Coordinative Self-Assembly and Solution-Phase X-ray Structural Characterization of Cavity-Tailored Porphyrin Boxes

The challenge of building functional, hollow, metal-linked supramolecules that can begin to mimic the remarkable behavior of clefts, cavities, and pores in enzymes and zeolites has attracted tremendous attention from the coordination chemistry community.1 Reversible ligation, together with well-defined local metal coordina-tion motifs, often allows for one-pot assembly of supramolecules of predetermined architecture in high or even quantitative synthetic yield. Among the many interesting architectures described (includ-ing triangles,2 rectangles,3 higher polygons,4 and various polyhe-dra5), squares6 are particularly ubiquitous, as the required 90 ° bond angles are easily generated based on octahedral or square-planar metal coordination. We have explored in some detail the synthetic and functional chemistry of “molecular squares ” featuring porphy-rins as edges7 and Re(CO)3Cl units as corners.8 We find that the nanometer-sized cavities defined by the squares can be chemicall