Single-Atom Ligand Changes Affect Breathing in an Extended Metal-Organic Framework

2-Phenylpyridine-5,4'-dicarboxylic acid (1, dcppy), a derivative of 4,4'-biphenyldicarboxylic (2, bpdc) was used as the organic linking component for several metal organic frameworks (MOFs). The pyridine component of 1 does not interfere with the solvothermal synthetic procedure, and hence both 1 and 2 form similar isoreticular MOFs. Zr4+-based UiO-67-dcppy, Al3+-based DUT-5-dcppy, Zn2+-based DMOF-1-dcppy, and interpenetrated Zn2+-based BMOF-1-dcppy were readily synthesized from 1. Similarly, isostructural frameworks from 2 were prepared (UiO-67, DUT-5, DMOF-1-bpdc, and interpenetrated BMOF-1-bpdc). The structures and physical properties of these frameworks were characterized by powder X-ray diffraction (PXRD), single X-ray diffraction (XRD), thermogravimetric analysis (TGA), and gas sorption analysis. Generally, frameworks prepared from 1 or 2 displayed similar properties; however, gas sorption data showed that BMOF-1-dcppy displayed a very large hysteresis with N-2 and CO2 suggestive of possible framework flexibility. In contrast, the analogous framework prepared from 2 (BMOF-1-bpdc) showed low uptake of N-2 and CO2. The substantial difference in the gas sorption behavior of these MOFs is attributed to the pyridine nature of 1 that results in weakened pi-pi interactions between the interpenetrated nets.