N-Coordinated Copper(II) Complexes with 2-S-Methyl-5,5-dimethylimidazolin-4-one (L). Crystal Structure of [CuL4H2O][CuCl4]

The reaction between CuX(2) (X = Cl, Br, NO3, ClO4) and 2-S-methyl-5,5-dimethylimidazolin-4-one (L) yields complexes having stoichiometry CuL(2)Cl(2) . 1/2H(2)O (1), CuL(2)Br(2) (2), CuL(4)X(2) . 2H(2)O [X = NO3 (3), ClO4 (4)]. The X-ray crystal structure solved for 1 showed that it contains discrete [CuL(4) . H2O](2+) and [CuCl4](2-) ions, separated by normal van der Waals contacts. The [CuL(4)H(2)O](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) - y(2) 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.