ORGANOMETALLIC COMPLEXES FOR NONLINEAR OPTICS - X - MOLECULAR QUADRATIC AND CUBIC HYPERPOLARIZABILITIES OF SYSTEMATICALLY VARIED (CYCLOPENTADIENYL) BIS(PHOSPHINE)RUTHENIUM SIGMA-ARYLACETYLIDES - X-RAY CRYSTAL-STRUCTURE OF RU((E)-4,4'-CCC6H4CH=CHC6H4NO2)(PPH3)(2)(ETA-C5H5)

The complexes Ru(4,4'-CC6H4C6H4NO2)PPh3)(2)(eta-C5H5) and Ru(4,4'-C dr op CC6H4C drop CC6H4NO2)(PPh3),(eta-C5H5) have been prepared and the l atter structurally characterized; they belong to a series of organomet allic donor-bridge-acceptor compounds containing (cyclopentadienyl)bis (phosphine)ruthenium(II) centres as donors, conjugated arylacetylide b ridges, and nitro acceptor groups. Electrochemical data for the series of complexes Ru(C drop CR)(PR'(3))(2)(eta-C5H5) (R=Ph, 4-C6H4NO2, R'= Ph, Me; R=4,4'-C6H4C6H4NO2, (E)-4,4'-C6H4CH=CHC6H4NO2, 4,4'-C6H4C drop CC6H4NO2, 4,4'-C6H4N=CHC6H4NO2, R'=Ph) are consistent with an Ru-II/I II couple whose oxidation potentials vary strongly with chain-lengthen ing from one-ring to two-ring acetylide ligand, but show little variat ion with changes at the bridging unit of the two-ring acetylide ligand . The molecular quadratic and cubic optical nonlinearities of the seri es of complexes have been determined by hyper-Rayleigh scattering (HRS ) and Z-scan techniques, respectively. Molecular first hyperpolarizabi lities by HRS at 1064 nm are dispersively enhanced; experimental and t wo-level corrected data suggest an increase in nonlinearity on chain-l engthening of the bridge, in proceeding from C6H4 to C6H4C6H4 and then C6H4C drop CC6H4 and C6H4CH=CHC6H4, a general trend that is reproduce d by semiempirical ZINDO computations. Cubic hyperpolarizabilities by Z-scan at 800 nm are negative for complexes with nitro acceptor groups , probably a result of two-photon dispersion, with absolute values (up to 850 X 10(-36) esu) large for small organometallic complexes; as wi th quadratic nonlinearities, cubic nonlinearities increase substantial ly on bridge lengthening, with little variation on phosphine substitut ion. (C) 1997 Elsevier Science S.A.