title: Q18Mg6(B5O10)3(B7O14)2F (Q = Rb and Cs): new borates containing two large isolated polyborate anions with similar topological structures.
abstract: Two novel isomorphic borates, Q18Mg6(B5O10)3(B7O14)2F (Q = Rb and Cs), were synthesized from high-temperature solutions. These borates are created from two kinds of isolated polyborate anionic groups, [B5O10] and [B7O14], and are further examples of two kinds of isolated polyborate anions coexisting in one borate structure. Although the title compounds are new structures, they are similar to the structures of the KBe2BO3F2 (KBBF) series of compounds, for example, Na2Be4B4O11 and γ-KBe2B3O7, which can be regarded as the substitution of [BO3] and [B2O5]/[B3O6] groups with [B7O14] and [B5O10] groups, respectively. It is found that the coexisting B-O groups tend to have similar structures. Also, the isolation of [B5O10] and [B7O14] in the title compounds mainly derives from the special role of magnesium tetrahedra, which has a similar role to that of the BeO4 tetrahedra in the KBBF series compounds. Electron-density maps and bond-overlap population (BOP) were calculated to illustrate this feature.
authors.affiliation: Key Laboratory of Functional Materials and Devices for Special Environments of CAS, Xinjiang Key Laboratory of Electronic Information Materials and Devices, Xinjiang Technical Institute of Physics & Chemistry of CAS, 40-1 South Beijing Road, Urumqi 830011 (P. R. China); University of Chinese Academy of Sciences, Beijing 100049 (P. R. China).
authors.forename: Zheng
authors.initials: Z
authors.lastname: Wang
authors.forename: Min
authors.initials: M
authors.lastname: Zhang
authors.forename: Xin
authors.initials: X
authors.lastname: Su
authors.forename: Shilie
authors.initials: S
authors.lastname: Pan
authors.forename: Zhihua
authors.initials: Z
authors.lastname: Yang
authors.forename: Hui
authors.initials: H
authors.lastname: Zhang
authors.forename: Lu
authors.initials: L
authors.lastname: Liu
keywords: borates; isolated BO groups; polyanions; topological structures