ChromiumIII chloride: Encyclopedia II - ChromiumIII chloride - Chemical properties

ChromiumIII chloride - Chemical properties

Chromium(III) chloride is a Lewis acid, classified as "hard" according to the Hard-Soft Acid-Base theory. However it is also a chloro complex which is quite inert to substitution, so in fact it is ordinarily quite unreactive. The low reactivity of the d³ Cr³⁺ ion can be explained using crystal field theory. One way of opening CrCl₃ up to substitution in solution is to reduce even a trace amount to CrCl₂, for example using zinc in hydrochloric acid. This chromium(II) compound undergoes substitution easily, and it can exchange electrons with CrCl₃ via a chloride bridge, allowing all of the CrCl₃ to react quickly.

The most common form of CrCl₃ sold commercially is a dark green hexahydrate with the structure [CrCl₂(H₂O)₄]Cl.2H₂O, and like the anhydrous form it is also very inert towards substitution.

If substitution reactions are performed in the presence of a trace of Cr²⁺, then CrCl₃ can undergo substitution with ligands such as water (giving violet [Cr(H₂O)₆]³⁺) or pyridine:

CrCl₃ + 3 C₅H₅N → [CrCl₃(C₅H₅N)₃]

Such complexes are usually octahedral.

With molten alkali metal chlorides such as potassium chloride, CrCl₃ gives octahedral complexes of the type K₃CrCl₆, as well as K₃Cr₂Cl₉ which is also octahedral but where the two chromiums are linked via three chloride bridges.

Adapted from the Wikipedia article "Chemical properties", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki