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

Abstract

The complexes [Ru{2-(CC)C₅H₃NR-5}(PPh₃)₂(η-C₅H₅)] (R = NO₂ 1 or H 2), [Ni{2-(CC)C₅H₃NR-5}(PPh₃)(η-C₅H₅)] (R = NO₂ 3 or H 4) and [Au{2-(CC)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 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 nitrophenylacetlylide 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°_M^II/III – E°_NO2/NO2^– was evaluated for 1–4, results for M = Ru vs. Ni being consistent with experimentally determined non-linearities, i.e. smaller ΔE° and larger non-linearities for ruthenium vs. nickel.