Self-assembly of charged corannulene with cesium ions: Always in the bowl

Abstract

Cesium salts of mono- and doubly-reduced bowl-shaped corannulene have been prepared in the presence of different O-donors and isolated as bulk crystalline solids. Crystallization of corannulene monoanions with cesium ions from diglyme afforded green blocks of [Cs(diglyme)+(C20H10−)] (1). Its X-ray structural investigation revealed the formation of a 1D polymer built on simultaneous binding of large cesium ion to the convex and concave faces of the adjacent C20H10•− anions, with each bowl functioning in the rare η5-endo:η6-exo bridging mode. The coordination environment of the Cs+ ion is completed by a side-bound diglyme molecule. The cesium salt of corannulene dianion, C20H102−, was crystallized in the presence of dicyclohexano-18-crown-6 ether as [Cs2(dc-18-crown-6)1.52+(C20H102−)] (2). This product has a discrete linear tetranuclear structure built by aggregation of two terminal exo-hub-bound {Cs(dc-18-crown-6)(C20H102−)}− anionic moieties with the central {Cs2(dc-18-crown-6)}2+ cationic gluing block. The cesium ions of the latter, sharing one crown ether molecule, occupy the concave cavities of the doubly-charged corannulene bowls. As a result, each bowl functions in the symmetric η5-endo:η5-exo bridging mode which has not been previously seen. The bowl depths of the resulting carbanions in 1 and 2 are 0.915(15) Å and 0.852(13) Å, respectively, vs. that of 0.875(2) Å in neutral corannulene.