A series of complexes of the general formula [CoL4(ClO4)2] have been prepared and studied; L = pyridine (py), 3-methylpyridine (3-Mepy), 4-methylpyridine (4-Mepy), 3,5-dimethylpyridine (3,5-Me2py), 4-ethylpyridine (4-Etpy), 3-ethyl-4-methylpyridine (3-Et-4-Mepy), 4-n-propylpyridine (4-Prnpy), 4-isopropylpyridine (4-Pripy), or 3-bromopyridine (3-Brpy). Also prepared were [Mn(py)4(ClO4)2], [Cu(py)4(ClO4)2], and [Zn(py)4](ClO4)2. Magnetic susceptibility measurements, infrared spectra, and near-infrared and visible absorption spectra show that the solid Co(II) complexes are tetragonally distorted octahedral species. However, the pyridine base solutions of the complexes display bands typical of a regular octahedral arrangement of ligands about cobalt(II). Dq and Bcomplex values were calculated from the visible and near-infrared spectral data.