Uranium Pentachloride, UCl₅

Uranium Pentachloride, UCl₅, is formed in small quantity during the preparation of uranous chloride by chlorination of uranium or its oxides, either by heating in a stream of chlorine or of carbon tetrachloride vapour; it forms as a sublimate further from the heated material than the tetrachloride. It exists in two forms: long lustrous needle-shaped crystals, dark green by reflected, but ruby red by transmitted, light, and a light brown mobile powder. Both forms are very hygroscopic and are decomposed by water. The pentachloride cannot be volatilised without decomposition, for on heating it dissociates into uranous chloride and chlorine. In an atmosphere of carbon dioxide the dissociation is complete at 235° C.