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

Two new sodium aluminum borates, Na3 AlB8 O15 and Na3 Al2 B7 O15 , have been successfully synthesized by the high-temperature solution method. They crystallize in the different space groups, P21 /c and P2/c, respectively. The B-O configurations of β-Na2 B6 O10 , Na3 AlB8 O15 and Na3 Al2 B7 O15 are compared to feature complicated different dimensional open-framework structures caused by the substitution of [BO4 ] by [AlO4 ] covalent tetrahedra. Moreover, the experimental results indicate that Na3 AlB8 O15 and Na3 Al2 B7 O15 have short ultraviolet (UV) cutoff edges (<187 nm). The first-principles calculations show that Na3 AlB8 O15 and Na3 Al2 B7 O15 have moderate birefringence (0.075 and 0.041@1064 nm, respectively).