Department of Chemistry and Center for Optical Materials Science and Engineering Technologies (COMSET), Clemson University, Clemson, South Carolina 29634-0973, USA.
Inorg Chem. 2011 Jul 18;50(14):6809-13. doi: 10.1021/ic2008705. Epub 2011 Jun 13.
The synthesis and structure of the isostructural acentric compounds Sr(3)Be(2)B(5)O(12)(OH) (1) and Ba(3)Be(2)B(5)O(12)(OH) (2) are reported for the first time. These compounds crystallize in the space group R3m, and the unit cell parameters are a = 10.277(15) Å and c = 8.484(17) Å for 1 and a = 10.5615(15) Å and c = 8.8574(18) Å for 2. The structures consist of a network of [Be(2)B(4)O(12)(OH)] units interwoven with a network consisting of MO(9) polyhedra (M = Sr, Ba) and BO(3) triangles and exemplify how acentric building blocks such as BO(3), BO(4), and BeO(4) can be especially suitable to build noncentrosymmetric long-range structures. Both networks are centered on the 3-fold rotation axis and present themselves in alternating fashion along [001]. Acentricity is imparted by the alignment of the polarities of BO(3) and BeO(4) environments. Infrared spectroscopy has been used to confirm the local geometries of B and Be, as well as the presence of hydroxide in the crystal structure. Another interesting feature of these compounds is the presence of disorder involving Be and B at the tetrahedral Be site. The degree of the disorder has been confirmed by observing a noticeable shortening of average Be-O bond distances.
首次报道了等结构非中心化合物 Sr(3)Be(2)B(5)O(12)(OH) (1) 和 Ba(3)Be(2)B(5)O(12)(OH) (2) 的合成和结构。这些化合物在空间群 R3m 中结晶，其晶胞参数分别为 1 为 a = 10.277(15) Å 和 c = 8.484(17) Å，2 为 a = 10.5615(15) Å 和 c = 8.8574(18) Å。结构由交错的[Be(2)B(4)O(12)(OH)]单元组成的网络和由 MO(9)多面体（M = Sr, Ba）和 BO(3)三角形组成的网络组成，例证了非中心构建块，如BO(3)、BO(4)和BeO(4)，如何特别适合构建非中心远程结构。两个网络都以 3 重旋转轴为中心，并沿[001]交替出现。非中心性是由 BO(3)和 BeO(4)环境极性的对齐赋予的。红外光谱已用于确认 B 和 Be 的局部几何形状以及晶体结构中存在的氢氧化物。这些化合物的另一个有趣特征是存在涉及四面体 Be 位的 Be 和 B 的无序。通过观察平均 Be-O 键距离的明显缩短，证实了无序的程度。
