Influence of apical ligands on Cu–(C[dbnd]C) interaction in Copper(I) halides (Cl−, Br−, I−) π-complexes with an 1,2,4-triazole allyl-derivative: Syntheses, crystal structures and NMR spectroscopy

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New multifunctional 1,2,4-triazole based allyl-derivative as the ligand L (3-allylsulfanyl-4-allyl-5-phenyl-4H-1,2,4-triazole) revealed an ability to form stable binuclear copper(I) π-complexes. A series of related Cu(I) halides π-complexes, [Cu2(L)2X2] (X = Cl, 1a; Br, 1b; I, 1c), [Cu2(L)2I2]2 (1c’), [Cu2(L)2(CuCl2)2] (2), [Cu2(L)2Cu2Br4] (3) was obtained by alternating-current electrochemical synthesis, starting from acetonitrile solutions of the ligand L and CuX2 (in the case of 1a, 1b, 2, 3) or I2 (1c, 1c’). This is the first notice of using iodine being reduced at copper electrodes under alternating current in the presence of a ligand for copper(I) iodide complexes synthesis. The crystal structures were determined by means of single crystal X-ray diffraction. The organic ligand acts as multidentate chelating σ,π-donor using triazole (tr) and η2-allyl moieties, resulting in a formation of the dimeric {Cu2N4} core with a trigonal-pyramidal (2 N, CC + X) environment of the Cu cation. Packing polymorphism was revealed for the iodine complex. In the case of 2 and 3 the Cu centers participate in a formation of both – metal-organic cations and copper(I) halide anions. In structure 3, the copper(I)-halide subunit is organized in the Cu2(μ2-Br)2Br2 cluster that links organometallic moieties leading to a 1D ladder fragment. High inertia of complexes in acetonitrile solutions enabled a comparative evaluation of a strength of the Cu(I)–(CC) interaction by means of 1H NMR spectra. NMR spectroscopic studies are consistent with the structural analysis.