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−C6H5Cr(CO)3]+[PF6]− compounds and mononuclear precursors [N≡C−(spacer)−C≡ C−C6H5Cr(CO)3] have been synthesised [where M = FeII or RuII; Cp = η5‐C5H5 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 ν(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−C6H5−C≡C−(η6‐C6H5)Cr(CO)3] (1Cr) determined by X‐ray diffraction [monoclinic 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 hyperpolarisability 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. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)