Ruthenium Oxychlorides

When ruthenium tetroxide is covered with water, to which caesium chloride acidulated with hydrochloric acid is subsequently added, caesium oxychlor-ruthenate, Cs₂RuO₂Cl₄ or 2CsCl.RuOCl₂, is formed. On crystallisation dark purple isometric octahedra, cubes, and rhombic dodecahedra separate out. These are soluble in cold hydrochloric acid, from which they may be recrystallised unchanged.

The reaction may be represented as follows:

RuO₄ + 4HCl + 2CsCl = Cs₂RuO₂Cl₄ + 2H₂O + Cl₂.

A characteristic reaction for these crystals is their behaviour towards water, which instantly decomposes them, the water becoming black.

On boiling with concentrated hydrochloric acid chlorine is disengaged, caesium chlor-ruthenate remaining behind. Thus:

Cs₂RuO₂Cl₄ + 4HCl = Cs₂RuCl₆ + 2H₂O + Cl₂.

Ruthenium Tribromide, RuBr₃, is most readily obtained by evaporation of an aqueous solution of the tetroxide with concentrated hydro-bromic acid:

2RuO₄ + 16HBr = 2RuBr₃ + 5Br₂ + 8H₂O.

The salt is dark brown in colour dissolving in water to a bright red solution, which decomposes slowly on keeping, but rapidly on warming, yielding a black precipitate. With sulphuretted hydrogen the solution yields ruthenium sulphide.

When heated the solid bromide evolves bromine. It absorbs dry ammonia gas, yielding an addition compound of composition 2RuBr₃.7NH₃.

With bromides of the alkali metals double salts known as brom-ruthenites are formed. Of these the potassium salt is most important.