Spin State of the Iron(II) Complex with a New Representative of the 2,6-Bis(pyrazol-3-yl)pyridine Series and the Effect of Protonation in Solution

Reaction of a new representative of the 2,6-bis(pyrazol-3-yl)pyridine series (L) containing protonatable amino groups with iron(II) perchlorate hexahydrate yielded a new complex [Fe(L)2](ClO4)2, which was characterized by X-ray diffraction analysis (CCDC no. 2448780), and the possibility of its in situ protonation by tetrafluoroboric acid was evaluated. Using an approach based on the analysis of temperature-dependent changes in the 1H NMR chemical shifts, it was established that in the temperature range 200–325 K, the obtained complex exists in the high-spin state, which is retained both in the presence of the protonating agent (HBF4) in solution and in the crystalline state.