Crystal structures of Ca(ClO(4))(2)·4H(2)O and Ca(ClO(4))(2)·6H(2)O

The title compounds, calcium perchlorate tetra­hydrate and calcium perchlorate hexa­hydrate, were crystallized at low temperatures according to the solid–liquid phase diagram. The structure of the tetra­hydrate consists of one Ca(2+) cation eightfold coordinated in a square-anti­prismatic fashion by four water mol­ecules and four O atoms of four perchlorate tetra­hedra, forming chains parallel to [01-1] by sharing corners of the ClO(4) tetra­hedra. The structure of the hexa­hydrate contains two different Ca(2+) cations, each coordinated by six water mol­ecules and two O atoms of two perchlorate tetra­hedra, forming [Ca(H(2)O)(6)(ClO(4))](2) dimers by sharing two ClO(4) tetra­hedra. The dimers are arranged in sheets parallel (001) and alternate with layers of non-coordinating ClO(4) tetra­hedra. O—H⋯O hydrogen bonds between the water mol­ecules as donor and ClO(4) tetra­hedra and water mol­ecules as acceptor groups lead to the formation of a three-dimensional network in the two structures. Ca(ClO(4))(2)·6H(2)O was refined as a two-component inversion twin, with an approximate twin component ratio of 1:1 in each of the two structures.