DFT Prediction and Experimental Investigation of Valence Tautomerism in Cobalt-Dioxolene Complexes
datasetposted on 20.03.2019, 12:49 by Gemma K. Gransbury, Marie-Emmanuelle Boulon, Simon Petrie, Robert W. Gable, Roger J. Mulder, Lorenzo Sorace, Robert Stranger, Colette Boskovic
The family of complexes of general formula [Co(Mentpa)(Xdiox)]+ (tpa = tris(2-pyridylmethyl)amine, n = 0–3 corresponds to successive methylation of the 6-position of the pyridine rings; X = Br4, Cl4, H4, 3,5-Me2, 3,5-tBu2; diox = dioxolene) was investigated by density functional theory (DFT) calculations to predict the likelihood of valence tautomerism (VT). The OPBE functional with relativistic and solvent corrections allowed accurate reproduction of trends in spin-state energetics, affording the prediction of VT in complex [Co(Me3tpa)(Br4diox)]+ (1+). One-electron oxidation of neutral precursor [CoII(Me3tpa)(Br4cat)] (1) enabled isolation of target compounds 1(PF6) and 1(BPh4). Solution variable-temperature UV–vis absorption and Evans method magnetic susceptibility data confirm DFT predictions that 1+ exists in a temperature-dependent valence tautomeric equilibrium between low-spin Co(III)-catecholate and high-spin Co(II)-semiquinonate forms. The solution VT transition temperature of 1+ is solvent-tunable with critical temperatures in the range of 291–359 K for the solvents measured. Solid-state magnetic susceptibility measurements of 1(PF6) and 1(BPh4) reveal the onset of VT transitions above room temperature.
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Evans methodBr 4VT transitionsvalence tautomerismsusceptibility measurementsCo IIExperimental InvestigationOne-electron oxidationpyridine ringsPFDFT PredictionH 4Cobalt-Dioxolene ComplexesUVtemperature-dependent valence tautomeric equilibriumOPBE6- positiondioxCl 4BPhDFT predictionsspin-state energeticsValence Tautomerismtparoom temperaturesusceptibility datasolution VT transition temperature