Crystal structure of boralsilite and its relation to a family of boroaluminosilicates, sillimanite, and andalusite
Crystal structure of boralsilite and its relation to a family of boroaluminosilicates, sillimanite, and andalusite
复制标题
硼硅石的晶体结构及其与硼铝硅酸盐、硅线石和红柱石族的关系
DOI：
--
复制
发表时间：
1999
期刊：
影响因子：
--
通讯作者：
E. Grew
中科院分区：
文献类型：
--
作者：
D. Peacor;R. C. Rouse;E. Grew
硼铝石Al 16 B6 Si 2 O37属单斜晶系，空间群C2/m，a = 14.767（1），B = 5.574（1），c = 15.079（1）°，β = 91.96（1）°，Z = 2。用直接方法求解结构，并使用1193个观察到的反射将其细化为0.026的未加权残差。其结构与硅线石、红柱石、镁铝石、合成硼酸铝（Al 18 B4 O 33）和硼铝石密切相关。这些结构都是基于平行于c（ε 5.6 π）排列的边缘共享AlO 6八面体链的主链，并位于具有ε B ε 7.5 π的伪四棱柱子晶胞的顶点和中心。在硼铝石结构中，AlO 6八面体链通过Si 2 O 7二硅酸盐基团、BO 4四面体、BO 3三角形和AlO 5三角双锥交联。给定的BO 4或SiO 4四面体或BO 3三角形与一个链的两个相邻的Al O 6八面体共享两个顶点，并且第三个顶点与相邻链的八面体顶点共享，从而交联Al O 6八面体链。通过AlO 5三角双锥的顶点共享提供进一步的连接。这些双锥与平行于AlO 6八面体链的B或Si多面体交替形成四种多面体交联链，具有交替的原子对[5] Al 1-Si，[5] Al 2-[4]B2，[5] Al 3-[3]B1和[5] Al 4-[3]B3。在AlO 6八面体链之间交联的单元可替代地被视为由Si 2 O 7二聚体、边缘共享的AlO 5三角双锥的三聚体组成（加上一个B三角形和B四面体），以及边缘共享的AlO 5三角双锥的二聚体（加上B三角形和四面体），在硅线石、红柱石、红柱石、韦丁石、莫来石、和合成的Al 18 B4 O 33。各种链间单元的可折叠性和多样性似乎部分地由Al和B通过氧呈现各种配位的能力所产生的灵活性以及某些阴离子和阳离子位点的部分空位的可能性导致。
Abstract Boralsilite, Al16B6Si2O37, is monoclinic, space group C2/m, with a = 14.767(1), b = 5.574(1), c = 15.079(1) Å, β = 91.96(1)°, and Z = 2. The structure was solved with direct methods and refined to an unweighted residual of 0.026 using 1193 observed reflections. The structure is closely related to those of sillimanite, andalusite, grandidierite, synthetic aluminum borate (Al18B4O33), and werdingite. These structures are all based on a backbone of chains of edge-sharing AlO6 octahedra arranged parallel to c (≅ 5.6 Å) and at the vertices and center of a pseudo-tetragonal subcell having a ≅ b ≅ 7.5 Å. In the boralsilite structure, AlO6 octahedral chains are cross-linked by Si2O7 disilicate groups, BO4 tetrahedra, BO3 triangles, and AlO5 trigonal bipyramids. A given BO4 or SiO4 tetrahedron or BO3 triangle shares two vertices with two adjacent AlO6 octahedra of one chain and a third vertex with an octahedron vertex of an adjacent chain, thus cross-linking the AlO6 octahedral chains. Further linkage is provided through vertex-sharing of AlO5 trigonal bipyramids. These bipyramids alternate with B or Si polyhedra parallel to AlO6 octahedral chains to form four kinds of cross-linking chains of polyhedra, with alternate atom pairs [5]Al1-Si, [5]Al2-[4]B2, [5]Al3-[3]B1, and [5]Al4-[3]B3. The units which cross-link between chains of AlO6 octahedra can alternatively be viewed as consisting of Si2O7 dimers, trimers of edge-sharing AlO5 trigonal bipyramids (plus a B triangle and B tetrahedron), and dimers of edge-sharing AlO5 trigonal bipyramids (plus B triangles and tetrahedra), Variations on these themes are found in the structures of sillimanite, andalusite, grandidierite, werdingite, mullite, and synthetic Al18B4O33. The interchangeability and variety of the various interchain units appears to result in part from the flexibility produced by the ability of Al and B to assume a variety of coordinations by oxygen and from the potential for partial vacancy of some anion and cation sites.