A Luminescent Zn(II)-Based (4,4)-Grid Layer Templated by 2,5-Bis(pyridin-4-yl)thiazolo[5,4- d ]thiazole for Recyclable Iodine Capture

Abstract

Compound [Zn2(bpdc)2(BPTT)2]·BPTT (1) has been obtained by the reactions of Zn(NO3)2·6H2O, 4,4’-biphenyldicarboxylic acid (H2bpdc), and 2,5-bis(pyridin-4-yl)thiazolo[5,4-d]thiazole (BPTT), a rigid and planar π-conjugated ligand, under hydro(solvo)thermal conditions. Single-crystal X-ray diffraction analysis indicates that 1 adopts a two-dimensional layer structure with a (4,4) gridlike topology based on paddlewheel {Zn2(COO)4N2} secondary building units, where the two Zn(II) centers both show a {ZnO4N} square pyramidal geometry with a Zn···Zn separation of 2.9306(5) Å. Noteworthy, one free BPTT per formula, as a template, is located in the mesh of the (4,4)-grid layer. The BPTT template forms remarkable π···π stacking interactions (centroid-to-centroid distance is 3.639 Å) with the BPTT terminals in two neighboring layers and CH···N interactions (C···N distance is 3.578 Å) with the phenyl CH of the bpdc2– bridges. Compound 1 shows good thermal stability approaching 320 °C and is highly stable in various solvents and aqueous solutions with a wide range of pH values from 2 to 12. Upon excitation at 365 nm, 1 emits intense blue fluorescence centered at 471 nm in the solid state. Interestingly, 1 exhibits good reversibility and recyclability to quickly capture volatile iodine, leading to crystal color change and fluorescence quenching response up to 85%.