Two Novel 3D Borates: Porous-layer and Layer-pillar Frameworks

Two new borates, NaK[B{BO(OH)}{BO(OH)}] (1) and Na[Al{BO(OH)}{BO}{BO(OH)}] (2), have been made by a solvothermal method. Structure 1 is made of two types of oxoboron clusters ([BO(OH)] and [BO(OH)]) and BO tetrahedra to form a 3D porous layer, in which the [BO(OH)] clusters are bridged by BO groups to produce a 2D B-O layer with 11-membered ring (MR) windows, while the [BO(OH)] clusters as 2-connected pillars join the adjacent B-O layers to make a 3-D porous layer. Structure 2 is built from two types of oxoboron clusters ([BO(OH)] and [BO]), AlO units and BO(OH) triangles to produce 3D pillar-layered aluminoborate (ABO), in which the [BO] clusters are linked together to form a 2-D B-O layer; the [BO(OH)] clusters and AlO groups join each other to form 1D tubular ABO; and the BO(OH) triangles act as linkers to connect the adjacent B-O layer and the ABO tubes, resulting in 3D pillar-layered ABO. Interestingly, the ABO tubes decorated with the BO(OH) triangles act as pillars to make a 3D layer-pillared structure. UV-vis diffuse spectra indicate that both have cut-off edges below 190 nm, and the calculated band gaps are 5.75 and 5.78 eV, respectively.