Synthesis, structures, and luminescence properties of interconvertible Au(I)2Zn(II) and Au(I)3Zn(II) complexes with mixed bis(diphenylphosphino)methane and D-penicillaminate

The reaction of the digold(I) complex [Au2(dppm)(D-pen)2](2-) ([1](2-); dppm = bis(diphenylphosphino)methane and D-pen = D-penicillaminate) with Zn(2+) in a 1:1 ratio gave the heterometallic Au(I)2Zn(II) trinuclear complex [Au2Zn(dppm)(D-pen)2] ([3]), in which the Zn(2+) ion is coordinated by [1](2-) in an N2O2S2 octahedral geometry with the trans(O) configuration, forming an 8-membered Au2ZnS2P2C metalloring. A similar reaction using the newly prepared and crystallographically characterized trigold(I) complex [Au3(dppm)2(D-pen)2](-) ([2](-)) produced the Au(I)3Zn(II) tetranuclear complex [Au3Zn(dppm)2(D-pen)2](+) ([4](+)), in which the Zn(2+) ion is coordinated by [2](-) in a similar octahedral geometry to form a Au3ZnS2P4C2 12-membered metalloring. Complex [3] was converted to [4](+) by treatment with [Au2(dppm)2](2+) in a 2:1 ratio, whereas [4](+) reverted to [3] upon treatment with a mixture of [Au(d-pen)2](2-) and Zn(2+) in a 1:1 ratio, indicative of the facile insertion/removal of the [Au(dppm)](+) moiety with retention of the geometry of the trans(O)-[Zn(D-pen-N,O,S)2](2-) unit. An analogous interconversion that requires the insertion/removal of the [Au(dppm)](+) moiety was also recognized between [1](2-) and [2](-). NMR spectroscopy revealed that [4](+) is in equilibrium with [3] and [Au2(dppm)2](2+) in solution, the ratio of which is largely dependent on the solvent polarity. The luminescence properties of these complexes were also investigated, revealing the importance of the intramolecular aurophilic interaction, as well as the Zn(II) coordination, for enhancement of the emission quantum efficiencies.