A Fluorescent Anionic MOF with Zn₄(trz)₂ Chain for Highly Selective Visual Sensing of Contaminants: Cr(III) Ion and TNP

Heavy-metal ions and nitroaromatic substances are highly toxic and harmful to human health and the ecological environment. It is an urgent issue to selectively detect and capture these toxic substances. By introducing the triazole ligand to the π-conjugated aromatic carboxylate system and borrowing the organic template open framework idea, a stable fluorescent framework [Me2NH2]4­[Zn6(qptc)3­(trz)4]·6H2O (1) (H4qptc = terphenyl-2,5,2′5′-tetra­carboxylic acid, trz = 1,2,4-triazole) has been successfully synthesized, which features Zn4(trz)2 chain-based 3D anionic structure with channels filled by [Me2NH2]+ cations. It is worth noting that the material exhibits selective adsorption and recyclable detection of heavy-metal Cr3+ ion in aqueous solutions, which may be the synergy from the metal charge, bond ability of metal ions to carboxylate oxygen atom, and soft–hard acid–base properties. Furthermore, it can selectively sense of 2,4,6-trinitrophenol with a large quenching coefficient Ksv of 2.08 × 106 M–1.重金属离子与硝基芳香族化合物对人体健康及生态环境具有极强毒性与危害性，对这类有毒物质进行选择性检测与捕获是当前亟待解决的重要课题。本研究通过将三唑配体（triazole ligand）引入π共轭芳香羧酸酯体系，并借鉴有机模板开放骨架理念，成功合成了稳定的荧光框架材料[Me₂NH₂]₄[Zn₆(qptc)₃(trz)₄]·6H₂O（1）（其中H₄qptc为三联苯-2,5,2′,5′-四羧酸，trz为1,2,4-三唑）。该框架具有以Zn₄(trz)₂链为结构基元的三维阴离子骨架，其孔道内填充有[Me₂NH₂]⁺阳离子。值得注意的是，该材料在水溶液中可对重金属Cr³⁺离子实现选择性吸附与可循环检测，其性能可能源于金属电荷、金属离子与羧酸氧原子的配位键合能力以及软硬酸碱性质的协同作用。此外，该材料还可对2,4,6-三硝基苯酚实现选择性荧光传感，其荧光猝灭系数Ksv高达2.08 × 10⁶ M⁻¹。