Synthesis and Electronic Structure of Hypervalent Lead(II, IV) Compounds Based on the Azobenzene Tridentate Ligand

Although lead is known to form different oxidation states, it is still rare to compare the electronic properties between different oxidation states of lead with the same ligand. Herein, with the azobenzene tridentate ligand, we synthesized two types of hypervalent lead compounds where lead has different oxidation states. We evaluated the influence of different oxidation states on the electronic structure of the π-conjugated framework. From optical measurements and theoretical investigation, it was revealed that the intramolecular nitrogen–lead (N–Pb) interactions and the molecular orbitals of the azobenzene skeleton should be varied. The hypervalent lead(II) compound exhibited higher affinity (Lewis acidity) to the coordinating reagents than the hypervalent lead(IV) compound. Furthermore, we found that the extensive accessible space around the hypervalent element center increases in binding constants for additional bulky ligands such as ethylenediamine. We demonstrate here that changes in the oxidation state of hypervalent lead can induce drastic perturbations in the π-conjugated system, and furthermore, clear changes were observed in the optical properties and molecular coordination behaviors. These information should be of great significance not only for unveiling fundamental property of lead but also for applying lead element to advanced materials.