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

Two new borophosphates, Cs 3 B 3 P 4 O 16 and Li(NH 4 ) 2 B 3 P 4 O 16 , and two new fluoroborophosphates, K 4 B 2 P 2 O 9 F 2 and Rb 3 B 2 PO 5 F 4 , have been obtained via 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, P 2 1 / c . Two-dimensional (2D) [B 3 P 4 O 16 ] ∞ layers and a 3D [B 3 P 4 O 16 ] ∞ network can be found in Cs 3 B 3 P 4 O 16 and Li(NH 4 ) 2 B 3 P 4 O 16 , respectively, while isolated [B 2 P 2 O 9 F 2 ] and [B 2 PO 5 F 4 ] exist in K 4 B 2 P 2 O 9 F 2 and Rb 3 B 2 PO 5 F 4 , respectively. The effect of the alkali metal cation size on the framework structures of Cs 3 B 3 P 4 O 16 and Li(NH 4 ) 2 B 3 P 4 O 16 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.