Experimental Confirmation of a Predicted Porous Hydrogen‐Bonded Organic Framework

Abstract

Hydrogen‐bonded organic frameworks (HOFs) with low densities and high porosities are rare and challenging to design because most molecules have a strong energetic preference for close packing. Crystal structure prediction (CSP) can rank the crystal packings available to an organic molecule based on their relative lattice energies. This has become a powerful tool for the a priori design of porous molecular crystals. Previously, we combined CSP with structure‐property predictions to generate energy‐structure‐function (ESF) maps for a series of triptycene‐based molecules with quinoxaline groups. From these ESF maps, triptycene trisquinoxalinedione (TH5) was predicted to form a previously unknown low‐energy HOF (TH5‐A) with a remarkably low density of 0.374 g cm−3 and three‐dimensional (3D) pores. Here, we demonstrate the reliability of those ESF maps by discovering this TH5‐A polymorph experimentally. This material has a high accessible surface area of 3,284 m2 g−1, as measured by nitrogen adsorption, making it one of the most porous HOFs reported to date.

Water-Tolerant Hydrogen-Bonded Organic Framework Based on Phenylbis(benzimidazol-2-yl)methanol: Synthesis, Structural Characterization, and Organic-Vapor-Adsorption Properties

“…Thus, we examined the removal of EtOAc from 1 ·(EtOAc). The SCSC desorption of EtOAc was induced by heating a crystalline sample of 1 ·(EtOAc) at 100 °C for 6 h under reduced pressure or by treating the samples with 8 MPa of scCO 2 at 60 °C for 2 h. It should be noted here that guest desorption using scCO 2 is well established and has already been applied to HOFs. − Figure c (left) shows the TGA curves recorded under a N 2 flow for 1 ·(EtOAc) and the crystals resulting from the desorption experiments, i.e., the desolvated form. For 1 ·(EtOAc), a 20% weight loss corresponding to the weight of EtOAc in 1 ·(EtOAc) was observed at ∼130 °C.…”

Porous isoreticular non-metal organic frameworks

“…The ability to position chemical functionality with atomic precision in crystalline porous frameworks has created properties that do not exist in classical porous materials, such as activated carbons. Porous crystalline solids can be divided into two classes: extended, covalently bonded frameworks, such as MOFs 1 , 2 and covalent organic frameworks (COFs) 13 , 14 ; and porous molecular crystals, such as hydrogen-bonded frameworks (HOFs) 7 , 8 , 15 , 16 and porous organic cages 17 . Porous bonded frameworks exploit strong, directional covalent or coordinate covalent bonding, which underpins the isoreticular principle 2 , whereby series of structurally related frameworks can be synthesized.…”

“…Here we show that chemical knowledge can be combined with computational crystal-structure prediction 6 (CSP) to design porous organic ammonium halide salts that contain no metals. The nodes in these salt frameworks are tightly packed ionic clusters that direct the materials to crystallize in specific ways, as demonstrated by the presence of well-defined spikes of low-energy, low-density isoreticular structures on the predicted lattice energy landscapes 7 , 8 . These energy landscapes allow us to select combinations of cations and anions that will form thermodynamically stable, porous salt frameworks with channel sizes, functionalities and geometries that can be predicted a priori.…”

Supramolecular polynuclear clusters sustained cubic hydrogen bonded frameworks with octahedral cages for reversible photochromism

“…The rational synthesis of porous HOFs with preorganized and highly symmetrical networks has been a long-term challenge 29 . Therefore, conventional hydrogen bonding motifs usually result in one-dimensional channels 30 instead of hierarchical cavities 31 , exhibiting poor adaptability to accommodate specific guest molecules 32 , 33 . The stacking manner of the building blocks defines the topology and porosity of HOFs 34 – 38 .…”