Synthesis, Characterisation of (Arene)tricarbonylchromium Complexes Linked to Cationic Fe and Ru Derivatives and Studies of First Hyperpolarisabilities by Hyper-Rayleigh Scattering

In order to investigate the non-linear optical properties, in particular second-order effects of binuclear organometallic complexes, a series of new cationic binuclear [MCp-(DPPE)N≡C-(spacer)-C≡C-C₆H ₅Cr(CO)₃]⁺[PF₆]^- compounds and mononuclear precursors [N≡C-(spacer)-C≡ C-C ₆H₅Cr(CO)₃] have been synthesised [where M = Fe^II or Ru^II; Cp = η⁵-C₅H ₅ and spacer = phenyl ring (C₆H₄), thiophene, (C₄H₂S), or bithiophene (C₄H₂S) ₂]. The Fe or Ru organometallic π-donor fragments were linked by an extended π system to the acceptor Cr(CO)₃ fragment. The effect of π back-donation involving the second Fe or Ru metal centre and the π* orbitals of the N≡C-coordinated group, was probed by the V_(N≡C) stretching bands on the IR spectra and also by NMR spectroscopic data. The planarity, largely due to the π-electron resonance, found on the solid state structure of the mononuclear complex [N≡C-C ₆H₅-C≡C-(η⁶-C₆H ₅)Cr(CO)₃] (1Cr) determined by X-ray diffraction [mono-clinic system, P2₁/c space group, with a = 10.326(2) Å, b = 13.209(5) Å, c = 11.799(2) Å and Z = 4] emphasises the electronic effect of this building block. The significant values of first hyperpolarisabihty β determined by hyper-Rayleigh scattering (HRS) indicate that the Fe containing compounds were more efficient on second-order non-linear optical properties than the ruthenium analogues and the parent mononuclear chromium compounds. (