Organometallic complexes for nonlinear optics.: Part 27. Syntheses and optical properties of some iron, ruthenium and osmium alkynyl complexes

The syntheses of the alkynyl complexes M(4-CCC6H4NO2)(dppe)(η-C5H5) [M=Fe (1), Ru (2), Os (3)], Os(4-CCC6H4NO2)(PPh3)2(η-C5H5) (4) and Ru(4-CCC6H4NO2)(CO)2(η-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-CCC6H4NO2)(PH3)2(η-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 phenyl–phenyl* in nature. Molecular quadratic optical nonlinearities have been measured using the hyper-Rayleigh scattering procedure at 1064 nm. β values vary as Fe≤Ru≤Os for metal variation and CO