Cyanamidonitrate-cobalt(II) complexes of pyrazole and imidazole ligands

New cyanamidonitrate-cobalt(II) complexes of the type [Co(NO 2 NCN) 2 L 4 ], where L=pz (pyrazole), mpz [3(5)-methyl-pyrazole], dmpz (3,5-dimethylpyrazole), inz (indazole, benzopyrazole), Br-pz (4-Br-pyrazole), and [Co(dmpz) 4 ](NO 2 NCN) 2 have been prepared and characterized by IR and electronic spectroscopy. The crystal structure of [Co(NO 2 NCN) 2 (pz) 4 ] was determined by X-ray crystallography. The donor set of Co(II) forms an octahedron with four tertiary nitrogens from pyrazole ligands situated in the equatorial plane and two nitrile nitrogens from cyanamidonitrates in the axial positions. The d–d transitions show that a similar molecular structure can be expected in other Co(II) complexes under study, except the [Co(dmpz) 4 ](NO 2 NCN) 2 which contains a tetrahedral complex cation and forms with [Co(NO 2 NCN) 2 (dmpz) 4 ] an isomeric pair. The central Co(II) atom in [Co(2-methylimidazole) 4 ] (NO 2 NCN) 2 complex is tetrahedraly coordinated with four tertiary nitrogens from the imidazole ligands and the formed cationic unit is balanced by free cyanamidonitrate anions. According to the electronic and infrared spectra the [Co(dmpz) 4 ](NO 2 NCN) 2 complex possesses an analogous molecular structure.