Niobium–oxygen interaction in mixed ligand melts

The niobium–oxygen interaction in chloride–fluoride melts has been studied by methods of linear sweep voltammetry, X-ray diffraction, IR-spectroscopy and optic crystallography. The chemical reactions and their products in NaCl–KCl–K₂NbF₇; NaCl–KCl–K₃NbOF₆ and NaCl–KCl–K₃NbO₂F₄ melts have been studied. Moreover, a comparative study of the Na₂O and Nb₂O₅ dissolution in NaCl–KCl–K₂NbF₇ melt in the molar ratio range O/Nb from 0 to 2.5 was carried out. The crucial role of the relative excess K₂NbF₇ fluorine in reactions of ligand substitution in the coordination shell of niobium is shown. When the fluorine concentration in the melt is limited by its content in complex niobium fluoride, only mono oxohalide complexes are identified in the liquid phase. The addition of “free” fluoride ions results in the formation of a wide range of oxohalide complexes up to niobates depending on the O/Nb ratio.