Single-crystal adsorbents: a new observation field for light aggregates.
Single-crystal adsorbents: a new observation field for light aggregates.
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单晶吸附剂：轻聚集体的新观察领域。
DOI：
10.1002/anie.200352982
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发表时间：
2004
影响因子：
--
通讯作者：
T. Saito
中科院分区：
文献类型：
--
作者：
S. Takamizawa;Ei;T. Saito
用气体笼形化合物测定低维聚集体的性质，在过去的50年里一直是研究者们感兴趣的问题。[1]研究原子/分子聚集体物理化学性质的最理想系统是单晶系统，因为它们具有极高的完整性和规则性。这种系统将有助于广泛的纯科学和应用科学;从基本物体到设备应用。单晶吸附剂是可以通过多孔固体的设计来达到的目标之一，并且由于其扩展的无机骨架而成为近年来广泛研究的主题。[2]理想的系统应该提供期待已久的方法，用于研究在宿主固体的内表面内产生的特定聚集体结构的物理化学性质。事实上，之前的所有观察结果都仅在粉末样品中进行了表征。[1，3]在这里，我们提出了一种新的方便的程序，用于通过将晶体吸附剂放置在气态客体气氛中将轻气体包含到单晶状态中，这对于以高分辨率确定所包含的轻聚集体（如氧）的精确分子/原子结构是有效的。我们之前报道了苯甲酸铑吡嗪的空晶体主体[RhII 2（bza）4（pyz）] n（1）（图1）[4]，其通过平滑的物理吸附过程从封闭的a相转变为开放的B相而产生CO2包合晶体; CO2客体被吸附到B晶格的产生的狭窄通道中。[5]然而，对于其他轻气体客体，例如氧气、氮气，特别是氢气或氦气，由于它们的弱物理吸附能力，仍然存在严重的困难。结果表明，晶体吸附剂1的a-b相变服从Clausius-Clapeyron方程的CO2气体的温度和压力。这种相关性表明，相变可以通过加压的各种气态客人（压力摆动），这在低温下产生包合物晶体，足以结晶的客人（温度摆动）诱导的可能性。我们试图通过使用氧气的摆动方法在1的单晶内构建低维聚集体;特定的簇可能通过未成对电子的磁相互作用表现出量子效应。[6]在氧气氛下，在298、90和10 K的温度下进行X射线衍射测量，所述氧气氛是通过将包含1的单晶和液氧的玻璃毛细管（在18 mm长的毛细管中为2 mm液体）密封在液氮浴中制备的。在温度升高至室温后，毛细管中氧气的压力估计为9 MPa。令人惊讶的是，晶体在高压和低温的条件下仍然保持完整和透明单晶X射线衍射分析表明，1的晶体在室温下已经经历了从a到ab晶格的相变，[7]其具有一维通道。（见图3a和B），而X射线晶体学不能定位通道中的氧分子，这可能是由于吸附的氧的热运动。这些结果表明，
Determination of the properties of low-dimensional aggregates using gas clathrate compounds has interested researchers for the past 50years.[1] The most ideal system for investigating the physicochemical properties of atomic/molecular aggregates would be single-crystal systems due to their extremely high degree of integrity and regularity. Such systems would contribute to a wide range of both pure and applied science; from basic objects to device applications. A single-crystal adsorbent is one of the goals that may be reached through the design of porous solids, and has been the subject of extensive study in recent years for its extended inorganic framework.[2] The ideal system should provide the long-awaited method for studying physicochemical properties of specific aggregate structures produced within the inner surface of the host solid. In fact, all previous observations were only characterized in powdered samples.[1, 3] Here, we present a new convenient procedure for the inclusion of a light gas into a single-crystalline state by placing a crystal adsorbent in a gaseous guest atmosphere, which is efficient for ascertaining exact molecular/atomic structures with high resolution for included light aggregates such as oxygen. We previously reported the empty crystal host of rhodium (ii) benzoate pyrazine,[RhII2 (bza) 4 (pyz)] n (1)(Figure 1),[4] which generated a CO2 inclusion crystal by transition from a closed a phase to an open b phase through the process of smooth physisorption; the CO2 guests are adsorbed into the generated narrow channels of the b lattice.[5] However, serious difficulties remain for other light-gas guests, such as oxygen, nitrogen, and especially hydrogen or helium due to their weak physisorbing capabilities. It was shown for crystal adsorbent 1 that the a–b phase transition obeys the Clausius–Clapeyron equation in terms of the temperature and pressure of the CO2 gas. This correlation indicates the possibility that a phase transition could be induced by pressurizing the various gaseous guests (pressure swing), which produces inclusion crystals at low temperature, sufficient to crystallize the included guests (temperature swing). We attempted to construct low-dimensional aggregates inside a single crystal of 1 by the swinging method using oxygen gas; the specific cluster is likely to exhibit quantum effects through the magnetic interaction of unpaired electrons.[6] X-ray diffraction measurements were conducted at temperatures of 298, 90, and 10 K under an oxygen atmosphere, which was prepared by sealing a glass capillary containing a single crystal of 1 and liquid oxygen (2 mm liquid in a 18 mm long capillary) in a liquid nitrogen bath. After the temperature was increased to room temperature, the pressure of the oxygen gas in the capillary was estimated to be% 9 MPa. Surprisingly, the crystal remained intact and transparent under the conditions of high pressure and low temperature (Figure 2).Single-crystal X-ray diffraction analysis demonstrated that the crystal of 1 had already undergone a phase transition from an a to ab lattice at room temperature,[7] which has onedimensional channels (see Figure3a and b), while X-ray crystallography could not locate the oxygen molecules in the channels, probably due to the thermal motion of the adsorbed oxygen. These results show that a bulk phase transition is