FIELD: chemical technology, inorganic chemistry. SUBSTANCE: niobium or tantalum oxide or hydroxyhalide is interacted with hydrogen fluoride and dehydrating agent at 50-200 C. Amount of hydrogen fluoride is 5 moles/1 mole parent substance, not less, mainly 10 moles hydrogen fluoride/1 mole parent substance. Phosgene or thionyl chloride or sulfuryl chloride but mainly phosgene were used as dehydrating agent. The depleted catalyst based on niobium or tantalum pentafluoride can be used as parent compounds. EFFECT: improved method of synthesis. 7 cl
