The tris(3-t-butyl-5-methylpyrazolyl)hydroborato and tris(2-pyridylthio)methyl derivatives, [TpBut,Me]ZnOCO2H and [κ4-Tptm]ZnOCO2H, are the first pair of terminal zinc bicarbonate complexes to be structurally characterized by using X-ray diffraction. In both cases, the bicarbonate ligand coordinates in a unidentate manner, comparable to that in human carbonic anhydrase I. While the bicarbonate complex [κ4-Tptm]ZnOCO2H is obtained by treatment of {[κ3-Tptm]Zn(μ–OH)}2 with CO2 in the presence of water, the bridging carbonate complex [Tptm]Zn(μ-CO3)Zn[Tptm] is obtained in the absence of water. The reactivity of {[κ3-Tptm]Zn(μ–OH)}2 towards CO2 is sufficiently high that the carbonate complex is obtained upon exposure to air.
