Enhanced sorption in an indium-acetylenedicarboxylate metal-organic framework with unexpected chains of cis -μ-OH-connected {InO 6 } octahedra.

Single crystals of the new metal-organic framework (MOF) In-adc (HHUD-4) were obtained through the reaction of linear acetylenedicarboxylic acid (H 2 adc) with In(NO 3 ) 3 · x H 2 O as a racemic conglomerate in the chiral tetragonal space groups P 4 3 22 and P 4 1 22. Fundamentally different from other MOFs with linear linkers and trans -μ-OH-connected infinite {MO 6 } secondary building units as in the MIL-53-type, the linear adc 2- linker leads to the formation of cis -μ-OH connected {InO 6 } polyhedra, which have otherwise only been found before for V-shaped ligands, as in CAU-10-H. A far-reaching implication of this finding is the possibility that trans -μ-OH/straight MIL-53-type MOFs will have polymorphs of CAU-10-H cis -μ-OH/helical topology and vice versa . HHUD-4 is a microporous MOF with a BET surface area of up to 940 m 2 g -1 and a micropore volume of up to 0.39 cm 3 g -1 . Additionally, HHUD-4 features good adsorption uptakes of 3.77 mmol g -1 for CO 2 and 1.25 mmol g -1 for CH 4 at 273 K and 1 bar, respectively, and a high isosteric heat of adsorption of 11.4 kJ mol -1 for H 2 with a maximum uptake of 6.36 mmol g -1 at 77 K and 1 bar. Vapor sorption experiments for water and volatile organic compounds (VOCs) such as benzene, cyclohexane and n -hexane yielded uptake values of 135, 269, 116 and 205 mg g -1 , respectively, at 293 K. While HHUD-4 showed unremarkable results for water uptake and low stability for water, it exhibited good stability with steep VOC uptake steps at low relative pressures and a high selectivity of 17 for benzene/cyclohexane mixtures.