Molybdenum Carbonyl, Mo(CO)₆

Molybdenum Carbonyl, Mo(CO)₆, is formed when the finely divided metal is subjected to the action of carbon monoxide at a pressure of 200 to 250 atmospheres and at a temperature of 200° C. The metallic molybdenum must be in a sufficiently active form, and is best prepared by reducing an oxychloride by means of hydrogen at a low temperature; obtained in this way, it is just pyrophoric when gently warmed. The carbonyl forms highly refractive white crystals, of density 1.96 at 15° C. The crystals volatilise before melting, and can be sublimed in an atmosphere of hydrogen or carbon monoxide at a temperature of 30° or 40° C. The vapours decompose into molybdenum and carbon monoxide on heating above 150° C. Its chemical properties resemble those of other carbonyls. It is readily attacked by oxidising agents, especially bromine, which liberates carbon monoxide and retains molybdic acid in suspension.

A reinvestigation of the composition of the carbonyl has shown that it is more exactly represented by the formula Mo₅(CO)₂₆. The substance is only slightly soluble in benzene, alcohol, and other common solvents, so that cryoscopic determinations of its molecular weight could not be made.