Abstract
Flexible metal-organic materials (FMOMs) with stepped isotherms can offer enhanced working capacity in storage applications such as adsorbed natural gas (ANG) storage. Unfortunately, whereas >1000 FMOMs are known, only a handful exhibit methane uptake of >150 cm(3)/cm(3) at 65 atm and 298 K, conditions relevant to ANG. Here, we report a double-walled 2-fold interpenetrated diamondoid (dia) network, X-dia-6-Ni, [Ni(2)L(4)(μ-H(2)O)](n), comprising a new azo linker ligand, L(-) (L(-) = (E)-3-(pyridin-4-yldiazenyl)benzoate) and 8-connected dinuclear molecular building blocks. X-dia-6-Ni exhibited gas (CO(2), N(2), CH(4)) and liquid (C8 hydrocarbons)-induced reversible transformations between its activated narrow-pore β phase and γ, a large-pore phase with ca. 33% increase in unit cell volume. Single-crystal X-ray diffraction (SCXRD) studies of the as-synthesized phase α, β, and γ revealed that structural transformations were enabled by twisting of the azo moiety and/or deformation of the MBB. Further insight into these transformations was gained from variable temperature powder XRD and in situ variable pressure powder XRD. Low-temperature N(2) and CO(2) sorption revealed stepped Type F-II isotherms with saturation uptakes of 422 and 401 cm(3)/g, respectively. X-dia-6-Ni exhibited uptake of 200 cm(3)/cm(3) (65 atm, 298 K) and a high CH(4) working capacity of 166 cm(3)/cm(3) (5-65 bar, 298 K, 33 cycles), the third highest value yet reported for an FMOM and the highest value for an FMOM with a Type F-II isotherm.