In
coordination chemistry
A coordination complex is a chemical compound consisting of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of chemical bond, bound molecules or ions, that are in turn known as ' ...
, hydration isomerism is a kind of
isomer
In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, the same number of atoms of each element (chemistry), element – but distinct arrangements of atoms in space. ''Isomerism'' refers to the exi ...
ism that is observed in some solids. Hydration isomers have identical formula but differ with respect to the numbers of
water ligands.
Examples
One example is the pair . The former has one
water of crystallization
In chemistry, water(s) of crystallization or water(s) of hydration are water molecules that are present inside crystals. Water is often incorporated in the formation of crystals from aqueous solutions. In some contexts, water of crystallization is ...
but the latter does not.
Another example is the pair of
titanium(III) chloride
Titanium(III) chloride is the inorganic compound with the formula TiCl3. At least four distinct species have this formula; additionally hydrated derivatives are known. TiCl3 is one of the most common halides of titanium and is an important cataly ...
s, . The former is violet and the latter, with two molecules of water of crystallization, is green.
[{{Greenwood&Earnshaw2nd, page = 965]
References
Isomerism
Coordination chemistry