Syntheses and quadratic hyperpolarizabilities of some (pyridylalkynyl)metal complexes

Abstract

The complexes [Ru{2-(C≡C)C5H3NR-5}(PPh3) 2(η-C5H5)] (R = NO2 1 or H 2), [Ni{2-(C≡C)C5H3NR-5}(PPh3)-(η-C 5H5)] (R = NO23 or H 4) and [Au{2-(C≡C)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 quinoidal 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 β 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 non-linearity upon replacement of PMe3 by PPh3 in progressing from 7 to 5. The bulk second-order susceptibilities of the series have been determined by Kurtz powder measurements at 1054 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 nitrophenylacetlylide complexes reveals that replacing nitrophenylacetylide by nitropyridylacetylide leads to a significant increase in MII/III oxidation potential for the ruthenium complexes, but to no change for the nickel examples. The parameter EoMII/II -EoNO2/NO2 - was evaluated for 1-4, results for M = Ru vs. Ni being consistent with experimentally determined non-linearities, i.e. smaller ΔEo and larger non-linearities for ruthenium vs. nickel. Show more