Two new nonaborates, Na2Ba0.5[B9O15]·H2O (1) and Na4Ca1.5[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.
Keywords: metal borates; oxoboron cluster; short cutoff edges; solvothermal syntheses.