Valence (chemistry)

Density functional theory

Solvent

Magnetic susceptibility

Stereochemistry

Physical chemistry

Organic chemistry

Computational chemistry

Tautomer

Crystallography

Chemistry

Inorganic Chemistry

The family of complexes of general formula [Co(Me ntpa)(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.

DFT Prediction and Experimental Investigation of Valence Tautomerism in Cobalt-Dioxolene Complexes