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首页> 外文期刊>Acta Crystallographica, Section B. Structural Science >Structural phase transitions in tetra(isopropyl-ammonium) decachlorotricadmate(II), [(CH_3)_2CHNH_3] _4Cd_3Cl_(10), crystal with a two-dimensional cadmium(II) halide network
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Structural phase transitions in tetra(isopropyl-ammonium) decachlorotricadmate(II), [(CH_3)_2CHNH_3] _4Cd_3Cl_(10), crystal with a two-dimensional cadmium(II) halide network

机译：四（异丙基铵）十氯三甲酸（II），[（CH_3）_2CHNH_3] _4Cd_3Cl_（10），具有二维卤化镉（II）网络的晶体的结构相变

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摘要

Single crystals of tetra(isopropylammonium) decachlorotricadmate(II) as a rare example of a two-dimensional cadmium(II) halide network of [Cd _3Cl_(10)]_n~(4-) have been synthesized and characterized by means of calorimetry and X-ray diffraction. The crystals exhibit polymorphism in a relatively narrow temperature range (three phase transitions at 353, 294 and 259 K). Our main focus was to establish the mechanism of these successive transformations. The crystal structure was solved and refined in the space group Cmce at 375 K (Phase I), Pbca at 320 K (Phase II) and P212121 (Phase III) at 275 K in the same unit-cell metric. The structure is composed of face-sharing polyanionic [Cd_3Cl_(10)] ~(4-) units which are interconnected at the bridging Cl atom into four-membered rings forming a unique two-dimensional network of [Cd _3Cl_(10)]n~(4-). The interstitial voids within the network are large enough to accommodate isopropylammonium cations and permit thermally activated rotations. While in Phase I isopropylammonium tetrahedra rotate almost freely about the C - N bond, the low-temperature phases are the playground of competition between the thermally activated disorder of isopropylammonium cations and stabilizing N - H?Cl hydrogen-bond interactions. The transition from Phase I to II is dominated by a displacive mechanism that leads to significant rearrangement of the polyanionic units. Cation order-disorder phenomena become prominent at lower temperatures.
机译：合成了四（异丙基铵）十氯三金属酸盐（II）单晶，作为[Cd _3Cl_（10）] _ n〜（4-）的二维卤化镉（II）网络的稀有实例，并通过量热法进行了表征。 X射线衍射。晶体在相对较窄的温度范围内表现出多态性（353、294和259 K处有三个相变）。我们的主要重点是建立这些连续转换的机制。在相同的晶胞度量标准下，在375 K（第一阶段）的Cmce空间群，第一阶段的320 K的Pbca（第二阶段）和275 K的P212121（第三阶段）中对晶体结构进行了解析和改进。该结构由面共享聚阴离子[Cd_3Cl_（10）]〜（4-）单元组成，这些单元在桥接Cl原子上互连成四元环，形成[Cd _3Cl_（10）] n的唯一二维网络〜（4-）。网络内的间隙空隙足够大以容纳异丙基铵阳离子并允许热激活的旋转。在第一相中，异丙基四面体四面体几乎自由地围绕C-N键旋转，而低温相则是异丙基铵阳离子的热活化无序与稳定N-H2Cl氢键相互作用之间竞争的场所。从相I到相II的转变主要受置换机理的控制，该机理导致聚阴离子单元的显着重排。阳离子有序现象在较低温度下变得很明显。

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