The cis-N,N'-diphenylazodioxide (az) ligand, formed from the reversible dimerization of nitrosobenzene, is capable of binding to both transition and main-group metals as a chelating ligand, but few azodioxide complexes have been structurally characterized in the literature. Removal of chloride from first-series transition metal salts MCl₂ or chlorido complexes M(bpy)Cl₂ (bpy = 2,2'-bipyridyl) by treatment with TlPF₆, followed by addition of excess nitrosobenzene, yields a range of first-transition-series azodioxide complex salts of the form [M(az)₄](PF₆)₂, [M(bpy)(az)₂](PF₆)₂, [M(bpy)₂(az)](PF₆)₂, or [{M(bpy)(az)(μ-Cl)}₂](PF₆)₂, for M = Mn, Co, Ni, Cu, and Zn. Structural characterization of these complexes by single-crystal X-ray diffraction reveals an unusual coordination number of 8 for [M(az)₄](PF₆)₂ (M = Mn, Co), with distorted tetragonal coordination geometry, while 6-coordinate complexes display either distorted octahedral or trigonal prismatic coordination depending on the metal and ligand set. The biological activity of these complexes toward a series of human cancer cell lines has been assessed, and [Co(az)₄](PF₆)₂ and [Co(bpy)(az)₂](PF₆)₂ were found to be cytotoxic toward the SK-HEP-1 liver cancer cell line, while [Zn(bpy)₂(az)](PF₆)₂ was found to be cytotoxic toward the MCF-7 breast cancer cell line.

Briana Schrage

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