Cations M₂(O₂C^tBu)₄⁺, Where M = Mo and W, and MoW(O₂C^tBu)₄⁺. Theoretical, Spectroscopic, and Structural Investigations

Abstract

With the aid of density function theory, the molecular and electronic structures of the molecules Mo2(O2CMe)4, MoW(O2CMe)4, and W2(O2CMe)4 and their single-electron oxidized radical cations have been determined; this includes calculated observables such as v(MM) and the delta --> delta* electronic transition energies. The calculated properties are compared with those for the corresponding pivalates, M2(O2CtBu)4 (M = Mo or W) and MoW(O2CtBu)4 and their radical cations prepared in situ by oxidation with Cp2FePF6. The EPR spectra of the radical cations are also reported. The EPR spectrum of the MoW(O2CtBu)4+ cation reveals that the unpaired electron is in a polarized MM delta orbital having 70% Mo and 30% W character. The MM stretching frequencies show good correlation with the MM bond lengths obtained from single-crystal X-ray diffraction studies of MoW(O2CtBu)4, W2(O2CtBu)4, and W2(O2CtBu)4+PF6- compounds, along with previously reported structures. These data provide benchmark parameters for valence trapped dicarboxylate bridged radical cations of the type [(tBuCO2)3M2]2(micro-O2C-X-CO2)+ (X = conjugated spacer).

Time-dependent density functional theory determination of the absorption spectra of naphthoquinones

“…Actually, the main problem with semi-empirical theories such as ZINDO/S is that, contrary to ab initio approaches, it is very difficult to know beforehand for which type of structure the predictions are likely to be meaningful or not [6]. Actually, the Time-Dependent Density Functional Theory (TD-DFT) originally proposed more than two decades ago by Runge and Gross [7], has become the most widely used tool for theoretically evaluating excited state energies [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. This success is due to its efficiency to quickly provide an accurate description of transition energies.…”

Mechanistic insight into proton-coupled mixed valency

“…This compares to PCET self-exchange rates observed in related metal complexes. 12 Previous studies have shown that electron transfer rates for PCET self-exchange reactions are often located between the EPR and electrochemical timescales, such as or AgPF6 in CD2Cl2 proved to be unsuccessful. The generated paramagnetic species gave rise to a spectrum that displayed excessive broadening, from which no characteristic resonances could be identified for the solvate.…”

Access to Stable Metalloradical Cations with Unsupported and Isomeric Metal–Metal Hemi‐Bonds

“…[4] An umber of supported dinuclear metalloradicals with two metal atoms held together to form ab ond by ab ridging ligand are known. [5] In contrast, stable but unsupported dinuclear metalloradicals are rare.Recently two unsupported dinuclear metalloradicals were isolated and studied by single crystal Xray diffraction, that is,[ M 2 Cp 2 (CO) 4 (PMe 3 ) 2 ]C + (M = Mo and W), where two metal atoms are held together by am ultiple bond (bond order = 1.5) with assistance from the electrondonating ligand PMe 3 . [6] Cobalt complexes have been widely used as efficient catalysts for organic transformations and CÀFb ond activations, [7] but the chemistry of dicobalt metalloradicals is relatively underdeveloped.…”