Extending Unique 1D Borate Chains to 3D Frameworks by Introducing Metallic Nodes

Two novel alkali/alkaline-earth borates, Ba₆[B₆O₉(OH)₆]₂(H₃BO₃) (1) and Li₇MAlB₁₂O₂₄ (M=Ba, Sr, Ca) (2 a–c), with 1D and 3D structures have been made hydrothermally and characterized. 1 features a rare 1D anionic chain built by hexaborate clusters of B₆O₁₁(OH)₆; each made of six BO₄/BO₂(OH)₂ tetrahedra. The anionic chains are embedded in the channels of a Ba₆-based wheel-cluster open-framework. On the basis of the structural analyses of 1, by incorporating Al atoms as the linkers and tuning the reaction conditions, the novel anhydrous 3D aluminoborates (ABOs) 2 a–c have been successfully obtained, constructed from B₆O₁₄-based cluster chains and AlO₆ octahedra. The 3D ABO framework and 3D Ba-O-Li network are interpenetrated to give a final dense structure. The study not only realized the expansion of the structure from the 1D chain of 1 to the 3D dense ABOs 2 a–c, but also obtained the first 3D AlO₆-containing ABOs made under hydrothermal conditions. Different from the previously known 4-connected zeolite-type ABOs, alternately arranged from AlO₄ tetrahedra and oxo-boron clusters, the AlO₆ octahedra in 2 a–c as the linkers join to six 1D B₆O₁₄-based cluster chains to produce 3D ABOs. The optical diffuse reflectance spectra reveal that 2 a–c have wide range transparency. In addition, the thermal property analysis proves that 2 a–c are congruently melting compounds and possess high thermostability.