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 N2 and CO2 suggestive
of possible framework flexibility. In contrast, the analogous framework
prepared from 2 (BMOF-1-bpdc) showed low uptake of N2 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 π–π
interactions between the interpenetrated nets.