Co-ordination Chemistry of Dimethylgold(III). Synthesis, Spectroscopic, and Structural Studies of Complexes with Neutral Aromatic Nitrogen-donor Ligands

Dimethylgold(III) nitrate reacts with neutral ligands to form the complexes [AuMe2(tpm)]N03.2H20 (tpm = tri-2-pyridylmethane) and [AuMe2L]N03 [L = tri-2-pyridylmethanol (tpmo), di-2-pyridylmethane (dpm), alpha, alpha-di-2-pyridyltoluene (dpt), di-1-pyrazolylmethane (dpzm), and tri-1-pyrazolylmethane (tpzm)]. The crystal structures of complexes of tpzm, tpm, and dpt have been determined by single-crystal X-ray diffraction at 295 K and refined by least-squares methods to R = 0.033, 0.029, and 0.042 for 3043, 1616, and 2529 independent 'observed' reflections, respectively. In these structures the [AuMe2L]+ cations have essentially cis-square-planar co-ordination for gold(III), AuC2N2, with Au-C 2.023(7)-2.041(12) A and Au-N 2.127(8)-2.142(8) A. In complexes of the potential tridentate ligands one pyridyl group is not co-ordinated in the tpm complex, and one pyrazolyl group is involved in a weak axial Au...N interaction [3.139(7) A] in the tpzm complex. Comparison of the 1H n.m.r. spectra of complexes of the potentially tridentate ligands (tpzm, tpm, and tpmo) with model complexes of bidentate ligands (dpzm, dpm, and dpt) suggests that the co-ordination behaviour of the ligands in methanol resembles that found in the solid state.