New Al-MOFs Based on Sulfonyldibenzoate Ions: A Rare Example of lntralayer Porosity

A new sulfone-functionalized metal-organic framework [Al(OH)(SDBA)].0.25DMF, denoted CAU-11, was synthesized using a V-shaped linker molecule 4,4'-sulfonyldibenzoic acid (H2SDBA). The crystal structure was solved from synchrotron X-ray powder diffraction data. Chains of trans corner-sharing AlO6 octahedra are interconnected by the carboxylate groups to form layers (ABAB stacking). Within the layers, hydrophobic lozenge-shaped pores with a diameter of 6.4 x 7.1 angstrom(2) are present inducing permanent porosity (alpha(BET) = 350 m(2) g(-1) and V-micro = 0.17 cm(3) g(-1)). With the application of HT-methods (HT = high throughput), the isoreticular carboxylate functionalized compound [Al(OH)(H2DPSTC)].0.5H(2)O (CAU-11-COOH) was synthesized using the linker molecule 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride (DPSDA), which hydrolyzes under the reaction conditions. Due to the additional noncoordinating carboxylic acid groups the pores are hydrophilic. Changing the molar ratio of Al3+ to linker lead to the discovery of a second new compound [Al-2(OH)(2)(DPSTC)(H2O)(2)].0.5H(2)O (CAU-12). In CAU-12 the linker molecule is fully deprotonated which leads to different connectivity compared to the structure of CAU-11-COOH. Thermal activation of CAU-12 leads to dehydration and transformation of the structure to [Al-2(OH)(2)(DPSTC)].nH(2)O (CAU-12-dehy). Coordinated water molecules were removed, and the coordination site is replaced by the previously noncoordinating O atom of the adjacent carboxylate group. The SO2-groups point into the pores resulting in a highly hydrophobic three-dimensional framework. The compounds exhibit high thermal stability in air at least up to 420 degrees C. Synthesis of CAU-11 can be easily scaled up in very high yields (98%).