TEMPERATURE-MEDIATED AND GASEOUS PHASE-MEDIATED REORGANIZATION AND PARAMAGNETIC DOPING OF SOLID ALUMINUM FLUORIDES - ESR AND AB-INITIO QUANTUM-CHEMICAL STUDIES

Based on cw-X-band ESR spectroscopic measurements of Mn2+ doped AlF3 p owder samples and DFT(B3LYP)/6-31 + G quantum chemical calculations i t is shown that structural reorganization of AlF, (AlF3 (amorphous) -- > AlF3 (crystalline)) are necessarily assisted by chemical reactions w ith the participation of water. It could be unambiguously demonstrated that Mn2+ ions are suitable spin probes for reorganization processes from amorphous to local crystalline regions in fluoride matrices, The resolution of the Mn-55-F-19- superhyperfine structure (both the forma tion of regular MnF64- species as well as the reduction of strain effe cts by transformation of the amorphous parts) is a sensitive indicator of the formation of local crystalline regions. DFT(B3LYP)/6-31 + G c alculations of (AlF3)(n)(H2O)(m) complexes (n: 1,2; m: 1-3) resulted i n first and acceptable ideas of structures, energetical stabilities, a nd vibrational frequencies of hydrated AlF3. The calculated strength o f the Al-O bond, resulting in the stable {AlF3-OH2} subunit, and the f avored splitting of Al-F-Al bonds by H2O molecules, are the main reaso ns for the immediate and spontaneous hydration of freshly prepared amo rphous AlF3. Independent of the size of the model complexes, stable su bstructures like {AIF(3)-H2O} and {F3AlFAlF2-OH2} can be recognized in all optimized structure models. (C) 1998 Academic Press.