Pyrazinetetracarboxylic Acid as an Assembler Ligand in Uranyl−Organic Frameworks
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- 作者：Bernardo Masci ; Pierre Thué ; ry
- 刊名：Crystal Growth & Design
- 出版年：2008
- 出版时间：May 2008
- 年：2008
- 卷：8
- 期：5
- 页码：1689 - 1696
- 全文大小：2439K
- 年卷期：v.8,no.5(May 2008)
- ISSN：1528-7505
文摘
The reaction of uranyl nitrate with pyrazinetetracarboxylic acid (H<SUB>4PZTC) has been investigated under different experimental conditions, and the crystal structures of the resulting complexes have been determined. In all cases, the uranyl ion is chelated in the ONO tridentate site, as in the complexes with pyridine-2,6-dicarboxylic acid, but much variety arises from the increased number of potential donor atoms. Hydrothermal synthesis in the presence of NEt4Br led to the complex [UO2(PZDC)(H2O)] (1), from in situ decarboxylation of H4PZTC into pyrazine-2,6-dicarboxylic acid (H2PZDC) upon prolonged heating. Complex 1crystallizes as ribbons held by bridging carboxylate groups and hydrogen bonds. In the presence of NaOH and under hydrothermal conditions, two species could be obtained: [(UO2)2(PZTC)(H2O)]·2H2O (2) and [UO2Na2(PZTC)(H2O)4] (3). In these compounds, [UO2(PZTC)]n2n− linear chains with bis-chelating PZTC ligands are further assembled either into a two-dimensional assemblage by other, carboxylate-bound bridging uranyl ions or into a three-dimensional framework by bridging [Na2(H2O)4]2+ dimers. In contrast, in [UO2K2(H2PZTC)2(H2O)2]·2H2O (4) and the two isomorphous compounds [UO2K2(H2PZTC)2]·4H2O (5) and [UO2Rb2(H2PZTC)2]·4H2O (6), which were not obtained under hydrothermal conditions, the ligand retains two protons and is bound to only one uranyl ion. The [UO2(H2PZTC)2]2− units are then assembled into a three-dimensional framework by bridging, oxo-bonded potassium ions in 4 or in layers by the carboxylic/ate-bound alkali-metal ions in 5 and 6 (with formation of a three-dimensional framework in the case of Rb+ through weaker Rb−acid bonds). In the last case, narrow channels contain the hydrogen-bonded water molecules. These results evidence the remarkable assembling potential of the H4−xPZTCx− ligand, with all 10 donor atoms coordinated in complexes 2 and 3 (x = 4) and bonding to as many as 7 metal atoms in 6 (x = 2).