Influence of the counter-anions on the [Ni(Him)6]2+ complex cation (Him = imidazole)

Four ionic Ni(II) complexes containing the [Ni(Him)₆]²⁺ (Him = imidazole) complex cation were prepared: [Ni(Him)₆](CO₃)·5H₂O (1), [Ni(Him)₆](ac)₂·H₂O (2, ac = acetate), [Ni(Him)₆](NO₃)₂ (3), and [Ni(Him)₆]SiF₆ (4); complexes 2 and 4 are new. The prepared complexes were characterized chemically and spectroscopically. Results of X-ray single crystal studies have shown that all four complexes exhibit ionic crystal structures comprising [Ni(Him)₆]²⁺ complex cations, the respective anion(s), and in case of 1 and 2, additional solvate water molecules. Ni(II) central atoms in all complexes 1—4 are hexa-coordinated by six N-atoms originating from monodentate Him ligands. While in 1 and 4 the NiN₆ chromophore is quite a regular octahedron with only one independent Ni—N bond, as imposed by local symmetry, in 2 and 3 the octahedra are slightly deformed. On the other hand, significant differences were observed in the orientation of Him rings within the respective coordination polyhedra.