Coinage metal(i) clusters supported by a 1,10-phenanthroline-phosphine: orange-to-NIR phosphorescence, metallophilic interactions and enhanced cytotoxicity†

A series of small coinage metal(I) clusters has been selectively synthesized using 2-(diphenylphosphino)-1,10-phenanthroline (L), a new promising dimetal-binding P,N,N′-ligand (L). Its reaction with CuI yields the complex [Cu₂L₂(μ₂-I)]₂[Cu₂I₄], while the treatment of L with Au(tht)Cl/Ag⁺ or Au(tht)Cl/Cu⁺ systems leads to the assembly of [Au₂AgL₂Cl₂]⁺, [Au₂CuL₂Cl₂]⁺, [CuAuL₂]²⁺ and [AgAuL₂]²⁺ clusters. Theoretical analysis revealed pronounced intermetallic close shell interactions in these di- and trinuclear ensembles. At 298 K, the title compounds exhibit an orange and near-infrared (NIR) phosphorescence with lifetimes of 0.344–38 μs and quantum efficiencies of 1–21%. Theoretical considerations suggest a ³(M+L)LCT type for the observed phosphorescence. In addition, the above clusters exhibit a strong dose-dependent cytotoxic effect on A549, HepG2, Hep2 and MRC5 human cells with IC₅₀ values ranging from 1.26 to 11.1 μM.