Can Entropically Unfavorable Topological Hydrogen-Bonded Networks Form From Tetrakis- or...

Control of network topology is one of the most important issues in reticular chemistry. Herein, we report the network structures of the missing pieces of carboxyphenylbenzene (CPB) derivatives, the simplest series of building blocks for hydrogen-bonded organic frameworks (HOFs), and elucidate their network topology in a crystalline state. 1,2,3,5-Tetrakis- and 1,2,3,4,5-pentakisCPBs (1235CPB and 12345CPB) form H-bonded networks with sql- and cem-topologies, respectively. Furthermore, it is remarkable that 1235CPB forms a more complicated cqe-topological network structure with three kinds of voids in crystalline states under the same crystallization condition, although the formation occurs infrequently. The network structure with cqe-topology is hitherto unknown in molecule-based framework materials. Other molecules in the series of CPB gave no H-bonded network with complicated topology, enabling us to estimate the limitation for generating entropically unfavorable networks on the basis of a simple consideration of the number of cases for the network formation. We also report thermal behaviors, porosity, and structural transformation of these H-bonded network crystals from a materials perspective.