Spectroscopic Evidence for Argentophilicity in Structurally Characterized Luminescent Binuclear Silver(I) Complexes

Abstract

A spectroscopic and structural investigation of binuclear silver(I) complexes supported by aliphatic phosphine ligands, namely [Ag(PCy3)(O2CCF3)]2 (1), [Ag2(μ-dcpm)2]X2 (X = CF3SO3, 2; PF6, 3; dcpm = bis(dicyclohexylphosphino)methane), and [Ag2(μ-dcpm)(μ-O2CCF3)2] (4), is described. X-ray structural analyses of 1−4 reveal Ag−Ag separations of 3.095(1), 2.948 (av), 2.923 (av), and 2.8892(9) Å, respectively. Due to the optical transparency of the phosphine ligands, the UV−vis absorption band at 261 nm in CH3CN for 2 and 3 is assigned to a 4dσ* → 5pσ transition originating from Ag(I)−Ag(I) interactions. The argentophilic nature of this band is verified by the resonance Raman spectrum of 2 with 273.9 nm excitation, where virtually all of the Raman intensity appears in the Ag−Ag stretch fundamental (80 cm-1) and overtone bands. Complexes 2 and 3 exhibit photoluminescence in the solid state at room temperature.