Luminescent Gold(I) and Silver(I) Complexes of 2-(Diphenylphosphino)-1-methylimidazole (dpim):  Characterization of a Three-Coordinate Au(I)−Ag(I) Dimer with a Short Metal−Metal Separation

The Au(I) and Ag(I) closed-shell metal dimers of 2-(diphenylphosphino)-1-methylimidazole, dpim, were investigated. dpim formed the discreet binuclear species [Ag₂(dpim)₂(CH₃CN)₂]²⁺ (1) when reacted with appropriate Ag(I) salts. Likewise, [Au₂(dpim)₂]²⁺ (3) and [AuAg(dpim)₃]²⁺ (4) were produced via reactions with (tht)AuCl, tht is tetrahydrothiophene, and Ag(I). Compound 3 exhibits an intense blue luminescence (λ_max = 483 nm) in the solid state. However, upon initial formation of 3, a small impurity of Cl^- was present giving rise to an orange emission (λ_max = 548 nm). Attempts to form [Au₂(dpim)₂]Cl₂ yielded only (dpim)AuCl (2), which is not visibly emissive. The rare three-coordinate heterobimetallic complex [AuAg(dpim)₃]²⁺ (4) exhibits intense luminescence in the solid-state resembling that of 3. The crystal structures of 1−4 were determined, revealing strong intramolecular aurophilic and argentophilic interactions in the dimeric compounds. Compound 1 has an Ag(I)−Ag(I) separation of 2.9932(9) Å, while compound 3 has a Au(I)−Au(I) separation of 2.8174(10) Å. Compound 4 represents the first example of a three-coordinate Au(I)−Ag(I) dimer and has a metal−metal separation of 2.8635(15) Å. The linear Au(I) monomer, 2, has no intermolecular Au(I)−Au(I) interactions, with the closest separation greater than 6.8 Å.