title: Crystal structure of [Co(NH3)6][Co(CO)4]2.
abstract: Hexaamminecobalt(II) bis-[tetra-carbonyl-cobaltate(-I)], [Co(NH3)6][Co(CO)4]2, was synthesized by reaction of liquid ammonia with Co2(CO)8. The Co(II) atom is coordinated by six ammine ligands. The resulting polyhedron, the hexa-amminecobalt(II) cation, exhibits point group symmetry -3. The Co(-I) atom is coordinated by four carbonyl ligands, leading to a tetra-carbonyl-cobaltate(-I) anion in the shape of a slightly distorted tetra-hedron, 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.
authors.affiliation: Anorganische Chemie, Fluorchemie, Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Strasse 4, 35032 Marburg, Germany.
authors.forename: Thomas G
authors.initials: TG
authors.lastname: Müller
authors.affiliation: Anorganische Chemie, Fluorchemie, Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Strasse 4, 35032 Marburg, Germany.
authors.forename: Florian
authors.initials: F
authors.lastname: Kraus
keywords: ammonia; cobalt carbon­yl; crystal structure; hydrogen bonding