Ion‐induced assembly: Supramolecular structures are obtained in solution by a new ion‐induced assembly of conjugated Schiff‐base macrocycles. A distinct color change accompanies the aggregation, as shown in the photo. Shown: Macrocycle (A); with NaBPh4 (B); with KBPh4 (C); with RbBPh4 (D); with CsBPh4 (E); and with NH4BPh4 (F) in CH2Cl2.

[reaction: see text] A new [3 + 3] Schiff base macrocycle incorporating naphthalene groups has been prepared. By examination of its properties, X-ray crystallography of model compounds, and calculations, it has been determined that the macrocycle exists predominantly as the keto-enamine tautomer. This unexpected tautomerization presents an unusual hexaketo interior in the macrocycle.

A family of molecular heptacadmium carboxylate clusters templated inside [3 + 3] Schiff base macrocycles has been isolated and studied by variable temperature solution and solid-state NMR spectroscopy, single-crystal X-ray diffraction (SCXRD), and density functional theory (DFT) calculations. These metallocavitand cluster complexes adopt bowl-shaped structures, induced by metal coordination, giving rise to interesting host-guest and supramolecular phenomena. Specifically, dimerization of these metallocavitands yields capsules with vacant coordination and hydrogen-bonding sites accessible to encapsulated guests. Strong host-guest interactions explain the exceptionally high packing coefficient (0.80) observed for encapsulated N,N-dimethylformamide (DMF). The guest-accessible hydrogen-bonding sites arise from an unusual mu(3)-OH ligand bridging three cadmium ions. Thermodynamic and kinetic studies show that dimerization is an entropy-driven process with a highly associative mechanism. In DMF the exchange rate of peripheral cluster supporting carboxylate ligands is intrinsically linked to the rate of dimerization and these two seemingly different events have a common rate-determining step. Investigation of guest dynamics with solid-state (2)H NMR spectroscopy revealed 3-fold rotation of an encapsulated DMF molecule. These studies provide a solid understanding of the host-guest and dynamic properties of a new family of metallocavitands and may help in designing new supramolecular catalysts and materials.