Toward Controlling the Solid State Valence Tautomeric Interconversion Character by Solvation

Abstract

Crystals of [Co(diox)2(4-NO2-py)2] (1) and [Co(diox)2(4-CN-py)2] (2) where diox are the o-dioxolene 3,5-di-t-butylsemiquinonate (SQ•–) and/or 3,5-di-t-butylcatecholate (Cat2–) ions, 4-NO2-py is 4-nitro-pyridine, 4-CN-py is 4-cyano-pyridine, are among the few known crystals presenting both thermally induced and photoinduced ls-[M+3(SQ•–)(Cat2–)] ↔ hs-[M2+(SQ•–)2] valence tautomeric interconversion (VTI). In 2, the thermal-induced VTI is cooperative, characterizing an abrupt conversion, and in 1 it is noncooperative. In this work, crystals of [Co(diox)2(4-NO2-py)2]·benzene (1BZ), [Co(diox)2(4-NO2-py)2]·toluene (1TL), [Co(diox)2(4-CN-py)2]·benzene (2BZ), and [Co(diox)2(4-CN-py)2]·toluene (2TL) have been prepared and analyzed by single crystal X-ray diffraction in order to investigate how solvation modulates thermally induced VTI. Crystallographic data were also successfully used together with the two-state equilibrium equation to estimate ΔH° and ΔS° VTI thermodynamic parameters. The solvate crystals, like t...