CO2 Fixation by Cu2+ and Zn2+ Complexes of a Terpyridinophane Aza Receptor. Crystal Structures of Cu2+ Complexes, pH-Metric, Spectroscopic, and Electrochemi

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• 作者：Bego&ntilde ; a Verdejo ; Juan Aguilar ; Enrique Garc&iacute ; a-Espa&ntilde ; a ; Pablo Gavi&ntilde ; a ; Julio Latorre ; Conxa Soriano ; Jos&eacute ; M. Llinares ; and Antonio Dom&eacute ; nech
• 刊名：Inorganic Chemistry
• 出版年：2006
• 出版时间：May 1, 2006
• 年：2006
• 卷：45
• 期：9
• 页码：3803 - 3815
• 全文大小：229K
• 年卷期：v.45,no.9(May 1, 2006)
• ISSN：1520-510X

文摘

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 withvalues 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 potentiometryin 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 squarepyramidal geometry. The base of the pyramid is formed by the three nitrogen atoms of pyridine and one oxygenatom 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 andthe other one by the three central nitrogen atoms of the polyamine chain. The square planar coordination geometryis completed by a carbonate group taken up from the atmosphere that behaves as a bridging ages/entities/mgr.gif">,ages/entities/mgr.gif">'-ligand betweenthe two centers. The pH-metric titrations on the ternary Cu²⁺-L-carbonate and Zn²⁺-L-carbonate systems showthe extensive formation of adduct species which above pH 6 are formed quantitatively in solution. The stoichiometriesof the main species formed in solution at pH = 6.8 agree with those found in the crystalline compounds. CO₂uptake by the Zn²⁺ and Cu²⁺ 1:1 complexes in aqueous solution has also been followed by recording the variationsin the band at ca. 300 nm. The formation of the Zn²⁺ carbamate moiety has been evidenced by ¹³C NMR and ESIspectroscopy.