Enhanced sorption in an indium-acetylenedicarboxylate metal-organic framework with unexpected chains of cis-mu-OH-connected {InO6} 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(NO3)(3)center dot xH(2)O as a racemic conglomerate in the chiral tetragonal space groups P4(3)22 and P4(1)22. Fundamentally different from other MOFs with linear linkers and trans-mu-OH-connected infinite {MO6} secondary building units as in the MIL-53-type, the linear adc(2-) linker leads to the formation of cis-mu-OH connected {InO6} 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-mu-OH/straight MIL-53-type MOFs will have polymorphs of CAU-10-H cis-mu-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 CO2 and 1.25 mmol g(-1) for CH4 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.