Creating well-defined nano-coordination spaces with properties that differ from those of the external environment is an ongoing goal within the supramolecular chemistry community. Systems that provide such spaces are attractive in the context of catalysis chemistry, metallopolymer chemistry, and nanomaterials. The use of metal-directed self-assembly is one of the more versatile and efficient methods for the creation of systems providing controlled nanospaces. This reflects the fact that, when appropriately designed, this kind of self-assembly can afford well-defined capsules and cages using only simple organic ligands. Here we detail and approach based on the use of pyridine dipyrrolate building blocks. This particular precursor can function as a bis-anionic ligand while providing an 18-π electron framework that bears analogy to the neutral terpyridine ligand. Detailed in this presentation will be a zinc(II)-directed cage-like self-assembled ensemble that is constructed from a specific pyridine dipyrrolate ligand, 2,6-bis(3,4-diethyl-5-carboxylate acid-1H-pyrrol-2yl)pyridine (compound 1, Scheme 1). The structure of the ligand itself was confirmed by X-ray crystallographic analysis and was shown to assemble into a supramolecular polymer in the solid state stabilized through hydrogen bonding interactions involving solvent molecules, such as DMF. Once characterized, compound 1 was used to fabricate a cage system. As inferred from X-ray crystallographic studies, the cage consists of zinc dimers with hydroxide bridges that, with the assistance of bound DMF solvent molecules, serve to fix the geometry and orientation of the pyridine dipyrrolate building blocks. Of note is that the cage displays responsive behavior undergoing changes in its emission and absorption features when exposed to certain anions. Scheme 1. Schematic representation of the Zn2+-stabilized cage-like assembly produced from compound 1 and the fluorescent response produced upon exposure to various anions in mixed solvent of DMF and methanol (1/4, v/v) excited at 365 nm. From left to right: benzoate, Br-, Cl-, CN-, PF6-, S6-, HSO4-, CH3SO3-, I-, NO3-, ClO4-, ReO4-, H2PO4-, BF4-, SCN-, toluene-4-sulfate.

Self-assembled pyridine-dipyrrolate cages

251st National Meeting (2016)

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