Niobium pentafluoride, structure

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. 

The V—F—V angle of 150° in the vanadium pentafluoride structure lies between those for the niobium and rhodium compounds. Thus, the structure cannot be described in terms of either of the close-packed arrangements. Although in the structure some approach toward close-packed planes of fluorine atoms can be seen, a comparison of volume per formula unit for the pentafluorides shows that for the second and... 

Typical examples of compounds that form chain-type structures are simple pentafluorides of tantalum and niobium, TaFs and Nbfs, which were investigated by Edwards [199]. The cry stal structure of NbF< consists of rings made up of four NbF6 octahedrons that are linked by fluorine ligands that are each shared by two neighboring octahedrons, as shown in Pig. 29. The main interatomic distances (in A) are as follows Nb-Nb 5.80, 3.90 and 4.13 Nh-P,(Ki -. 1.75 and 1.78 Nb-Ftal% - 2.06 and 2.07 angle Nl>F[jf d,e-Nh - 182.5°. 

The pentafluorides are made by direct fluorination of the metals or the pentachlor-ides. Both are volatile white solids (Nb mp 80°C, bp 235°C Ta mp 95°C, bp 229°C), giving colorless liquids and vapors. They have the tetranuclear structures shown in Fig. 18-B-3. Niobium(IV) fluoride is a black, nonvolatile, paramagnetic solid TaF4 is unknown. 

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