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

Abstract

Outer-shell s 0 /p 0 orbital mixing with d 10 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 Au 4 Cu 2 {[Au 4 (μ-C 2 ,N 3 -EtIm) 4 Cu 2 (μ-3,5-(CF 3 ) 2 Pz) 2 ], (4a)}, Au 2 Cu {[Au 2 (μ-C 2 ,N 3 -BzIm) 2 Cu(μ-3,5-(CF 3 ) 2 Pz)], (1) and [Au 2 (μ-C 2 , N 3 -MeIm) 2 Cu(μ-3,5-(CF 3 ) 2 Pz)], (3a)}, AuCu 2 {[Au(μ-C 2 ,N 3 -MeIm)Cu 2 (μ-3,5-(CF 3 ) 2 Pz) 2 ], (3b) and [Au(μ-C 2 ,N 3 -EtIm)Cu 2 (μ-3,5-(CF 3 ) 2 Pz) 2 ], (4b)} and stacked Au 3 /Cu 3 {[Au(μ-C 2 ,N 3 -BzIm)] 3 [Cu(μ-3,5-(CF 3 ) 2 Pz)] 3 , (2)} form upon reacting Au 3 {[Au(μ-C 2 ,N 3 -(N-R)Im)] 3 ((N-R)Im = imidazolate; R = benzyl/methyl/ethyl = BzIm/MeIm/EtIm)} with Cu 3 {[Cu(μ-3,5-(CF 3 ) 2 Pz)] 3 (3,5-(CF 3 ) 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 d 10 -d 10 polar-covalent bond with ligandunassisted Cu(I)-Au(I) distances of 2.8750(8) Å each-the shortest such an intermolecular distance ever reported between any two d 10 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 Au 3 and Cu 3 precursors), which bodes well for potential future utilization in inorganic and/or organic LED applications. Here, we show that outer 4s/p (Cu I ) and 6s/p (Au I ) orbitals can admix with the respective valence 3d and 5d orbitals to sensitize a bona fide polar-covalent metal-metal bond between two d 10 centers manifest by two rather short, 2.8750(8) Å, Cu(I)-Au(I) bonds without any ligand-bite-size assistance. The reduced symmetry in this family of complexes is also shown to impart higher extinction coefficients and phosphorescence quantum yields than those attained by the parent homometallic precursor complexes.Heterometallic complexes are remarkable molecules owing to their unique catalytic and optoelectronic properties (2, 3). Heterometallic species involving coinage metals have received immense attention owing to their fascinating structural a...

The Origin of the Photoluminescence Enhancement of Gold‐Doped Silver Nanoclusters: The Importance of Relativistic Effects and Heteronuclear Gold–Silver Bonds

“…Therefore, the more polarized Au−Ag bonds the isomer has, the more intense its fluorescence is. This is consistent with the very recent experimental finding by Omary and co‐workers that heteronuclear and polarizable metal–metal bonds will significantly increase photoluminescence quantum yields . This finding may rationalize why pure Au and Ag nanoclusters, which lack heteronuclear metal–metal bonds, have low photoluminescence quantum yields …”

Decisive Influence of the Metal in Multifunctional Gold, Silver, and Copper Metallacycles: High Quantum Yield Phosphorescence, Color Switching, and Liquid Crystalline Behavior

“…(98.8%, 87.7%, and 94.2% M = Cu, Ag, Au, at 4 K respectively); 23 and a RT value has recently been reported for M = Cu (82.2%). 40 Thus, quantum yield values at RT for a family of cyclic trinuclear [MPz*] 3 complexes have not been fully described to date.…”

Investigation of Solvatomorphism and Its Photophysical Implications for Archetypal Trinuclear Au3(1-Methylimidazolate)3

“…Therefore, to further rationalize the potential M-M interactions of the selected CTC, we performed electronic structure calculations by density functional theory (DFT), using the M06 meta-hybrid functional by Truhlar [ 35 ] and the CEP-31G(d) basis set [ 36 ]. This approach has successfully been applied in the theoretical description of CTCs [ 37 , 38 ] and other systems with predominantly non-covalent interactions [ 39 ]. Specifically, Galassi and co-workers used M06/CEP-31G(d) DFT computations to examine d 10 -d 10 metal-metal bonding in the aforementioned CTC, [Au 2 (μ-C 2 ,N 3 -MeIm) 2 Cu(µ-3,5-(CF 3 ) 2 Pz)], which renders a direct comparison to related systems possible [ 37 , 40 ].…”