Heptacoordinate Cobalt(II) Complexes with 2,6-Diacetylpyridine Bis(benzimidazolyl)hydrazone: Synthesis, Structures, and Magnetic Properties

The reactions of bis(hetaryl)hydrazone (Н2L) (condensation product of 2,6-diacetylpyridine and 2-hydrazinobenzimidazole) with cobalt(II) chloride and bromide afford complexes [Co(Н2L)(H2O)Cl]Cl (I) and [Co(Н2L)(H2O)Br]Br (II), where Н2L is the pentadentate ligand in the neutral form. The coordination polyhedron of the complexes corresponds to a distorted pentagonal bipyramid. The structures and properties of the compounds are studied by IR spectroscopy, 1H NMR spectroscopy, and magnetometry. The structure of complex I is determined by X-ray diffraction (XRD) (CIF file CСDC no. 2240176). The quantum-chemical simulation of the magnetic properties of compounds I and II is performed in the framework of the CASSCF/NEVPT2 method. The easy magnetization plane with a positive axial magnetic anisotropy parameter (D) takes place in the complexes. The experimental values of D obtained by the approximation of the magnetometry data (Dexp = 39.5 (for I) and 29.2 (for II) cm–1) are consistent with the calculated values (Dcalc = 30.7 (for I) and 28.1 (for II) cm–1).