Synthesis, Structure, and Spectroscopic Properties of the New Lanthanum(III) Fluoride Oxomolybdate(VI) La3FMo4O16

Influence of modifier cations on the local environment of aluminum in La2O3-Al2O3 and Y2O3-Al2O3 binary glasses

The local environment of aluminum in xLa₂O₃-(100 -x)Al₂O₃ (LA) and yY₂O₃-(100 -y)Al₂O₃ (YA) glasses is investigated using ²⁷Al MAS NMR and Raman scattering spectroscopy in the glass forming range, i.e., 27 ≤x≤ 50 and 26 ≤y≤ 37.5, respectively. The results suggest that four-fold Al (^[4]Al) is predominant in both glasses, with a content of approximately 90% in LA glasses and 60% in YA glasses; the remaining percentages are made up of five- (^[5]Al) and six-fold (^[6]Al) Al. In LA glasses, the fraction of ^[4]Al increases slightly with an increase in the La₂O₃ content, whereas, in YA glasses, the distribution of Al species does not change. Raman scattering spectroscopy reveals that, in LA glasses, the amount of non-bridging oxygen increases with an increase in x; moreover, ^[5]Al and ^[6]Al both increase with a decrease in x for x≤ 40. Comparing with alkali earth aluminate glasses, we discuss the relationship between the fundamental structure of the AlO₄ network and two parameters (the ratio of the number of oxygen atoms to that of Al and field strength).

On halide derivatives of rare-earth metal(III) oxidomolybdates(VI) and -tungstates(VI)

Halide derivatives of rare-earth metal(III) oxidomolybdates(VI) have been investigated comprehensively over the last decade comprising the halogens fluorine, chlorine, and bromine. Iodide-containing compounds are so far unknown. The simple composition REXMoO4 (RE=rare-earth element, X=halogen) is realized for X=F almost throughout the complete lanthanide series as well as for yttrium. While ytterbium and lutetium do not form any fluoride derivative, for lanthanum, only a fluoride-deprived compound with the formula La3FMo4O16 is realized. Moreover, molybdenum-rich compounds with the formula REXMo2O7 are also known for yttrium and the smaller lanthanoids. For X=Cl the composition REClMoO4 is known for yttrium and the whole lanthanide series, although, four different structure types were identified. Almost the same holds for X=Br, however, only two different structure types are realized in this class of compounds. In the case of halide derivatives of rare-earth metal(III) oxidotungstates(VI) the composition REXWO4 is found for chlorides and bromides only, so far. Due to the similar size of Mo6+ and W6+ cations, the structures found for the tungstates are basically the same as for the molybdates. With the larger lanthanides, the representatives for both chloride and bromide derivates exhibit similar structural motifs as seen in the molybdates, however, the crystal structure cannot be determined reliably. In case of the smaller lanthanoids, the chloride derivatives are isostructural with the respective molybdates, although the existence ranges differ slightly. The same is true for rare-earth metal(III) bromide oxidotungstates(VI).