Synthesis, structure and characterization of ZrPOF-DEA, a microporous zirconium phosphate framework material

A microporous zirconium phosphate material with the chemical composition |(C 4 H 12 N + ) 6 (H 3 O + ) 2 (H 2 O) 2 |[Zr 32 P 48 O 176 F 8 (OH) 16 ] (ZrPOF-DEA) has been synthesized ionothermally using diethylammonium chloride and oxalic acid to form the deep eutectic solvent. It is closely related to the analagous ethylammonium material ZrPOF-EA, which has already been shown to discriminate very well between CO 2 and CH 4 . The framework structures, with two different 8-ring channels running parallel to the x -axis, one of which intersects a 7-ring channel running parallel to the z -axis, proved to be identical. Only the positions of the non-framework cations and water molecules differ. The structure of ZrPOF-DEA ( Pbam , a   =   20.03757(1) Å, b   =   37.19099(1) Å, c   =   6.62488(1) Å) was solved from synchrotron powder diffraction data using the charge-flipping algorithm in Superflip . Difference Fourier analyses were then used to locate the non-framework species in the channels. Rietveld refinement of the final structure converged with R F   =   0.037 and R wp   =   0.138. Although this material, like ZrPOF-EA, is stable up to 410   °C, it does not discriminate as well between CO 2 and CH 4 . Thermogravimetric analysis shows that not all of the organic species have been removed at 410   °C, and this is presumably the reason for the poorer adsorption results.