Ligands with oxime functional groups are noted for their ability to stabilize normally inaccessible oxidation states, such as nickel (III) or copper (III). Our group has developed a distinctive tetradentate ligand with three oxime groups, which we have named TRIPHOX; the three oxime N atoms and the core N atom all act as donor atoms. Previously our group synthesized and structurally characterized [Ni(TRIPHOX)Cl2] (see figure); note that the tetradentate nature of the TRIPHOX ligand forces the Ni(II) central atom to adopt an octahedral geometry. The [Ni(TRIPHOX)Cl2] complex was prepared by adding one equivalent of TRIPHOX to a methanolic solution of NiCl2. The initial bright-green solution turned aquamarine-blue nearly instantaneously. In preliminary work we allowed FeCl2, CoCl2, and CuCl2 to react with TRIPHOX in methanol; each mixture produced a nearly instantaneous color change, suggesting the desired complexes – [Fe(TRIPHOX)Cl2], [Co(TRIPHOX)Cl2], and [Cu(TRIPHOX)Cl2], respectively – had been synthesized. We will employ chemical oxidants, such as K2S2O8, to access the higher oxidation states. Successful oxidations will initially be noted by a color change, as dictated by Ligand Field Theory. Ultimately, the actual charge of the metal centers will be confirmed by measuring the number of unpaired electrons with a magnetic susceptibility balance; the number of unpaired electrons will also allow us to determine if TRIPHOX is a strong-field or weak-field ligand.

High oxidation states of first-row transition-metal complexes with a tris-oxime ligand

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