Cupriphication of gold to sensitize d 10 -d 10 metal-metal bonds and near-unity phosphorescence quantum yields.

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 Au4 Cu2 {[Au4 (μ-C2 ,N3 -EtIm)4 Cu2 (µ-3,5-(CF3 )2 Pz)2 ], (4a)}, Au2 Cu {[Au2 (μ-C2 ,N3 -BzIm)2 Cu(µ-3,5-(CF3 )2 Pz)], (1) and [Au2 (μ-C2 ,N3 -MeIm)2 Cu(µ-3,5-(CF3 )2 Pz)], (3a)}, AuCu2 {[Au(μ-C2 ,N3 -MeIm)Cu2 (µ-3,5-(CF3 )2 Pz)2 ], (3b) and [Au(μ-C2 ,N3 -EtIm)Cu2 (µ-3,5-(CF3 )2 Pz)2 ], (4b)} and stacked Au3 /Cu3 {[Au(μ-C2 ,N3 -BzIm)]3 [Cu(µ-3,5-(CF3 )2 Pz)]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 )2 Pz)]3 (3,5-(CF3 )2 Pz = 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 (ΦPL = 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.