Controlling gas sorption by simple pore modification is important in molecular recognition and industrial separation processes. In particular, it is challenging to realize the inverse selectivity, which reduces the adsorption of a high‐affinity gas and increases the adsorption of a low‐affinity gas. Herein, an “opposite action” strategy is demonstrated for boosting CO2/C2H2 selectivity in porous coordination polymers (PCPs). A precise steric design of channel pores using an amino group as an additional interacting site enabled the synergetic increase in CO2 adsorption while suppressing the C2H2 adsorption. Based on this strategy, two new ultramicroporous PCP physisorbents that are isostructural were synthesised. They exhibited the highest CO2 uptake and CO2/C2H2 volume uptake ratio at 298 K. Origin of this specific selectivity was verified by detailed density functional theory calculations. The breakthrough separation performances with remarkable stability and recyclability of both the PCPs render them relevant materials for C2H2 purification from CO2/C2H2 mixtures.
Amorphous
coordination polymers and metal–organic frameworks
(MOFs) have attracted much attention owing to their various functionalities.
Here, we demonstrate the tunable water adsorption behavior of a series
of amorphous cyanide-bridged MOFs with different metals (M[Ni(CN)4]: MNi; M = Mn, Fe, and Co). All three compounds
adsorb up to six water molecules at a certain vapor pressure (P
ads) and undergo conversion to crystalline Hofmann-type
MOFs, M(H2O)2[Ni(CN)4]·4H2O (MNi–H
2
O; M = Mn, Fe, and Co). The P
ads of MnNi, FeNi, and CoNi for
water adsorption is P/P
0 = 0.4, 0.6, and 0.9, respectively. Although the amorphous nature
of these materials prevented structural elucidation using X-ray crystallography
techniques, the local-scale structure around the N-coordinated M2+ centers was analyzed using L2,3-, K-edge X-ray
absorption fine structure, and magnetic measurements. Upon hydration,
the coordination geometry of these metal centers changed from tetrahedral
to octahedral, resulting in significant reorganization of the MOF
local structure. On the other hand, Ni[Ni(CN)4] (NiNi) containing square-planar Ni2+ centers did
not undergo significant structural transformation and therefore abruptly
adsorbed H2O in the low-pressure region. We could thus
define how changes in the bond lengths and coordination geometry are
related to the adsorption properties of amorphous MOF systems.
The palladium-hydrogen system is one of the most famous hydrogen-storage systems. Although there has been much research on β-phase PdH(D) , we comprehensively investigated the nature of the interaction between Pd and H(D) in α-phase PdH(D) (x<0.03 at 303 K), and revealed the existence of Pd-H(D) chemical bond for the first time, by various in situ experimental techniques and first-principles theoretical calculations. The lattice expansion, magnetic susceptibility, and electrical resistivity all provide evidence. In situ solid-state H and H NMR spectroscopy and first-principles theoretical calculations revealed that a Pd-H(D) chemical bond exists in the α phase, but the bonding character of the Pd-H(D) bond in the α phase is quite different from that in the β phase; the nature of the Pd-H(D) bond in the α phase is a localized covalent bond whereas that in the β phase is a metallic bond.
Charge-driven self-assembly of cationic zirconium-based metal-organic polyhedra (MOPs) with polyoxometalates (POMs) lead to a series of porous crystalline salts, prepared by simple mixing of soluble precursors. Reactivity of immobilized POMs...
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