Cyclotetrabenzoin esters form porous solid-state structures with infinite one-dimensional channels and a Brunauer–Emmett–Teller surface area of ∼570 m2 g–1. Their assembly appears not to involve any strong covalent or noncovalent bonds between individual molecules. The isobutyric ester of cyclotetrabenzoin includes molecules of CS2 within its central cavity in an arrangement resembling an insulated wire.

A porous molecular crystal (PMC) assembled by close-packing of macrocyclic cyclotetrabenzoin acetate is an efficient adsorbent for selective CO 2 capture. The 7.1´7.1 Å square pore of PMC and its ester C=O group play important roles in improving its affinity for CO 2 molecules. Thermodynamically, the benzene walls of macrocycle strongly promote CO 2 adsorption via [p•••p] interactions at low pressure. In addition, the polar carbonyl groups pointing inward the square channels reduce the size of aperture to a 5.0´5.0 Å square, which offers kinetic selectivity for CO 2 capture. The PMC features water tolerance and high structural stability under vacuum and various gas adsorption conditions, which are rare among intrinsically porous organic molecules. In mixed-gas breakthrough experiments, it exhibits efficient CO 2 /N 2 and CO 2 /CH 4 separations under kinetic flow conditions. Most importantly, the moderate adsorbate-adsorbent interaction allows the PMC to be readily regenerated, and therefore applied to pressure swing adsorption (PSA) processes. The eluted N 2 and CH 4 are obtained with over 99.9% and 99.8% purity, respectively, and the separation performance is stable for 30 cycles. Coupled with its easy synthesis, these properties make cyclotetrabenzoin acetate a promising adsorbent for CO 2 separations from flue and natural gases. File list (2) download file view on ChemRxiv CO2 Separation-020421.pdf (1.34 MiB) download file view on ChemRxiv CO2 Separation-ESI-020421.pdf (1.56 MiB)

A porous molecular crystal (PMC) assembled by close-packing of macrocyclic cyclotetrabenzoin acetate is an efficient adsorbent for selective CO 2 capture. The 7.1´7.1 Å square pore of PMC and its ester C=O group play important roles in improving its affinity for CO 2 molecules. Thermodynamically, the benzene walls of macrocycle strongly promote CO 2 adsorption via [p•••p] interactions at low pressure. In addition, the polar carbonyl groups pointing inward the square channels reduce the size of aperture to a 5.0´5.0 Å square, which offers kinetic selectivity for CO 2 capture. The PMC features water tolerance and high structural stability under vacuum and various gas adsorption conditions, which are rare among intrinsically porous organic molecules. In mixed-gas breakthrough experiments, it exhibits efficient CO 2 /N 2 and CO 2 /CH 4 separations under kinetic flow conditions. Most importantly, the moderate adsorbate-adsorbent interaction allows the PMC to be readily regenerated, and therefore applied to pressure swing adsorption (PSA) processes. The eluted N 2 and CH 4 are obtained with over 99.9% and 99.8% purity, respectively, and the separation performance is stable for 30 cycles. Coupled with its easy synthesis, these properties make cyclotetrabenzoin acetate a promising adsorbent for CO 2 separations from flue and natural gases. File list (2) download file view on ChemRxiv CO2 Separation-020421.pdf (1.34 MiB) download file view on ChemRxiv CO2 Separation-ESI-020421.pdf (1.56 MiB)

Nitriles and terminal alkynes are important compounds in industrial and academic settings. Their supramolecular binding has been challenging without the intervention of metals, because of the small dimensions of their linear-C≡N and-C≡CH groups. Using a combination of crystallography and computation, we have shown that cyclotetrabenzoin esters can host terminal triple bonds of alkynes and nitriles in their electron-poor cavities. Within these cavities, π-clouds of triple bonds can establish favorable and virtually equidistant interactions with the four aromatic walls of the cyclotetrabenzoin skeleton. Binding is selective for aliphatic nitriles and terminal alkynes, with their aromatic counterparts residing outside of the cyclotetrabenzoin cavity. These findings are of relevance in the binding, separations, and activation of these and other linear molecular guests.

A porous molecular crystal (PMC) assembled by close-packing of macrocyclic cyclotetrabenzoin acetate is an efficient adsorbent for selective CO₂ capture. The 7.1´7.1 Å square pore of PMC and its ester C=O group play important roles in improving its affinity for CO₂ molecules. Thermodynamically, the benzene walls of macrocycle strongly promote CO₂ adsorption via [p···p] interactions at low pressure. In addition, the polar carbonyl groups pointing inward the square channels reduce the size of aperture to a 5.0´5.0 Å square, which offers kinetic selectivity for CO₂ capture. The PMC features water tolerance and high structural stability under vacuum and various gas adsorption conditions, which are rare among intrinsically porous organic molecules. In mixed-gas breakthrough experiments, it exhibits efficient CO₂/N₂ and CO₂/CH₄ separations under kinetic flow conditions. Most importantly, the moderate adsorbate–adsorbent interaction allows the PMC to be readily regenerated, and therefore applied to pressure swing adsorption (PSA) processes. The eluted N₂ and CH₄ are obtained with over 99.9% and 99.8% purity, respectively, and the separation performance is stable for 30 cycles. Coupled with its easy synthesis, these properties make cyclotetrabenzoin acetate a promising adsorbent for CO₂ separations from flue and natural gases.