Deconvoluting the Innocent vs. Non-Innocent Behavior of N,N-Diethylphenylazothioformamide Ligands with Copper Sources.

Redox-active ligands lead to ambiguity in often clearly defined oxidation states of both the metal center and the ligand. The arylazothioformamide (ATF) ligand class represents a redox-active ligand with three possible redox states (neutral, singly reduced, and doubly reduced). ATF--metal interactions result in strong colorimetric transitions allowing for the use of ATFs in metal detection and/or separations. While previous reports have discussed dissolution of zerovalent metals, the resulting oxidation states of coordination complexes have proved difficult to interpret through X-ray crystallographic analysis alone. This report describes the X-ray crystallographic analysis combined with computational modeling of the ATF ligand and metal complexes to deconvolute the metal and ligand oxidation state of ATF--metal complexes. Metal(ATF)₂ complexes that originated from zerovalent metals were found to exist as dicationic metal centers containing two singly reduced ATF ligands. When employing Cu^I salts instead of Cu⁰ to generate ATF--copper complexes, the Cu^I in the resulting complexes remained in its oxidation state, and the ATF ligand remained "innocent", existing in its neutral state. Although the use of CuX (X = Br or I) or [Cu(NCMe)₄]Y (Y = BF₄ or PF₆) generated species of the type: [(ATF)Cu(μ-X)]₂ and [Cu(ATF)₂]Y, respectively, the ATF ligand remained in its neutral state for each species type. [ABSTRACT FROM AUTHOR]