Zn and Fe complexes containing a redox active macrocyclic biquinazoline ligand

A series of iron and zinc complexes has been synthesized, coordinated by the macrocyclic biquinazoline ligand, 2-4:6-8-bis(3,3,4,4- tetramethyldihydropyrrolo)-10-15-(2,2′-biquinazolino)-[15]-1,3,5,8,10, 14-hexaene- 1,3,7,9,11,14-N₆ (Mabiq). The Mabiq ligand consists of a bipyrimidine moiety and two dihydropyrrole units. The electronic structures of the metal-Mabiq complexes have been characterized using spectroscopic and densityfunctional theory (DFT) computational methods. The parent zinc complex exhibits a ligand-centered reduction to generate the metal-coordinated Mabiq radical dianion, establishing the redox non-innocence of this ligand. Iron- Mabiq complexes have been isolated in three oxidation states. This redox series includes low-spin ferric and low-spin ferrous species, as well as an intermediate-spin Fe^II compound. In the latter complex, the iron ion is antiferromagnetically coupled to a Mabiq-centered π-radical. The results demonstrate the rich redox chemistry and electronic properties of metal complexes coordinated by the Mabiq ligand.