Crystal structure of [Co(NH3)6][Co(CO)4]2

Hexaamminecobalt(II) bis[tetracarbonylcobaltate(-I)], [Co(NH3)6][Co(CO)4]2, was synthesized by reaction of liquid ammonia with Co2(CO)8. The CoII atom is coordinated by six ammine ligands. The resulting polyhedron, the hexaamminecobalt(II) cation, exhibits point group symmetry -3. The Co-I atom is coordinated by four carbonyl ligands, leading to a tetracarbonylcobaltate(−I) anion in the shape of a slightly distorted tetrahedron, with point group symmetry 3. The crystal structure is related to that of high-pressure BaC2 (space group R-3m), with the [Co(NH3)6]2+ cations replacing the Ba sites and the [Co(CO)4]− anions replacing the C sites. N—H...O hydrogen bonds between cations and anions stabilize the structural set-up in the title compound