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

Gemma K Gransbury; Marie-Emmanuelle Boulon; Simon Petrie; Robert W Gable; Roger J Mulder; Lorenzo Sorace; Robert Stranger; Colette Boskovic

doi:10.1021/acs.inorgchem.8b03291

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

Inorg Chem. 2019 Apr 1;58(7):4230-4243. doi: 10.1021/acs.inorgchem.8b03291. Epub 2019 Mar 20.

Authors

Gemma K Gransbury¹, Marie-Emmanuelle Boulon², Simon Petrie³, Robert W Gable¹, Roger J Mulder⁴, Lorenzo Sorace², Robert Stranger³, Colette Boskovic¹

Affiliations

¹ School of Chemistry , University of Melbourne , Melbourne , VIC 3010 , Australia.
² UdR INSTM and Department of Chemistry "U. Schiff" , University of Florence , 50019 Sesto Fiorentino , FI , Italy.
³ Research School of Chemistry, College of Physical & Mathematical Sciences , Australian National University , Canberra , ACT 2601 , Australia.
⁴ CSIRO Manufacturing , Clayton , VIC 3168 , Australia.

PMID: 30892028
DOI: 10.1021/acs.inorgchem.8b03291

Abstract

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 [Co^II(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.