Structural Regulations of Layered Borates: From Centric Layers to Chiral Porous Layers

Three pentaborates were made by precise structural regulations under hydrothermal conditions, namely, K2Cs[B5O8(OH)]·0.5CO3 (1), KNa4Cs[B5O8(OH)]2·2OH (2), and NaBa[B5O8.5(OH)] (3). Compound 1 features the typical 2D layers constructed from the four-connected B5O10(OH) clusters. By adjustment of the reactants and pH values of the systems to remove interlayered CO32– groups, the centric layers in 1 were transformed to the chiral layers of 2. By further adjusting cationic templates based on host–guest charge matching, the B5O10(OH) cluster unit was transformed to B5O11(OH), which built the chiral porous layers of 3. The chiral compounds 2 and 3 exhibit moderate second harmonic generation (SHG) responses of 1.1 and 1.7 times that of KDP (KH2PO4). The structural regulations actualize the evolutions on both structural symmetries and dimensions.