Syntheses, structures and properties of two new members of the pentaborate family: NaKB5O8(OH)·H2O and KB5O8·2H2O

Abstract

Two new members of the pentaborate family, NaKB₅O₈(OH)·H₂O (I) and KB₅O₈·2H₂O (II), were successfully synthesized, which crystallize in the space groups of P and Fddd, respectively. In compound I, [B₅O₁₀(OH)] fundamental building blocks (FBBs) form a two-dimensional (2D) ²[B₅O₈(OH)]_∞ layer through corner-sharing, whereas in compound II, [B₅O₁₀] FBBs form two independent interpenetrating 3D ³[B₅O₈]_∞ networks by sharing common O atoms. The UV-vis-NIR diffuse reflectance spectrum and first-principles calculations suggest that the two compounds possess deep-ultraviolet (DUV) transparency windows. Real-space atom-cutting and response electron distribution anisotropy (REDA) analyses show that the birefringence of both compounds mainly originates from the π-conjugated units.