Self-assembly of a flexible tritopic aniline and 3-substituted 2-formylpyridine subcomponents around iron(II) templates gave rise to a low-spin FeII 4 L4 capsule, whereas a high-spin FeII 3 L2 sandwich species formed when a sterically hindered 6-methyl-2-formylpyridine was used. The FeII 4 L4 cage adopted a new structure type with S4 symmetry, having two mer-Δ and two mer-Ʌ metal vertices, as confirmed by NMR and X-ray crystallographic analysis. The flexibility of the face-capping ligand endows the resulting FeII 4 L4 framework with conformational plasticity, enabling it to adapt structurally from S4 to T or C3 symmetry upon guest binding. The cage also displayed negative allosteric cooperativity in simultaneously binding different guests within its cavity and at the apertures between its faces.
Keywords: Allosteric Regulation; Host-Guest Chemistry; Metal-Organic Cages; Structural Adaptation; Symmetry.
© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.