No abstract

The removal of CO 2 impurities from C 2 H 2 -containing gas mixtures is an important step in purifying C 2 H 2 , a feedstock chemical used in the production of several commodity chemicals. However, that C 2 H 2 and CO 2 exhibit similar size and physicochemical properties makes their separation by physisorption extremely difficult. In this work, we detail how two hybrid ultramicroporous materials (HUMs)-known variant SIFSIX-3-Ni and variant TIFSIX-2-Cu-i-exhibit exceptional CO 2 /C 2 H 2 and C 2 H 2 /CO 2 selectivity, respectively. SIFSIX-3-Ni sets a benchmark for CO 2 /C 2 H 2 selectivity at low partial pressures, whereas TIFSIX-2-Cu-i ranks among the best porous materials in the context of C 2 H 2 / CO 2 selectivity. The performance of these HUMs was confirmed by real-time dynamic breakthrough experiments. To our knowledge, such yin-yang inversion of selectivity in closely related compounds is unprecedented. We attribute this to the distinct sorbate binding sites in SIFSIX-3-Ni and TIFSIX-2-Cu-i, as revealed by modeling studies.

That the architecture of coordination polymers can be reasonably well predicted rests upon the simple premise that the Coordination geometry of metals can be propagated with rigid bridging ligands ("spacers"). It is therefore unsurprising that a wide range of one-,[" and three-dimensional[31 infinite frameworks have already been generated with simple, linear spacers such as 4,4'-bipyridine (1). However, that the issue of isomerism and its manifestation upon structure and bulk properties has not yet been addressed is perhaps surprising. Exploitation of spacers with conformational freedom, which are expected to engender supramolecular isomerism in the coordination polymer because of conformational isomerism, ["] has until recently remained largely unexplored.[" Here we report the dramatic effect on network morphology that conformational freedom in a ligand can impart to a coordination polymer. The architecture of the coordination polymers obtained from complexation of Co(NO,), with 1 is limited by meta1:ligand stoichiometry and thus far includes simple chains (1 :I),", ' I ladders (1 :1.5),[2",'1 and grids (1 :2).[2h-d,71 The latter two motifs can be regarded as polymeric forms of "molecular boxes" ['] and possess square, hydrophobic cavities (effective area about 8 x 8 A), which enclathrate up to four guest organic molecules.[" We anticipated that the extended spacer 2 would generate analogues with enhanced cavity size. However, reaction of Co(N0,);6H20 with 2 in solutions of MeOH/MeCN, MeOH! MeCN/ferrocene, and MeOH/CHCI, afforded three isomeric forms of [Co(N0,),(2),,,],, (3a-c, respectively).Complexes 3a-c have identical molecular formulas and asymmetric units; however, the conformational freedom of 2 manifests itself by sustaining three entirely different network structures. X-ray structural revealed statistically identical heptacoordinate environments at the Co" centers (Figure 1). The three pyridyl moieties form a "T-shaped" or meridional arrangerncnt at the metal atom; the remaining coordina- plane. b) Illustration of a single molecular hilayer of 3b and the channel5 of solvent (green. space-filling rcpresentalion) that run through the structure.

The application of supramolecular concepts such as selfassembly to the solid state offers an approach to crystal design and crystal engineering, namely supramolecular synthesis of solids, that is based upon the design of infinite networks. Selfassembly of more than one molecular component, modular selfassembly, is particularly attractive since it can be accomplished in one-pot reactions with existing molecular components and allows for facile fine-tuning of structural and functional features. The challenges and opportunities that face crystal engineering are illustrated by concentrating on the superstructural diversity that has been exhibited in 2D network structures. Despite the observed superstructural diversity, which can manifest itself in the form of supramolecular isomerism, and the range of molecular components that have been utilized, these structures have in common an inherent ability to mimic clays by intercalation of guest molecules.

Realization of ideal molecular sieves, in which the larger gas molecules are completely blocked without sacrificing high adsorption capacities of the preferred smaller gas molecules, can significantly reduce energy costs for gas separation and purification and thus facilitate a possible technological transformation from the traditional energy-intensive cryogenic distillation to the energy-efficient, adsorbent-based separation and purification in the future. Although extensive research endeavors are pursued to target ideal molecular sieves among diverse porous materials, over the past several decades, ideal molecular sieves for the separation and purification of light hydrocarbons are rarely realized. Herein, an ideal porous material, SIFSIX-14-Cu-i (also termed as UTSA-200), is reported with ultrafine tuning of pore size (3.4 Å) to effectively block ethylene (C H ) molecules but to take up a record-high amount of acetylene (C H , 58 cm cm under 0.01 bar and 298 K). The material therefore sets up new benchmarks for both the adsorption capacity and selectivity, and thus provides a record purification capacity for the removal of trace C H from C H with 1.18 mmol g C H uptake capacity from a 1/99 C H /C H mixture to produce 99.9999% pure C H (much higher than the acceptable purity of 99.996% for polymer-grade C H ), as demonstrated by experimental breakthrough curves.