Synthesis, structures, and luminescence properties of interconvertible Au^I₂Zn^II and Au^I₃Zn ^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 Zn²⁺ in a 1:1 ratio gave the heterometallic Au^I₂Zn^II trinuclear complex [Au₂Zn(dppm)(d-pen)₂] ([3]), in which the Zn²⁺ ion is coordinated by [1]^2- in an N₂O₂S ₂ 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^I₃Zn ^II tetranuclear complex [Au₃Zn(dppm)₂(d-pen) ₂]⁺ ([4]⁺), in which the Zn²⁺ 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 [Au ₂(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 Zn²⁺ 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.