Spin State of the Iron(II) and Cobalt(II) 2,6-Di(5-Amino-1H-Pyrazol-3-yl)pyridine Complexes in Solution and in Crystal

Abstract

The cobalt(II) and iron(II) complexes with 2,6-di(5-amino-1H-pyrazol-3-yl)pyridine (L), CoL₂(ClO₄)₂ (I) and FeL₂(ClO₄)₂ (II), are synthesized by the template reaction, isolated in the individual form, and characterized by elemental analysis, NMR spectroscopy, and thermogravimetry. The structures of complexes I and II (including the iron(II) complex obtained as two new solvate forms (FeL₂(ClO₄)₂ ∙ 2(C₂H₅)₂O ∙ H₃CN (IIa) and FeL₂(ClO₄)₂ ∙ (C₂H₅)₂O ∙ CH₃CN ∙ 0.75H₂O (IIb)) are confirmed by X-ray diffraction analysis. The data obtained in the crystal (by the X-ray diffraction method) and in solutions (using the proposed approach to an analysis of paramagnetic shifts in ¹H NMR spectra) indicate that the metal ion in the complexes exists in the high-spin state (S = 3/2 for Co(II) and S = 2 for Fe(II)) and undergoes no temperature-induced spin transition in a range of 120–300 K.