Steric effects and aurophilic interactions in crystals of Au2(μ-1,2-bis(diphenylphosphino)ethane)X2 and Au2(μ-1,2-bis(dicyclohexylphosphino)ethane)X2 (X = Cl, Br, I)

Crystals in the isostructural series Au2(μ-dppe)X2 (dppe is 1,2-bis(diphenylphosphino)ethane, X = Cl, Br, I) form centrosymmetric, dimeric structures with two short Au⋯Au contacts between the component molecules. We found no evidence for a second polymorph for any member of the Au2(μ-dppe)X2 series, although two polymorphs were observed previously for the related Au2(Ph2As(CH2)2AsPh2)X2 series. Crystals of Au2(μ-dcpe)X2 (where dcpe is 1,2-bis(dicyclohexylphosphino)ethane) show structures that differ appreciably from those of Au2(μ-dppe)X2. The bulky cyclohexyl substituents appear to be playing a major role in eliminating the formation of polymeric or dimeric structures. Au2(μ-dcpe)Cl2 has a monomeric structure without aurophilic interactions. In contrast, Au2(μ-dcpe)Br2 and Au2(μ-dcpe)I2 have similar structures with intramolecular aurophilic interactions. Au2(μ-dcpe)I2 displays a form of aggregation-induced emission. It displays a red-pink luminescence in crystalline form but is non-emissive in solution.

Aurophilic interactions in the crystal structures of the series Au2(μ-1,2-bis(diphenylphosphino)-ethane)X2 and Au2(μ-1,2-bis(dicyclohexylphosphino)ethane)X2 (X = Cl, Br, I) trade off with steric effects as a function of halogen atom and phenyl vs. cyclohexyl substituent. The shortest Au⋯Au distance of these is observed in Au2(μ-dcpe)I2.Figure optionsDownload as PowerPoint slide