Reactions of the dimeric cobalt complex [(L⁻Co)₂] (1, L=[(2,6-iPr₂C₆H₃)NC(Me)]₂) with polyarenes afforded a series of mononuclear and dinuclear complexes: [LCo(η⁴-anthracene)] (2), [LCo(μ-η⁴:η⁴-naphthalene)CoL] (3), and [LCo(μ-η⁴:η⁴-phenanthrene)CoL] (4). The pyrene complexes [{Na₂(Et₂O)₂}{LCo(μ-η³:η³-pyrene)CoL}] (5) and [{Na₂(Et₂O)₃}{LCo(η³-pyrene)}] (6) were obtained by treating precursor 1 with pyrene followed by reduction with Na metal. These complexes contain three potential redox active centers: the cobalt metal and both α-diimine and polyarene ligands. Through a combination of X-ray crystallography, EPR spectroscopy, magnetic susceptibility measurement, and DFT computations, the electronic configurations of these complexes were studied. It was determined that complexes 2–4 have a high-spin Co^I center coupled with a radical α-diimine ligand and a neutral polyarene ligand. Whereas, the ligand L in complexes 5 and 6 has been further reduced to the dianion, the cobalt remains in a formal (I) oxidation state, and the pyrene molecule is either neutral or monoanionic.

By tuning the length and rigidity of the spacer of bis(biurea) ligands L, three structural motifs of the A₂L₃ complexes (A represents anion, here orthophosphate PO₄³⁻), namely helicate, mesocate, and mono-bridged motif, have been assembled by coordination of the ligand to phosphate anion. Crystal structure analysis indicated that in the three complexes, each of the phosphate ions is coordinated by twelve hydrogen bonds from six surrounding urea groups. The anion coordination properties in solution have also been studied. The results further demonstrate the coordination behavior of phosphate ion, which shows strong tendency for coordination saturation and geometrical preference, thus allowing for the assembly of novel anion coordination-based structures as in transition-metal complexes.