Isoreticular Expansion in Porous Aluminum(III) andGallium(III) Phosphonates: Synthesis, Structure, and Properties Theissen, Jennifer Radke, Marvin Mangelsen, Sebastian Derveaux, Elien Narváez Adams, Roberth Mateo Wagner, Tobias Lopau, Jasper Näther, Christian Nelle, Christian Struve, Jörn Steinke, Felix Gándara Loe, Jesús Gys, Nick Hauffman, Tom Tiemann, Michael Tielens, Frederik Adriaensens, Peter Henke, Sebastian Marchal, Wouter Ameloot, Rob Stock, Norbert We report the synthesis, structural elucidation, and establishment of structure−property relationships for two metal−organic frameworks (MOFs), [M(OH)(H2BPD)]·xH2O (M = Al3+, Ga3+, x = 11–13), denoted as M-CAU-67, employing the ditopic linker molecule N,N′-4,4′ bipiperidine bis(methylenephosphonic acid) (H4BPD). The title compounds can be synthesized on a milligram scale under hydrothermal conditions, while gram-scale synthesis was realized under reflux conditions. Single-crystal X-ray diffraction (SCXRD) revealed an isoreticular, expanded MIL-91 type structure, representing a rare case of isoreticular expansion in porous metal phosphonates. The framework structure was confirmed by Rietveld refinement against powder X-ray diffraction (PXRD) data and further validated by solid-state NMR spectroscopy (31P MAS, 27Al 3Q MAS). Solvent-exchange experiments and variable-humidity/temperature PXRD data revealed high framework flexibility. The compounds show permanent microporosity and a complex, polarity- and size-dependent sorption behavior toward gases and vapors. American Chemical Society (ACS) 2026 info:eu-repo/semantics/article doc-type:article text http://purl.org/coar/resource_type/c_6501 https://ris.uni-paderborn.de/record/67327 Theissen J, Radke M, Mangelsen S, et al. Isoreticular Expansion in Porous Aluminum(III) andGallium(III) Phosphonates: Synthesis, Structure, and Properties. <i>Chemistry of Materials</i>. 2026;38(16):8463-8475. doi:<a href="https://doi.org/10.1021/acs.chemmater.6c01336">10.1021/acs.chemmater.6c01336</a> eng info:eu-repo/semantics/altIdentifier/doi/10.1021/acs.chemmater.6c01336 info:eu-repo/semantics/altIdentifier/issn/0897-4756 info:eu-repo/semantics/altIdentifier/issn/1520-5002 info:eu-repo/semantics/openAccess