Osmium(IV) chloride explained

Osmium(IV) chloride or osmium tetrachloride is the inorganic compound composed of osmium and chlorine with the empirical formula OsCl₄. It exists in two polymorphs (crystalline forms). The compound is used to prepare other osmium complexes.

Preparation, structure, reactions

It was first reported in 1909 as the product of chlorination of osmium metal.^[1] This route affords the high temperature polymorph:^[2]

Os + 2 Cl₂ → OsCl₄This reddish-black polymorph is orthorhombic and adopts a structure in which osmium centres are octahedrally coordinated, sharing opposite edges of the OsCl₆ octahedra to form a chain.^[3] A brown, apparently cubic polymorph forms upon reduction of osmium tetroxide with thionyl chloride:^[4]

OsO₄ + 2 SOCl₂ → OsCl₄ + 2 Cl₂ + 2 SO₂

Osmium tetraoxide dissolves in hydrochloric acid to give the hexachloroosmate anion:

OsO₄ + 10 HCl → H₂OsCl₆ + 2 Cl₂ + 4 H₂O

Notes and References

1. Über das Osmium, seine analytische Bestimmung, seine Oxyde und seine Chloride . Otto Ruff and Ferd. Bornemann . . 1910 . 65 . 429–456 . 10.1002/zaac.19100650126.
2. Book: Cotton, S. A. . Chemistry of Precious Metals . Chapman and Hall . London . 1997 . 0-7514-0413-6.
3. Book: Wells A.F. . 1984 . Structural Inorganic Chemistry . 5th . Oxford Science Publications . 0-19-855370-6.
4. Paul Machmer . On the polymorphism of osmium tetrachloride . . 1967 . 610a . 10.1039/C1967000610A . 12.