Reversible Phase Transformations in a Double-Walled Diamondoid Coordination Network with a Stepped Isotherm for Methane.

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 cm³/cm³ 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, [Ni₂L₄(μ-H₂O)]_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 (CO₂, N₂, CH₄) 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 N₂ and CO₂ sorption revealed stepped Type F-II isotherms with saturation uptakes of 422 and 401 cm³/g, respectively. X-dia-6-Ni exhibited uptake of 200 cm³/cm³ (65 atm, 298 K) and a high CH₄ working capacity of 166 cm³/cm³ (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.

SUBMITTER: Li X 

PROVIDER: S-EPMC11240251 | biostudies-literature | 2024 Jul

REPOSITORIES: biostudies-literature