Gold(III) complexes with nitriles containing aromatic nuclei: crystal and molecular structure of trichloro(p-toluonitrile)gold(III)

Abstract

Anhydrous gold(III) chloride reacts with nitriles to give complexes of the type [AuCl₃(NCR)](R = C₆H₄CH₃-p, CH₂C₆H₅, or C₆H₅), in spite of the ability of gold(III) chloride to metallate unsubstituted or methyl-substituted aromatic rings. An X-ray diffraction study of the p-toluonitrile derivative at 190 K confirmed that the product is a gold(III) end-on nitrile complex with gold in its usual square co-ordination. The product crystallizes in the monoclinic space group P2₁/n, with a= 6.669(2), b= 12.574(3), c= 13.740(3)Å, β= 90.30(2)°, and Z= 4. Refinement converged to R= 0.021 for 1 246 independent ‘observed’ reflections. The Au–Cl bond lengths are 2.236(2) and 2.284(2), 2.271(2)Å for the chlorine atom trans to the nitrile and for the cis chlorines, respectively; Au–N 1.980(6)Å. Complexes of formula AuCl₂(NCR)(R = C₆H₄CH₃-p or CH₂C₆H₅), obtained with a large excess of the nitrile and over long reaction times, are suggested to be, on the basis of spectroscopic data, ionic mixed-valence species of the type [AuCl₂(NCR)₂][AuCl₂].