Allosterically Regulated Guest Binding Determines Framework Symmetry for an FeII4L4 Cage

Abstract

AbstractSelf‐assembly of a flexible tritopic aniline and 3‐substituted 2‐formylpyridine subcomponents around iron(II) templates gave rise to a low‐spin FeII4L4 capsule, whereas a high‐spin FeII3L2 sandwich species formed when a sterically hindered 6‐methyl‐2‐formylpyridine was used. The FeII4L4 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 FeII4L4 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.