ortho-Nitrosocumene (o-NC) exhibits dynamic N,N bonding, interchanging monomer and E/Z-azodioxide dimer structures, the extent of which depends on the environment. As a solid, o-NC is a Z-dimer; in organic solvent, the monomer is favored; and in water, dimers are favored. A supramolecular assembly of o-NC is observed as a separate species by NMR in water, shown to be a novel nanometer-sized aggregate containing ∼2000 molecules.