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)

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.