Intercluster porous nanocomposites from combination of [AlO4Al12(OH)24(H2O)12]7+ cation and Anderson-type [Al1−x Cr x Mo6O24H6]3− anion: XRD, TG-DTA, SEM-EDAX and EPR studies

The synthesis of intercluster porous nanocomposites obtained from polyoxometallate compounds such as the [AlO4Al12(OH)24(H2O)12]7+ cation (named Al13) and the Anderson-type [Al1−xCrxMo6O24H6]3− anion (named Al1−xCrxMo6) has been performed in order to study the interaction between the two cluster ions, the stability of the XMo6 planar configuration, the products obtained after thermal treatment, the structure and the local symmetry of the Cr3+ species. Chemical, thermal, structural and spectroscopic characterizations of the original and thermally treated phases have been followed by different techniques such as TG-DTA, XRD, SEM-EDAX, and mainly by EPR. All the results have shown that the structure of the intercluster nanocomposites (Al13)(Al1−xCrxMo6)2 precursors is similar to that reported by Son et al. for the chromium-free (Al13)(AlMo6)2 intercluster nanocomposite [Son et al., J. Am. Chem. Soc. 122 (2000) 7432]. After thermal treatment in air at several temperatures of the (Al13)(Al1−xCrxMo6)2 nanocomposites the following phases have been observed and characterised: (i) at 400 °C an amorphous phase containing dispersed Cr3+ ions; (ii) at 700 °C a crystalline phase corresponding to Cr2(MoO4)3/Al2(MoO4)3 solid solutions; (iii) at 950 °C α-Al2O3/Cr2O3 solid solutions with a random dispersion of the Cr3+ ions.