Structural and reactivity studies on 4,4$prime;-dimethyl-2,2$prime;-bipyridine acetylacetonate copper(II) nitrate (CASIOPEINA III-iaS) with methionine, by UV?visible and EPR techniques*1

Abstract

When the nitrate form of [(4,4′-dimethyl-2,2′-bipyridine)(acetylacetonate) copper(II)] nitrate (Casiopeı́na III ia) was reacted with methionine under two different reaction conditions: room temperature and reflux in methanol, it was found that substitution of acetylacetonate (acac) occurred and this process was monitored by UV–Vis spectrophotometry. Electron paramagnetic resonance (EPR) spectroscopy was used to analyse changes in the electronic environment of Cu(II) in the initial and final compounds. Both compounds showed axial geometry with g||>g⊥. A detailed study of the iono-covalent features of the Cu(II) ligand bonds was made, showing that in-plane σ and π bonds were relatively more weakly covalent than π-out-of-plane bonds. Additionally, it was possible to obtain suitable crystals for X-ray analysis. Suitable crystals of 4,4′-dimethyl-2,2′-bipyridine acetylacetonate copper(II) perchlorate (Cas III ia ClO4)1 and 4,4′-dimethyl-2,2′-bipyridine methionine copper(II) nitrate (Cas IV met)2 were obtained and structure solved by X-ray diffraction. The crystallographic data for (Cas III ia ClO4) space group P21/c, a=7.3310(10) Å, α=90°, b=13.669(3) Å, β=95.23(3)°, c=18.973(4) Å, γ=90°, V=1893.3(6) Å3, z=4, are presented. For Cas IV met it was found a space group P21, a=1.982(2) Å, α=90°, b=6.952(10) Å, β=112.11(3)°, c=13.299(3) Å, γ=90°, V=1026.3(3) Å3, z=2.