Stabilization of CuII–I Bonds Using 2‐Benzoylpyridine Thiosemicarbazones – Synthesis, Structure, Spectroscopy, Fluo­rescence, and Cyclic Voltammetry

Abstract

AbstractThe reactions of copper(I) iodide with N1‐substituted 2‐benzoylpyridine thiosemicarbazones [(C6H5)(C5H4N)C2=N3–N2H–C(=S)–N1HR (R = Me, HLMe; Et, HLEt; Ph, HLPh)] in acetonitrile/dichloromethane mixtures have formed the complexes [Cu2III2(μ4‐N,N,S‐LMe)2] (1), [CuIII(κ3‐N,N,S‐LEt)] (4), and [CuIII(κ3‐N,N,S‐LPh)] (7) through proton‐coupled electron transfer (PCET), and these complexes have rare CuII–I bonds. The above thio ligands with copper(I) bromide and copper(I) chloride also formed similar CuII–Br and CuII–Cl bonds in complexes of stoichiometry [CuIIX(κ3‐N,N,S‐L)] (L = LMe, LEt, LPh, X = Br 2, 5, 8; X = Cl 3, 6, 9) by PCET. All of the complexes have been characterized by elemental analysis, infrared spectroscopy, electronic absorption spectroscopy, ESR spectroscopy, magnetic susceptibility measurements, molecular fluorescence, cyclic voltammetry, and single‐crystal X‐ray crystallography. The thio ligands coordinate as monoanionic N,N,S donors in 1–9. The ESR data support the divalent oxidation state of the metal centers in the complexes, and the ESR parameters follow the trend g∥ > g⟂ > 2 with G values in the range 2–4, which suggests a d ground state for the copper(II) complexes with variable exchange interaction in the solid complexes. The geometry around each copper(II) center is distorted square planar (mononuclear, 2–9) or square pyramidal (dinuclear, 1). The stabilization of copper(II)–iodide bonds as well as the formation of CuII–Br and CuII–Cl bonds from thio ligands and copper(I) halides by a PCET process represents basic research of topical interest.