Magnetooptical and structural investigations of five dimeric cobalt(II) complexes mimicking metalloenzyme active sites

摘要

Four novel cobalt(II) complexes mimicking metalloenzyme active sites, novel C _(14)H _(22)Cl _(12)Co _2O _(132)C _3H _8O (1), C _(28)H _(36)Cl _(24)Co _4O _(284)C _4H _8O _2 (2), C _(16)H _(22)Cl _(12)Co _2O _(13)C _2HCl _3O _2 (3), C _(16)H _(22)Cl _(12)Co _2O _(13) (4), and one known C _(40)H _(78)Cl _8Co _2O _(17) (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 P1?, P2 _1/c, P1?, 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.