Osmium chloride or osmium tetrachloride is the inorganic compound

Inorganic compound

Inorganic compounds have traditionally been considered to be of inanimate, non-biological origin. In contrast, organic compounds have an explicit biological origin. However, over the past century, the classification of inorganic vs organic compounds has become less important to scientists,...

 composed of osmium

Osmium

Osmium is a chemical element with the symbol Os and atomic number 76. Osmium is a hard, brittle, blue-gray or blue-blacktransition metal in the platinum family, and is the densest natural element. Osmium is twice as dense as lead. The density of osmium is , slightly greater than that of iridium,...

 and chlorine

Chlorine

Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...

 with the empirical formula

Empirical formula

In chemistry, the empirical formula of a chemical compound is the simplest positive integer ratio of atoms of each element present in a compound. An empirical formula makes no reference to isomerism, structure, or absolute number of atoms. The empirical formula is used as standard for most ionic...

 OsCl₄. It exists in two polymorph

Polymorphism (materials science)

Polymorphism in materials science is the ability of a solid material to exist in more than one form or crystal structure. Polymorphism can potentially be found in any crystalline material including polymers, minerals, and metals, and is related to allotropy, which refers to chemical elements...

s (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.
This route affords the high temperature polymorph:

Os + 2 Cl₂ → OsCl₄

This reddish-black polymorph is orthorhombic

Orthorhombic crystal system

In crystallography, the orthorhombic crystal system is one of the seven lattice point groups. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with a rectangular base and height , such that a,...

 and adopts a structure in which osmium centres are octahedrally coordinated, sharing opposite edges of the OsCl₆ octahedra to form a chain. A brown, apparently cubic polymorph forms upon reduction of osmium tetroxide with thionyl chloride

Thionyl chloride

Thionyl chloride is an inorganic compound with the formula SOCl2. It is a reactive chemical reagent used in chlorination reactions. It is a colorless, distillable liquid at room temperature and pressure that decomposes above 140 °C. Thionyl chloride is sometimes confused with sulfuryl...

:

OsO₄ + 4 SOCl₂ → OsCl₄ + 2 Cl₂ + 4 SO₂

Osmium tetraoxide dissolves in hydrochloric acid

Hydrochloric acid

Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....

to give the hexachloroosmate anion:

OsO₄ + 8 HCl → H₂OsCl₆ + Cl₂ + 4 H₂O