Two New Nonaborates with {B₉} Cluster Open-Frameworks and Short Cutoff Edges

Two new nonaborates, Na₂Ba_0.5[B₉O₁₅]·H₂O (1) and Na₄Ca_1.5[B₉O₁₆(OH)₂] (2), have been solvothermally made with mixed alkali and alkaline-earth metal cationic templates. 1 and 2 are constructed by two different types of nonaborate clusters. In 1, the [B₉O₁₉]¹¹⁻ cluster is composed of three corner-sharing [B₃O₇]⁵⁻ clusters, of which two of them interconnect to the 1D B₃O₇-based chains and are further bridged to the 3D framework with 7 types of 10-MR channels by another [B₃O₇]⁵⁻ bridging cluster. The [B₉O₁₈(OH)₂]¹¹⁻ cluster in 2 is made of four BO₄-sharing [B₃O₈]⁷⁻ clusters. As a 4-connected node, the interconnections of [B₉O₁₈(OH)₂]¹¹⁻ construct the unpreceded 2D layer with large 14-MR windows, which are further joined by H-bonds to the 3D supramolecular framework. UV–Vis absorption spectra reveal that both 1 and 2 have short cutoff edges below 190 nm, exhibiting bandgaps of 6.31 and 6.39 eV, respectively, indicating their potential applications in deep UV (DUV) regions.