| Autor: |
Xu, W., Luo, Q., Wang, H., Francesconi, L. C., Stark, R. E., Akins, D. L. |
| Zdroj: |
The Journal of Physical Chemistry - Part B; January 2003, Vol. 107 Issue: 2 p497-501, 5p |
| Abstrakt: |
Polyoxoanions have enormous potential as drug delivery hosts, as catalysts, as agents for sequestering nuclear waste heavy metals, and as luminescent materials for laser and optical devices applications. We report the encapsulation of the polyoxoanion [Eu(H2O)3(α-1- P2W17O61)]7- within Mobil crystalline material (MCM)-41. For proper host−guest interaction, it was necessary to functionalize the surface walls of MCM-41 through use of a silylation reagent, specifically, (aminopropyl)triethoxysilane. A stable and integrated [Eu(H2O)3(α-1-P2W17O61)]7- polyoxoanion was shown to be formed inside the channels of modified MCM-41. X-ray diffraction, 29Si magic angle spinning (MAS) NMR, UV−vis absorption, emission and excitation spectra, and Raman scattering measurements have been used to structurally characterize the various products. Cross-polarization 29Si MAS NMR has been shown to better reveal the surface structural character of the modified MCM-41 than does regular 29Si MAS NMR. We find (when compared to bulk polyoxoanion) that the Raman spectrum of the polyoxoanion/MCM-41 composite system exhibits red shifts for the symmetric stretching (νs) of the W−Ot (where Ot represents a terminal oxygen) and P−O−W bands. These latter observations are interpreted as suggesting that electrostatic interaction between the negative-charged terminal oxygen (Ot) of the polyoxoanion and the −NH3+ terminal functional group, associated with the silylation agent on the walls of MCM-41, leads to an increase in the lengths of adjacent W−O and P−O bonds. Given the shape and dimensions of the polyoxoanion and the diameter of the pores in MCM-41, as well as the effects of encapsulation on emission and Raman spectra, we conclude that the anion (i) is encapsulated with its long axis parallel to the pore axis and (ii) couples to the surface through interaction with terminal oxygens that are not directly bonded to the europium atom. |
| Databáze: |
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