CaH2O62

CaH2O62 is not a standard chemical formula, but in many contexts it denotes the hexaaquacalcium(II) cation, [Ca(H2O)6]2+. This aquated calcium ion is the dominant form of Ca2+ in aqueous solutions of calcium salts and represents the first hydration shell around the calcium ion.

In [Ca(H2O)6]2+, the calcium center is coordinated by six water molecules in an approximately octahedral geometry. Ca–O bond lengths are typically around 2.40 Å. The hydration shell is dynamic, with rapid exchange of ligands with the surrounding water.

The hexaaqua ion is colorless in solution. It behaves as a Lewis acid, accepting electron density from ligands and participating in hydrolysis reactions. Upon deprotonation of the coordinated water, hydrolyzed species such as [Ca(H2O)5(OH)]+ can form, and at higher pH calcium can precipitate as calcium hydroxide or carbonates depending on counterions. The pKa for the first hydrolysis step is commonly cited near 12–13 under standard conditions, though exact values depend on temperature, ionic strength, and coordination environment.

In aqueous environments, [Ca(H2O)6]2+ is the principal hydration form of calcium and serves as a model for studying calcium hydration in geochemistry and biochemistry. Understanding its properties helps explain ion pairing, water structure around Ca2+, and behavior during crystallization.

The hexaaquacalcium(II) ion is related to other hexaaqua ions, such as [Mg(H2O)6]2+, and is a common reference in coordination chemistry and aqueous geochemistry.