Variable dimensionality of the anion framework in four new borophosphates and fluoroborophosphates with short cutoff edges.

Two new borophosphates, CsBPO and Li(NH)BPO, and two new fluoroborophosphates, KBPOF and RbBPOF, have been obtained the high-temperature solution method. Single-crystal X-ray diffraction indicates that all of them exhibit various anion frameworks although they crystallize in the same space group, 2/. Two-dimensional (2D) [BPO] layers and a 3D [BPO] network can be found in CsBPO and Li(NH)BPO, respectively, while isolated [BPOF] and [BPOF] exist in KBPOF and RbBPOF, respectively. The effect of the alkali metal cation size on the framework structures of CsBPO and Li(NH)BPO has been discussed in detail. The IR spectra confirm their structural validity. UV-Vis-NIR diffuse reflectance spectroscopy indicates that the new compounds exhibit short cutoff edges. In addition, theoretical calculations were carried out to understand their electronic structures and optical properties.