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Arrays with local centers of symmetry in space groups Pca2(1) and Pna2(1)

机译:在空间群Pca2(1)和Pna2(1)中具有局部对称中心的阵列

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Of the several hundred structures in the Cambridge Structural Database [version 4.6 (1992), Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge, England] having space groups Pca2(1) or Pna2(1), and more than one molecule in the asymmetric unit (Z > 4), approximately three-quarters contain local centers of symmetry. These local centers, which are not crystallographic centers, occur predominantly near x = 1/8, y = a in Pca2(1) or near x = 1/8, y = 0 in Pna2(1); this also holds for the limited number of examples we have examined of pseudo-centrosymmetric molecules with Z = 4. Local centers at these points create unusual correlations between corresponding atoms in the two molecules. [References: 12]
机译:在剑桥结构数据库[版本4.6(1992),剑桥晶体数据中心,联合路12号,剑桥,英国)的数百个结构中,具有空间群Pca2(1)或Pna2(1),并且空间结构中有一个以上分子非对称单位(Z> 4),大约四分之三包含局部对称中心。这些不是晶体学中心的局部中心主要发生在Pca2(1)中的x = 1/8,y = a附近或在Pna2(1)中的x = 1/8,y = 0附近;对于我们已经检查的Z = 4的拟中心对称分子的有限数量的例子,这也成立。在这些点上的局部中心会在两个分子中的相应原子之间产生异常的相关性。 [参考:12]

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