Intramolecular pi-dimerization in a 1,1'-bis(verdazyl)ferrocene diradical.

The solid state structure of 1,1'-bis(verdazyl)ferrocene reveals the two radical moieties associated intramolecularly to give the first example of a pi-dimer of a stable verdazyl radical. The pi-dimer structure is not maintained in solution. Magnetic characterization indicates that the radicals are sufficiently strongly antiferromagnetically coupled so as to render the molecule diamagnetic at room temperature.