Flexible metal-organic framework compounds: In situ studies for selective CO2 capture

Results are presented that explore the dynamic structural changes occurring in two highly flexible nanocrystalline metal-organic framework (MOF) compounds during the adsorption and desorption of pure gases and binary mixtures. The Ni(1,2-bis(4-pyridyl) ethylene)[Ni(CN)(4)] and catena-bis(dibenzoylmethanato)-(4,4'-bipyridyl) nickel(II) chosen for this study are 3-D and 1-D porous coordination polymers (PCP) with a similar gate opening pressure response for CO2 isotherms at 303 K, but with differing degrees of flexibility for structural change to accommodate guest molecules. As such, they serve as a potential model system for evaluating the complex kinetics associated with dynamic structure changes occurring in response to gas adsorption in flexible MOF systems. Insights into the crystallo-graphic changes occurring as the MOF pore structure expands and contracts in response to interactions with CO2, N-2, and CO2/N-2 mixtures have been obtained from in situ small-angle neutron scattering and neutron diffraction, combined with ex situ X-ray diffraction structure measurements. The role of structure in carbon capture functionality is discussed with reference to the ongoing characterization challenges and a possible materials-by-design approach. Published by Elsevier B.V.