Niobium pentafluoride

Perchloric acid (HCIO4 Ho —13.0), fluorosulfuric acid (HSO3F Ho — 15.1), and trifluoromethanesulfonic acid (CF3SO3H Ho —14.1) are considered to be superacids, as is truly anhydrous hydrogen fluoride. Complexing with Lewis acidic metal fluorides of higher valence, such as antimony, tantalum, or niobium pentafluoride, greatly enhances the acidity of all these acids. 

Niobium Penta.fIuoride, Niobium pentafluoride is prepared best by direct fluorination of the metal with either fluorine or anhydrous hydrofluoric acid at 250—300°C. The volatile NbF is condensed in a pyrex or quartz cold trap, from which it can be vacuum-sublimed at 120°C to yield colorless monoclinic crystals. It is very hygroscopic and reacts vigorously with water to give a clear solution of hydrofluoric acid and H2NbOF ... 

The linked MeF6 octahedron structure remains unchanged when moving from solid to gaseous phase [200]. Various researchers indicate that the gaseous phase above niobium pentafluoride, NbFs, predominantly consists of trimers, (NbF5)3 with a D3h symmetiy [201-203]. 

Typical chain-type crystal structure is observed for compounds with the general formula MNbOF4. Table 30 presents cell parameters of tantalum and niobium pentafluorides and of other compounds with X Me = 5. 

Niobium pentafluoride is used in making other fluoro compounds of niobium. 

Niobium pentafluoride is obtained as an intermediate during the recovery of niobium metal from its ores (See Niobium). It also can be prepared by direct fluorination of niobium metal at 250 to 300°C, either by fluorine gas or anhydrous hydrofluoric acid. The pentafluoride vapors are condensed in a pyrex or quartz tube from which it is sublimed at 120°C under vacuum and collected as colorless crystals. 

Niobium Pentafluoride, NbFs, is the only known compound of niobium and fluorine, and even this cannot be obtained in the free state by a wet method because of the extreme readiness with which it hydrolyses. Niobium pentoxide dissolves readily in hydrofluoric acid, but evaporation of the solution leaves a residue of the unchanged oxide. Niobium pentafluoride has been prepared synthetically 1 by passing dry fluorine over the gently heated metal contained in a boat in a platinum tube. The product is freed from platinum tetrafluoride, a little of which is formed at the same time, by distillation in vacuo at 100° to 110° . An alternative method consists in treating niobium pentachloride with anhydrous hydrogen fluoride in a freezing mixture and purifying by redistillation.3... 

Niobium pentafluoride forms colourless, highly refractive prisms density 8 2932 at 18° C. It melts at 75 5° C.f and boils at 217° to 220° C. under a pressure of 760 mm. of mercury. It is extremely hygroscopic and deliquesces rapidly in air. It is reduced by hydrogen at 286° C. in contact with platinum to an unstable lower blue fluoride. Excess of concentrated alkali hydroxide or alkali carbonate solutions attack it with formation of the alkali niobate. It dissolves in toluene, paraffin, carbon bisulphide, and other organic solvents. 

Double Fluorides of Niobium Pentafluoride.—Niobium pentafluoride shows a strong tendency to form stable double fluorides with the fluorides of other metals. These are conveniently prepared by the action of carbonates of the metals on solutions of niobium pentoxide in a large excess of hydrofluoric add, or by the addition of a large excess of hydrofluoric acid to solutions of the oxyfluorides of the metals. In the absence of excess of hydrofluoric add hydrolysis takes place as usual with the formation of niobium oxytrifluoride, NbOF3. The precipitation of these double fluorides indicates the probable existence in solution of niobium pentafluoride stability is imparted by the formation of complex anions containing several fluorine atoms. 

Tantalum Pentafluoride, TaFs, is the only known fluoride of tantalum, and has been successfully isolated by methods that avoid hydrolysis (1) Tantalum and fluorine are brought into reaction exactly as in the preparation of niobium pentafluoride.1 (2) Tantalum penta-chloride is treated in the cold with dry hydrofluoric add the hydrochloric acid liberated and excess of hydrofluoric add are evaporated oft, and the resulting tantalum pentafluoride is purified by redistillation in a platinum crucible between 300° and 400° C.2 (3) The double barium tantalum fluoride, 3BaF2.2TaF5, is very strongly heated in a platinum tube, one end of which is kept cold. ... 

The reactivity of polyfluorinated cyclohexadienes toward antimony or niobium pentafluorides has some peculiarities. The equilibrium mixture of 1,4- and 1,3-cyclohexadienes is formed from pure isomers of each and a catalytic amount of MF5 at room temperature where the non-conjugated diene predominates [167], With an excess of SbF5 both isomers disproportionate to give a mixture of aromatic compounds and cyclohexene polyfluoroaromatics and the corresponding cyclohexene [167,168] ... 

The major use of C1F3 is in the nuclear industry which converts unclean spent fuel reprocessing, uranium metal into gaseous uranium hexafluoride. Other applications are low temperature etchant for single crystalline silicon [63,64], It is also used as a fluorinating reagent and in the synthesis of GIF and conversion of metals to metal fluorides such as tantalum and niobium metals to tantalum pentafluoride and niobium pentafluoride, respectively. 

Na2Mo04 SODIUM MOLYBDATE 1127 NbF5[g] NIOBIUM PENTAFLUORIDE (GAS) 1169... 

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