Short hydrogen bonds: Diadducts of substituted pyridine N-oxides: Synthesis, spectroscopic studies, and X-ray structure

Hydrogen-bonded diadducts of substituted pyridine N-oxides, stabilized by [AuCl₄]^-, have been prepared and studied by spectroscopic techniques. The presence of a broad absorption around 800 cm^-1 in the i.r. spectra, and the existence of bands characteristic of the ligands and [AuCl₄]^-, in the u.v. spectra, indicate a short O ⋯ H ⋯ O hydrogen bond. An X-ray diffraction study of one of the diadducts, [H(3Me-pyo)₂][AuCl₄](3Me-pyo = 3-methylpyridine N-oxide), revealed an O ⋯ O distance of 2.406(9) Å. The complex crystallizes in the triclinic space group P1̄, with a = 6.857(4), b = 8.011(1), c = 8.797(2) Å, α = 105.05(2), β = 66.89(3), γ = 89.39(2)°, and Z = 1. The structure was refined to R = 0.063 using 2 339 reflections collected on a CAD4 diffractometer. On the basis of Au ⋯ O contacts, an uncommon distorted octahedral environment for Au^III may be assumed in the solid state.