Two
new porous three-dimensional cadmium(II) metal–organic
frameworks (MOFs) containing thiophene-appended carboxylate acid ligands,
formulated as [Cd(L1)(4,4′-Bipy)]
n
.2n(DMF) (1) and [Cd(L2)(4,4′-Bipy)]
n
.2n(DMF) (2) [where L1 = 5-{(thiophen-2-ylmethyl)amino}isophthalate, L2 = 5-{(thiophen-3-ylmethyl)amino}isophthalate,
4,4′-Bipy = 4,4′-bipyridine, and DMF = N,N′-dimethylformamide] have been synthesized
and structurally characterized. The gas adsorption analysis of the
activated MOFs shows that they specifically capture CO2 (uptake amount 4.36 mmol/g under 1 bar at 195 K) over N2 and CH4. Moreover, both MOFs show a gate-opening–closing
phenomenon, which features the S-shaped isotherms with impressive
hysteretic desorption during the CO2 adsorption–desorption
process at 195 K. Ideal adsorbed solution theory (IAST) calculations
of these MOFs displayed that the obtained selectivity values for CO2/CH4 (50:50) and CO2/N2 (15:85)
are approximately 8.6–23 and 93–565, respectively. Configurational
bias Monte Carlo simulation was performed to understand the mechanism
behind the better CO2 adsorption by these MOFs. Catalytic
activity of the MOFs for the CO2 fixation reactions with
different epoxides to form cyclic carbonates were tested. These MOFs
demonstrated a significantly high conversion (94–99%) of epichlorohydrin
to the corresponding cyclic carbonate within 8 h of reaction time
at 1 bar of CO2 pressure, at 70 °C, and they can be
reused up to five cycles without losing considerably their activity.