Studies on lanthanide(III) complexes of nuclear substituted diphenylcarbazones

Abstract

La(III), Ce(III), Pr(III), Nd(III), Sm(III), Dy(III) and Ho(III) complexes of 1,5-di(2,5-dimethylphenyl)carbazone and 1 ,5-di(5-chloro- 2-methylphenyl)carbazone have been synthesised and characterized on the basis of elemental analysis, molar conductances, magnetic moments and spectral studies (electronic absorption, infrared and ¹H-NMR spectra). The complexes conform to the composition Ln[(DPC)₂(NO₃)₂]NO₃2H₂O. The substituted diphenylcarbazones act as neutral bidentate ligands and the complexes appear to be six-coordinated. The IR data suggest coordination of the ligand to the metal ions in the

bidentate fashion through the oxygen of the carbonyl (>C=O) group and nitrogen of azo(-N=N-) group. Presence of two water molecules is indicated which are outside the coordination sphere. The antimicrobial screening of the ligands and their complexes

has been carried out. Proton-ligand and metal-ligand formation constants of the above complexes have also been determined <i style="mso-bidi-font-style: normal">p</i>H-metrically in 50% (v/v) aqueous dioxane medium at 25°, 35° and 45°C and ionic strength μ=0.1<i style="mso-bidi-font-style:normal">M</i> (NaClO₄). The thermodynamic parameters of complex formation have been evaluated. Stabilities (log<i style="mso-bidi-font-style:normal">K</i>₁ values) of the chelates are found to increase with decrease in ionic radii of the metals, i.e., La(III)<ce(iii)<pr(iii) <nd="" (iii)<gd(iii)<sm(iii)<dy(iii)<ho(iii)<="" er(iii)<yb(iii).="" the="" validity="" of="" born's="" relation="" has="" also="" been="" tested="" for="" binary="" complexes.="" log<i="" style="mso-bidi-font-style:normal"> K₁ values have been correlated with standard oxidation potentials and ionization potentials of the lanthanides.

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