Molybdenum and Tungsten Phosphides

Molybdenum and Tungsten Phosphides have been prepared by heating the trioxides of these elements with phosphoric acid to about 1400° C. in a carbon crucible. They appeared as steel-grey crystals having densities of 5 to 6, far below the densities of the metals. Molybdenum phosphide could be oxidised by heating in the air or with chlorine. The tungsten compound was less reactive and could be burnt only in oxygen or with potassium chlorate. It was not attacked by acids. Wohler assigned the formulae MoP and W₄P₂ to these substances.

A phosphide WP has been prepared by heating the diphosphide with copper phosphide in a graphite crucible. This had a similar appearance to Wohler's phosphide, W₄P₂, but a density of 8.5. It was more easily oxidised, being attacked by chlorine and hot nitric oxide, and by nitro-hydrofluoric acid. A higher phosphide, WP₂, was also prepared by the action of phosphine on WCl₆ at a red heat. This compound burned in the air, and was in most respects more reactive than WP. Nitrogen was found to displace the phosphorus at a high temperature, giving the very stable nitride.

The phosphides of manganese and of the metals of the iron group are numerous and important.