Bonding and Structure of Oxofluoroniobate-Based Glasses

Glasses based on the oxofluoroniobate anion have been characterized by vibrational and solid-state NMR spectroscopy. The mechanism of glass formation in the systems K₂NbOF₅–MF₃ (M = Al, In) has been suggested. A glass network is built from the chains of corner-sharing octahedra through −Nb–F­(O)–M– and −Nb–F–Nb– bridges. Isolated NbOF₅^2– octahedra are also present, which is consistent with the glass composition. The high ionic mobility of NbOF₅^2– due to its fast reorientations results in equalization of the Nb–O and Nb–F distances, which is reflected in the appearance of the IR band at 700–800 cm^–1 not observed in the Raman spectrum. Its assignment to bridging −Nb–O–Nb– species accepted in the literature was not proven