Synthesis and structural characterization of a new chiral porous hybrid organic–inorganic material based on γ-zirconium phosphates and l-(+)-phosphoserine

In the present work, a chiral layered derivative of γ-zirconium phosphate (γ-ZrP) containing l-(+)-phosphoserine (γ-ZrP-PS*) covalently attached to inorganic layers has been prepared by means of topotactic exchange reaction. This organic–inorganic derivative is characterized by X-ray diffractometry, Solid 13C–NMR and FT-IR spectrophotometries and thermal analyses. A maximum level of topotactic replacement of 20% is achieved. Under both the acidic environment of the interlayer region of γ-ZrP and the acidic synthesis conditions, the hydrolysis of the ester bond of PS* is expected to take place to some extent. For this reason, it was impossible to exceed the recent percentage, which in turn reflects the relative moderate stability of the above mentioned bond under these conditions. In order to be more certain with regard to an expected further hydrolysis for this bond after separation, a sample of γ-ZrP-PS* was stored in a desiccator over a saturated solution of BaCl2 (90% relative humidity) for three months, and then the sample re-analyzed once again. Surprisingly, the results show that the sample still keeps almost the same level of exchange (i.e., 20%). Second, it is revealed that the sample almost gives the same spectroscopic and thermal behavior. This could be attributed to the less acidic character of the partially exchanged inorganic layers of the sample in comparison with that of the precursor γ-ZrP. Therefore, the PS* molecules persist and stay there into the interlayer gallery without further hydrolysis.

Graphical abstract• Red: oxygen• White: zirconium• Cyan: carbon• Yellow: phosphorus• Blue: nitrogenFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► l-(+)-Phosphoserine (PS*) is exchanged with γ-ZrP by means of topotactic exchange. ► The maximum exchange level is 20%. ► γ-ZrP is functionalized with chiral amino acid group. ► γ-ZrP-PS* has large chiral space for huge guest molecules to be intercalated.