CsB 3 O 4 (OH) 2 : a new deep-ultraviolet birefringent crystal with [B 3 O 4 (OH) 2 ] anionic group.

A new cesium hydroxyborate CsB 3 O 4 (OH) 2 , was designed and synthesized by a hydrothermal method. Remarkably, CsB 3 O 4 (OH) 2 presents novel [B 3 O 4 (OH) 2 ] ∞ chains formed by [B 3 O 4 (OH) 2 ] fundamental building blocks (FBBs). The report of less common [B 3 O 4 (OH) 2 ] FBBs and [B 3 O 4 (OH) 2 ] ∞ chains in CsB 3 O 4 (OH) 2 enriches the structural diversity of hydroxyborates. In addition, CsB 3 O 4 (OH) 2 has a wide transparent window in the DUV spectral range and a large birefringence.