵-C₅H₅)₂(µ-CO)(CO)₂{µ-CH(CN)}]1 and [Fe₂(η⁵-C₅H₅)₂(µ-CO)(CO)₂{µ-C(CN)₂}]2 have been obtained from the sulfonium cation [Fe₂(η⁵-C₅H₅)₂(µ-CO)(CO)₂{µ-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 P2₁/m, a= 6.408(1), b= 13.58(1), c= 8.004(1)Å, β= 93.17(2)°, Z= 2, 2225 measured, 1392 unique observed reflections [I > 2.0σ(I)], R= 0.035, R′= 0.036; cis-2, orthorhombic, space group Pnma, a= 10.346(3), b= 12.313(4), c= 12.590(3)Å, Z= 4, 1645 measured, 1115 unique observed reflections [I > 2.0σ(I)], R= 0.027, R′= 0.029. The dynamic behaviour of the two complexes in the solid state has been investigated by variable-temperature ¹H spin–lattice relaxation time measurements and ¹³C 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.