Unveiling the Transient Template in the Self-Assembly of a Molecular Oxide Nanowheel

A Hidden Template The entropic challenge inherent in forming a ring-shaped molecule generally increases considerably with the size of the ring. Assuming that a linear precursor must bind its ends together, extending its length diminishes the likelihood of the opposite ends approaching one another. In the absence of an external force, how then can a family of molybdenum oxide rings, several nanometers in diameter (quite large at the molecular scale), self-assemble? Miras et al. (p. 72 , see the cover; see the Perspective by Whitmire ) have now uncovered an internal template guiding the process. By carefully controlling conditions in a flow reactor, they were able to halt the assembly process partway through and characterize a smaller molybdenum oxide core cluster, around which the larger ring was forming. Ejection of this template then yielded the hollow finished product.