Magnetooptical and Structural Investigations of Five Dimeric Cobalt(II) Complexes Mimicking Metalloenzyme Active Sites

Four novel cobalt­(II) complexes mimicking metalloenzyme
active
sites, novel C14H22Cl12Co2O13·2C3H8O (1),
C28H36Cl24Co4O28·4C4H8O2 (2),
C16H22Cl12Co2O13·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 P1̅, P21/c, P1̅,
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 CoII 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.