Rational Design and Resolution to the Mystery of the Structure of Cyclo[18]carbon

C-18 is a cyclo[18]carbon that consists of 18 carbon atoms. Beyond the detection of an intermediate gas phase species, the synthesis of a solid-state C-18 and elucidation of its bonding structure have remained significant scientific challenges over the past half century. Until recently, this unorthodox carbon allotrope was conceptually feasible, while experimentally elusive in the solid state. Finally, this carbon allotrope has made its long-awaited debut when a collaborative research effort successfully synthesized and revealed the structure of cyclocarbon. The long 50 years of waiting is now over with the unveiling of this new form of chemistry's most celebrated element. This article highlights the discovery of this new allotrope from the carbon family, and discusses its chemical structure, potential applications, and challenges for future research.