Temperature- and gaseous phase-mediated reorganization and paramagnetic doping of solid aluminum fluorides: ESR and ab initio quantum chemical studies
- Humboldt Univ. of Berlin (Germany). Inst. of Chemistry
Based on cw-X-band ESR spectroscopic measurements of Mn{sup 2+} doped AlF{sub 3} powder samples and DFT (B3LYP)/6-31+G{sup *} quantum chemical calculations it is shown that structural reorganization of AlF{sub 3} (AlF{sub 3} (amorphous) {yields} AlF{sub 3} (crystalline)) are necessarily assisted by chemical reactions with the precipitation of water. It could be unambiguously demonstrated that Mn{sup 2+} ions are suitable spin probes for reorganization processes from amorphous to local crystalline regions in fluoride matrices. The resolution of the {sup 55}Mn-{sup 19}F- superhyperfine structure (both the formation of regular MnF{sub 6}{sup 4{minus}}-species as well as the reduction of strain effects by transformation of the amorphous parts) is a sensitive indicator of the formation of local crystalline regions. DFT(B3LYP)/6-31+G{sup *} calculations of (AlF{sub 3}){sub n}(H{sub 2}O){sub m} complexes (n: 1,2; m: 1--3) resulted in first and acceptable ideas of structures, energetical stabilities, and vibrational frequencies of hydrated AlF{sub 3}. The calculated strength of the Al-O bond, resulting in the stable {l_brace}AlF{sub 3}-OH{sub 2}{r_brace} subunit, and the favored splitting of Al-F-Al bonds by H{sub 2}O molecules, are the main reasons for the immediate and spontaneous hydration of freshly prepared amorphous AlF{sub 3}. Independent of the size of the model complexes, stable substructures like {l_brace}AlF{sub 3}-H{sub 2}O{r_brace} and {l_brace}F{sub 3}AlFAlF{sub 2}-OH{sub 2}{r_brace} can be recognized in all optimized structure models.
- Sponsoring Organization:
- Deutsche Forschungsgemeinschaft, Bonn (Germany)
- OSTI ID:
- 653127
- Journal Information:
- Journal of Solid State Chemistry, Vol. 139, Issue 1; Other Information: PBD: Aug 1998
- Country of Publication:
- United States
- Language:
- English
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