ORGANOMETALLIC COMPLEXES FOR NONLINEAR OPTICS - 15 - MOLECULAR QUADRATIC HYPERPOLARIZABILITIES OF TRANS-BIS(BIS(DIPHENYLPHOSPHINO)METHANE)RUTHENIUM SIGMA-ARYL-ACETYLIDE AND SIGMA-PYRIDYL-ACETYLIDE - X-RAY CRYSTAL-STRUCTURE OF TRANS-[RU(2-C-CC5H3N-5-NO2)CL(DPPM)(2)]

The complexes trans-[Ru(2-C=CC5H3N-5-R)Cl(dppm)(2)] [R = H (6), NO2 (7 )] have been prepared and 7 has been structurally characterized; compa rison with the structural study of trans-[Ru(4-C=CC6H4NO2)Cl(dppm)(2)] (3) reveals a decrease in Ru-C(I) distance and increase in Ru-Cl(1) d istance, consistent with stronger sigma-bonding by the nitropyridylalk ynyl ligand in 7 compared to the nitrophenylalkynyl ligand in 3. Elect rochemical data for 3, 6, 7, precursor dichloro complexes [RuCl2(dppm) (2)] [cis (1a), trans (1b)], and related alkynyl complexes trans-[Ru(4 -C=CC6H4R)Cl(dppm)(2)] [R=H (2), 4-C6H4NO2 (4), (E)-4CH=CHC6H4NO2 (5)] have been determined by cyclic voltammetry. Introduction of nitro sub stituent in progressing from 2 to 3 or 6 to 7 leads to a substantial i ncrease in E degrees(Ru)(II/III), most of which is lost on chain-lengt hening the alkynyl ligand in progressing from 3 to 4 or 5. Replacement of phenyl by pyridyl in progressing from 2 to 6 or 3 to 7 results in a 0.1 V increase in E degrees(Ru)(II/III) The optical spectra of repre sentative complexes have been examined. Introduction of a nitro substi tuent onto the phenylalkynyl ligand, in progressing from 2 to 3, resul ts in a substantial (ca. 11 000 cm(-1)) red-shift in the intense MLCT band of the Ru-II-C=C-Ar-NO2 moiety. Complexes 3, 4 and 5 exhibit siza ble solvatochromic shifts, suggestive of significant optical nonlinear ities. Quadratic hyperpolarizabilities for 2-7 were determined by hype r-Rayleigh scattering (HRS) at 1064 nm; measurements are consistent wi th an increase in beta(HRS) upon incorporation of nitro substituent (p rogressing from 2 to 3 or 6 to 7), chain-lengthening the alkynyl ligan d (progressing from 3 to 4 and then to 5) and replacing phenyl by pyri dyl in progressing from 2 to 6, general trends that are maintained wit h the two-level-corrected data, and which parallel shifts in lambda(ma x) to low energy. The observed and two-level-corrected beta(HRS) value s for 7 are lower than expected; it is perhaps significant that lambda (max) for 7 is close to the second-harmonic. (C) 1998 Elsevier Science S.A. All rights reserved.