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−C 6 H 5 Cr(CO) 3 ] + [PF 6 ] − compounds and mononuclear precursors [N≡C−(spacer)−C≡ C−C 6 H 5 Cr(CO) 3 ] have been synthesised [where M = Fe II or Ru II ; Cp = η 5 ‐C 5 H 5 and spacer = phenyl ring (C 6 H 4 ), thiophene, (C 4 H 2 S), or bithiophene (C 4 H 2 S) 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−C 6 H 5 −C≡C−(η 6 ‐C 6 H 5 )Cr(CO) 3 ] ( 1Cr ) determined by X‐ray diffraction [monoclinic system, P 2 1 / 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)