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

Abstract

Abstract The reactions of copper(I) iodide with N 1 ‐substituted 2‐benzoylpyridine thiosemicarbazones [(C 6 H 5 )(C 5 H 4 N)C 2 =N 3 –N 2 H–C(=S)–N 1 HR (R = Me, HL Me ; Et, HL Et ; Ph, HL Ph )] in acetonitrile/dichloromethane mixtures have formed the complexes [Cu 2 II I 2 (μ 4 ‐N,N,S‐L Me ) 2 ] ( 1 ), [Cu II I(κ 3 ‐N,N,S‐L Et )] ( 4 ), and [Cu II I(κ 3 ‐N,N,S‐L Ph )] ( 7 ) through proton‐coupled electron transfer (PCET), and these complexes have rare Cu II –I bonds. The above thio ligands with copper(I) bromide and copper(I) chloride also formed similar Cu II –Br and Cu II –Cl bonds in complexes of stoichiometry [Cu II X(κ 3 ‐N,N,S‐L)] (L = L Me , L Et , L Ph , 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 Cu II –Br and Cu II –Cl bonds from thio ligands and copper(I) halides by a PCET process represents basic research of topical interest.