The donor ability of the chelated carbonate ligand: protonation and metallation of [(L)Co(O2CO)]+ complexes in aqueous solution

The syntheses and X-ray structures of Co(Me-tpa)O(2)COZnCl(3)], Co(pmea)O(2)COZnCl(3)].H(2)O Co(trpyn)O(2)COZn(OH(2))(4)OCO(2)Co(trpyn)](ZnCl(4))(2).H(2)O, Co(trpyn)(O(2)COH)]ZnCl(4).3H(2)O and Co(trpyn)(O(2)CO)]ClO(4) are reported (Me-tpa = (6-methyl-2-pyridyl)methyl]bis(2-pyridylmethyl)amine, pmea = bis(2-pyridylmethyl)-2-(2-pyridylethyl)amine, trpyn = tris(2-(1-pyrazolyl)ethyl)amine). The chelated bicarbonate complex Co(trpyn)(O(2)COH)]ZnCl(4).3H(2)O is isolated as a crystalline solid from an acidic solution of the parent carbonate Co(trpyn)(O(2)CO)]ClO(4), and X-ray structural analysis shows that lengthening of the Cdouble bond, length as m-dash]O(exo) bond and shortening of the C-O(endo) bond accompanies protonation. The bimetallic complex Co(Me-tpa)O(2)COZnCl(3)] results from the unexpected coordination of ZnCl(3)(-) to the exo O atom of a chelated carbonate ligand. This complex is obtained from both acidic and neutral solutions in which Zn(2+)] = 1.0 M, while the structurally similar complex Co(pmea)O(2)COZnCl(3)].H(2)O is isolated from an analogous neutral solution. The trimetallic complex Co(trpyn)O(2)COZn(OH(2))(4)OCO(2)Co(trpyn)](ZnCl(4))(2).H(2)O crystallises on prolonged standing of Co(trpyn)(O(2)CO)]ClO(4) in a neutral solution having Zn(2+)] = 1.0 M. The Zn-O bond lengths in all three complexes are indicative of bonds of significant strength. DFT calculations show that the nature of the bonding interaction between the Co(iii) ion and the endo O atoms of the carbonate ligand remain essentially unaffected by coordination of Zn(2+) to the exo O atom. They also show that such coordination of Zn(2+) decreases the C-O(exo) bond order.