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

Abstract

Two novel alkali/alkaline-earth borates, Ba6 [B6 O9 (OH)6 ]2 (H3 BO3 ) (1) and Li7 MAlB12 O24 (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 B6 O11 (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 B6 O14 -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 B6 O14 -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.