The MnNbOF 5 –BaF 2 and MnNbOF 5 –PbF 2 systems have a wider glass region than the binary system NbO 2 F–BaF 2 . According to thermogravimetric analysis data, the glasses in these systems are characterized by lower glass transition temperatures than the similar binary glass 50NbO 2 F · 50BaF 2 . The thermal stability range and the degree of thermal stability of the glasses depend on the modifying cation. As demonstrated by IR and Raman spectroscopy, the glass structure is built from Nb(O,F)6 polyhedra linked into a glass network by oxygen and fluoride bridges. This is explained by the fact that the starting component MnNbOF 5 · 4H 2 O decomposes to NbO 2 F upon melting. The manganese cations form their own polyhedra, which are incorporated into the glass network. The modifying cations exert a considerable effect on the glass network structure and on shortand medium-range order domains. DOI: 10.1134/S0036023606100032 SYNTHESIS AND PROPERTIES OF INORGANIC COMPOUNDS