STRUCTURAL CHARACTERIZATION OF ZINC(II) COMPLEXES OF OCTAETHYLOXOPHLORIN DIANION AND OCTAETHYLOXOPHLORIN RADICAL-ANION

The zinc(II) complex of octaethyloxophlorin dianion, Zn(II)(OEPOH), readily dissolves in pyridine (py) to form red, air-sensitive solutions from which crystalline {(py)Zn(II)(OEPOH..py)} has been isolated. The X-ray crystal structure reveals the presence of a five-coordinate zinc with an axial pyridine ligand and a planar oxophlorin macrocycle. The meso-hydroxyl substituent is hydrogen bonded to a second pyridine. Oxidation of red pyridine solutions of Zn(II)(OEPOH) gives green solutions from which crystals of the stable free radical complex {(py)Zn(II)(OEPO.)}(py) have been isolated. The X-ray crystal structure shows that the zinc(II) ion is five-coordinate with a single axial pyridine ligand. A second, uncoordinated pyridine is trapped on the opposite side of the oxophlorin radical. The structure suffers from inversion disorder as is typical for five-coordinate porphyrin complexes and from disorder of the meso-oxo substituent. The crystal packings of these two closely related substances, which differ only by an electron and a proton, are compared.