Structure, Molecular Motion, and Phase Transition of a Highly Disordered Crystal Co(NH_3)_6(ClO_4)_3
Structure, Molecular Motion, and Phase Transition of a Highly Disordered Crystal Co(NH_3)_6(ClO_4)_3
复制标题
高度无序晶体Co(NH_3)_6(ClO_4)_3的结构、分子运动和相变
DOI：
10.1039/c2ra01184k
复制
发表时间：
2012
期刊：
影响因子：
3.9
通讯作者：
Holderna-Natkaniec K
中科院分区：
文献类型：
--
作者：
Gorska N.;Inaba A.;Hirao Y.;Mikuli E.;Holderna-Natkaniec K
通过绝热量热法鉴定了配位化合物 [Co(NH3)6](ClO4)3 的四个晶相。有序-无序相变 (II→I) 发生在 TC1 = 334.2 K 处，熵变为 6.4 J K−1 mol−1。 340 K 的 X 射线单晶衍射表明 I 相是立方体（Z = 4），并且存在两种类型的阴离子，且具有不同类型的无序性。在 200 K 的第二阶段，五个阴离子（十二个中的一个）变得有序，三个阳离子（四个中的一个）变形以提供较低的对称性，仍然处于立方体系（Z = 32）。这归因于 NH⋯O 氢键相互作用引发的阴离子的定向排列。 1H-NMR 研究表明，一些 NH3 配体因氢键而取向，而一些阳离子像 I 相一样各向同性地重新取向。根据 TC1 以下的过剩热容估计，在 II 相晶格中重新取向有序阴离子所需的能量为 40 kJ mol−1，这对应于破坏氢键所需的能量 8 kJ mol−1。虽然 111.7 K (III→II) 和 97.6 K (IV→II) 处的转变（熵变为 5.7 J K−1 mol−1）不会对动力学产生实质性影响，但它们归因于在 II 相中仍然无序的阴离子的进一步定向排序。
Four crystalline phases of the coordination compound [Co(NH3)6](ClO4)3 are identified by adiabatic calorimetry. An order–disorder phase transition (II→I) occurs at TC1 = 334.2 K with an entropy change of 6.4 J K−1 mol−1. The X-ray single-crystal diffraction at 340 K demonstrates that phase I is cubic (Z = 4) and that two types of anions exist with different types of disorder. In phase II at 200 K, five anions (out of twelve) become ordered and three cations (out of four) are deformed to give a lower symmetry, still in a cubic system (Z = 32). This is attributed to orientational ordering of the anions triggered by NH⋯O hydrogen-bonding interactions. The 1H-NMR study suggests that some NH3 ligands are oriented because of hydrogen bonding, whereas some cations reorient isotropically like in phase I. The energy required to reorient an ordered anion in the crystal lattice of phase II is estimated from the excess heat capacity below TC1 to be 40 kJ mol−1, which corresponds to the energy needed to break the hydrogen bond, 8 kJ mol−1. While the transitions at 111.7 K (III→II) and 97.6 K (IV→II), with an entropy change of 5.7 J K−1 mol−1, do not substantially affect the dynamics, they are attributed to further orientational ordering of the anions still disordered in phase II.