Crystal structures of Ca(ClO4)2·4H2O and Ca(ClO4)2·6H2O

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.