Four novel cobalt(II) complexes mimicking metalloenzyme active sites, novel C14H22Cl12Co2O13 center dot 2C(3)H(8)O (1), C28H36Cl24Co4O28 center dot 4C(4)H(8)O(2) (2), C16H22Cl12Co2O13 center dot C2HCl3O2 (3), C16H22Cl12Co2O13 (4), and one known C40H78Cl8Co2O17 (5) are composed of the same core of two high-spin cobalt(II) centers triply bridged by water and two trichloroacetato (1-4) or two pivalate (5) groups but differ in terminal ligands. The crystal structures of new compounds 1-4 belong to the space groups P (1) over bar, P2(1)/c, P (1) over bar, and Pbcn, respectively. All five investigated complexes contain Co atoms in distorted octahedral coordination. The complexes were characterized by magnetic susceptibility and magnetization measurements and by variable-temperature variable-field magnetic circular dichroism spectroscopy. Experimental data were analyzed in the frame of the theoretical model, which includes an unquenched orbital moment of the Co-II ions. All investigated compounds are antiferromagnetically coupled with exchange constants in the range -1.5 to -2.1 cm(-1). However, there is a significant difference between the crystal-field-splitting parameters.