Synthesis, Characterization, and Amine Intercalation Behavior of Zirconium N-(Phosphonomethyl)iminodiacetic Acid Layered Compounds

New types of zirconium layered compounds containing the N-(phosphonomethyl)iminodiacetic acid group (PMIDAH2) have been synthesized and characterized. A mixed phosphate/phosphonate compound, Zr2(PO4)(O3PCH2N{CH2COOH}2)(O3PCH2N{CH2COOHCH2COO-})(H2O)2 (I) was obtained when a mixture of phosphoric acid and diacetatoiminophosphonic acid (H2PMIDAH2) solution in the ratio of 1:1 was heated with the zirconyl chloride in the presence of HF. The layer structure of this compound is different from that of any known layered zirconium phosphonate compounds. The bridging of metal atoms by the phosphate groups within the layer is similar to that found in γ-ZrP, while the mode of phosphonate binding is similar to that found for α-ZrP. When the above reaction was carried out with additional phosphoric acid, a similar layered structure but with composition Zr2(PO4)(O3PC5H7O4N)(O3PC5H8O4N) x (HPO4)1 - x (H2O)2 (II) was obtained. In this compound some of the phosphonate groups are replaced by the HPO4 2- groups. When the ratio of phosphoric acid to H2PMIDAH2 was 4, the compound obtained has the maximum replacement. The value of x for this compound in the above formula is 0.5. Further addition of phosphonic acid yields a new phase with composition Zr(O3PC5H8O4N) x (HPO4)1 - x (III). 31P solid-state MAS NMR and XRD patterns suggest that this new phase is structurally similar to α-ZrP. Intercalation reactions with primary alkylamines, C n H2 n +1NH2 (n = 3−8), were carried out with all these phases. The results show that 2 mol of amines were taken up by compound I to form [Zr2(PO4)(PMIDAH2)(PMIDAH)(H2O)2]·2RNH2, while 1.5 mol of amine was intercalated into compound III, forming Zr(PMIDAH2) x (HPO4)1 - x ·1.5RNH2. In both compounds the amines appear to pack as double layers. The ion-exchange behavior of these compounds is also discussed.