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 Co-2(CO)(8). The Co-II atom is coordinated by six ammine ligands. The resulting polyhedron, the hexaamminecobalt(II) cation, exhibits point group symmetry (3) over bar. The Co-II-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 (3) over barm), with the [Co(NH3)6]2+ cations replacing the Ba sites and the [Co(CO)(4)](-) anions replacing the C sites. N-H center dot center dot center dot O hydrogen bonds between cations and anions stabilize the structural set-up in the title compound.