Two metallacyclic tetranuclear Fe (III) complexes, Fe2 (μ-O) (μ-RCOO) 2 (tpon) 2 (BPh4) 4 R = Me (1), Ph (2), where the flexible ditopic ligand tpon (N, N, N′, N′-tetrakis (2-pyridylmethyl) octane-1, 8-diamine) links two μ-oxo-bis (μ-carboxylato) triple-bridged dinuclear units, have been prepared. Single-crystal X-ray diffraction establishes that both complexes adopt a 26-membered macrocyclic framework featuring an internal cavity capable of guest inclusion. Notably, incorporation of a monoatomic μ-oxo bridge enforces an outward orientation of the ligand alkyl chains, thereby suppressing the “zipper effect” observed in the previously reported Mn (II) analogue and facilitating the encapsulation of an acetone molecule. UV–vis absorption and diffuse-reflectance spectra confirm that the tetranuclear scaffold remains intact in both the solid state and in solution. These results demonstrate that modulating local coordination directionality via μ-oxo bridging is an effective strategy for controlling the global conformation and host–guest properties of large metallasupramolecular architectures.
SUGIYAMA et al. (2026) studied this question.