Azoalkane-DDQ Arrays in the Solid State. New Donor-Acceptor Interactions for Crystal Engineering

A new set of donor-acceptor (DA) complexes between azoalkanes and 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) is reported. Bis(cis-azoalkane)s are found to bind DDQ in solution, with complex formation constants in CH2Cl2 that range from 22–76 M−1. Bis(azo)/DDQ crystalline solids are isolable and their crystal structures have been determined. Short intermolecular contacts in the crystals between the azo nitrogens and quinone ring carbons of 2.9–3.1 Å denote D-A “bonds” whose geometry is consistent with azo HOMO (n°)/DDQ LUMO (π*) overlap. The DA “bonding” promotes one-dimensional supramolecular ordering in the cocrystal which is organized as parallel (-DD-A-)n strands. Thus, the azo/DDQ DA “bond” serves as a new crystal engineering synthon for preparing one-dimensional, two-component solids.