Ba2B5O8(OH)2(NO3)·3H2O: the design of an alkaline earth metal borate-nitrate optimized from a hydroxylic borate

The first alkaline earth metal borate-nitrate, namely Ba2B5O8(OH)2(NO3)·3H2O (BBNOH), has been synthesized by the hydrothermal method. BBNOH crystallizes in the space group of P21/c and shows two-dimensional (2D) 2∞[B5O8(OH)2]3- borate anion layers, and the hydrated barium cations and the [NO3]- anions are located between the layers. The process of optimizing the structure of Ba2B5O8(OH)2OH to BBNOH has been discussed. The first principles calculation has been used to calculate the birefringence of Ba2B5O8(OH)2(NO3)·3H2O, and the value is 0.033@1064 nm, which is mainly originated from the borate anions and the π conjugated [NO3]- anions.