(NH4)B4O5(PO4) was obtained as crystalline colorless powder via a solid state reaction in a closed system by using NH4H2PO4 and B2O3 at 400 °C under vacuum conditions. Single-crystal X-ray diffraction revealed a new structure type (Pbca, no. 61, Z = 8, a = 8.1998(19), b = 13.3359(17), c = 13.4682(16) Å, R1 = 0.0472, wR2 = 0.1289, 2121 data, 149 parameters). It comprises a three-dimensional anionic framework built up by PO4, BO4 and BO3 units with charge balancing ammonium cations in the resulting one-dimensional channels. It represents only the third three-dimensional (3D) mixed-coordinated borophosphate revealing a new fundamental building unit. The titled compound is characterized by X-ray diffraction and electrostatic calculations. Besides, optical and thermal properties are investigated by FT-IR, UV-vis and thermogravimetry.
Wessels et al. (2026) studied this question.