Crystal, molecular, and electronic structures of pentaammineruthenium(III)-thioether complexes

Abstract

The nature of Ru(III)-thioether bonding has been probed by a combination of structural, spectroscopic, and molecular orbital methods. The first structural studies of pentaammineruthenium(III)L complexes (L = tetrahydrothiophene, methyl ethyl thioether, and dimethyl thioether) are presented. Crystals of (NH3)5RuSC4H8·1.5S 2O6·3H2O are triclinic, space group P1, with a = 10.3622 (6) Å, b = 13.3864 (4) Å, c = 8.2345 (5) Å, α = 98.135 (4)°, β = 113.602 (5)°, γ = 98.773 (4)°, V = 1008.2 (2) Å3, Z = 2, RF (RwF) = 0.028 (0.044) for 3436 reflections. Crystals of (NH3)5RuSC3H8·1.5PF 6·1.5F are triclinic, space group P1, with a = 10.1911 (8) Å, b = 11.5361 (9) Å, c = 8.2431 (5) Å, α = 109.056 (5)°, β = 97.696 (6)°, γ = 73.237 (7)°, V = 876.2 (2) Å3, Z = 2, RF (RwF) = 0.029 (0.052) for 3366 reflections. Crystals of (NH3)5RuSC2H 6·2Cl·PF6 are orthorhombic, space group Imm2, with a = 7.780 (2) Å, b = 10.971 (1) Å, c = 8.936 (1) Å, V = 762.7 (3) Å3, Z = 2, RF (RwF) = 0.035 (0.047) for 818 reflections. The structures consist of (NH3)5RuIIIL cations separated by the various anions and, in one case, lattice water molecules. The cations exhibit distorted octahedral coordination geometries; Ru-N and Ru-S bond distances span the ranges 2.097 (2)-2.126 (2) and 2.3666 (7)-2.384 (2) Å, respectively. Combined steric and electronic effects serve to tilt the SC2 planes away from the cis ammine groups. Crystals of the dimethyl thioether derivative are twinned. Ab initio molecular orbital calculations were performed on the (NH3)5RuIII-dimethyl thioether complex with the use of effective core potentials for the inner atomic electrons and extended valence basis sets. Geometry optimization yields good agreement between calculated and experimental structures. The interactions between the high-lying thioether donor orbitals and the Ru(III) 4d orbitals are discussed in detail and the factors determining the unusual thioether coordination geometry are elucidated. Electronic population analysis of the dimethyl thioether complex indicates that the Ru atom carries a positive charge of 0.90e, reduced from the formal triple charge by donation of 0.43e from the thioether ligand and an average of 0.33e from each ammine group. Excited-state calculations with the INDO/S semiempirical MO method on the (NH3)5RuIII(tetrahydrothiophene) chromophore allow the four observed electronic absorptions in the 20 000-50 000-cm-1 region to be assigned. Two of these are S → Ru(III) charge-transfer absorptions to the half-filled Ru dxy orbital. A third is to the empty dx2-y2 orbital which is lowered in energy owing to the surprisingly weak thioether ligand field associated with the peculiar mode of thioether bonding. © 1989 American Chemical Society.