Isolated molybdenum-based microporous POMs for selective adsorption of gases.

Dodecanuclear, icosanuclear and octanuclear porous MOF-like POM materials [MoV12O 12 (μ 2 -O) 4 (μ 3 -O) 12 (Htrz) 4 (trz) 4 ]· n H 2 O ( n = 22, 1; n = 92, 2; Htrz = 1 H -1,2,3-triazole), [MoV8O 8 (μ 2 -O) 12 (Htrz) 8 ] ½ ·[MoV12O 12 (μ 2 -O) 4 (μ 3 -O) 12 (Htrz) 4 (trz) 4 ]·44H 2 O (3), and [MoV8O 8 (μ 2 -O) 12 (Htrz) 8 ]·62H 2 O (4) have been obtained and well characterized. Higher Mo 12 agglomerates have been fabricated in acidic solution, while isolated Mo 8 species formed in weak alkaline conditions. Fortuitously, their additive 3 is precipitated in a neutral environment. Structural analyses indicate that there are diversiform pores present in 1-4, which are formed by polyoxometalates (POMs) themselves and intermolecular accumulations, or even induced by free disordered water molecules. Obvious downfield shifts have been found in the solid 13 C NMR spectra for the coordinated 1,2,3-triazoles in 1 and 2. In particular, isolated single species of polyoxometalate-based porous framework POMOF 4 can be identified in the solution 13 C NMR spectrum and further supported by solid and solution UV-vis spectroscopy. Moreover, gas adsorption tests indicate that 1 is the most promising CO 2 adsorbent of these four materials, compared with other common gases O 2 , H 2 , CH 4 and N 2 under different pressures. The peculiarities of this sort of POMOFs, as well as the relationships and interactions with gases, have been discussed.