Structural Insights into Borates with an Anion‐Templated Open‐Framework Configuration: Asymmetric K2BaB16O26 versus Centrosymmetric K3CsB20O32 and Na2M2NB18O30 (M=Rb, Cs; N=Ba, Pb)

Abstract Five new mixed‐metal borate crystals, namely, K 2 BaB 16 O 26 , K 3 CsB 20 O 32 , Na 2 Cs 2 BaB 18 O 30 , Na 2 Rb 2 PbB 18 O 30 , and Na 2 Cs 2 PbB 18 O 30 , have been synthesized by the high‐temperature solution method. These structures were characterized by single‐crystal X‐ray diffraction and their B−O configurations are shown to feature complicated three‐dimensional (3D) open‐framework structures incorporating different types of channels. For all five compounds, the frameworks can be reduced to four‐connected (4‐c) uninodal nets with sra ‐, dia ‐ and nbo ‐type topologies by assigning the [B 5 O 10 ] 5− and [B 3 O 7 ] 5− clusters as basic nodes. First‐principles calculations have shown that the multiple cations in mixed‐metal borates influence the ground‐state electronic structures and associated optical absorptions. In addition, the crystal structures, thermal stabilities, and IR spectra of the title compounds have also been performed.