The other synthesis conditions and P/Zr results are shown in Section I of Supplementary information for reproducibility. and, respectively, which we expected to synthesize by the above method. In the structure with P/Zr = 2, both phosphonic acids in HEDP were introduced into the Zr-O-network layer and lost the ability to dissociate proton (Fig. ). On the other hand, in the structure with P/Zr = 4, one phosphonic acid was fixed in Zr-O-network, and the other phosphonic acid remained movable and titratable (-PO3H2) (Fig. ). The ZrHEDP sample can include both structures with P/Zr = 2 and 4. If there is no unreacted and remaining HEDP in the ZrHEDP samples, the ratio of the structure with P/Zr = 4 is estimated as follows: