Synthesis, Structure, and Properties of Corona[6]arenes and Their Assembly with Anions in the Crystalline State

The synthesis, conformational structure, electronic property, and anion complexation of novel coronarenes were systematically studied. A number of corona[4]­arene[2]­tetrazines that contain different combinations of nitrogen atoms with O, S, SO₂, and CH₂ as bridging units were synthesized conveniently by means of a fragment coupling strategy based on efficient nucleophilic aromatic substitution reaction of easily available aromatic dinucleophiles and 3,6-dichlorotetrazine. The resulting macrocycles adopt crownlike conformational structures with the nitrogen bridge(s) forming conjugation with carbonyl and the other heteroatom linkages with tetrazine. CV and DPV measurements showed that the tetrazine-bearing coronarenes were electron deficient with reduction potentials ranging from −896 to −960 mV. Owing mainly to noncovalent anion−π attractive interactions, N₂,O₄-corona­[4]­arene­[2]­tetrazine formed complexes with anions of varied geometries and shapes yielding diverse assembled structures in the solid state.