Krüger Hannes, Kahlenberg Volker, Friese Karen
Institut für Mineralogie und Petrographie, Leopold-Franzens-Universität, 6020 Innsbruck, Austria.
Acta Crystallogr B. 2006 Jun;62(Pt 3):440-6. doi: 10.1107/S010876810600663X. Epub 2006 May 15.
The structure of metastable, incommensurately modulated Na(2)Si(3)O(7) has been determined from single-crystal X-ray diffraction data. In contrast to previous investigations which stated that the compound crystallizes in an orthorhombic space group, this study shows that the compound is monoclinic with a pseudo-orthorhombic cell and is affected by twinning. The structure is described in the (3 + 1)-dimensional superspace. Crenel-type modulation functions are used to account for an aperiodic sequence of right- and left-handed zweier single chains of silicate tetrahedra. The modulation mainly affects one of the two symmetrically independent tetrahedral chains, which are connected to build up Si(3)O(7) layers. Sodium cations are coordinated by five oxygen ligands and provide linkage between adjacent tetrahedral sheets. Distortions of the silicate tetrahedra and crystal chemical relationships of the title compound to sodium and lithium di- and metasilicates are discussed in detail.
通过单晶X射线衍射数据确定了亚稳、非公度调制的Na₂Si₃O₇的结构。与之前称该化合物结晶于正交空间群的研究不同，本研究表明该化合物为单斜晶系，具有假正交晶胞且受孪晶影响。该结构在(3 + 1)维超空间中描述。采用城垛型调制函数来解释硅酸盐四面体右手和左手双聚单链的非周期序列。这种调制主要影响两个对称独立的四面体链中的一个，这两个链相互连接形成[Si₃O₇]²⁻层。钠离子由五个氧配体配位，并在相邻四面体片层之间提供连接。详细讨论了硅酸盐四面体的畸变以及该标题化合物与钠和锂的二硅酸盐和偏硅酸盐之间的晶体化学关系。
