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

Four ionic Ni(II) complexes containing the [Ni(H im ) 6 ] 2+ (H im = imidazole) complex cation were prepared: [Ni(H im ) 6 ](CO 3 )·5H 2 O ( 1 ), [Ni(H im ) 6 ]( ac ) 2 ·H 2 O ( 2 , ac = acetate), [Ni(H im ) 6 ](NO 3 ) 2 ( 3 ), and [Ni(H im ) 6 ]SiF 6 ( 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(H im ) 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 H im ligands. While in 1 and 4 the NiN 6 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 H im rings within the respective coordination polyhedra.