Equilibrium Studies in Solution Involving Nickel(II) Complexes of Flexidentate Schiff Base Ligands: Isolation and Structural Characterization of the Planar Red and Octahedral Green Species Involved in the Equilibrium

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)AuCI, tht is tetrahydrothiophene, and Ag(I). Compound 3 exhibits an intense blue luminescence ((lambda)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 ((lambda)max = 548 nm). Attempts to form [Au2(dpim)2]Cl2 yielded only (dpim)AuCI (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) A, while compound 3 has a Au(I)-Au(I) separation of 2.8174(10) A. 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) A. The linear Au(I) monomer, 2, has no intermolecular Au(I)-Au(I) interactions, with the closest separation greater than 6.8 A.