(718a) Structure and Basic Adsorption Properties of Tcpb, a High Porosity Hydrogen-Bonded Organic Frameworks (HOFs)

A highly porous, molecular crystal has been recently introduced in literature by Zentzer et.al. (Chem. Comm. 51, 11642-11645, 2015). 1,3,5-Tris(4-carboxyphenyl)benzene (tcpb) crystallizes into a complex 8-fold polycatenated assembly of (6,3) hexagonal nets formed through hydrogen bonds and Ï?-stacking. tcpb is part of a new class of materials in which hydrogen bonds stabilize an organic framework (HOF) in an ordered fashion to produce a porous structure of the molecule itself. The self-assembly of the structure occurs by simple temperature crystallization which is rather different than the synthesis of other adsorbents. The solid can be dissolved easily in a suitable solvent, and re-crystallized without any loss in adsorption characteristics. Controlling the self-assembly can conceptually result in development of adsorbents with many different morphologies, particle size distributions, on surfaces, in cavities, in micro-scale which may enable new adsorption technologies.

Compared to other adsorbents, the number of hydrogen-bonded organic frameworks (HOFs) examined in literature is very few and almost no adsorption equilibrium data for these structures exist, especially for gases. A possible explanation for this lack of interest may have been the very low external porosity of molecular crystals in general. With BET surface area around 1,000 square meter per gram, tcpb provides a system where large porosity (hence adsorption capacity) is provided in a hydrogen-bonded network in 3D. In tcpb, the porosity is external to the molecule. Not to be confused with internal porosity of molecules (many in crystal form) which have been quite extensively studied for pharmaceutical applications. The porosity of tcpb (and HOFs) is formed by the assembly of the molecules rather than the shape of each individual molecule.

In this presentation, we will describe the structure, describe the several methods to recrystallize the solid, and present basic properties including BET surface area and adsorption of H2 and CO2.