Coinage Metal Complexes Supported by the Tri- and Tetraphosphine Ligands

A series of tri- and tetranuclear phosphine complexes of d¹⁰ metal ions supported by the polydentate ligands, bis­(diphenylphosphinomethyl)­phenylphosphine (PPP) and tris­(diphenylphosphinomethyl)­phosphine (PPPP), were synthesized. All the compounds under study, [AuM₂(PPP)₂]³⁺ (M = Au (1), Cu (2), Ag (3)), [M₄(PPPP)₂]⁴⁺ (M = Ag (4), Au (5)), [AuAg₃(PPPP)₂]⁴⁺ (6), and [Au₂Cu₂(PPPP)₂(NCMe)₄]⁴⁺ (7), were characterized crystallographically. The trinuclear clusters 1–3 contain a linear metal core, while in the isostructural tetranuclear complexes 4–6 the metal framework has a plane star-shaped arrangement. Cluster 7 adopts a structural motif that involves a digold unit bridged by two arms of the PPPP phosphines and decorated two spatially separated Cu^I ions chelated by the remaining P donors. The NMR spectroscopic investigation in DMSO solution revealed the heterometallic clusters 2, 3, and 6 are stereochemically nonrigid and undergo reversible metal ions redistribution between several species, accompanied by their solvation–desolvation. The complexes 1–3 and 5–7 exhibit room temperature luminescence in the solid state (Φ_em = 6–64%) in the spectral region from 450 to 563 nm. The phosphorescence observed originates from the triplet excited states, determined by the metal cluster-centered d_σ* → p_σ transitions.