Paddle Wheel Based Triazolyl Isophthalate MOFs: Impact of Linker Modification on Crystal Structure and Gas Sorption Properties

Syntheses
and comprehensive characterization of two closely related series of
isomorphous metal–organic frameworks (MOFs) based on triazolyl
isophthalate linkers with the general formula ∞3[M2(R1–R2–trz–ia)2] (M = Cu, Zn) are presented. Using solvothermal synthesis
and synthesis of microcrystalline materials on the gram scale by refluxing
a solution of the starting materials, 11 MOFs are readily available
for a systematic investigation of structure–property relationships.
The networks of the two series are assigned to rutile (rtl) (1–4) and α-PbO2 (apo) (5–9) topology,
respectively. Due to the orientation of the triazole substituents
toward the cavities, both the pore volume and the pore diameter can
be adjusted by choice of the alkyl substituents. Compounds 1–9 exhibit pronounced microporosity with calculated
porosities of 31–53% and show thermal stability up to 390 °C
as confirmed by simultaneous thermal analysis. Systematic investigation
of adsorption properties by CO2 (298 K) and N2 (77 K) adsorption studies reveal remarkable network flexibility
induced by alkyl substituents on the linker. Fine-tuning of the gate
opening pressure and of the hysteresis shape is possible by adjusting
the substitution pattern and by choice of the metal ion.