Samarium subchloride, SmCl₂

Samarium subchloride, SmCl₂, is prepared by strongly heating samarium chloride in a current of pure, dry hydrogen or ammonia. It is a dark brown, crystalline solid of density 3.69 at 22°, insoluble in alcohol, pyridine, carbon disulphide, chloroform, or benzene. It dissolves readily in water, giving a dark reddish-brown solution. The colour slowly disappears, hydrogen being evolved and samarium hydroxide precipitated. The rapidity with which the colour disappears is greatly enhanced by shaking the solution in air: -

6SmCl₂ + 6H₂O = 4SmCl₃ + 2Sm(OH)₃ + 3H₂; 12SmCl₂ + 6H₂O + 3O₂ = 8SmCl₃ + 4Sm(OH)₃