Intrinsic Molybdenum-Based POMOFs with Impressive Gas Adsorptions and Photochromism

Novel molybdenum(VI/V) POM-based self-constructed frameworks [(Mo12O24)-O-VI(mu(2)-O)(12)(trz)(6)(H2O)(6)] . 6Hma . 18H(2)O (1, Htrz=1H-1,2,3-triazole, ma=methylamine), [(Mo7O14)-O-VI(mu(2)-O)(8)(trz)(5)(H2O)] . 7Hma . 5H(2)O (2), Na-3[(Mo6O6)-O-V(mu(2)-O)(9)(Htrz)(3)(trz)(3)] . 7.5H(2)O (3) and [(Mo8O8)-O-V(mu(2)-O)(12)(Htrz)(8)] . 30H(2)O (4) have been covalently decorated with tri-coordinated deprotonated/protonated 1,2,3-triazoles. Channels with an inner diameter of 7.5 angstrom were found in 1, whereas a tunnel composed of stacking molecules with an inner diameter of 4.1 angstrom along the b-axis exists in 2; it is occupied by free disordered methylamines, showing selective adsorption of O-2 and CO2 at 25 degrees C. Obvious downfield shifts were observed by C-13 NMR spectroscopies for methylamines inside the confined channels in 1 and 2. There are diversified pores in 3 and 4, which are formed by the molecules themselves and intermolecular accumulations. Adsorption tests indicate that 3 and 4 are fine adsorption materials for CH4 and CO2 under low pressure that rely on the environments built by the POMs. Correspondingly, 1 and 2 display reversible photoresponsive thermochromism that is subtlety influenced by the channels. The polyoxometalate organic frameworks (POMOFs) with multiple functional adsorptions are easy to assemble. Their photo-/thermoresponse properties offer a new pathway for the self-constructions of one-off hybrid materials that possess the good properties of both POMs and MOFs.

Automated summary

The study demonstrates that novel POMOFs materials can be constructed by modifying with 1,2,3-triazoles, which can selectively adsorb gas molecules and exhibit reversible photoresponsive thermochromism.