Double Concave Cesium Encapsulation by Two Charged Sumanenyl Bowls.

The controlled reaction of Na and Cs, two alkali metals of different ionic sizes and binding abilities, with sumanene (C21 H12 ) affords a novel type of organometallic sandwich [Cs(C21 H11- )2 ]- , which crystallized as a solvent-separated ion pair with a [Na(18-crown-6)(THF)2 ]+ cation (where THF=tetrahydrofuran). The unprecedented double concave encapsulation of a metal ion by two bowl-shaped sumanenyl anions in [Cs(C21 H11- )2 ]- was revealed crystallographically. Evaluation of bonding and energetics of the remarkable product was accomplished computationally (B2PLYP-D/TZVP/ZORA), providing insights into its formation.