title: CO2 Fixation by Cu2+ and Zn2+ complexes of a terpyridinophane aza receptor. Crystal structures of Cu2+ complexes, pH-metric, spectroscopic, and electrochemical studies.
abstract: The synthesis of the terpyridinophane-type polyamine 2,6,9,12,16-pentaaza[17]-(5,5' ')-cyclo-(2,2':6',2' ')-terpyridinophane heptahydrobromide tetrahydrate (L.7HBr.4H2O) is described. L presents six protonation constants with values in the range 9.21-3.27 logarithmic units. L interacts with Cu2+ and Zn2+ forming in both cases, neutral, protonated, and hydroxylated mono- and binuclear complexes whose constants have been calculated by potentiometry in 0.15 M NaClO4 at 298.1 K. The crystal structures of the compounds [Cu(HL-carb)(H2O)](ClO4)3.2H2O (1) and [Cu2(H2L)(CO3)]2(ClO4)8.9H2O (2) have been solved by X-ray diffraction. In 1, the metal center presents square pyramidal geometry. The base of the pyramid is formed by the three nitrogen atoms of pyridine and one oxygen atom of a CO2 group which is forming a carbamate bond with the central nitrogen atom of the polyamine chain. The axial position is occupied by a water molecule. In 2, one Cu2+ is bound by the three pyridine nitrogens and the other one by the three central nitrogen atoms of the polyamine chain. The square planar coordination geometry is completed by a carbonate group taken up from the atmosphere that behaves as a bridging mu,mu'-ligand between the two centers. The pH-metric titrations on the ternary Cu2+-L-carbonate and Zn2+-L-carbonate systems show the extensive formation of adduct species which above pH 6 are formed quantitatively in solution. The stoichiometries of the main species formed in solution at pH = 6.8 agree with those found in the crystalline compounds. CO2 uptake by the Zn2+ and Cu2+ 1:1 complexes in aqueous solution has also been followed by recording the variations in the band at ca. 300 nm. The formation of the Zn2+ carbamate moiety has been evidenced by 13C NMR and ESI spectroscopy.
authors.affiliation: Departamento de Química Inorganica, Instituto de Ciencia Molecular, Universidad de Valencia, Edificio de Institutos de Paterna, Apartado de Correos 22085, 46071 Valencia, Spain.
authors.forename: Begoña
authors.initials: B
authors.lastname: Verdejo
authors.forename: Juan
authors.initials: J
authors.lastname: Aguilar
authors.forename: Enrique
authors.initials: E
authors.lastname: García-España
authors.forename: Pablo
authors.initials: P
authors.lastname: Gaviña
authors.forename: Julio
authors.initials: J
authors.lastname: Latorre
authors.forename: Conxa
authors.initials: C
authors.lastname: Soriano
authors.forename: José M
authors.initials: JM
authors.lastname: Llinares
authors.forename: Antonio
authors.initials: A
authors.lastname: Doménech
mesh_terms: D002245:Carbon Dioxide / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004563:Electrochemistry; D006863:Hydrogen-Ion Concentration; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D010944:Plants / Q000378:metabolism; D011073:Polyamines / Q000138:chemical synthesis* / Q000737:chemistry; D013057:Spectrum Analysis; D015032:Zinc / Q000737:chemistry*
chemical_list: D009942:Organometallic Compounds; D011073:Polyamines; D002245:Carbon Dioxide; D003300:Copper; D015032:Zinc