Syntheses and quadratic hyperpolarizabilities of some (pyridylalkynyl)metal complexes: crystal structures of [Ni{2-(C=C)C5H3NNO2-5}(PPh3)(eta-C5H5)], [Au{2-(C=C)C5H3NNOz-5}(PPh3)] and [Au{2-(C=C)C5H4N}(PPh3)]

The complexes [Ru{2-(C drop C)C5H3NR-5}(PPh3)(2)(eta-C5H5)] (R = NO2 1 or H 2), [Ni{2-(C drop C)C5H3NR-5}(PPh3)(eta-C5H5)](R = NO2 3 or H 4) and [Au{2-C drop C5H3NR-5}L](L = PPh3, R = NO2 5 or H 6; L = PMe3, R = NO2 7) have been synthesized and 3, 5 and 6 structurally characterized; no significant increase in quinoidar vinylidene contribution to the acetylide ground-state structure is apparent on progression from structurally characterized phenylacetylide complexes to the new pyridylacetylide complexes, or upon replacement of 5-H by 5-NO2 in progressing from 6 to 5. The molecular quadratic optical non-linearities of 1-7 have been determined by hyper-Rayleigh scattering (HRS). The HRS measurements at 1064 nm are consistent with an increase in beta upon replacement of phenyl by an N-heterocyclic ring (replacing a nitrophenylacetylide by a nitropyridylacetylide ligand) for the ruthenium and gold systems, but with no change for the nickel complexes, and with an increase in nonlinearity upon replacement of PMe3 by PPh, in progressing from 7 to 5. The bulk second-order susceptibilities of the series have been determined by Kurtz powder measurements at 1064 nm, with the only significant response (about eight times that of urea) being that of 3; this complex was the only one of the three structurally characterized to pack non-centrosymmetrically in the crystal lattice. Electrochemical data for 1-4 have been obtained; comparison to analogous nitrophenylacetrylide complexes reveals that replacing nitrophenylacetylide by nitropyridylacetylide leads to a significant increase in M-II/III oxidation potential for the ruthenium complexes, but to no change for the nickel examples. The parameter E degrees(MII/III) - E degrees(NO2/NO2-) was evaluated for 1-4, results for M = Ru vs. Ni being consistent with experimentally determined non-linearities, i.e. smaller Delta E degrees and larger nonlinearities for ruthenium vs. nickel.