N-COORDINATED COPPER(II) COMPLEXES WITH 2-S-METHYL-5,5-DIMETHYLIMIDAZOLIN-4-ONE (L). CRYSTAL STRUCTURE OF [CuL4H2O][CuCl4]

Abstract

The reaction between CuX₂ (X = Cl, Br, NO₃, ClO₄) and 2-S-methyl-5,5-dimethylimidazolin-4-one (L) yields complexes having stoichiometry CuL₂Cl₂ · 1/2H₂O (1), CuL₂Br₂ (2), CuL₄X₂ · 2H₂O [X = NO₃ (3), ClO₄ (4)]. The X-ray crystal structure solved for 1 showed that it contains discrete [CuL₄ · H₂O]²⁺ and [CuCl₄]^2- ions, separated by normal van der Waals contacts. The [CuL₄H₂O]²⁺ cation has crystallographic C ₄ symmetry, with the copper atom and the oxygen of the water molecule lying on a four-fold axis of the space group P4/n and the metal atom in a square-pyramidal coordination geometry, obtained by a square basal plane defined by four N atoms and the apex occupied by the water molecule. The [CuCl₄]^2- anion shows a very flattened tetrahedral geometry. FT-IR and FT-Raman spectra of 1–4 show that 2,3 and 4 also are N(3)-coordinated to copper; nitrate and perchlorate do not coordinate. The v(CuO) vibrations are present at about 380 cm^?1 for 3 and 4, while for 2 v(CuBr) are at 224 and 215 cm^?1. Esr data for 1–4 recorded on solid samples highlight a d_x ² - y² ground state for the cation of 1, 3, and 4 which is typical for tetragonally elongated monomeric copper(II) complexes. Compound 2 exhibits two couples of g values characteristic of two independent copper centres both with compressed tetrahedral geometry. The deconvoluted reflectance spectra of 1–4 substantially confirm the presence of CuN₄ and CuBr₄ chromophores in 2 and a trans-CuN₄O₂ chromophore in 3 and 4. For the latter complexes an orbital sequence d_{x² - y²} > d_xy > d_z² > d_xy, d_yz is also suggested on the basis of the similarity between L and imidazole type ligands.