The Effect of Pendent Groups upon Flexibility in Coordination Networks with Square Lattice Topology

Gas or vapor-inducedphase transformations in flexiblecoordinationnetworks (CNs) offer the potential to exceed the performance of theirrigid counterparts for separation and storage applications. However,whereas ligand modification has been used to alter the propertiesof such stimulus-responsive materials, they remain understudied comparedwith their rigid counterparts. Here, we report that a family of Zn2+ CNs with square lattice (sql) topology, differingonly through the substituents attached to a linker, exhibit variableflexibility. Structural and CO2 sorption studies on the sql networks, [Zn(5-Ria)(bphy)](n),ia = isophthalic acid, bphy = 1,2-bis(pyridin-4-yl)hydrazine, R = -CH3, -OCH3, -C(CH3)(3), -N N-Ph, and -N N-Ph(CH3)(2), 2-6, respectively,revealed that the substituent moieties influenced both structuraland gas sorption properties. Whereas 2-3 exhibited rigidity, 4, 5, and 6 exhibited reversible transformation from small pore to large porephases. Overall, the insight into the profound effect of pendent moietiesof linkers upon phase transformations in this family of layered CNsshould be transferable to other CN classes.

Automated summary

Gas or vapor-induced phase transformations in flexible coordination networks (CNs) have the potential to outperform their rigid counterparts for separation and storage applications. Ligand modification has been used to alter the properties of these materials, but they have received less attention compared to rigid CNs. In this study, a family of Zn2+ CNs with variable flexibility was investigated, and it was found that the substituent moieties attached to a linker influenced both the structure and gas sorption properties of the networks. Some networks exhibited reversible transformation from small pore to large pore phases. The insights from this study can be applied to other classes of CNs.