Department of Nanosystem Science, Graduate School of Nanobioscience, Yokohama City University, 22-2 Seto, Kanazawa-ku, Yokohama 236-0027, Japan.
J Am Chem Soc. 2010 Mar 24;132(11):3783-92. doi: 10.1021/ja9091598.
For the purpose of investigating the correlation between host gas adsorption ability and structural flexibility, the combination of metal benzoate complexes [M(II)(2)(bza)(4)] (M(II) = Rh (a), Cu (b); bza = benzoate) and pyrazine derivatives (pyz = pyrazine (1), 2-mpyz = 2-methylpyrazine (2), 2,3-dmpyz = 2,3-dimethylpyrazine (3)) yields a series of one-dimensionally assembled complexes. The study of the adsorption properties of this series was examined for CO(2), H(2), N(2), O(2), and Ar gases at 195 K (CO(2)) or at 77 K (all others). The adsorption manners of these complexes are similar for each gas, while the pressure at which adsorption started or rapidly grew increased with a rise in the number of methyl groups in the case of adsorbable gases. The maximum amount of adsorption was a positive integer, e.g., 3 molecules per M(2) unit for 1 and 2 and 2 molecules per M(2) unit for 3 in the case of CO(2) adsorption for all complexes at 0.1 MPa of adsorbable gases. Structural transformation was observed accompanying gas adsorption. This transformation was observed when the adsorption amount reached 1 molecule per M(2) unit, suggesting a correlation of the adsorption amount and dynamic adsorption behavior. Single-crystal X-ray analyses of nonincluded crystals and CO(2) inclusions for all hosts (1-3) revealed that large structural changes occurred through CO(2) adsorption to increase the inner space for adsorption gases, depending on the substituents on the pyrazine ring. These facts were confirmed as a transition by DSC measurements using a mixed CO(2)/N(2) gas atmosphere. Solid-state (1)H and (2)H NMR studies of the crystalline sample of 1a and its partially deuterated samples of 1a' (deuterated phenyl group) and 1a'' (deuterated pyrazine) revealed rapid 180 degree-flip motions of the aromatic rings of the host skeletons, which form the walls of the channels. These "rotating" motions would help the diffusion of CO(2) molecules through a narrow channel at relatively low pressure. Indeed, the motions of phenyl groups and methyl-substituted pyrazine moieties of phenyl deuterated 3a were confirmed to be very slow by solid-state (1)H and (2)H NMR spectra, where the amount of adsorbed gas molecules was small for 3a at 0.1 MPa of CO(2).
为了研究主体气体吸附能力与结构柔韧性之间的关系，我们将金属苯甲酸配合物[M(II)(2)(bza)(4)]（M(II)=Rh(a)，Cu(b)；bza=苯甲酸）与吡嗪衍生物（pyz=吡嗪(1)，2-mpyz=2-甲基吡嗪(2)，2,3-dmpyz=2,3-二甲基吡嗪(3)）组合在一起，生成了一系列一维组装的配合物。我们对该系列物质的 CO(2)、H(2)、N(2)、O(2)和 Ar 气体的吸附特性进行了研究，研究温度为 195 K（CO(2)）或 77 K（其他气体）。对于每种气体，这些配合物的吸附方式相似，但对于可吸附气体，吸附起始或快速增长的压力随着甲基数量的增加而升高。在 0.1 MPa 可吸附气体的情况下，CO(2)的最大吸附量均为正整数，例如 1 和 2 中每个 M(2)单元吸附 3 个分子，3 中每个 M(2)单元吸附 2 个分子。在气体吸附过程中观察到了结构转变。当吸附量达到每个 M(2)单元 1 个分子时，观察到了这种转变，这表明吸附量与动态吸附行为之间存在相关性。对所有主体（1-3）的非包含晶体和 CO(2)包含物的单晶 X 射线分析表明，通过 CO(2)吸附发生了较大的结构变化，以增加吸附气体的内部空间，这取决于吡嗪环上的取代基。这些事实通过使用混合 CO(2)/N(2)气体气氛的 DSC 测量得到了确认，被视为一种转变。对 1a 的结晶样品及其部分氘代样品 1a'（氘代苯基）和 1a''（氘代吡嗪）的固态（1）H 和（2）H NMR 研究表明，主体骨架的芳香环发生了快速的 180 度翻转运动，这些芳香环构成了通道的壁。这些“旋转”运动有助于 CO(2)分子在相对较低的压力下通过狭窄的通道扩散。事实上，通过固态（1）H 和（2）H NMR 光谱证实，对于 3a，苯基和取代的甲基吡嗪部分的运动非常缓慢，在 0.1 MPa 的 CO(2)下，3a 的吸附气体分子数量很少。
