Hydration isomerism

In coordination chemistry, hydration isomerism is a kind of isomerism 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 [CrCl(H₂O)₅]Cl₂•H₂O and [Cr(H₂O)₆]Cl₃.^[1] The former has one water of crystallization but the latter does not.

Another example is the pair of titanium(III) chlorides, [Ti(H₂O)₆]Cl₃ and [Ti(H₂O)₄Cl₂]Cl(H₂O)₂. The former is violet and the latter, with two molecules of water of crystallization, is green.^[2]

References

^ Barbier, J. P.; Kappenstein, C.; Hugel, R. (1972). "The Hydration Isomers of Chromium(III) Chloride". Journal of Chemical Education. 49 (3): 204. Bibcode:1972JChEd..49..204B. doi:10.1021/ed049p204.
^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 965. ISBN 978-0-08-037941-8.

[1] Barbier, J. P.; Kappenstein, C.; Hugel, R. (1972). "The Hydration Isomers of Chromium(III) Chloride". Journal of Chemical Education. 49 (3): 204. Bibcode:1972JChEd..49..204B. doi:10.1021/ed049p204.

[2] Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 965. ISBN 978-0-08-037941-8.

[1]

[2]