The structures of crystalline halides MX

We may make two generalizations about crystalline metal halides. First, fluorides differ in structure from the other halides of a given metal except in the case of molecular halides (for example, Sbp3 and SbCl3 both crystallize as discrete molecules) and those of the alkali metals, all the halides of which are essentially ionic crystals. In many cases the fluoride of a metal has a 3D structure whereas the chloride, bromide, and iodide form crystals consisting of layer, or sometimes chain, complexes. (For exceptions, particularly fluorides MF3-MF5, see Table 9.9.) Second, many fluorides and oxides of similar formula-type are isostructural, while chlorides, bromides, and iodides often have the same types of structure as sulphides, selenides, and tellurides. The following examples illustrate these points  

MX3 6 7+2 8 + 1 9 ReOa and related structures (Table 9.16) LaFa YF3 UCI3 6 8 + 1 (YCla iBila PuBra 4 6 AuFs Zrla 3 4 4 SbFa AlaOs AuaCla 

---