A series of four novel alkaline earth metal-organic frameworks constructed of Ca(ii), Sr(ii), Ba(ii) ions and tetrahedral MTB linker: structural diversity, stability study and low/high-pressure gas adsorption properties.

A series of four novel microporous alkaline earth metal-organic frameworks (AE-MOFs) containing methanetetrabenzoate linker (MTB) with composition {[Ca 4 (μ 8 -MTB) 2 ]·2DMF·4H 2 O} n (UPJS-6), {[Ca 4 (μ 4 -O)(μ 8 -MTB) 3/2 (H 2 O) 4 ]·4DMF·4H 2 O} n (UPJS-7), {[Sr 3 (μ 7 -MTB) 3/2 ]·4DMF·7H 2 O} n (UPJS-8) and {[Ba 3 (μ 7 -MTB) 3/2 (H 2 O) 6 ]·2DMF·4H 2 O} n (UPJS-9) (UPJS = University of Pavol Jozef Safarik) have been successfully prepared and characterized. The framework stability and thermal robustness of prepared materials were investigated using thermogravimetric analysis (TGA) and high-energy powder X-ray diffraction (HE-PXRD). MOFs were tested as adsorbents for different gases at various pressures and temperatures. Nitrogen and argon adsorption showed that the activated samples have moderate BET surface areas: 103 m 2 g -1 (N 2 )/126 m 2 g -1 (Ar) for UPJS-7'', 320 m 2 g -1 (N 2 )/358 m 2 g -1 (Ar) for UPJS-9'' and UPJS-8'' adsorbs only a limited amount of N 2 and Ar. It should be noted that all prepared compounds adsorb carbon dioxide with storage capacities ranging from 3.9 to 2.4 wt% at 20 °C and 1 atm, and 16.4-13.5 wt% at 30 °C and 20 bar. Methane adsorption isotherms show no adsorption at low pressures and with increasing pressure the storage capacity increases to 4.0-2.9 wt% of CH 4 at 30 °C and 20 bar. Compounds displayed the highest hydrogen uptake of 3.7-1.8 wt% at -196 °C and 800 Torr among MTB containing MOFs.