Phase transitions in [Ca(H2O)4](ClO4)2 studied by differential scanning calorimetry, X-ray single crystal diffraction and neutron powder diffraction

Four phase transitions at: T-C1(h) = 267.1 K, T-C2(h) = 258.8 K, T-C3(h) = 254.1 K and T-C4(h) = 195.4 K (on heating) and at T-C1(c) = 263.8 K, T-C2(c) = 255.4 K, T-C3(c) = 246.0 K (on cooling) were determined for [Ca(H2O)(4)](ClO4)(2) between 90 and 295 K by means of differential scanning calorimetry (DSC). Phase transitions discovered at T-C1, T-C2 and T-C3 are connected with small change of the crystal structure. Namely, there are scant but statistically significant differences between unit cell parameters (angles: alpha, beta, gamma) and torsion angles in the structure of [Ca(H2O)(4)](ClO4)(2) at 293 and 240 K. The space group (P (1) over bar; No. 2) is the same for high, intermediate and low temperature phase, however, changes of perchlorate anions orientations are distinctly visible. (C) 2008 Elsevier B.V. All rights reserved.