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

摘要

Two novel alkali/alkaline-earth borates, Ba_6[B_6O_9(OH)_6]_2(H_3BO_3) (1) and Li_7MAlB_(12)O_(24) (M=Ba, Sr, Ca) (2a–c), with 1D and 3D structures have been made hydrothermally and characterized. 1 features a rare 1D anionic chain built by hexaborate clusters of B_6O_(11)(OH)_6; each made of six BO_4/BO_2(OH)_2 tetrahedra. The anionic chains are embedded in the channels of a Ba_6-based wheel-cluster openframework. 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) 2a–c have been successfully obtained, constructed from B_6O_(14)-based cluster chains and AlO_6 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 2a–c, but also obtained the first 3D AlO_6- containing ABOs made under hydrothermal conditions. Different from the previously known 4-connected zeolite-type ABOs, alternately arranged from AlO_4 tetrahedra and oxoboron clusters, the AlO_6 octahedra in 2a–c as the linkers join to six 1D B_6O_(14)-based cluster chains to produce 3D ABOs. The optical diffuse reflectance spectra reveal that 2a–c have wide range transparency. In addition, the thermal property analysis proves that 2a–c are congruently melting compounds and possess high thermostability.