From β‐Na2B6O10 to Na3AlB8O15 and Na3Al2B7O15: Structural Tuning of Anionic‐Group Architectures by Substitution of [BO4] by [AlO4] Covalent Tetrahedra

Abstract Two new sodium aluminum borates, Na 3 AlB 8 O 15 and Na 3 Al 2 B 7 O 15 , have been successfully synthesized by the high‐temperature solution method. They crystallize in the different space groups, P 2 1 / c and P 2/ c , respectively. The B−O configurations of β‐Na 2 B 6 O 10 , Na 3 AlB 8 O 15 and Na 3 Al 2 B 7 O 15 are compared to feature complicated different dimensional open‐framework structures caused by the substitution of [BO 4 ] by [AlO 4 ] covalent tetrahedra. Moreover, the experimental results indicate that Na 3 AlB 8 O 15 and Na 3 Al 2 B 7 O 15 have short ultraviolet (UV) cutoff edges (<187 nm). The first‐principles calculations show that Na 3 AlB 8 O 15 and Na 3 Al 2 B 7 O 15 have moderate birefringence (0.075 and 0.041@1064 nm, respectively).