Hexafluoroaluminate ion

Ion transport measurements indicate that Na" ions carry most of the current, yet aluminum is deposited. A charge transfer probably occurs at the cathode interface and hexafluoroaluminate ions are discharged, forming aluminum and F ions to neutralize the charge of the current carrying Na" ... 

The electrolyte is a molten cryolite salt NaAlFg) which melts at 940 °C and decomposes into sodium and hexafluoroaluminate ions (AIF ) [1,69]... 

The common structural element in the crystal lattice of fluoroaluminates is the hexafluoroaluminate octahedron, AIF. The differing stmctural features of the fluoroaluminates confer distinct physical properties to the species as compared to aluminum trifluoride. For example, in A1F. all corners are shared and the crystal becomes a giant molecule of very high melting point (13). In KAIF, all four equatorial atoms of each octahedron are shared and a layer lattice results. When the ratio of fluorine to aluminum is 6, as in cryoHte, Na AlF, the AIFp ions are separate and bound in position by the balancing metal ions. Fluorine atoms may be shared between octahedrons. When opposite corners of each octahedron are shared with a corner of each neighboring octahedron, an infinite chain is formed as, for example, in TI AIF [33897-68-6]. More complex relations exist in chioUte, wherein one-third of the hexafluoroaluminate octahedra share four corners each and two-thirds share only two corners (14). 

Solutions of hexafluoroaluminic acid can be prepared by dissolving A1203 in aqueous HF.480 On addition of the appropriate cation, salts of the AIF " ion are precipitated. Concentrated solutions of the acid are only stable for short times, and give /3-AlF3,3H20 on standing. 

Plan We use the rules that were presented above and refer to Tables 22.6 and 22.7. Solution (a) The complex ion is [AlFs] . There are six Qiexa-) F ions (fluoro) as ligands, so we have hexafluoro. The complex ion is an anion, so the ending of the metal ion (aluminum) must be changed to -ate hexafluoroaluminate. Aluminum has only the +3 oxidation state, so we do not use a Roman numeral. The positive counter ion is named first and separated from the anion by a space sodium hexafluoroaluminate. 

---