title: The donor ability of the chelated carbonate ligand: protonation and metallation of [(L)Co(O2CO)]+ complexes in aqueous solution.
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)]ZnCl(4).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)]ZnCl(4).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=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 exo O 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 endo O atoms of the carbonate ligand remain essentially unaffected by coordination of Zn2+ to the exo O atom. They also show that such coordination of Zn2+ decreases the C-Oexo bond order.
authors.affiliation: Department of Chemistry, University of Otago, P.O. Box 56, Dunedin, New Zealand.
authors.forename: Lisa F
authors.initials: LF
authors.lastname: McClintock
authors.forename: Germán
authors.initials: G
authors.lastname: Cavigliasso
authors.forename: Robert
authors.initials: R
authors.lastname: Stranger
authors.forename: Allan G
authors.initials: AG
authors.lastname: Blackman
mesh_terms: D002254:Carbonates / Q000737:chemistry*; D002614:Chelating Agents / Q000138:chemical synthesis / Q000737:chemistry*; D003035:Cobalt / Q000737:chemistry*; D018360:Crystallography, X-Ray; D008024:Ligands; D008956:Models, Chemical; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D011522:Protons; D012996:Solutions / Q000737:chemistry; D013237:Stereoisomerism; D014867:Water / Q000737:chemistry
chemical_list: D002254:Carbonates; D002614:Chelating Agents; D008024:Ligands; D009942:Organometallic Compounds; D011522:Protons; D012996:Solutions; D014867:Water; D003035:Cobalt