Studies of oxalate-bridged MM quadruple bonds and their radical cations (M = Mo or W): On the matter of linkage isomers

Malcolm H. Chisholm, Jason S. D'Acchioli, Christopher M. Hadad, Nathan J. Patmore

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Abstract

Electronic structure calculations employing density functional theory (DFT) and time-dependent density functional theory (TD-DFT) have been carried out on the model complexes {[(HCO2)3M2] 2(μ-O2CCO2)}0/+ (M = Mo or W) in D2h symmetry, where the oxalate bridge forms either five- or six-membered rings with the M2 centres; the complexes are hereafter referred to as μ(5,5)0/+ and μ(6,6)0/+, respectively. The calculations predict that the neutral complexes should exist as the μ(5,5) linkage isomer, while the radical cations favour the μ(6,6) isomer by ca. 4-6 kJ mol-1. For the μ(5,5) isomers, the rotational barriers about the oxalate C-C bond have been calculated to be 15.9 and 27.2 kJ mol-1 for M = Mo and W, respectively. For the cationic μ(5,5)+ isomers the barrier is higher, being 36.8 and 50.6 kJ mol-1 for M = Mo and W, respectively. The calculated Raman and visible near-IR spectra for the μ(5,5)0/+ and μ(6,6) 0/+ are compared with experimental data obtained for the {[( tBuCO2)3M2]2(μ-O 2CCO2)}0/+ complexes, hereafter referred to as M4OXA0/+ (M = Mo or W). The experimental data more closely correlate with that calculated for the μ(5,5)0/+ linkage isomers, and the 13C-NMR spectrum of the mixed metal complex Mo 2W2OXA indicates the presence of the 5-membered oxalate-bridged species (Jcc = 100 Hz).

Original languageEnglish
Pages (from-to)1852-1857
Number of pages6
JournalDalton Transactions
Issue number10
Early online date15 Apr 2005
DOIs
Publication statusPublished - 21 May 2005
Externally publishedYes

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