- Macrocyclic Platforms for the Construction of Tetranuclear Oxo and Hydroxo Zinc Clusters
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The design of ligands that can act as platforms for the controlled, "bottom-up" synthesis of transition-metal clusters is a promising approach to accessing enzymatic mimics and new small-molecule reaction chemistry. This approach is exemplified here through the coordination chemistry of two compartmental Schiff-base calixpyrroles (H4L) that usually act as dinucleating ligands for transition metals. While reactions between H4L and Zn{N(SiMe3)2}2 form the expected dinuclear Zn "Pacman" complexes Zn2(L), reactions with ZnEt2 result in the tetranuclear Zn alkyl complexes Zn4Et4(THF)4(L), in which open, "bowl-shaped" structures are adopted due to the flexibility of the macrocyclic platform. The outcome of hydrolysis reactions of these tetranuclear complexes is found to depend on the macrocyclic cavity size, with the smaller macrocycle favoring oxo formation in Zn4(μ4-O)Et2(L) and the larger macrocycle favoring complete hydrolysis to form the hydroxide-bridged cluster Zn4(μ2-OH)4(L). This latter complex reacts with carbon dioxide at elevated temperature, re-forming the free macrocycle H4L and eliminating ZnCO3. (Chemical Equation Presented).
- Cadenbach, Thomas,Pankhurst, James R.,Hofmann, Tommy A.,Curcio, Massimiliano,Arnold, Polly L.,Love, Jason B.
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- Characterization of zinc carbonate hydroxides synthesized by precipitation from zinc acetate and potassium carbonate solutions
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Addition of potassium carbonate solution to zinc acetate solution at room temperature causes the precipitation of a white solid, whose composition and structure depend on the initial concentrations of the reagents. Hydrozincite, Zn5(CO3)2(OH)6, forms when the K2CO3 concentration is low and a new K-containing zinc carbonate hydroxide phase forms when the K2CO3 concentration is high. The chemical formula of the new phase has been determined to be Zn(CO3)0.61(OH)0.78·0.233K 2CO3 by TGA, CHNO and AA analysis. The new phase is insoluble in water and extensive water washing of the new phase does not change its composition or structure, suggesting the new phase is a single phase compound salt. Exposure of the new phase to a stream of humidified CO 2 causes disproportionation to separate phases of ZnCO3 and K2CO3. Pure ZnCO3 was synthesized for comparison by a new procedure under atmospheric conditions instead of the more common hydrothermal synthesis of ZnCO3.
- Zhang,Fortier,Dahn
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p. 1939 - 1948
(2008/10/09)
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