Synthesis, Structure, Thermal and Magnetic Properties of a New Open-framework Borophosphate: NH₄Mn(H₂O)₂BP₂O₈·H₂O^†

Using new template agent, a new borophosphate compound, NH₄Mn(H₂O)₂BP₂O₈·H₂O was hydrothermally prepared and structurally characterized. It crystallizes in a hexagonal space group P6₁22 with lattice parameters a=0.9652(2) nm, c=1.5792(5) nm, V=1.2740(5) nm³ and Z=6. The structure has a three-dimensional open-frame work with borophosphate helical ribbons ¹_∞{[BP₂O₈]³⁻ and MnO₄(H₂O)₂ octahedra. The water molecules are positioned inside the helical channels. Very interestingly, the ammonium ions are located outside the loop of the free helical ribbons via the strong hydrogen bonds, which is different from the borophosphate analogue reported. The magnetization of the title compound is paramagnetic down to 5 K of the Curie-Weiss type within the measured range of 5–300 K with ⊖=−7.3 K, indicative of very weak antiferromagnetic interactions. The thermal decomposition of the compound was also described.