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

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.