Ba2ZnSc(BO3)3 and Ba4Zn5Sc2(BO3)8: first examples of borates in the Zn–Sc–B–O system featuring special structure configurations

Abstract

As the first reported examples of borates in the Zn–Sc–B–O system, Ba₂ZnSc(BO₃)₃ and Ba₄Zn₅Sc₂(BO₃)₈ were synthesized through a high-temperature solution method. The structure of Ba₂ZnSc(BO₃)₃ can be described as ZnO₄ tetrahedra connecting ScO₆ octahedra to form a [ZnScO₉]¹³⁻ dimer, which further bonds with seven BO₃ triangles to form a ²_∞[ZnSc(BO₃)₃] layer, and the Ba atoms distribute in the voids between the layers. In contrast, in Ba₄Zn₅Sc₂(BO₃)₈, Zn–O chains composed of 4- and 6-coordinated Zn atoms link with Sc₂O₈ dimers to form a Zn–Sc–O layer, and the BO₃ triangles and Ba atoms fill in the voids between the layers. Interestingly, the special [Zn₂(BO₃)₆]¹⁴⁻ cluster is found in Ba₂ZnSc(BO₃)₃, which is different from the 2D layers or 3D frameworks of the Zn–B–O configurations in other zincoborates. Moreover, the lowest-coordinated ScO₅ polyhedra, as well as the coexistence of two types of ZnO_n units (n = 4 and 6), are observed for the first time in Ba₄Zn₅Sc₂(BO₃)₈. These fascinating results can promote the design of novel borates with BO₃ units and enrich the borate structure chemistry.