Analysis of the Spin State of the Iron Complexes with Hydroxysubstituted 2,6-Bis(pyrazol-3-yl)pyridines for Deprotonation in Solution

Abstract

The earlier described iron(II) complexes [Fe(L^H)₂](ClO₄)₂ and [Fe(L^F)₂](ClO₄)₂ are synthesized by simple mixing in an NMR tube of iron(II) perchlorate hexahydrate in deuterated methanol with the corresponding 2,6-bis(pyrazol-3-yl)pyridine containing the phenyl (L^H) or ortho-difluorophenyl (L^F) group in the first position of the pyrazolyl fragment and capable of deprotonating the hydroxy group in the fifth position. The complexes exist in the high-spin state according to an analysis of the temperature dependences of the chemical shifts of their signals in the ¹H NMR spectra. Using the same approach, a possibility of the in situ reversible deprotonation of the pH-sensitive hydroxy groups in the ligands under the action of 1,8-diazabicyclo[5.4.0]undec-7-ene is demonstrated. A possibility of spin equilibrium shifting due to deprotonation is checked.