| Summary: | Metal-organic framework materials have been the subject of great interest in recent years as their enormous chemical and structural diversity offers opportunities for potential applications. We have developed synthetic routes to a series of new zinc organophosphonate materials, exemplified by the zinc carboxyethylphosphonate (NH\(_4\))\(_2\)[Zn\(_2\)(O\(_3\)PCH\(_2\)CH\(_2\)COO)\(_2\)]·5H\(_2\)O, prepared under hydrothermal conditions in a Teflon-lined autoclave. In common with many other MOFs, it has a low molecular weight and three-dimensional porous framework structure, with pores of ca.7.6 Å diameter providing potential access to a high internal surface area, but unlike most has the advantage of containing exchangeable ammonium cations within the pores. The ability to undergo ion exchange is of interest in its own right, but also enables fine-turning of the properties of these materials. MOFs have already shown considerable promise for hydrogen storage owing to their high uptake capacity at low temperature and excellent kinetics and reversibility. In some MOFs and zeolites the hydrogen physisorption properties have been successfully improved by varying the exchangeable cations or adding exposed metal sites. Here we report the results of ion exchange experiments on (NH\(_4\))\(_2\)[Zn\(_2\)(O\(_3\)PCH\(_2\)CH\(_2\)COO)\(_2\)]·5H\(_2\)O with a view to producing MOF materials with enhanced hydrogen physisorption properties.
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