Tuning the Moisture and Thermal Stability of Metal-Organic Frameworks through Incorporation of Pendant Hydrophobic Groups

An isostructural series of NbO-type porous metal-organic frameworks (MOFs) with different dialkoxy-substituents of formula Cu-2(TPTC-OR) (TPTC-OR = 2',5'-di{alkyl}oxy-[1,1':4',1 ''-terphenyl]-3,3 '',5,5 ''-tetracarboxylate, R = Me, Et, Pr-n, (n)Hex) has been synthesized and characterized. The moisture stability of the materials has been evaluated, and a new superhydrophobic porous MOF has been identified. The relationship between pendant side chain length and thermal stability has been analyzed by in situ synchrotron powder X-ray diffraction, showing decreased thermal stability as the side chain length is increased, contradictory to thermogravimetric decomposition studies. Additionally, the four materials exhibit moderate Brunauer-Emmett Teller (BET) and Langmuir surface areas (1127-1396 m(2) g(-1) and 1414-1658 m(2) g(-1)) and H-2 capacity up to 1.9 wt % at 77 K and 1 bar.