Cationic Metal–Organic Frameworks Based on Linear Zwitterionic Ligands for Cr 2 O 7 2– and Ammonia Sensing

作者：Zhiyuan Li, Wenyan Cai, Xiaoman Yang, Aling Zhou, Yi Zhu, Huan Wang, Xin Zhou, Kecai Xiong, Qingfu Zhang, Yanli Gai · 发表于：Crystal Growth & Design · 年份：2020 · DOI：10.1021/acs.cgd.0c00247 · 被引用次数：57 · 研究领域：Metal-Organic Frameworks: Synthesis and Applications、Polyoxometalates: Synthesis and Applications、Magnetism in coordination complexes

A series of cationic lanthanide-based metal–organic frameworks (MOFs), {[Ln 3 (bcbp) 3 (NO 3 ) 7 ]·NO 3 ·ClO 4 } n (Ln = Tb ( 1 ), Gd ( 2 ), Eu ( 3 ); H 2 bcbpCl 2 = 1,1′-bis(4-carboxyphenyl)(4,4′-bipyridinium) dichloride), have been synthesized under solvothermal conditions and structurally characterized. Single-crystal X-ray diffraction analyses reveal that compounds 1 – 3 are isostructural, in which Ln 3 -SBUs (SBUs = secondary building units) are connected with six adjacent Ln 3 -SBUs by six protonated bcbp ligands, leading to cationic lanthanide-based metal–organic frameworks. In addition, the counteranions (nitrate anions and perchlorate anions) reside in the frameworks via weak C–H···O hydrogen bonds. Furthermore, Eu-MOF displays strong red luminescence, which is further proven to be a highly selective and sensitive luminescent sensor toward Cr 2 O 7 2– with a high quenching coefficient and low detection limit. Interestingly, Eu-MOF is also sensitive to ammonia and exhibits a rapid color change from yellow to blue-gray that can be distinguished by the naked eye when it is exposed to ammonia vapor. The UV–vis, IR, Raman, and EPR data reveal that the color change can be ascribed to an electron-transfer process and the radical generation caused by the nucleophilic attack of ammonia molecules.