Organometallic complexes for nonlinear optics Part 32: Synthesis, optical spectroscopy and theoretical studies of some osmium alkynyl complexes

The complexes trans-[Os(CdropCPh)Cl(dppe)(2)] (1), trans-[Os(4-CdropCC(6)H(4)C-CPh)Cl(dppe)(2)] (2), and 1,3,5-{trans-[OsCl(dppe)(2)(4-CdropCC(6)H(4)CdropC)]}(3)C6H3 (3) have been prepared. Cyclic voltammetric studies reveal a quasi-reversible oxidation process for each complex at 0.36-0.39 V (with respect to the ferrocene/ferrocenium couple at 0.56 V), assigned to the Os-II/III couple. In situ oxidation of 1-3 using an optically transparent thin-layer electrochemical (OTTLE) cell affords the UV-Vis-NIR spectra of the corresponding cationic complexes 1(+) -3(+); a low-energy band is observed in the near-IR region (11000 - 14000 cm(-1)) in each case, in contrast to the neutral complexes 1-3 which are optically transparent below 20000 cm(-1). Density functional theory calculations on the model compounds trans -[Os(CdropCPh)Cl(PH3)(4)] and trans-[Os(4-CdropCC(6)H(4)CdropCPh)Cl(PH3)(4)] have been used to rationalize the observed optical spectra and suggest that the low-energy bands in the spectra of the cationic complexes can be assigned to transitions involving orbitals delocalized over the metal, chloro and alkynyl ligands. These intense bands have potential utility in switching nonlinear optical response, of interest in optical technology. (C) 2003 Published by Elsevier Science B.V.