Structural and spectroscopic studies on four-, five-, and six-coordinate complexes of zinc, copper, nickel, and cobalt: Structural models for the bicarbonate intermediate of the carbonic anhydrase catalytic cycle

The molecular structures and electronic spectra of a series of four-, five-, and six-coordinate complexes of cobalt, nickel, copper, and zinc, stabilized by tris(pyrazolyl)hydroborato ligands, have been determined. The structural variations that are observed for the series of nitrate and carbonate complexes reveal that the preference for bidentate coordination of these ligands increases across the series Zn < Co ≪ Cu and Ni.