Crystal structures of Sr(ClO₄)₂·3H₂O, Sr(ClO₄)₂·4H₂O and Sr(ClO₄)₂·9H₂O

Abstract

The title compounds, strontium perchlorate trihydrate {di-μ-aqua-aquadi-μ-perchlorato-strontium, [Sr(ClO 4 ) 2 (H 2 O) 3 ] n }, strontium perchlorate tetrahydrate {di-μ-aqua-bis(triaquadiperchloratostrontium), [Sr 2 (ClO 4 ) 4 (H 2 O) 8 ]} and strontium perchlorate nonahydrate {heptaaquadiperchloratostrontium dihydrate, [Sr(ClO 4 ) 2 (H 2 O) 7 ]·2H 2 O}, were crystallized at low temperatures according to the solid–liquid phase diagram. The structures of the tri- and tetrahydrate consist of Sr 2+ 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 [SrO 9 ] polyhedra in the trihydrate are connected by sharing water molecules and thus forming chains parallel to [100]. In the tetrahydrate, dimers of two [SrO 9 ] polyhedra connected by two sharing water molecules are formed. The structure of the nonahydrate contains one Sr 2+ 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 m 2 m ). The structure contains additional non-coordinating water molecules, which are located on twofold rotation axes. 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 each of the three structures.