Na2Rb2SrB18O30 with [B9O19]11− fundamental building block consisting of three [B3O7]5− groups.

A new sodium rubidium strontium borate, Na2Rb2SrB18O30, has been successfully synthesized via the high temperature solution method and characterized by single crystal X ray diffraction. The compound crystallizes in the monoclinic space group P21/c (No. 14) with the following cell parameters: a=8.464(5) Å, b=8.516(5) Å, c=17.110(10) Å, β=92.281(8)°, V=1232.3(12) Å3, Z=2. The fundamental building block (FBB) of Na2Rb2SrB18O30 is [B9O19]11−, which consists of three [B3O7]5− groups bridged by oxygen atoms. The FBB connects with adjacent ones through the terminal oxygen atoms condensed into a three dimensional (3D) 3∞[B9O15] network with three types of channels, and two of them are occupied by Rb+ and Sr2+ cations. Besides, the structure comparison and categorization between the borates with [B9O19]11− FBB were investigated via the topological analysis for the first time. Also, theoretical analyses of the band structures and partial densities of states (PDOS) calculations were carried out to elaborate the relationship between crystal structures and optical properties by first‐principles calculation. [ABSTRACT FROM AUTHOR]