Four different complexes of the cobalt(II) acetate-pyridine-water system were obtained as dominant species by crystallization from a series of dichloromethane and toluene solutions. The complexes were characterized by terms of X-ray crystal structure determination. Factors in solution properties leading to crystallization of certain complexes are discussed. Furthermore, trends in terms of structure and binding energies in a systematic series of mononuclear cobalt(II) complexes were studied using density functional calculations. (C) 2011 Elsevier B.V. All rights reserved.