Structural and spectroscopic studies of model metal-imidazole and metal-thioether complexes

In part I, the crystal structures and spectroscopy of novel pseudotetrahedral ML{dollar}sb2{dollar} complexes of the ligand L = 2,2{dollar}spprime{dollar}-bis(2-imidazolyl)biphenyl with Cu(II), Ni(II), Co(II), and Cu(I) are described. An unparalleled degree of geometric control for the tetrakis(imidazole) ligand sets has effectively suppressed the LF driven distortion of Cu(II)N{dollar}sb4{dollar} and Ni(II)N{dollar}sb4{dollar} complexes towards planarity. Intraligand N{dollar}sb2{dollar}M/N{dollar}spprimesb2{dollar}M dihedral angles range from 86.4(2){dollar}spcirc{dollar} to 89.3(2){dollar}spcirc{dollar} for these four complexes. Owing to geometrical constraints within the 9-membered chelate rings, the intraligand N{dollar}sb2{dollar}M angles exceed 109{dollar}spcirc{dollar} and result in D{dollar}sb{lcub}rm 2d{rcub}{dollar} flattening of the MN{dollar}sb4{dollar} units in the order: Cu(II) {dollar}>{dollar} Ni(II) {dollar}>{dollar} Co(II) {dollar}sim{dollar} Cu(I). Electronic absorption spectra are discussed. These chromophores are relevant models for blue copper proteins or native and derivatized superoxide dismutases with Cu(I, II), Ni(II), or Co(II) in the pseudotetrahedral binding sites.; In part II, 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 pentammine Ru(III)L complexes (L = tetrahydrothiophene, methylethylthioether and dimethylthioether) and pentammine Ru(II) dimethylthioether are presented. The (NH{dollar}sb3{dollar}){dollar}sb5{dollar}Ru(II,III)L cations exhibit distorted octahedral coordination geometries; Ru(III)-N and Ru(III)-S bond distances span the ranges 2.097(2)-2.126(2) and 2.3666(7)-2.384(2)A, respectively. Combined steric and electronic effects serve to tilt the SC{dollar}sb2{dollar} planes away from the cis ammine groups. Crystals of the dimethylthioether derivative are twinned. Ab initio molecular orbital calculations were performed on the (NH{dollar}sb3{dollar}){dollar}sb5{dollar}Ru(III)dimethylthioether complex. 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. Excited-state calculations on the (NH{dollar}sb3{dollar}){dollar}sb5{dollar}Ru(III)tetrahydrothiophene chromophore allow the four observed electronic absorptions in the 20000-50000 cm{dollar}sp{lcub}-1{rcub}{dollar} region to be assigned. Two of these are S {dollar}to{dollar} Ru(III) charge-transfer absorptions to the half-filled Ru d{dollar}sb{lcub}rm xy{rcub}{dollar} orbital. A third is to the empty d{dollar}sb{lcub}rm xsp2-ysp2{rcub}{dollar} orbital which is lowered in energy owing to the surprisingly weak thioether ligand-field associated with the peculiar mode of thioether bonding. The spectrum of (NH{dollar}sb3{dollar}){dollar}sb5{dollar}Ru(II)S(CH{dollar}sb3{dollar}){dollar}sb2sp{lcub}2+{rcub}{dollar} is discussed.