Synthesis and Characterization of Some Lanthanide(III) Chelates of 2,6-Diacetylpyridine Dioxime

Abstract

A series of lanthanide(III) chelates of the type [Ln(H₂dapd)₂(X)₂](X) (where Ln³⁺ = La, Pr, Nd, Sm, Gd and Dy; H₂dapd = 2,6-diacetylpyridine dioxime and X⁻ = NO₃ or Cl) have been synthesized by the direct reaction of 2,6-diacetylpyridine dioxime with lanthanide(III) nitrates or chlorides in ethanol and 2,2-dimethoxypropane. The chelates have been characterized by analysis, conductance, x-ray powder diffraction patterns, magnetic, electronic and vibrational spectral studies. The analytical and conductometric titration studies reveal the presence of 1:2 (metal:ligand) stoichiometry and molar conductance data in ethanol indicate 1:1 electrolytes in all the lanthanide chelates. The lanthanidea(III) chelates with H₂dapd are x-ray isomorphous. The cell parameters a, b and c, along with the number of molecules per unit cell z calculated from x-ray powder diffraction patterns, suggest the same “orthorhombic” type of lattice for the present lanthanide(III) chelates. The magnetic moment values show little deviation from Van Vleck values. The electronic spectra, recorded in methanol at room temperature, are dominated by ligand absorption bands and exhibit only slight shift and marked enhancement in the intensity of the bands. The infrared spectra suggest cis-coordination of the neutral H₂dapd ligand molecules through pyridine nitrogen and oxime group nitrogen atoms and monodentate nitrate coordination to all lanthanide(III) chelates. Thermogravimetric studies of the chelates are also reported.