A cation size effect on the framework structures in ABi2SeO3F5 (A = K and Rb): first examples of alkali metal bismuth selenite fluorides

Shuangshuang Shi; Min Luo; Chensheng Lin; Ning Ye

doi:10.1039/c8dt00450a

A cation size effect on the framework structures in ABi₂SeO₃F₅ (A = K and Rb): first examples of alkali metal bismuth selenite fluorides

Dalton Trans. 2018 May 8;47(18):6598-6604. doi: 10.1039/c8dt00450a.

Authors

Shuangshuang Shi¹, Min Luo, Chensheng Lin, Ning Ye

Affiliation

¹ Key Laboratory of Optoelectronic Materials Chemistry and Physics, Collaborative Innovation Center for Optoelectronic Semiconductors and Efficient Devices, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, P. R. China. lm8901@fjirsm.ac.cn nye@fjirsm.ac.cn.

PMID: 29700544
DOI: 10.1039/c8dt00450a

Abstract

Two new centric alkali metal bismuth selenite fluorides, ABi2SeO3F5 (A = K and Rb), have been synthesized through a soft hydrothermal method. KBi2SeO3F5 crystallizes in an orthorhombic crystal system with the centric space group Pbcm possessing a three-dimensional (3D) network made up of SeO3 trigonal pyramids and asymmetric BiO3F5 polyhedra. As regards compound RbBi2SeO3F5, it crystallizes in a triclinic crystal system with a centric space group of P1[combining macron], which contains alternant two-dimensional (2D) [Bi2SeO3F5]∞1- layers separated by Rb+ cations. In terms of structure, the differences between KBi2SeO3F5 and RbBi2SeO3F5 originate from the size of alkali metal cations, which has a great influence on the framework geometry and the dimensionalities of crystals. The UV-vis diffuse reflectance spectroscopy study of powder samples indicates that the band gaps of KBi2SeO3F5 and RbBi2SeO3F5 are approximately 4.08 and 4.18 eV, respectively, which are the largest ones among the known bismuth selenites owing to the existence of alkali metal cations as well as fluorine anions in crystals. Furthermore, theoretical calculations show that the optical absorption of two compounds is mainly attributed to the contribution of BiOxFy polyhedra and [SeO3]2- anionic groups.