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.