A Robust Aluminum Metal-Organic Framework with Temperature-Induced Breathing Effect

A robust, yet flexible, Al-based metal-organic framework (MOF), Al2(OH)2(bpydc)·0.5H2O (1np), is synthesized via a hydrothermal strategy utilizing 2,2′-bipyridine-5,5′-dicarboxylate (bpydc2–) as the organic ligand. The structure of 1np is built from infinite trans chains of corner-sharing AlO4(OH)2 octahedra interconnected by bpydc2– ligands, forming a three-dimensional framework. 1np is robust, because of its superior thermal, hydrothermal, and chemical stability. The flexibility of 1np is reflected in the activation by the removal of unreacted H2bpydc molecules and/or occluded solvent molecules, followed by degassing at 250 °C, leading to the large pore form (1lp) of the title compound. A reversible structural change from 1lp to 1np is achieved via the hydration in water at 200 °C. The unusual combination of rigidity and flexibility enables precise control and fixation of the swelling magnitude in this MOF material.