Octahedrally shaped crystals of Zr(Bisacac)2 and Hf(Bisacac)2, M(IV) derivatives of bis-acetylacetone (tetra-acetyl-ethane), H2Bisacac, were obtained in quantitative yield by a simple and reproducible synthetic procedure. The coordination spheres of Zr and Hf were found to be very closely related to those in molecular beta-diketonates, M(acac)4, according to the data of EXAFS spectroscopy. The structures are highly disordered, reflecting the multitude of conformations possible for each M(IV) centre. Crystal structure models involving metal centres with tetrahedrally arranged binding nodes were proposed for M(Bisacac)2. The produced materials are microporous with pronounced temperature-dependent affinity and selectivity to hydrogen gas absorption.
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