Crystal structure of hydrogenbis(pyridine N-oxide) tetrachloroaurate-(III), revealing a short hydrogen bond

Abstract

An X-ray diffraction study of the title compound [H(pyo)₂][AuCl₄](pyo = pyridine N-oxide) was done to investigate the dimeric cation [H(pyo)₂]⁺ with a short hydrogen bond. The compound crystallizes in the triclinic space group P and has lattice parameters a= 7.276(6), b= 8.631(3). c= 6.799(8)Å, α= 105.4(3), β= 96.4(3), and γ= 67.9(2)°. The structure was solved both by the direct method and by the heavy-atom method using a CAD-4 SDP system. The final value for R(F₀) was 0.044 for 1 343 unique reflections. The structure consists of discrete [AuCl₄]^– anions and [H(pyo)₂]⁺ cations with the gold and the bridging hydrogen atoms located at centres of symmetry. The hydrogen bond is symmetric as a result of crystallographic requirements. Two pyridine N-oxide molecules are hydrogen-bonded to form the planar dimeric cation,[H(pyo)₂]⁺. The [AuCl₄]^– anion has no bonded interaction with any adjacent anion or cation, indicating four-co-ordinated planar gold. The 0 ⋯ 0 distance [2.41(1)Å] is within the usual range observed for short hydrogen bonds. The structure of this compound, its spectral data, and its comparison with the structures of known compounds having similar dimeric cations are of significance because of the importance of gold complexes in chrysotherapy (gold treatment).