Studies on gold(II) complexes with hard and soft donor ligands. 3. Complexes with N-(2-pyridylmethyl)-2-mercaptoaniline

Article abstract of DOI:10.1021/ic00036a009

The synthesis and characterization of gold(II) complexes with N-(2-pyridylmethyl)-2-mercaptoaniline (Hpma) are reported. Both mononuclear and dinuclear complexes are isolated by using different synthetic procedures. The solution EPR spectra of the mononuclear complexes Au(pma)X (X = Cl, Br) (1a,b) are identical and consist of four hyperfine lines of equal intensity due to the interaction of the unpaired electron with one ¹⁹⁷Au nucleus (I = 3/2). The solution EPR spectra of the dinuclear complexes Au₂(pma)X₄ (1c,d) exhibiting unsymmetrical seven-line pattern with varying intensities show that the unpaired electron is interacting with two inequivalent ¹⁹⁷Au nuclei. A spontaneous dissociation of these mixed-valent Au(II)/Au(III) compounds occurs in nitrobenzene solution, and ultimately a four-line EPR pattern is obtained. The Au(4f) ESCA spectrum of 1c clearly shows the presence of the Au(II) and Au(III) centers. Another dimeric compound [Au(pma)Cl]₂ (1e) exhibits only a broad EPR signal in solution. Though the stoichiometries of compounds 1a and 1e are found to be identical, their structural differences are clearly reflected in their solution EPR spectra and cyclic voltammetric results. The electronic spectra of compounds 1a-e exhibit low-energy ligand field transitions in the red and near-infrared (near-IR) regions followed by intense LMCT bands in the visible region. The very small hyperfine coupling originating from the gold in these complexes is strongly indicative of the low metal character of the highest occupied molecular orbital. The large delocalization of the unpaired electron largely accounts for the experimentally observed g values.