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Sequential Topotactic Transformations Traverse Metastable Phases in Complex Aluminophosphate Frameworks with Tunable
Jiahui Zhu1,2, Chenyang Nie1,2, Yuanhao Li1,2
1National Engineering Research Center of Lower-Carbon Catalysis Technology, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian116023, China.
Abstract:
Crystalline porous frameworks are irreplaceable platforms for catalysis, separation, new energy, sensing, and biomedicine, yet the majority exist as inaccessible metastable structures across an extensive structural landscape. Here we introduce a sequential topotactic transformation (STT) strategy, in which a simple steaming treatment induces a cascade of structurally correlated topotactic transformations, systematically uncovering a family of hidden metastable frameworks. Using this STT approach, the small-pore aluminophosphate molecular sieve (AlPO MS) DNL-17 undergoes sequential crystalline-state transitions to yield three previously unknown MSs (DNL-18, DNL-19, and DNL-20). Structural characterization and DFT calculations reveal that these transformations preserve partial ABC-6 stacking motif through selective bond cleavage and framework-fragment sliding. This strategy not only accesses diverse metastable states but also enables pore-size modulation from small-pore to ultramicroporous regimes, leading to efficient propane/propylene and water/carbon dioxide separations. It broadens the structural diversity of MSs and provides a strategy for tailoring pore architectures toward application-specific performance.