Theoretical study of the mechanism of valence tautomerism in cobalt complexes

Daisuke Sato, Yoshihito Shiota, Gergely Juhász, Kazunari Yoshizawa

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49 Citations (Scopus)


Valence tautomerism is studied in the [CoII-HS(sq) 2(bpy)]/[CoIII-LS(sq)(cat)(bpy)] mononuclear cobalt complex by using DFT methods (HS, high spin; LS, low spin; cat, catecholate; sq, semiquinone; bpy, 2,2′-bipyridine). Calculations at the B3LYP* level of theory reproduce well the energy gap between the CoII-HS and CoIII-LS forms giving an energy gap of 4.4 kcal/mol, which is comparable to the experimental value of 8.9 kcal/mol. Potential energy surfaces and crossing seams of the electronic states of the doublet, quartet, and sextet spin states are calculated along minimum energy paths connecting the energy minima corresponding to the different spin states. The calculated minimum energy crossing points (MECPs) are located at 8.8 kcal/mol in the doublet/sextet surfaces, at 10.2 kcal/mol in the doublet/quartet surfaces, and at 8.4 kcal/mol in the quartet/sextet surfaces relative to the doublet ground state. Considering the energy of the three spin states and the crossing points, the one-step relaxation mechanism between the CoII-HS and CoIII-LS forms is the most probable. This research shows that mapping MECPs can be a useful strategy to analyze the potential energy surfaces of systems with complex deformation modes.

Original languageEnglish
Pages (from-to)12928-12935
Number of pages8
JournalJournal of Physical Chemistry A
Issue number49
Publication statusPublished - Dec 16 2010

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry


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