Alkali Metal-Directed Hierarchical Assembly of Pyridine-Dipyrrolate Metallomacrocycles

The encapsulation of alkali metal ions in macrocyclic frameworks has attracted growing interest as a testbed for how host-guest compatibility can influence structure. However, the role of the cations beyond directing simple encapsulation generally remains poorly understood. Herein, a series of alkali metal-regulated macrocyclic coordination polymers (Polymer-K, Polymer-Rb, and Polymer-Cs) are described. The underlying scaffold was constructed from a pyridine-dipyrrolate precursor (Ligand 1) and [Zn(acac)2]. A combination of single crystal X-ray crystallographic analyses and theoretical calculations revealed the dual roles of the alkali metal ions, namely as encapsulated species within the macrocyclic cavity and as linkers between adjacent macrocycles. Within this series, the interactions between the alkali metal ions and the framework oxygen donors were found to vary systematically with ionic size. In contrast, the supramolecular interactions with surrounding frameworks proved to be governed primarily by electrostatic interactions. In particular, the identity of the alkali metal ions influences the electronic properties, chain connectivity, packing arrangement, and pore characteristics of the polymers, highlighting their key role in directing both the local coordination environment and hierarchical structural organization within a congeneric set of materials.