Zirconium metal-organic frameworks containing a biselenophene linker: Synthesis, characterization, and luminescent properties

The bicyclic ditopic linker 2,2'-biselenophene-5,5'-dicarboxylic acid (HSpSp), specifically designed for metal-organic framework (MOF) construction, has been synthesized in good yield and fully characterized. The corresponding zirconium MOF (Zr-MOF) [ZrO(OH)(SpSp)Cl] (1; where missing linkers are replaced by chloride anions as shown by X-ray fluorescence and elemental analysis) is isostructural with its bithiophene and bithiazole analogues. Starting from 1, an extension of the biselenophene-based Zr-MOF family has been successfully achieved, exploiting the structural analogy of the five-membered heterocycles selenophene, thiophene, and thiazole. Thus, three mixed-linker MOFs containing variable amounts of different bis(heterocyclic) dicarboxylic acids have been prepared and fully characterized: the two double-mixed [ZrO(OH)(SpSp)(TpTp)Cl] (2; HTpTp = 2,2'-bithiophene-5,5'-dicarboxylic acid) and [ZrO(OH)(SpSp)(TzTz)Cl] (3; HTzTz = 2,2'-bithiazole-5,5'-dicarboxylic acid) materials, as well as the triple-mixed [ZrO(OH)(SpSp)(TpTp)(TzTz)Cl] (4) compound. The four MOFs are luminescent under UV irradiation, exhibiting emission wavelengths falling in the blue-green visible region, as observed for their constitutive linkers. These materials open new horizons in the preparation of porous luminescent sensors or multicolor emitters for light-emitting diodes.