Spectroscopic and Thermodynamic Properties of Some Transition Metal Complexes Derived from 2-(Hydroxyimino)-1-(2-hydroxyphenyl)butane-1,3-dione

The protonation constants of the syn ketoxime, 2-(hydroxyimino)-1-(2-hydroxyphenyl)butane-1,3-dione (HPDO) were determined by a pH-metric method in solutions of dioxane, methanol and dimethylformamide (75 % v/v) at 20 ± 0.1 °C and ionic strength of 0.1 mol·L−1 supported by KNO3. The complexation reaction of the ligand HPDO with the transition metal ions Cu(II), Ni(II), Co(II), Cr(III), Fe(III), and Mn(II) in solution has been also studied potentiometrically. The stability constants of the respective species were determined and show that their values decrease in the order: 1,4-dioxane < DMF < methanol. The stability of the chelates is highly affected by the relative permittivity (εr) and the donor number of the solvents. In addition, the complexes of [Cu(PDO)(Cl)]2·EtOH 1, [Ni(PDO)(H2O)(Cl)]2·2H2O 2, [Co(PDO)(Cl)]2·EtOH 3, [Fe(PDO)(Cl)2(EtOH)3]·EtOH 4, and [VO(PDO)H2O]2SO4·4H2O 5 were prepared and characterized by elemental analysis, IR, UV/Vis spectra, magnetic measurements and thermal analysis. Magnetic and spectral data suggest the formation of (i) neutral polymerized molecules accompanied by inclusion of lattice or coordinated water molecules, and (ii) a paramagnetic octahedral structure around metal ions in all cases. The geometry optimization of the syn structure of the ligand HPDO has been also calculated by HyperChem 8.0 software.