Anomalous solution esr spectra observed for halogenocopper (II) complexes with tripodlike ligands

Halogenocopper(II) complexes with tripodlike ligands (L), [Cu(L)X]Y (X = Br^- I^- and; Y = C1O₄ and PF₆), showed more than four hyperfine lines (5-9 lines) in the solution ESR spectra at room temperature. This was attributed to the interaction between the unpaired electron of the copper(II) ion and the nuclear spins of both the copper atom (^{63, 65}Cu, I = 3/2) and the halogen atom (^{79, 81}Br, I = 3/2; ¹²⁷I, I = 5/2). The above discussion was confirmed by the crystal structure determination of three compounds, [Cu(N₃S)N₃]C1O₄ (1), [Cu(N₃S)Br]C1O₄ (2), and [Cu(N₂S₂P)I]C1O₄ (3), where (N₃S) and (N₂S₂P) represent bis(2-pyridylmethyl)(2-(methylthio)ethyl)amine and bis(2-(methylthio)ethyl)(2-pyridylmethyl)amine, respectively. Crystal data: 1, space group P2₁/a, a = 16.316 (5) Å, 6 = 8.379 (1) Å, c = 14.409 (2) Å, β = 100.69 (2)° 2, space group P2₁/o, a = 14.600(7) Å, b = 17.155 (8) Å, c = 7.686 (1) Å, β = 94.89 (2)°; 3, space group P2₁/n, a = 17.292 (3) Å, b = 14.411 (2) Å, c = 7.8202 (7) Å, β = 100.29 (1)°. Complex 1 has a square-pyramidal structure; the sulfur atom of the thioether group is at the apical position of the square plane, and the azide ion is in the plane of the coordination sphere. The structural properties of 2 are essentially the same as those of 1 except that the N₃ ion in 1 is replaced by Br^- ion in 2. Complex 1 shows four hyperfine lines in the solution ESR spectrum, whereas five lines are observed for compound 2, indicating that the presence of Br^- ion at the corner of the square plane causes the unusual ESR spectrum. Complex 3 has a distorted-trigonal-bipyramidal structure where the unpaired electron in the d_z2 orbital of the copper(II) ion can interact with the iodine atom through -bonding. In the series of X = I^- complexes, hyperfine lines decrease from nine to seven with the variation of ligand from tris(2-(methylthio)ethyl)amine to tris(2-pyridylmethyl)amine. A similar situation was also found for the X = Br’ complexes. These were successfully explained on the assumption that the interaction between the unpaired electron and the nuclear spin of the halogen atom is dependent on the character of the tripodlike ligand L.