The separation of styrene (St) and ethylbenzene (EB) mixtures is important in the chemical industry. Here, we explore the St and EB adsorption selectivity of two pillar-shaped macrocyclic pillar[n]arenes (EtP5 and EtP6; n = 5 and 6). Both crystalline and amorphous EtP6 can capture St from a St-EB mixture with remarkably high selectivity. We show that EtP6 can be used to separate St from a 50:50 v/v St:EB mixture, yielding in a single adsorption cycle St with a purity of >99%. Single-crystal structures, powder X-ray diffraction patterns, and molecular simulations all suggest that this selectivity is due to a guest-induced structural change in EtP6 rather than a simple cavity/pore size effect. This restructuring means that the material “self-heals” upon each recrystallization, and St separation can be carried out over multiple cycles with no loss of performance.

The predictive simulation of molecular liquids requires models that are not only accurate, but computationally efficient enough to handle the large systems and long time scales required for reliable prediction of macroscopic properties. We present a new approach to the systematic approximation of the first-principles potential energy surface (PES) of molecular liquids using the GAP (Gaussian Approximation Potential) framework. The approach allows us to create potentials at several different levels of accuracy in reproducing the true PES, which allows us to test the level of quantum chemistry that is necessary to accurately predict its macroscopic properties. We test the approach by building potentials for liquid methane (CH 4 ), which is difficult to model from first principles because its behavior is dominated by weak dispersion interactions with a significant many-body component. We find that an accurate, consistent prediction of its bulk density across a wide range of temperature and pressure requires not only many-body dispersion, but also quantum nuclear effects to be modeled accurately. * max.veit@epfl.ch; Current address:

We report the design and synthesis of an amide functionalized microporous organic polymer (Am-MOP) prepared from trimesic acid and p-phenylenediamine using thionyl chloride as a reagent. Polar amide (-CONH-) functional groups act as a linking unit between the node and spacer and constitute the pore wall of the continuous polymeric network. The strong covalent bonds between the building blocks (trimesic acid and p-phenylenediamine) through amide bond linkages provide high thermal and chemical stability to Am-MOP. The presence of a highly polar pore surface allows selective CO2 uptake at 195 K over other gases such as N2, Ar, and O2. The CO2 molecule interacts with amide functional groups via Lewis acid-base type interactions as demonstrated through DFT calculations. Furthermore, for the first time Am-MOP with basic functional groups has been exploited for the Knoevenagel condensation reaction between aldehydes and active methylene compounds. Availability of a large number of catalytic sites per volume and confined microporosity gives enhanced catalytic efficiency and high selectivity for small substrate molecules.

Rationalization of structure and properties of amorphous porous solids at the microscopic level is essential in developing advanced materials. We delineate the structural modeling of a designed tetraphenylethene-based amorphous conjugated microporous polymer TPE-CMP (1) and its gas storage and photophysical properties. The polymer 1 exhibits high specific surface area of 854 m 2 /g. 1 showed appreciable CO 2 (32.4 wt %) uptake at 195 K up to 1 atm and 31.6 wt % at 273 K up to 35 bar. The structural model of 1 obtained through computational methods is quantitatively consistent with experimental observations. The microporous structural model of 1 was further validated by a calculation of CO 2 adsorption isotherm obtained through GCMC simulations. Quantum chemical calculations were employed to understand the nature of interactions of CO 2 with the constituents of the framework 1. π−π interaction with strength of 19 kJ/mol was observed between CO 2 and the phenyl rings of TPE. 1 shows strong turn-on greenish-yellow emission due to the restriction of phenyl ring rotation of TPE node. This framework induced emission (FIE) of microporous polymer 1 is further exploited for light-harvesting applications by noncovalent encapsulation of a suitable acceptor dye, rhodamine B (RhB), in the framework.

Here we report the synthesis, structure and porous properties of a 3D pillared-layer porous framework of Mn(ii)-Mn(iii), {[Mn(bipy)(HO)][Mn(CN)]·2(bipy)·4HO} (1). The guest-removed framework (1a) shows significant uptake of CH, whereas it excludes the other two C2 hydrocarbons (CH and CH). Furthermore, excellent separation proficiency for CH from a mixture of CH and CH (1 : 99, v/v) is realized in a breakthrough column experiment under ambient conditions.

An understanding of solid-state crystal dynamics or flexibility in metal-organic frameworks (MOFs) showing multiple structural changes is highly demanding for the design of materials with potential applications in sensing and recognition. However, entangled MOFs showing such flexible behavior pose a great challenge in terms of extracting information on their dynamics because of their poor single-crystallinity. In this article, detailed experimental studies on a twofold entangled MOF (f-MOF-1) are reported, which unveil its structural response toward external stimuli such as temperature, pressure, and guest molecules. The crystallographic study shows multiple structural changes in f-MOF-1, by which the 3 D net deforms and slides upon guest removal. Two distinct desolvated phases, that is, f-MOF-1 a and f-MOF-1 b, could be isolated; the former is a metastable one and transformable to the latter phase upon heating. The two phases show different gated CO adsorption profiles. DFT-based calculations provide an insight into the selective and gated adsorption behavior with CO of f-MOF-1 b. The gate-opening threshold pressure of CO adsorption can be tuned strategically by changing the chemical functionality of the linker from ethanylene (-CH -CH -) in f-MOF-1 to an azo (-N=N-) functionality in an analogous MOF, f-MOF-2. The modulation of functionality has an indirect influence on the gate-opening pressure owing to the difference in inter-net interaction. The framework of f-MOF-1 is highly responsive toward CO gas molecules, and these results are supported by DFT calculations.

Interpenetrating metal organic frameworks are interesting functional materials exhibiting exceptional framework properties. Uptake or exclusion of guest molecules can induce sliding in the framework making it porous or non-porous. To understand this dynamic nature and how framework interaction changes during sliding, metal organic framework (MOF) 508 {Zn(BDC)( 4,4′-Bipy) 0.5 · DMF(H 2 O) 0.5 } was selected for study. We have investigated structural transformation in MOF-508 under variable conditions of temperature, pressure and gas loading using Raman spectroscopy and substantiated it with IR studies and density functional theory (DFT) calculations. Conformational changes in the organic linkers leading to the sliding of the framework result in changes in Raman spectra. These changes in the organic linkers are measured as a function of high pressure and low temperature, suggesting that the dynamism in MOF-508 framework is driven by ligand conformation change and inter-linker interactions. The presence of Raman signatures of adsorbed CO 2 and its librational mode at 149 cm À1 suggests cooperative adsorption of CO 2 in the MOF-508 framework, which is also confirmed from DFT calculations that give a binding energy of 34 kJ/mol.Additional supporting information may be found in the online version of this article at the publisher's web site.Understanding guest and pressure-induced porosity

An atomistic model of the metal-organic framework (MOF) ZIF-8/graphene oxide (GO) interface has been constructed using a combination of density functional theory calculations and force-field-based molecular dynamics simulations. Two microscopic models of GO were constructed integrating basal plane and both basal and edge plane functional groups, called GO-OH and GO-COH, respectively. Analysis of the MOF/GO site-to-site interactions, surface coverage, and GO conformation/stiffness and a full characterization of the interfacial region is provided with a special emphasis on the influence of the chemical composition of GO. It was evidenced that the structure of the GO/ZIF-8 composite at the interface is stabilized by a relatively homogeneous set of interactions between the hydrogen atoms of the -NH and -OH terminal functions of ZIF-8 and the oxygen atoms of the epoxy, hydroxyl, and carboxylic groups of GO, leading to an optimal coverage of the MOF surface by GO. Such a scenario implies a significant distortion of the first GO layer brought into contact with the MOF surface, leading to an interfacial region with a relatively small width. This computational exploration strongly suggests that a very good compatibility between these two components would lead, in turn, to the preparation of defect-free ZIF-8/GO films. These predictions are correlated with an experimental effort that consists of successfully prepared homogeneous MOF/GO films that were further characterized by transmission electron microscopy and mechanical testing.