A Simulation Study on the Topotactic Transformations from Aluminophosphate AlPO₄-21 to AlPO₄-25

Aluminophosphate AlPO₄-21 (AWO), formulated |(CH₃)₂NH₂|[Al₃P₃O₁₂(OH)], has been synthesized solvothermally by using dimethylamine as the template. Single-crystal X-ray diffraction analysis shows that AlPO₄-21 crystallizes in the monoclinic space group P2₁/n with a = 8.687(2) Å, b = 17.428(5) Å, c = 9.159(2) Å, β = 109.60(2)°, V = 1306.3(5) ų, and Z = 4. XRD analysis shows that AlPO₄-21 transforms to AlPO₄-25 (ATV) upon calcination at 500 °C. The molecular dynamics simulation approach was used to investigate the topotactic transformations from AlPO₄-21. The simulation study suggests that AlPO₄-21 is energetically favored to transform to AlPO₄-25, as well as other hypothetical forms, by the changing of the UUDD chains to the UDUD chains.