title: Biliverdine-based metalloradicals: sterically enhanced noninnocence.
abstract: This is a first density functional theory survey of transition-metal biliverdines (Blv), where we have chosen to focus on key Mn, Fe, Co, and Cu complexes. According to the calculations, the complexes are invariably noninnocent, featuring Blv*2- ligand radicals. In this, biliverdine complexes resemble metallocorroles, but the parallels are only approximate. Briefly, metallobiliverdines exhibit a much greater tendency to adopt noninnocent electronic structures than analogous metallocorroles. The O...O nonbonded contacts in biliverdines apparently preclude the formation of short metal-N bonds that, in turn, could stabilize high-valent metal ions. Thus, while most copper corroles (Cor) exhibit diamagnetic CuIII ground states, copper biliverdines are clearly Cu(II)Blv*2- species. In the same spirit, while chloroiron corroles are best described as FeIII(S = 3/2)Cor*2-,the analogous biliverdine derivative seems best described as Fe(III)(S = 5/2)Blv*2-, i.e., featuring a high-spin FeIII center with long (>2.0 A) Fe-N bond distances. Overall, the results highlight the important role that steric effects may play in modulating the electronic structures and the potentially noninnocent nature of transition-metal complexes.
authors.affiliation: Department of Chemistry, University of Tromsø, N-9037 Tromsø, Norway.
authors.forename: Ingar
authors.initials: I
authors.lastname: Wasbotten
authors.forename: Abhik
authors.initials: A
authors.lastname: Ghosh
mesh_terms: D001664:Biliverdine / Q000737:chemistry*; D002712:Chlorides / Q000737:chemistry; D005609:Free Radicals / Q000737:chemistry; D019216:Metals, Heavy / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation
chemical_list: D002712:Chlorides; D005609:Free Radicals; D019216:Metals, Heavy; D001664:Biliverdine