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Issue 37, 2008
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The donor ability of the chelated carbonate ligand: protonation and metallation of [(L)Co(O2CO)]+ complexes in aqueous solution

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Abstract

The syntheses and X-ray structures of [Co(Me-tpa)O2COZnCl3], [Co(pmea)O2COZnCl3]·H2O [Co(trpyn)O2COZn(OH2)4OCO2Co(trpyn)](ZnCl4)2·H2O, [Co(trpyn)(O2COH)]ZnCl4·3H2O and [Co(trpyn)(O2CO)]ClO4 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)(O2COH)]ZnCl4·3H2O is isolated as a crystalline solid from an acidic solution of the parent carbonate [Co(trpyn)(O2CO)]ClO4, and X-ray structural analysis shows that lengthening of the C[double bond, length as m-dash]Oexo bond and shortening of the C–Oendo bond accompanies protonation. The bimetallic complex [Co(Me-tpa)O2COZnCl3] results from the unexpected coordination of ZnCl3 to the exoO atom of a chelated carbonate ligand. This complex is obtained from both acidic and neutral solutions in which [Zn2+] = 1.0 M, while the structurally similar complex [Co(pmea)O2COZnCl3]·H2O is isolated from an analogous neutral solution. The trimetallic complex [Co(trpyn)O2COZn(OH2)4OCO2Co(trpyn)](ZnCl4)2·H2O crystallises on prolonged standing of [Co(trpyn)(O2CO)]ClO4 in a neutral solution having [Zn2+] = 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 endoO atoms of the carbonate ligand remain essentially unaffected by coordination of Zn2+ to the exoO atom. They also show that such coordination of Zn2+ decreases the C–Oexo bond order.

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

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Publication details

The article was received on 24 Apr 2008, accepted on 06 Jun 2008 and first published on 31 Jul 2008


Article type: Paper
DOI: 10.1039/B806981F
Citation: Dalton Trans., 2008,0, 4984-4992
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    The donor ability of the chelated carbonate ligand: protonation and metallation of [(L)Co(O2CO)]+ complexes in aqueous solution

    L. F. McClintock, G. Cavigliasso, R. Stranger and A. G. Blackman, Dalton Trans., 2008, 0, 4984
    DOI: 10.1039/B806981F

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