COORDINATION CHEMISTRY OF DIMETHYLGOLD(III) AND METHYLMERCURY(II) - SYNTHESIS, H-1-NMR AND STRUCTURAL STUDIES OF POLY(PYRAZOL-1-YL)BORATE COMPLEXES

Dimethylgold(III) and methylmercury(II) form complexes Me2AuL and MeHgL where L are poly-(pyrazol-1-yl)borate ligands [HB(pz)3]^- and [B(pz)4]^-. The structure of Me2Au(HB(pz)3) has been determined by single-crystal X-ray diffraction at 295 K and refined by least-squares methods to R 0.056 for 2194 independent ‘observed’ reflections. This complex has square-planar coordination for the gold atom involving two coordinated pyrazole rings and one uncoordinated ring, in contrast to the isoelectronic cation [Me2Au((pz)3CH)]⁺ which has square planar coordination with a weak axial Au^…N interaction. Variable temperature ¹H n.m.r. spectra in CD2Cl2 indicate presence of rapid equilibria between pyrazole ring environments at ambient temperature and, for the MeHg^II complexes, down to -90°C. For the Me2Au^III complexes spectra at -90°C indicate presence of pyrazole ring environments in ratios 2:1 (L = [HB(pz)3]^-) and 2:1:1 (L = [B(pz)4]^-). Crystal data for Me2Au(HB(pz)3): rhombohedral, space group R3c, a 17.98(1) Å, α 117.98(5)°, Z 18.