Organometallic complexes for nonlinear optics. 14. Syntheses and second-order nonlinear optical properties of ruthenium, nickel and gold σ-acetylides of 1,3,5-triethynylbenzene: X-ray crystal structures of 1-(HC ≡ C)-3,5-C₆H₃(trans-C ≡ CRuCl(dppm)₂)₂ and 1,3,5-C₆H₃(C ≡ CAu(PPh₃))₃

The complexes 1-(HC ≡ C)-3,5-C₆H₃[M]₂ ([M] = trans-C ≡ CRuCl(dppm)₂ (1), C ≡ CNi(PPh₃)(η⁵-C₅H₅) (2)) and 1,3,5-C₆H₃(C ≡ CAu(PPh₃))₃ (3) have been prepared by extensions of well-established σ-acetylide synthetic methodologies, and 1 and 3 have been structurally characterized. Steric restrictions preclude coordination of three trans-RuCl(dppm)₂ or Ni(PPh₃)(η⁵-C₅H₅) moieties about the central 1,3,5-triethynylbenzene unit, a problem which the smaller Au(PPh₃) group does not experience. The quadratic optical nonlinearities at 1.06 μm have been investigated by hyper-Rayleigh scattering with the C_2h symmetry complexes 1 and 2 having significantly larger β_HRS than their monometallic [M]C ≡ CPh ([M] = trans-RuCl(dppm)₂ (4) and Ni(PPh₃)(η5-C₅H₅) (5)) counterparts. The D_3h symmetry octopolar complex 3 has a similar nonlinearity to its dipolar monometallic analogue Au(C ≡ CPh)(PPh₃) (6). Complexes 1, 2 and 3 have λ_max similar to 4, 5 and 6 (i.e., no loss of optical transparency is observed), but have significantly larger oscillator strengths for the important optical transitions.