Accessing dynamic disorder in AlPO <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si12.svg" display="inline" id="d1e231"> <mml:msub> <mml:mrow/> <mml:mrow> <mml:mn>4</mml:mn> </mml:mrow> </mml:msub> </mml:math> -5 with single crysta

The aluminium phosphate framework materials, such as AlPO 4 -5, exhibit an inherent structural flexibility due to the connectivity of their rigid tetrahedral building blocks. This structural flexibility is critical to their ability to accommodate a wide range of organic guest molecules and/or heteroatoms, where subtle distortions of the framework do not compromise the overall framework integrity. Here, we use a combination of single-crystal diffuse scattering and ab initio molecular dynamics simulations to understand the framework dynamics in AlPO 4 -5. AlPO 4 -5 adopts the AFI topology, where the average structure is typically described as a framework in which one of the Al-O-P bond angles approaches 180 °. This configuration is considered both energetically unfavorable and unrealistic, creating a form of bond frustration that is alleviated by collective distortions that keep the Al- and P-tetrahedra rigid. Through a combination of synchrotron based diffuse X-ray scattering and ab initio molecular dynamic simulations we demonstrate that in the ALPO-5 framework these distortions are likely dynamic and the real structure dynamically transforms between different distorted states, which can be approximated by a three-fold superstructure along the c -axis. • Single-crystal diffuse scattering of calcined AlPO 4 -5 was studied using synchrotron radiation. • AlPO4-5 shows incommensurate modulated structure analogous to zeolite SSZ-24. • The combination of ab initio molecular dynamics and single-crystal diffuse scattering show a dynamic disordered three-fold superstructure along the crystal c -axis.