Fixation of atmospheric carbon dioxide by a series of hydroxo complexes of divalent metal ions and the implication for the catalytic role of metal ion in carbonic anhydrase. Synthesis, characterization, and molecular structure of [LM(OH)]n (n = 1 or 2) and LM(.mu.-CO3)ML (M(II) = Mn, Fe, Co, Ni, Cu, Zn; L = HB(3,5-iso-Pr2pz)3)

Abstract

By using the hindered tris(pyrazoly)borate ligand HB(3,5-iPr[sub 2]pz)[sub 3], (hydrotris(3,5-diisopropyl-1-pyrazolyl)-borate), a series of hydroxo complexes of first-row divalent metal ions (Mn (1), Fe (2), Co (3), Ni (4), Cu (5), Zn (6)) was synthesized. X-ray crystallography was applied to 1-5, establishing that all these hydroxo complexes have a dinuclear structure solely bridged with a bis(hydroxo) unit. The structure of 6 was characterized by spectroscopy, which indicates that 6 is monomeric. All these hydroxo complexes were found to react with CO[sub 2], even atmospheric CO[sub 2], to afford [mu]-carbonato dinuclear complexes of Mn (7), Fe (8), Co (9), Ni (10), Cu (11), and Zn (12). The molecular structures of the complexes 8-12 were determined. A variety of coordination modes of the carbonate group was seen. In 10 and 11, the carbonate group is bound to both metal centers bidentately in a symmetric fashion, while in 8 and 9, the carbonate coordination modes are described as an unsymmetric bidentate. The carbonate group in 12 is coordinated to one zinc ion bidentately, but it is bound to the other zinc ion unidentately. From IR data, the coordination mode of the carbonate group in 7 was suggested to be similar to those found inmore » 8 and 9. Thus, the order of the coordination distortions of the carbonate groups in this series of [mu]-carbonato dinuclear complexes is determined. 40 refs., 8 figs., 4 tabs.« less