rtl-M-MOFs (M = Cu, Zn) with a T-shaped bifunctional pyrazole-isophthalate ligand showing flexibility and S-shaped Type F-IV sorption isotherms with high saturation uptakes for M = Cu
Two new rtl-MOFs rtl-[Cu(HIsa-az-dmpz)] and rtl-[Zn(HIsa-az-dmpz)] have been synthesized by using the new bifunctional ligand 5-(4-(3,5-dimethyl-1H-pyrazolyl)azo)isophthalic acid (H3Isa-az-dmpz). Both frameworks are potentially porous structures with DMF molecules included into the channels of the as synthesized materials. The flexible MOF rtl-[Cu(HIsa-az-dmpz)] undergoes a reversible phase change into a closed form upon activation. Consequently, rtl-[Cu(HIsa-az-dmpz)] shows S-shaped Type F-IV adsorption profiles or gate-opening effect at cryogenic temperatures with high saturation uptakes of 360 cm3/g for N2 at 77 K and 310 cm3/g for CO2 at 195 K. These profiles together with the reversibility could be reproduced upon repeated measurements on the same materials. The gravimetric high-pressure CO2 adsorption shows a gate-opening at ~10 bar with an uptake of 332 mg/g. rtl-[Zn(HIsa-az-dmpz)] undergoes an irreversible transformation into a non-porous phase upon activation.