A series of CuX (X = Br, I) modules bearing Ba-MOFs: Structures, fluorescence and sensing properties

Abstract

As one of the alkaline earth metal ions with high coordination numbers, barium ion (Ba2+) typically shows versatile coordination modes when coordinating with organic ligands to construct metal-organic frameworks (MOFs) featuring novel structural attributes. In this work, on basis of diverse coordination modes between Ba²⁺ and isonicotinic acid (HINA) or its derivatives, three MOFs namely Ba2(Cu2Br2)(3-F-INA)4(H2O) (1, 3-F-INA = 3-fluoroisonicotinate), Ba2(H2O)7Cu4Br3(INA)5 (2) and Ba2K5(DMF)3[Cu7I6(INA)10](H2O)3.5 (3) with novel structure features are synthesized and characterized. In these compounds, CuX (X = Br, I) participates in the assembly reaction via coordination with the pyridine N atom of the isonicotinate ligand, featuring one-dimensional (1D) chain-like architectures that are incorporated into the resultant 3D MOFs. Significantly, by varying the substituent groups on HINA and altering the halogen species, the luminescent properties of the as-synthesized MOFs could be tuned. Notably, compound 3 exhibits a bright orange emission and demonstrates a selective fluorescence (FL) quenching response toward sulfur-containing small molecule of cysteine (Cys), highlighting its potential utility in FL-based biomolecular sensing. Furthermore, 3 also displays sensitive FL sensing toward Fe³⁺ ions. This study represents the first report of Ba-CuX-INA frameworks exhibiting FL sensing properties, thereby providing a valuable foundation for the development of novel FL CuX-based MOFs for sensing applications.