LOW-TEMPERATURE STRUCTURES OF [PY(2)H](+)[CO(CO)(4)](-) (PY=PYRIDINE) AND [(TMEN)H](+)[CO(CO)(4)](-) (TMEN=N,N,N',N')-TETRAMETHYLETHYLENEDIAMINE)

The crystal structures of salts arising from the reaction of HCo(CO)(4) with pyridine and methylethylenediamine, respectively, have been determined. The former, bis(pyridine) hydrogen tetracarbonylcobaltate(1-), consists of a [(C5H5N)(2)H](+) cation, with a symmetrical (within experimental error) N...H...N hydrogen bond, and a Co(CO)(4)(-) anion which is distorted towards C-2v symmetry. The latter, dimethyl [2-(dimethylamino)-ethyl]ammonium tetracarbonylcobaltate(1-), involves protonated tetramethylethylenediamine, [(C6H16N2)H](+), which forms an intramolecular N-H...N hydrogen bond, and a Co(CO)(4)(-) anion of C-s symmetry. No unusual interactions between anions and cations are observed. In each structure the cation exhibits the shortest N...N separation observed to date for this hydrogen-bonded cation: 2.634 (4) Angstrom for [(C5H5N)(2)H](+) and 2.711 (5) Angstrom for the (tmenH+ cation.