Crystal structures of Sr(ClO4)(2)center dot 3H(2)O, Sr(ClO4)(2)center dot 4H(2)O and Sr(ClO4)(2)center dot 9H(2)O

The title compounds, strontium perchlorate trihydrate {di-mu-aqua-aquadi-mu perchlorato-strontium, [Sr(ClO4)(2)(H2O)(3)](n)}, strontium perchlorate tetrahydrate {di-mu-aqua-bis(triaquadiperchloratostrontium), [Sr-2(ClO4)(4)(H2O)(8)]} and strontium perchlorate nonahydrate {heptaaquadiperchloratostrontium dihydrate, [Sr(ClO4)(2)(H2O)(7)]center dot 2H(2)O}, were crystallized at low temperatures according to the solid-liquid phase diagram. The structures of the tri- and tetrahydrate consist of Sr2+ cations coordinated by five water molecules and four O atoms of four perchlorate tetrahedra in a distorted tricapped trigonal-prismatic coordination mode. The asymmetric unit of the trihydrate contains two formula units. Two [SrO9] polyhedra in the trihydrate are connected by sharing water molecules and thus forming chains parallel to [100]. In the tetrahydrate, dimers of two [SrO9] polyhedra connected by two sharing water molecules are formed. The structure of the nonahydrate contains one Sr2+ cation coordinated by seven water molecules and by two O atoms of two perchlorate tetrahedra (point group symmetry.. m), forming a tricapped trigonal prism (point group symmetry m2m). The structure contains additional non-coordinating water molecules, which are located on twofold rotation axes. O-H center dot center dot center dot O hydrogen bonds between the water molecules as donor and ClO4 tetrahedra and water molecules as acceptor groups lead to the formation of a three-dimensional network in each of the three structures.