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The binding domains within a mixed matrix membrane (MMM) that is selective for CO2 comprising MFM-300(Al) and the polymer 6FDA-Durene-DABA have been established via in situ synchrotron IR microspectroscopy. The MOF crystals are fully accessible and play a critical role in the binding of CO2, creating a selective pathway to promote permeation of CO2 within and through the MMM. This study reveals directly the molecular mechanism for the overall enhanced performance of this MMM in terms of permeability, solubility and selectivity for CO2.

High-free-volume glassy polymers, such as polymers of intrinsic microporosity (PIMs) and poly(trimethylsilylpropyne), have attracted attention as membrane materials due to their high permeability. However, loss of free volume over time, or aging, limits their applicability. Introduction of a secondary filler phase can reduce this aging but either cost or instability rules out scale up for many fillers. Here, we report a cheap, acid-tolerant, nanoparticulate hypercrosslinked polymer ‘sponge’ as an alternative filler. On adding the filler, permeability is enhanced and aging is strongly retarded. This is accompanied by a CO2/N2 selectivity that increases over time, surpassing the Robeson upper bound.

Big softy! A soft porous molecular crystal composed of organic cages exhibits complex multistep gas sorption isotherms (see figure), analogous to those observed in soft porous metal–organic frameworks. Softness is induced by frustrated packing of the cages and structural flexibility leads to kinetic guest trapping.

Pulling the old switcheroo: Microporosity can be switched “on” and “off” in a crystalline molecular organic solid composed of cage molecules (see scheme). The switch is facilitated by conformational flexibility in the soft organic crystal state.

Spherical capsules of the type [{(Mo)Mo(5)}(12){Mo(2)(ligand)}(30)](n-) exhibiting 20 {Mo(9)O(9)} pores with crown ether functions allowed us to perform a sophisticated study of the title phenomenon based on synthetic work as well as NMR spectroscopy. The pores of the host system interact in solution specifically with guests that can be noncovalently bonded, such as formamidinium and acetamidinium cations, while having different affinities to the pores. The exchange between the guest species present in solution and in the pores was investigated, including, besides the extreme scenarios of complete pore closing and complete opening, that of stepwise pore plugging. Because of this option it was possible to model for the first time passive transmembrane cation transport based on gated pores/channels. These have the appropriate dimensions and can even adopt different structure flexibilities in response to different cations. The present investigation is based on related syntheses as well as on numerous detailed (7)Li NMR studies of Li(+) transport/exchange equilibria in dependence of the pore environment/guest situations. One compound containing capsules with sulfate ligands (2) could be obtained in which all the pores are plugged with formamidinium cations and another corresponding one was obtained with additionally encapsulated Ca(2+) ions (3); these were taken up after temporary release of some of the formamidinium plugs/guests upon short heating of the related solution.

By the deliberate choice of the internal ligands of the porous nanocapsules [{(Mo)Mo(5)}(12){Mo(2)(ligand)}(30)](n-), the respective cavities' shells can be differently sized/functionalized. This allows one to trap the same large number of water molecules, that is, 100 in a capsule cavity with formate ligands having a larger space available, as well as in a cavity containing sulfates and hypophosphites, that is, with less space. Whereas the 100 molecules fill the space completely in the second case in which they are organized in three shells, a four-shell system with underoccupation and broken hydrogen bonds is observed in the other case. This is an unprecedented result in terms of the structurally well defined special forms of "higher and lower density" water molecule assemblies. Precisely, by replacing the larger ligands in the mentioned nanocapsule type by formates, voids in the capsule cavity of (HC(NH(2))(2))(22)[{(HC(NH(2))(2))(20)+(H(2)O)(100)} subset{(Mo)Mo(5)O(21)(H(2)O)(6)}(12){Mo(2)O(4)(HCO(2))}(30)]ca. 200 H(2)O are generated that get filled with water molecules concomitant with an expansion of the three to four shell {H(2)O}(100) cluster. The water shells in both capsules containing different ligands are organized in the form of dodecahedra (partly with underoccupation) and a strongly distorted rhombicosidodecahedron spanned by a {H(2)O}(60)={(H(2)O)(5)}(12) aggregate. The well-defined water shells only emerge if cations cannot enter into the capsules, which is achieved by closing the pores with plugs/guests such as formamidinium cations. The work is based on the syntheses of two new compounds, related single-crystal X-ray diffraction studies, and molecular dynamics simulations, which show remarkably that water molecule shell structuring occurs in the capsules due to the confined conditions even in the case of open pores and at room temperature if cation uptake is prevented.

Ubiquitous water is apart from its anomalies, for several reasons the most mysterious compound. According to its basic role in life processes it has even been considered as a biomolecule especially in context of the important role of confined “high and low density water”. C. Bo, A. Muller et al. report on page 1844 ff., confined higher and lower density water assemblies encapsulated in the same type of porous capsule that exhibit differently functionalized internal shells (see picture).

Based on a combined theoretical-experimental study, we propose that substituted m-phenylene ligands (m-N-Phi-N) can act as tuneable strong ferromagnetic couplers connecting Cu(II) ions; a new complex presenting that bridge with J close to +15 cm(-1) has been suggested and synthesized.