X-ray diffraction studies of some group VIA compounds.

Of the known halides of chromium, molybdenum and tungsten only about one-third have been studied by X-ray structural techniques (see Table 1). The structures reported for these halides can be divided into three categories. 1. The two or three-dimensional lattice type is the most common. The lattice usually contains MX6 octahedra (M = Cr, Mo, W I X = halogen), the overall packing of which gives the appropriate polymeric form of the halide. Examples of this type are the di- and tri-halides of chromium. 2, Molecular crystals are formed by some halides. Amongst known structures this is confined at present to the hexahalides, e.g., WC16. 3. Polynuclear complexes may be formed by some of the halides, e.g. dimeric molybdenum pentachloride (MO2C110).