Three mixed-alkaline-metal borates with {Li@B12Ox(OH)24−x} (x = 18, 22) clusters: from isolated oxoboron cluster to unusual layer

Abstract

Three new mixed-alkaline-metal borates, namely KNa₈[Li@B₁₂O₁₈(OH)₆](CO₃)₂ (1), Cs₁₀[Li@B₁₂O₂₀(OH)₂]₂·6H₂O (2) and Cs₅[Li@B₁₂O₂₀(OH)₂]·3H₂O (3), have been synthesized under hydro/solvothermal conditions. Compound 1 is a borate carbonate with the isolated [Li@B₁₂O₁₈(OH)₆]⁵⁻ clusters and interesting layers formed by Na⁺ and CO₃²⁻ ions, forming a 2D supramolecular structure with a 3,6-connecting binodal system. After changing the synthetic conditions, the isolated [Li@B₁₂O₁₈(OH)₆]⁵⁻ clusters are successfully extended to the layers in 2 and 3 by condensation reactions with the elimination of water molecules between oxoboron clusters. Each new fundamental building block [Li@B₁₂O₂₂(OH)₂]⁹⁻ in 2 and 3 connects with four neighboring units to form a 2D layer via B–O–B bonds for the first time, and 14-membered rings are also observed. Such a layer structure is first observed in dodecaborates. Since compound 3 crystallizes in the non-centrosymmetric space group, the second harmonic generation measurement and the dipole moments calculation have been carried out.