Determination of the crystal structure of magnesium perchlorate hydrates by X-ray powder diffraction and the charge-flipping method.

X-ray powder diffraction (XRD) data were used to solve the crystal structures of phases in the magnesium perchlorate hydrate system, Mg(ClO(4))(2)·nH(2)O (n = 4, 2). A heating stage and humidity generator interfaced to an environmental cell enabled in-situ XRD analyses of dehydration reactions under controlled temperatures and partial pressures of H(2)O (P(H(2)O)). The crystal structures were determined using an ab initio charge-flipping method and were refined using fundamental-parameter Rietveld methods. Dehydration of magnesium perchlorate hexahydrate to tetrahydrate (348 K) results in a decrease in symmetry (space group = C2), where isolated Mg(2+) cations are equatorially coordinated by four H(2)O molecules with two ClO(4) tetrahedra at the apices. Further dehydration to the dihydrate (423 K) leads to bridging of the isolated packets to form double corner-sharing chains of octahedra and polyhedra (space group = C2/m).