Structural details of carboxylic acid-based Hydrogen-bonded Organic Frameworks (HOFs)

Crystalline porous molecular frameworks formed through intermolecular hydrogen bonding are often called hydrogen-bonded organic frameworks (HOFs) by analogy to metal organic frameworks (MOFs) and covalent organic frameworks (COFs). Although the origin may go back to the 1960s, HOFs have recently been investigated as a new family of functional porous materials. In this review, HOFs composed of tritopic, tetratopic, and hexatopic carboxylic acid derivatives are reviewed by considering structural aspects such as isostructurality. These derivatives typically form H-bonded hcb, dia, sql, hxl, and pcu networks depending on the numbers, positions, and orientations of the carboxy groups in the molecule. We show detailed structures for selected HOFs indicating the low-dimensional networks formed through H-bonding of the molecule and higher-dimensional structures formed by assembly of the network. The networks can be designed and predicted from the molecular structure, while the latter is still difficult to design. We hope that this review will contribute to the well-controlled construction of HOFs. Crystalline porous molecular frameworks formed through intermolecular hydrogen bonding calling hydrogen-bonded organic frameworks (HOFs) have recently been investigated as a new family of functional porous materials. In this review, HOFs composed of tritopic, tetratopic, and hexatopic carboxylic acid derivatives, which form H-bonded network such as those with hcb, sql, and hxl topologies depending on the numbers, positions, and orientations of the carboxy groups and conformational flexibility of the molecular skeletons, are reviewed by considering structural aspects such as isostructurality.