Orbital Symmetry Control of Electronic Coupling in a Symmetrical, All-Carbon-Bridged “Mixed Valence” Compound: Synthesis, Spectroscopy, and Electronic Structure of [{Mo(dppe)(η-C7H7)}2(μ-C4)]n+ (n = 0, 1, or 2)

Metal coordination to a dimetallaoctatetrayne

The reactions of the ditungstaoctatetrayne [(Tp*)(CO)₂W([triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash])W(CO)₂(Tp*)] with several metal complexes have been investigated. Addition of [Co₂(CO)₈] occurs across the internal C[triple bond, length as m-dash]C bonds, whereas [AuCl(SMe₂)] initially delivers 'AuCl' across the W[triple bond, length as m-dash]C carbyne bonds before undergoing further reaction to oxidise the tungsten and replace the carbonyl ligands with chloride in [(Tp*)Cl₂W([triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash])WCl₂(Tp*)] with retention of the ditungstaoctatetrayne bridge. Reaction with [AuCl(PR₃)] (R = Ph, Cy) in the presence of AgPF₆ prevents this oxidation and adds [AuPR₃]⁺ across the W[triple bond, length as m-dash]C bonds to give dicationic derivatives. Finally, the reaction with [Pt(nbe)₃] (nbe = norbornene, bicyclo[2.2.1]hept-2-ene) and 1,5-cyclooctadiene (COD) adds a 'Pt(COD)' unit to one or both tungsten-carbon bonds, allowing both the mono- and diplatinum complexes to be isolated.

A Spectroscopic and Computationally Minimal Approach to the Analysis of Charge-Transfer Processes in Conformationally Fluxional Mixed-Valence and Heterobimetallic Complexes

Class II mixed-valence bimetallic complexes {[Cp'(PP)M]C≡C-C≡N[M'(PP)'Cp']}²⁺ (M, M'=Ru, Fe; PP=dppe, (PPh₃ )₂ ; Cp'=Cp*, Cp) exist as conformational ensembles in fluid solution, with a population of structures ranging from cis- to trans-like geometries. Each conformer gives rise to its own series of low-energy intervalence charge-transfer (IVCT) and local d-d transitions, which overlap in the NIR region, giving complex band envelopes in the NIR absorption spectrum, which prevent any meaningful attempt at analysis of the band shape. However, DFT and time-dependent (TD)DFT calculations with dispersion-corrected global-hybrid (BLYP35-D3) or local hybrid (lh-SsirPW92-D3) functionals on a small number of optimised structures chosen to sample the ground state potential energy hypersurfaces of each of these complexes has proven sufficient to explain the major features of the electronic spectra. Although modest in terms of computational expense, this approach provides a more accurate description of the underlying molecular electronic structure than would be possible through analysis of the IVCT band by using the static point-charge model of Marcus-Hush theory and derivatives, or TDDFT calculations from a single (global) minimum energy geometry.

Quantum-chemical insights into mixed-valence systems: within and beyond the Robin–Day scheme

The application of quantum-chemical methods to both organic and transition-metal mixed-valence systems is reviewed, with particular emphasis on how to describe correctly delocalisation vs. localisation near the borderline between Robin–Day classes II and III.