Takamizawa Satoshi, Nakata Ei-Ichi, Miyake Ryosuke
International Graduate School of Arts and Sciences, Yokohama City University, Kanazawa-ku, Yokohama, Kanagawa 236-0027, Japan.
Dalton Trans. 2009 Mar 14(10):1752-60. doi: 10.1039/b813178c. Epub 2009 Jan 12.
In order to investigate the methane-included condition in porous materials and its response to external stimuli, the methane adsorption state of a single-crystal adsorbent, Cu(ii)(2)(bza)(4)(pyz), was studied by single-crystal X-ray analysis and adsorption measurement as functions of temperature (90-298 K) and pressure (3.2-42 MPa). The included methane molecule was encapsulated into the channel of the adsorbent and stabilized through the interactions between the surrounding aromatic rings. The single-crystal host readily adsorbed methane gas and easily achieved the saturated condition with the included amount of 2 methane molecules per Cu(2) unit. The results from the gas adsorption measurements were consistent with the results from the crystallographic structures. Single-crystal X-ray analysis showed that the methane-saturated crystal has a critical temperature of the crystal phase transition from the C2/c to the P1 space group between 150 and 200 K. In temperature swinging, the thermal factors of the atoms of the guest methane and host skeleton monotonically decreased as the temperature decreased. In contrast, in pressure swinging at 298 K, the thermal factors gradually decreased as the pressure increased, after passing 11 MPa only the thermal factor of the guest methane decreased in response to an increase in gas pressure while those of the host skeleton remained almost constant. It is suggested that the channel acts as "force guide," propagating the outside gas pressure into the crystal inside through a guest-guest interaction in the included gas array. In addition, the difference in the pressure dependencies of the thermal factors on the host and guest suggested that the structural susceptibility to external gas pressure and temperature is different between open porous solids and non-porous solids.
为了研究多孔材料中含甲烷的情况及其对外部刺激的响应，通过单晶X射线分析和吸附测量，研究了单晶吸附剂Cu(ii)(2)(bza)(4)(pyz)在温度（90 - 298 K）和压力（3.2 - 42 MPa）作用下的甲烷吸附状态。所包含的甲烷分子被封装在吸附剂的通道中，并通过周围芳香环之间的相互作用得以稳定。单晶主体很容易吸附甲烷气体，并且每Cu(2)单元包含2个甲烷分子时很容易达到饱和状态。气体吸附测量结果与晶体结构结果一致。单晶X射线分析表明，甲烷饱和晶体在150至200 K之间存在从C2/c到P1空间群的晶相转变临界温度。在温度摆动过程中，客体甲烷和主体骨架原子的热因子随着温度降低而单调下降。相比之下，在298 K的压力摆动过程中，热因子随着压力增加而逐渐降低，在超过11 MPa后，只有客体甲烷的热因子随着气体压力增加而降低，而主体骨架的热因子几乎保持不变。这表明通道起到“力引导”的作用，通过所包含气体阵列中的客体 - 客体相互作用将外部气体压力传递到晶体内部。此外，热因子对主体和客体的压力依赖性差异表明，开放多孔固体和无孔固体对外部气体压力和温度的结构敏感性不同。
