Easy γ-to-α transformation of zirconium phosphate/polyphenylphosphonate salts: Porosity and hydrogen physisorption

The preparation of organic–inorganic materials based on the topotactic exchange reactions of the γ phase of zirconium phosphate and polyphenyl bisphosphonates is reported. The treatment of these materials with hypophosphoric, phosphorous and methylphosphonic acids easily led to an isomerization of the γ phases to their α allotropes. These reactions rendered finely engineered supramolecular structures by means of mild, simple processes performed in the solid–liquid interface. This kind of clean γ-to-α transformations described in our work has few precedents in the literature and allows for the effortless preparation of libraries of similar materials in which the testing of a given set of properties versus subtle structural changes may be easily performed. Using this rationale we have produced materials able to store up to 1.7% (w/w) of H2 at 77 K and 1 atm with such high ultramicroporosity that the DOE-goal H2 densities established for 2010 could be complied at pressures well below 5 atm.