Antimony Tetrachloride, SbCl₄

Antimony Tetrachloride, SbCl₄ does not yet appear to have been isolated, but many double compounds formed from it have been obtained, including 2CsCl.SbCl₄, 2RbCl.SbCl₄, TlCl.SbCl₄ and possibly 3KCl.2SbCl₄. Many other compounds contain both tervalent and quadrivalent antimony; while still more are known only in the form of isomorphous mixtures with corresponding compounds such as platinum tetrachloride and tin tetrachloride. All these compounds are dark brown or deep violet in colour, a darkening of colour being an indication of the presence of quadrivalent antimony. All these double compounds, with the exception of one containing both thallic and thallous chlorides, with the probable formula TlCl.TlCl₃.2SbCl₄, tend to decompose into mixtures of compounds containing tervalent and quinquevalent antimony. The equilibrium, in solution,

SbCl₃ + SbCl₅ ⇔ 2SbCl₄

appears to be greatly dependent upon the temperature and the possibility of ionisation. The presence of sulphuric acid and of salts favours the formation of antimony tetrachloride, and the mixture becomes darker, indicating an increasing proportion of the tetrachloride, upon addition of hydrochloric acid, or with stronger heating.