Borates A Novel Twofold Interpenetrating 3D Diamondoid Borate Framework Constructed from B₄ and B₅ Clusters

Borates with extended structures and interpenetrating system built from different types of cluster units are extremely rare. In this paper, we report a novel mixed-alkali-metal borate Na₃Li₂[B₄O₇][B₅O₈(OH)₂] (1) synthesized under solvothermal conditions, showing a three-dimensional twofold interpenetrating system constructed from two types of oxoboron clusters (B₄O₉ and B₅O₁₀(OH)₂) setting as the first example in borates. And 1 also features an intricate 3-D Li-O−Na cationic network. In this work, we made a detailed comparison with other reported borates from 1-D chain, 2-D layer to 3-D framework containing B₄ and B₅ clusters and further demonstrated that such 3-D framework of 1 can be achieved by controlling the alkalinity of solution to prompt the concentration of two different oxoboron clusters with rich terminal hydroxyl groups together. Indeed, it can be regarded as a good interpretation of hydrolysis-condensation processes in dimensional transformation of borates making it possible for the rational design of various structural borates in the future. Moreover, 1 displays fluorescence emission around 472 nm, making it an appropriate candidate for optoelectronic applications.