Jagiellonian University, Faculty of Chemistry, Department of Chemical Physics, Ingardena 3, 30-060 Kraków, Poland.
Spectrochim Acta A Mol Biomol Spectrosc. 2013 Nov;115:504-10. doi: 10.1016/j.saa.2013.06.069. Epub 2013 Jul 1.
One phase transition (PT) at TC(h)=252.9K (on heating) and at TC(c)=226.5K (on cooling) was detected by DSC for [Sr(H2O)6]Cl2 in 123-295K range. Thermal hysteresis of this PT equals to 26.4K. Entropy change (ΔS) value at this first-order type phase transition equals to ca. 1.5Jmol(-1)K(-1). The temperature dependences of the full width at half maximum (FWHM) values of the infrared bands associated with ρt(H2O)E and δas(HOH)E modes (at ca. 417 and 1628cm(-1), respectively) suggest that the observed phase transition is associated with a sudden change of a speed of the H2O reorientational motions. The H2O ligands in the high temperature phase reorientate quickly (correlation times 10(-11)-10(-13)s) with the activation energy of ca. 2kJmol(-1). Below TC(c) probably a part of the H2O ligands stop their reorientation, while the remainders continue their fast reorientation but with the activation energy of ca. 8kJmol(-1). Far and middle infrared spectra indicated characteristic changes at the vicinity of PT with decreasing of temperature, which suggested lowering of the crystal structure symmetry. Splitting of the band (at 3601cm(-1)) connected with vas(OH) mode near the TC(c) suggests lowering of the crystal lattice symmetry. All these facts suggest that the discovered PT is connected both with a change of the reorientational dynamics of the H2O ligands and with the change of the crystal structure.
在 123-295K 范围内，通过 DSC 检测到 [Sr(H2O)6]Cl2 发生了一个相变 (PT)，其 TC(h)=252.9K（加热时）和 TC(c)=226.5K（冷却时）。该 PT 的热滞后为 26.4K。这个一级相变的熵变 (ΔS) 值约为 1.5Jmol(-1)K(-1)。与 ρt(H2O)E 和 δas(HOH)E 模式相关的红外带的半峰全宽 (FWHM) 值的温度依赖性表明，观察到的相变与 H2O 重定向运动速度的突然变化有关。在高温相中，H2O 配体快速重定向（相关时间 10(-11)-10(-13)s），其活化能约为 2kJmol(-1)。在 TC(c)以下，可能一部分 H2O 配体停止其重定向，而其余部分继续快速重定向，但活化能约为 8kJmol(-1)。远红外和中红外光谱在相变附近表明随着温度的降低出现了特征变化，这表明晶体结构对称性降低。与 vas(OH)模式相关的 3601cm(-1) 处的带分裂表明晶格对称性降低。所有这些事实表明，发现的 PT 与 H2O 配体的重定向动力学变化以及晶体结构变化都有关。
