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

Abstract

Gas or vapor-induced phase transformations in flexible coordination networks (CNs) offer the potential to exceed the performance of their rigid counterparts for separation and storage applications. However, whereas ligand modification has been used to alter the properties of such stimulus-responsive materials, they remain understudied compared with their rigid counterparts. Here, we report that a family of Zn 2+ CNs with square lattice ( sql ) topology, differing only through the substituents attached to a linker, exhibit variable flexibility. Structural and CO 2 sorption studies on the sql networks, [Zn(5- R ia)(bphy)] n , ia = isophthalic acid, bphy = 1,2-bis(pyridin-4-yl)hydrazine, R = −CH 3 , −OCH 3 , −C(CH 3 ) 3 , -N=N-Ph, and -N=N-Ph(CH 3 ) 2 , 2 – 6 , respectively, revealed that the substituent moieties influenced both structural and gas sorption properties. Whereas 2 – 3 exhibited rigidity, 4 , 5 , and 6 exhibited reversible transformation from small pore to large pore phases. Overall, the insight into the profound effect of pendent moieties of linkers upon phase transformations in this family of layered CNs should be transferable to other CN classes.

Modulation of the Dynamics of a Two-Dimensional Interweaving Metal–Organic Framework through Induced Hydrogen Bonding

“…Among the many ways to classify MOFs, one is by their structural flexibility, with relatively rigid MOFs representing a large group and flexible or dynamic-porous MOFs comprising a much smaller group. , Here, flexibility refers to the dynamic responses of MOF structures to stimuli such as changes in temperature, − pressure, , light, and electrical fields or, most commonly, during host–guest interactions . Interestingly, MOFs respond to stimuli through diverse mechanical mechanisms such as breathing, swelling, linker rotation, or subnetwork displacement, , all of which involve deformation of their pores and appear, on isotherms, as peculiar singularities .…”