Combining High Resolution and High Energy X ray powder diffraction as a tool to investigate porous materials

Much research is currently focussed upon the synthesis, properties and applications of metal-organic framework (MOF) materials [1]. These are hybrid, inorganic–organic solids with extended structures constructed from metal centres linked by polydentate ligands that may present considerable porosity once solvent or excess organic ligand is removed from the structure after synthesis. Although the open structures of purely inorganic solids, such as zeolites and their analogues, have been well-studied for many years [2], MOFs have brought significant novelty to the field of porous materials. There are a number of reasons for this, including the possibility of post-synthesis functionalisation of the organic components of structures to tune selectivity towards guest uptake [3].

The main part of this contribution is aimed to explain the remarkable CO₂ uptake features of MOF Fe₂(BPEB)₃ [4] using high-resolution and high-energy powder X-ray diffraction (PXRD) in situ and in operando during gas adsorption, followed by classical Rietveld approach to a total scattering analysis of the PXRD data. As the gas pressure increases and the CO₂ molecules start their journey through the triangular channel of the MOF (Figure 1), it has been possible to follow the evolution of cell parameters, locate and estimate the CO₂ molecules as a function of p(CO₂), and, last but not least, unravel the host-guest interactions.

Some preliminary results will be also presented on a second application of coordination polymers, which sees Fluorous metal-organic frameworks (FMOFs) and non-porous coordination polymers (FN-PCPs) fabricated with fluorinated azolate spacers, as promising low-dielectric constant (low-k) materials.

 References
[1] C. J. Kepert in Inorganic Materials Series: Porous Materials. (Eds.: D. O’Hare, D. W. Bruce, R. I. Walton), Wiley, New York, 2010.
[2] R. M. Barrer, Zeolites and Clay Minerals as Sorbents and Molecular Sieves, Academic Press, London, 1978
[3] H. Sato, R. Matsuda, K. Sugimoto, M. Takata, S. Kitagawa, Nat. Mater. 2010, 9, 661–666.
[4] Galli, S.; Maspero, A.; Giacobbe, C.; Palmisano, G.; Nardo, L.; Comotti, A.; Bassanetti, I.; Sozzani, P.; Masciocchi, N.. J. Mater. Chem. A 2014, 2, 12208-12221.