Three-dimensional (3D) covalent organic frameworks (COFs) are rare because there is a limited choice of organic building blocks that offer multiple reactive sites in a polyhedral geometry. Here, we synthesized an organic cage molecule ( Cage-6-NH 2 ) that was used as a triangular prism node to yield the first cage-based 3D COF, 3D-CageCOF-1 . This COF adopts an unreported 2-fold interpenetrated acs topology and exhibits reversible dynamic behavior, switching between a small-pore ( sp ) structure and a large-pore ( lp ) structure. It also shows high CO 2 uptake and captures water at low humidity (<40%). This demonstrates the potential for expanding the structural complexity of 3D COFs by using organic cages as the building units.

Organic molecules tend to close pack to form dense structures when they are crystallised from organic solvents. Porous molecular crystals defy this rule: they contain open space, which is typically stabilised by inclusion of solvent in the interconnected pores during crystallisation. The design and discovery of such structures is often challenging and time consuming, in part because it is difficult to predict solvent effects on crystal form stability. Here, we combine crystal structure prediction (CSP) with a robotic crystallisation screen to accelerate the discovery of stable hydrogen-bonded frameworks. We exemplify this strategy by finding new phases of two well-studied molecules in a computationally targeted way.Specifically, we find a new 'hidden' porous polymorph of trimesic acid, d-TMA, that has a guest-free hexagonal pore structure, as well as three new solvent-stabilized diamondoid frameworks of adamantane-1,3,5,7-tetracarboxylic acid (ADTA). Beyond porous solids, this hybrid computationalexperimental approach could be applied to a wide range of materials problems, such as organic electronics and drug formulation.

Owing to environmental pollution and energy depletion, efficient separation of energy gases has attracted widespread attention. Low-cost and efficient adsorbents for gas separation are greatly needed. Here we report a family of quaternary pyridinium-type porous aromatic frameworks with tunable channels. After carefully choosing and adjusting the sterically hindered counter ions via a facile ion exchange approach, the pore diameters are tuned at an angstrom scale in the range of 3.4-7 Å. The designed pore sizes may bring benefits to capturing or sieving gas molecules with varied diameters to separate them efficiently by size-exclusive effects. By combining their specific separation properties, a five-component (hydrogen, nitrogen, oxygen, carbon dioxide and methane) gas mixture can be separated completely. The porous aromatic frameworks may hold promise for practical and commercial applications as polymeric sieves.

Porous aromatic frameworks (PAF-32s) derived from tetrahedral monomers as basic building units are successfully synthesized via Friedel-Crafts alkylation reaction in the present of inexpensive catalyst FeCl 3. The resulted PAF-32 materials possess high stabilities and high surface areas up to 1679 m 2 g-1. In particular, amino and hydroxyl functional groups are introduced in the networks. The corresponding functionalized PAF materials (PAF-32-NH 2 and PAF-32-OH) display enhanced CO 2 adsorption capacities and higher heat of adsorption (Q st) than the non-functionalized PAF-32.

A molecular crystal of a 2-D hydrogen-bonded organic framework (HOF) undergoes an unusual structural transformation after solvent removal from the crystal pores during activation. The conformationally flexible host molecule, ABTPA , adapts its molecular conformation during activation to initiate a framework expansion. The microcrystalline activated phase was characterized by three-dimensional electron diffraction (3D ED), which revealed that ABTPA uses out-of-plane anthracene units as adaptive structural anchors. These units change orientation to generate an expanded, lower density framework material in the activated structure. The porous HOF, ABTPA-2 , has robust dynamic porosity (SA BET = 1183 m 2 g –1 ) and exhibits negative area thermal expansion. We use crystal structure prediction (CSP) to understand the underlying energetics behind the structural transformation and discuss the challenges facing CSP for such flexible molecules.