Osmium Dichloride, OsCl₂

Osmium Dichloride, OsCl₂, was stated to result1 when osmium is heated in chlorine, but it is very doubtful if it has ever been successfully obtained in this way.

In 1910, Ruff and Bornemann definitely proved that osmium dichloride is capable of existence, for they prepared it by heating the trichloride to 500° C. under reduced pressure.

Obtained in this manner, osmium dichloride is a dark brown powder, practically insoluble in water, but attacked by prolonged boiling with water, yielding a pale yellow solution. Concentrated nitric acid and aqua regia slowly attack it, giving osmium tetroxide; whilst concentrated alkali solutions slowly attack it in the cold, yielding clear but deep brown solutions.

Unlike platinum dichloride, osmium dichloride does not yield chlorosmous acid, H₂OsCl₄, analogous to chlor-platinous acid, H₂PtCl₄, with concentrated hydrochloric acid.