Organometallic complexes for nonlinear optics. Part 27. Syntheses and optical properties of Some Iron, Ruthenium and Osmium Alkynyl Complexes

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Inorganica Chimica Acta, 2003, 352 (6), pp. 9 - 18
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The syntheses of the alkynyl complexes M(4-C6-point triple bond; length half of m-dashCC6H4NO2)(dppe)(?-C5H5) [M=Fe (1), Ru (2), Os (3)], Os(4-C6-point triple bond; length half of m-dashCC6H4NO2)(PPh3)2(?-C5H5) (4) and Ru(4-C6-point triple bond; length half of m-dashCC6H4NO2)(CO)2(?-C5H5) (5) are reported. Structural studies reveal a decrease in Ru---C(1) distance on proceeding from 5 to 2, consistent with greater back-donation of electron density to the alkynyl ligand from the more electron-rich metal center in 2. Electrochemical data show that the MII/III couple for the dicarbonyl complex 5 is at a significantly more positive potential than that of the related diphosphine complex 2, consistent with ligand variation modifying the electron richness and hence donor strength of the metal center. Time-dependent density functional calculations on model complexes M(4-C6-point triple bond; length half of m-dashCC6H4NO2)(PH3)2(?-C5H5) (M=Fe, Ru, Os) have been employed to assign the intense low-energy optical transition in these complexes as MLCT in character, the higher energy band being phenylphenyl* in nature. Molecular quadratic optical nonlinearities have been measured using the hyper-Rayleigh scattering procedure at 1064 nm. ? values vary as Fe?Ru?Os for metal variation and CO<phosphines for co-ligand variation, the latter consistent with the variation in donor strength of the metal center inferred from electrochemical and crystallographic data. The observed trend in ? on metal variation follows the trend in backbonding energies calculated by DFT.
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