A Self-Assembled Metal-Organic Framework for Enhanced UO22+ Fluorescent Sensing: Integration of Octa-Nuclear Zinc Cluster with Hexakis(4-Carboxyphenoxy)Cyclotriphosphazene

Abstract

A novel metal-organic framework based on octa-nuclear zinc clusters, namely, [Zn4(L)(OH)2(H2O)4] (Zn-MOF) (H6L=hexakis(4-carboxylatophenoxy)cyclotriphosphazene), has been synthesized and structurally characterized by solvothermal method. Single-crystal X-ray diffraction shows that eight zinc ions form linear octa-nuclear cluster via μ3-OH group, and each hexakis(4-carboxylatophenoxy)-cyclotriphosphazene connects four octa-nuclear clusters to construct 3D frameworks with one-dimensional pore structures. Zn-MOF exhibits proper fluorescence properties, water stability as well as thermal stability, which can be applied as a convenient fluorescent probe for the detection of radioactive uranyl cations (UO22+) and ferric ions (Fe3+) through fluorescence quenching behavior. The corresponding Ksv values can reach 7.44×103 M-1 and 1.49×104 M-1. Meanwhile, the theoretical calculations fully indicated that the introduction of UO22+ effectively inhibited Metal-to-Ligand Charge Transfer (MLCT) of Zn-MOF, which in turn led to the fluorescence quenching phenomenon. Therefore, Zn-MOF prepared using crystal engineering can be used to construct an efficient and reliable fluorescent probe using in the fields of environmental monitoring and nuclear waste treatment.