Synthesis and X-ray crystal structures of metal complexes of three isomeric bibenzodiazines: Discrete and polymeric assemblies

Thirteen complexes of three isomeric bibenzodiazines were prepared and X-ray crystal structures were determined for seven of these. It is shown that 2,2′-biquinazoline prefers to form mononuclear complexes with chelation involving the less hindered nitrogen donors. Complexes of 4,4′-biquinazoline failed to provide suitable crystals for X-ray structure determination. 2,2′-Biquinoxaline is shown to offer two modes of coordination; in the first it acts as a “stepped-linear” bridging ligand using the two less hindered nitrogens, while in the second mode it chelates to copper(I) centres using its more hindered nitrogens. The presence of the fused benzo rings leads to a higher propensity for π–π stacking of the heterocyclic ligands within such complexes.