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 (λmax = 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
(λmax = 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.