An isoreticular series of metal-organic frameworks with dendritic hexacarboxylate ligands and exceptionally high gas-uptake capacity.

Metal–organic frameworks (MOFs) are newly emerging porous materials. Owing to their large surface area and tunable pore size and geometry, they have been studied for applications in gas storage and separation, especially in hydrogen and methane storage and carbon dioxide capture. It has been well established that the high-pressure gravimetric hydrogen-adsorption capacity of an MOF is directly proportional to its surface area. However, MOFs of high surface areas tend to decompose upon activation. In our previous work, we described an approach toward stable MOFs with high surface areas by incorporating mesocavities with microwindows. To extend this work, we now present an isoreticular series of (3,24)-connected MOFs made from dendritic hexacarboxylate ligands, one of which has a Langmuir surface area as high as 6033 mg . In addition, the gas-adsorption properties of this new isoreticular MOF series have been studied. To construct the (3,24)-connected isoreticular MOF series, the ligands should have C3 symmetry with three coplanar isophthalate moieties. Bearing this in mind, we designed and synthesized two dendritic hexacarboxylic acids: H6ptei and H6ttei (Figure 1a). The ensuing solvothermal reactions between these carboxylic acids and copper salts led to two isostructural MOFs with the same (3,24)-connected network (Figure 1b), designated PCN-68 (Cu3(H2O)3(ptei)·13H2O·33dmf) and PCN-610 (Cu3(H2O)3(ttei)·19H2O·22dmf) (PCN stands for porous coordination