CO₂-Promoted Assembly of Nonplanar B₁₂O₂₄-Ring as a Fundamental Building Block in Lithium–Sodium Alkali Borates during Carbon Capture

The crystalline structure of Li₃NaB₄O₈, a reaction product resulting from CO₂ absorption by lithium-sodium orthoborate ((Li_0.5Na_0.5)₃BO₃), a recently developed sorbent for high-temperature carbon capture, is herein elucidated. The compound crystallizes to form a peculiar isolate borate fundamental building block consisting of six 3-membered borate rings interlinked through mutual tetrahedral borates to form a nonplanar 6-membered borate ring of chemical formula B₁₂O₂₄. The identification of this structure allows closing of the loop regarding the reaction mechanism characterizing CO₂ capture by lithium-sodium orthoborate, sheds light on previously made observations regarding the evolution of the physicochemical properties of the melt during carbon capture, and provides valuable information for future studies and process simulations involving this promising new material for carbon capture.