PNAS Plus: Cupriphication of gold to sensitize d10–d10 metal–metal bonds and near-unity phosphorescence quantum yields

摘要

Outer-shell s⁰/p⁰ orbital mixing with d¹⁰ orbitals and symmetry reduction upon cupriphication of cyclic trinuclear trigonal-planar gold(I) complexes are found to sensitize ground-state Cu(I)–Au(I) covalent bonds and near-unity phosphorescence quantum yields. Heterobimetallic Au4Cu2 {[Au4(μ-C²,N³-EtIm)4Cu2(µ-3,5-(CF3)2Pz)2], (4a)}, Au2Cu {[Au2(μ-C²,N³-BzIm)2Cu(µ-3,5-(CF3)2Pz)], (1) and [Au2(μ-C²,N³-MeIm)2Cu(µ-3,5-(CF3)₂Pz)], (3a)}, AuCu₂ {[Au(μ-C²,N³-MeIm)Cu₂(µ-3,5-(CF₃)₂Pz)₂], (3b) and [Au(μ-C²,N³-EtIm)Cu₂(µ-3,5-(CF₃)₂Pz)₂], (4b)} and stacked Au₃/Cu₃ {[Au(μ-C²,N³-BzIm)]₃[Cu(µ-3,5-(CF₃)₂Pz)]₃, (2)} form upon reacting Au₃ {[Au(μ-C²,N³-(N-R)Im)]₃ ((N-R)Im = imidazolate; R = benzyl/methyl/ethyl = BzIm/MeIm/EtIm)} with Cu₃ {[Cu(μ-3,5-(CF₃)₂Pz)]₃ (3,5-(CF₃)₂Pz = 3,5-bis(trifluoromethyl)pyrazolate)}. The crystal structures of 1 and 3a reveal stair-step infinite chains whereby adjacent dimer-of-trimer units are noncovalently packed via two Au(I)⋯Cu(I) metallophilic interactions, whereas 4a exhibits a hexanuclear cluster structure wherein two monomer-of-trimer units are linked by a genuine d¹⁰–d¹⁰ polar-covalent bond with ligand-unassisted Cu(I)–Au(I) distances of 2.8750(8) Å each—the shortest such an intermolecular distance ever reported between any two d¹⁰ centers so as to deem it a “metal–metal bond” vis-à-vis “metallophilic interaction.” Density-functional calculations estimate 35–43 kcal/mol binding energy, akin to typical M–M single-bond energies. Congruently, FTIR spectra of 4a show multiple far-IR bands within 65–200 cm⁻¹, assignable to v_Cu-Au as validated by both the Harvey–Gray method of crystallographic-distance-to-force-constant correlation and dispersive density functional theory computations. Notably, the heterobimetallic complexes herein exhibit photophysical properties that are favorable to those for their homometallic congeners, due to threefold-to-twofold symmetry reduction, resulting in cuprophilic sensitization in extinction coefficient and solid-state photoluminescence quantum yields approaching unity (Φ_PL = 0.90–0.97 vs. 0–0.83 for Au₃ and Cu₃ precursors), which bodes well for potential future utilization in inorganic and/or organic LED applications.