Exploring New Assembly Modes of Uranyl Terephthalate: Templated Syntheses and Structural Regulation of a Series of Rare 2D → 3D Polycatenated Frameworks

• Published in: Inorganic chemistry Vol. 56; no. 14; pp. 7694 - 7706
• Main Authors: Mei, Lei, Wang, Cong-zhi, Zhu, Liu-zheng, Gao, Zeng-qiang, Chai, Zhi-fang, Gibson, John K, Shi, Wei-qun
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 17.07.2017; American Chemical Society (ACS)
• Subjects: INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.7b00312

The reaction of uranyl nitrate with terephthalic acid (H 2 TP) under hydrothermal conditions in the presence of an organic base, 1,3-(4,4′-bispyridyl)­propane (BPP) or 4,4′-bipyridine (BPY), provided four uranyl terephthalate compounds with different entangled structures by a pH-tuning method. [UO2(TP)1.5]­(H2 BPP)0.5·2H2O (1) obtained in a relatively acidic solution (final aqueous pH, 4.28) crystallizes in the form of a noninterpenetrated honeycomb-like two-dimensional network structure. An elevation of the solution pH (final pH, 5.21) promotes the formation of a dimeric uranyl-mediated polycatenated framework, [(UO2)2(μ-OH)2(TP)2]2(H2 BPP)2·4.5H2O (2). Another new polycatenated framework with a monomeric uranyl unit, [(UO2)2(TP)3]­(H2 BPP) (3), begins to emerge as a minor accompanying product of 2 when the pH is increased up to 6.61, and turns out to be a significant product at pH 7.00. When more rigid but small-size BPY molecules replace BPP molecules, [UO2(TP)1.5]­(H2 BPP)0.5 (4) with a polycatenated framework similar to 3 was obtained in a relatively acidic solution (final pH, 4.81). The successful preparation of 2–4 represents the first report of uranyl–organic polycatenated frameworks derived from a simple H 2 TP linker. A direct comparison between these polycatenated frameworks and previously reported uranyl terephthalate compounds suggests that the template and cavity-filling effects of organic bases (such as BPP or BPY), in combination with specific hydrothermal conditions, promote the formation of uranyl terephthalate polycatenated frameworks.