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Removal of chloride from CoCl 2 with TlPF 6 in acetonitrile, followed by addition of excess nitrosobenzene, yielded the eight-coordinate cobalt(II) complex salt [Co{Ph(O)NN(O)Ph} 4 ](PF 6 ) 2 , shown by single-crystal X-ray analysis to have a distorted tetragonal geometry. The analogous treatment of the bipyridyl complex Co(bpy)Cl 2 yielded the mixed-ligand cobalt(II) complex salt [Co(bpy){Ph(O)NN(O)Ph} 2 ](PF 6 ) 2 , whose single-crystal X-ray structure displays a trigonal prismatic geometry, similar to that of the iron(II) cation in the previously known complex salt [Fe{Ph(O)NN(O)Ph} 3 ](FeCl 4 ) 2 . The use of TlPF 6 to generate solvated metal complex cations from chloride salts or chlorido complexes, followed by the addition of nitrosobenzene, is shown to be a useful synthetic strategy for the preparation of azodioxide complex cations with the noncoordinating, diamagnetic PF 6 - counteranion. Coordination number appears to be more important than d electron count in determining the geometry and metal-ligand bond distances of diphenylazodioxide complexes., Competing Interests: The authors declare no competing financial interest.