The δ Bond and Trigonal Paddlewheels Before the Dawn of the Quintuple Bond

Quantum spin coherence and electron spin distribution channels in vanadyl-containing lantern complexes

We herein investigate the heterobimetallic lantern complexes [PtVO(SOCR)4] as charge neutral electronic qubits based on vanadyl complexes (S = 1/2) with nuclear spin-free donor atoms. The derivatives with R = Me (1) and Ph (2) give highly resolved X-band EPR spectra in frozen CH2Cl2/toluene solution, which evidence the usual hyperfine coupling with the 51V nucleus (I = 7/2) and an additional superhyperfine interaction with the I = 1/2 nucleus of the 195Pt isotope (natural abundance ca. 34%). DFT calculations ascribe the spin density delocalization on the Pt2+ ion to a combination of π and δ pathways, with the former representing the predominant channel. Spin relaxation measurements in frozen CD2Cl2/toluene-d8 solution between 90 and 10 K yield Tm values (1-6 μs in 1 and 2-11 μs in 2) which compare favorably with those of known vanadyl-based qubits in similar matrices. Coherent spin manipulations indeed prove possible at 70 K, as shown by the observation of Rabi oscillations in nutation experiments. The results indicate that the heavy Group 10 metal ion is not detrimental to the coherence properties of the vanadyl moiety and that Pt-VO lanterns can be used as robust spin-coherent building blocks in materials science and quantum technologies.

A theoretical study of M-M' polar-covalent bonding in heterobimetallic multinuclear organometallic complexes of monovalent group 11 metal centres

Complexes with closed-shell (d¹⁰-d¹⁰) interactions have been studied for their interesting luminescence properties in organic light-emitting diode (OLED) devices. The present computational study aims at understanding the chemical bonding/interactions in a series of molecules with unusually short metal-metal bond distances between monovalent coinage-metal (d¹⁰-d¹⁰) centres. The investigated molecules include pentanuclear complexes with M or M' = Cu(I), Ag(I), or Au(I) and Mes = 2,4,6-Me₃C₆H₂. In such complexes, the M-M' distances are up to 50-100 pm shorter than typical metallophilic bonds in homometallic analogues. Characterization and analysis of the chemical bond strength was performed using ab initio methods, density functional theory methods including a semi-empirical treatment of dispersion interactions (DFT-D3) and semi-empirical calculations at the extended Hückel theory (EHT) level. Population analysis suggests that hybridization occurs by mixing the (n + 1)s and (n + 1)p orbitals of M with the (nd) orbitals of M'. The orbital mixing plays a pivotal role in the polydentated polar-covalency/dative M-M' bonds that distinguish this bonding from the weaker metallophilic interactions.

Cupriphication of gold to sensitize d10-d10 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 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.

Unprecedented W2(0) quadruply bonded complex supported by π-donor ligands

A quadruply bonded complex W2(DippF)2K2 with a W2(0) core was synthesized and structurally characterized. The observed W-W distance of 2.407(1) Å and DFT calculations are consistent to the unprecedented electronic structure in D(2h) symmetry of σ(2)π(2)π(2)δ(2)δ(2)δ*(2) where the HOMO is the δ* orbital.