Bismuth trifluoride

Bismuth(III) fluoride or bismuth trifluoride is a chemical compound of bismuth and fluorine. The chemical formula is BiF₃. It is a grey-white powder melting at 649 Ã‚°C.

It occurs in nature as the rare mineral gananite.

Synthesis

Bismuth fluoride can be prepared by reacting bismuth(III) oxide with hydrofluoric acid:

Structure

α-BiF₃ has a cubic crystalline structure (Pearson symbol cF16, space group Fm-3m, No. 225). BiF₃ is the prototype for the D0₃ structure, which is adopted by several intermetallics, including Mg₃Pr, Cu₃Sb, Fe₃Si, and AlFe₃, as well as by the hydride LaH_3.0. The unit cell is face-centered cubic with Bi at the face centers and vertices, and F at the octahedral site (mid-edges, center), and tetrahedral sites (centers of the 8 sub cubes) - thus the primitive cell contains 4 Bi and 12 F. Alternatively, with the unit cell shifted (1/4,1/4,1/4) the description can be of a fcc cell with face, edge, corner, and centers filled with F, and half (4 of) the octant centers with F, the other half with Bi (each octant type tetrahedrally arranged). The edge length of the BiF₃ cell is 0.5853 nm.

β-BiF₃ has the YF₃ structure where the bismuth atom has distorted 9 coordination, tricapped trigonal prism. This structure is generally considered to be ionic, and contrasts with fluorides of the lighter members of group 15, phosphorus trifluoride, PF₃, arsenic trifluoride, AsF₃ and antimony trifluoride, SbF₃, where MX₃ molecular units are present in the solid.

Reactions

BiF₃ is unaffected by water and is almost insoluble. It does not form complexes readily but the following, BiF₃.3HF and BiF₄^− in NH₄BiF₄, are known. The addition compound H₃BiF₆ is hydrolysed by water forming BiOF.

Uses

BiF₃ has received research attention as a possible electrode material for lithium batteries and as a luminescence host material for lanthanum-doped phosphors.

References