Cyclotetrabenzoin: Facile Synthesis of a Shape-Persistent Molecular Square and Its Assembly into Hydrogen-Bonded Nanotubes

Cyanide-catalyzed benzoin condensation of terephthaldehyde produces a cyclic tetramer, which we propose to name cyclotetrabenzoin. Cyclotetrabenzoin is a square-shaped macrocycle ornamented with four alpha-hydroxyketone functionalities pointing away from the central cavity, the dimensions of which are 6.9 x 6.9 angstrom. In the solid state, these functional groups extensively hydrogen bond, resulting in a microporous three-dimensional organic framework with one-dimensional nanotube channels. This material exhibits permanent-albeit low-porosity, with a Langmuir surface area of 52 m(2)g(-1). Cyclotetrabenzoin's easy and inexpensive synthesis and purification may inspire the creation of other shape-persistent macrocycles and porous molecular crystals by benzoin condensation.