Properties of Less Common Molybdenum Sulphides

Compound Formula Colour Crystal Form Remarks 

Sesqui sulphide M02S3 Steel grey Needles Harder,denser than M0S2 

Pentasulphide M02S5 Dark brown Amorphous Only as hydrates 

Trisulphide M0S3 Brown/black Amorphous Decomposes to M0S2 on heating 

The instability of the electronic structure caused by the unfilled inner orbit of a transition metal leads to a very variable valency. Molybdenum exhibits valencies of 2,3,4,5 or 6 in different compounds, and it is considered that it has zero valency in its hexacarbonyl Mo(CO)g. Because of this variability in its valency, many of its reaction products are mixtures of compounds in which it has different valencies. In solid form such products may be quite homogeneous in composition, and best represented by a nonstoichiometric molecular formula. The hypothetical simple compounds present in such products cannot be separated readily from one another because valency shifts occur in processing. 

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Table 3.4 Properties of Less Common Molybdenum Sulphides...

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