Ding Fenghua, Griffith Kent J, Zhang Weiguo, Cui Shaoxin, Zhang Chi, Wang Yiran, Kamp Kendall, Yu Hongwei, Halasyamani P Shiv, Yang Zhihua, Pan Shilie, Poeppelmeier Kenneth R
Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States.
Department of Chemistry, University of Houston, Houston, Texas 77204, United States.
J Am Chem Soc. 2023 Mar 8;145(9):4928-4933. doi: 10.1021/jacs.2c12069. Epub 2023 Feb 22.
Noncentrosymmetric (NCS) structures are of particular interest owing to their symmetry-dependent physical properties, e.g., pyroelectricity, ferroelectricity, piezoelectricity, and nonlinear optical (NLO) behavior. Among them, chiral materials exhibit polarization rotation and host topological properties. Borates often contribute to NCS and chiral structures via their triangular [BO] and tetrahedral [BO] units and their numerous superstructure motifs. However, no chiral compound with the linear [BO] unit has been reported to date. Herein, an NCS and chiral mixed-alkali-metal borate, NaRb(BO(OH))(BO), with a linear BO unit in the structure was synthesized and characterized. The structure features a combination of three types of basic building units (BBUs), [BO], [BO], and [BO] with sp-, sp-, and sp-hybridization of boron atoms, respectively. It crystallizes in the trigonal space group 32 (No. 155), one of the 65 Sohncke space groups. Two enantiomers of NaRb(BO(OH))(BO) were found, and their crystallographic relationships are discussed. These results not only expand the small family of NCS structures with the rare linear BO unit but also prompt recognition to the fact that NLO materials have generally overlooked the existence of two enantiomers in achiral Sohncke space groups.
非中心对称（NCS）结构因其依赖对称性的物理性质而备受关注，例如热电性、铁电性、压电性和非线性光学（NLO）行为。其中，手性材料表现出偏振旋转和主体拓扑性质。硼酸盐通常通过其三角形[BO]和四面体[BO]单元以及众多超结构 motif 形成 NCS 和手性结构。然而，迄今为止尚未报道过具有线性[BO]单元的手性化合物。在此，合成并表征了一种结构中具有线性 BO 单元的 NCS 和手性混合碱金属硼酸盐 NaRb(BO(OH))(BO)。该结构具有三种基本构筑单元（BBU）的组合，即[BO]、[BO]和[BO]，硼原子分别为 sp-、sp-和 sp-杂化。它结晶于三方空间群 32（No. 155），这是 65 个 Sohncke 空间群之一。发现了 NaRb(BO(OH))(BO)的两种对映体，并讨论了它们的晶体学关系。这些结果不仅扩展了具有罕见线性 BO 单元的 NCS 结构的小家族，还促使人们认识到 NLO 材料通常忽略了非手性 Sohncke 空间群中两种对映体的存在。
