CsB3O4(OH)2: a new deep-ultraviolet birefringent crystal with [B3O4(OH)2] anionic group

A new cesium hydroxyborate CsB3O4(OH)2, was designed and synthesized by a hydrothermal method. Remarkably, CsB3O4(OH)2 presents novel [B3O4(OH)2]∞ chains formed by [B3O4(OH)2] fundamental building blocks (FBBs). The report of less common [B3O4(OH)2] FBBs and [B3O4(OH)2]∞ chains in CsB3O4(OH)2 enriches the structural diversity of hydroxyborates. In addition, CsB3O4(OH)2 has a wide transparent window in the DUV spectral range and a large birefringence.