The First Examples of Lithium-Containing Mixed-Alkali Strontium Borates with Different Dimensional Anionic...

Three new mixed-alkali strontium borates, Li₂ KSr₆ (BO₃ )₅ , Li₂ Rb₇ Sr₂₄ (BO₃ )₁₉ , and Li₂ Rb₂ SrB₁₈ O₃₀ , have been synthesized by the high-temperature solution method by adjusting the molar ratios of the reactants. They represent the first examples of lithium-containing mixed-alkali strontium borates. The structures of the three compounds show different dimensional anionic architectures, with Li₂ KSr₆ (BO₃ )₅ and Li₂ Rb₇ Sr₂₄ (BO₃ )₁₉ possessing isolated BO₃ units, whereas Li₂ Rb₂ SrB₁₈ O₃₀ has three-dimensional (3D) $$ open frameworks with three types of channels occupied by the strontium and rubidium atoms. Interestingly, Li₂ KSr₆ (BO₃ )₅ is the first example of a $$ chain composed of LiO₅ linked through the sharing of vertexes and edges. However, in Li₂ Rb₇ Sr₂₄ (BO₃ )₁₉ , isolated LiO₃ units can be observed, which is also rare in borates. Detailed analysis and comparisons of the structures of the anhydrous mixed-alkali- and alkaline-earth-metal borates and nine-polymeric fundamental building blocks have been made. Furthermore, Li₂ Rb₇ Sr₂₄ (BO₃ )₁₉ and Li₂ Rb₂ SrB₁₈ O₃₀ present short cutoff edges (<190 nm), which was confirmed by the UV/Vis/NIR diffuse reflectance spectra. These attributes make them attractive for deep-UV optical materials.