Synthesis, Structure and Coordination Self-Assembly of Azacalix[4-n]pyridine[n]pyrazines (n=1–3)

We herein report the synthesis and metal-directed coordination self-assembly behaviors of three new macrocyclic azacalix[4]aromatics that comprise various numbers of pyridine and pyrazine rings bridged by N-CH₃ groups. Structural characterization of 1–3 explored that their conformations are fluxional in solution and each adopts a 1,3-alternate configuration in crystalline solids. The macrocyclic skeletons in azacalixaromatic 1–3 afford a good platform to designedly arrange coordination sites in a unique way relative to conventional multidentate ligands. Solid-state structures of three coordination self-assembled silver complexes (13–15) of 1–3 determined by X-ray crystallography suggest that the nitrogen atoms on procumbent aromatics have better coordination ability than those on perpendicular aromatics and dictate the whole coordination self-assemblies. Unique discrete and 1D chain-like structures were thus obtained. This system may afford a deeper insight into the coordination self-assembly studies of heteroatom-bridged calixaromatics, possibly extending potential application of this novel macrocyclic polydentate organic compounds in the synthesis of functional metal organic framework formation.