Osmium

Osmium metal does not normally react with air. When heated, osmium tetraoxide, OsO₄ is formed:

Os(s) + 2 O₂(g) OsO₂(s)

Osmium will react with F₂ under pressure and elevated temperatures. At 600 °C and 400 atmosphere pressure, osmium(VII) fluoride, OsF₇, is formed. Under lower temperature and pressure, osmium(VI) fluoride, OsF₆, is formed.

2 Os(s) + 7 F₂(g) 2 OsF₇(s) [yellow]
Os(s) + 3 F₂(g) 2 OsF₆(s) [yellow]


For chlorine and bromine, reaction under heat and pressure, gives the corresponding Os(IV) halides:

Os(s) + 2 Cl₂(g) OsCl₄(s) [red]
Os(s) + 2 Br₂(g) OsBr₄(s) [black]

Osmium reacts with water [1]:

Os(s) + 2 H₂O(l) OsO₂(s) + 4 H⁺(aq) + 4 e⁻              E° = -0.687 V
Os(s) + 4 H₂O(l) OsO₄²⁻(aq) + 8 H⁺(aq) + 6 e⁻        E° = -0.994 V
Os(s) + 4 H₂O(l) OsO₄ + 8 H⁺(aq) + 8 e⁻                  E° = -0.85 V