Selenophene-based mixed-linker metal-organic frameworks: synthesis, characterization and luminescent properties

Metal-Organic Frameworks (MOFs) are a class of nanoporous materials that in recent years have gained great attention for their widespread application in several fields of materials science (catalysis, luminescence, gas storage and separation). MOFs have an extraordinary versatility in their design achieved through a tailored combination of organic linkers and inorganic nodes. This characteristic gives to MOFs unique advantages, including control of their pore size, high specific surface areas and the possibility to include suitable functional groups on their linkers' skeleton. In this work, we describe the synthesis and full characterization of the bicyclic ditopic linker 2,2'-biselenophene-5,5'-dicarboxylic acid (H2SpSp) specifically designed for MOFs construction. Afterwards, the corresponding zirconium MOF [Zr6O4(OH)4(SpSp)3.8Cl4.4] (1) has been prepared and the crystallographic analysis has revealed that it is isostructural with its bitiophene and bithiazole analogues. Therefore, three new mixed-linker MOFs containing biselenophene (H2SpSp), bithiophene (H2ThTh) and bithiazole (H2TzTz) linkers have been synthesized, in detail the two double-mixed [Zr6O4(OH)4(SpSp)2.6(ThTh)1.3Cl4.2] (2) and [Zr6O4(OH)4(SpSp)2(TzTz)1.8Cl4.4] (3), as well as the triple-mixed [Zr6O4(OH)4(SpSp)1.6(ThTh)1.2(TzTz)1.4Cl3.6] (4). Compounds 1-4 have been tested for luminescent applications, emitting at wavelengths falling in the blue-green visible region under UV irradiation.