Absorption spectral analysis of 4f–4f transitions for the complexation of Pr(III) and Nd(III) with thiosemicarbazide in absence and presence of Zn(II) in aqueous and organic solvents

The complexation of thiosemicarbazide with Pr(III) and Nd(III) in absence and presence of Zn(II), a soft metal ion in aqueous and organic solvents like CH3OH,CH3CN, dioxane (C4H8O2) and DMF (C3H7NO) and their equimolar mixtures are discussed by employing absorption difference and comparative absorption spectrophotometry. Complexation of thiosemicarbazide with Pr(III) and Nd(III) is indicated by the changes in the absorption intensity following the subsequent changes in the oscillator strength of different 4f–4f bands and Judd-Ofelt intensity (Tλ) parameters. The other spectral parameters like energy interaction parameters namely Slater–Condon (Fk), Racah (Ek), Lande (ξ4f), Nephelauxetic ratio (β) and bonding parameters (b1/2) are further computed to explain the nature of complexation. The difference in the energy parameters with respect to donor atoms and solvents reveal that the chemical environment around the lanthanide ions has great impact on f–f transition and any change in the environment result in modification of the spectra. Various solvents and their equimolar mixtures are also used to discuss the participation of solvents in the complexation.

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► Decrease in the values of energies on complexation.
► Red shift in 4f–4f bands of Pr(III) and Nd(III) in presence of thiosemicarbazide.
► Significant variation in intensity parameters in presence of Zn(II).
► Maximum intensification in DMF.
► Greater stability in heterobimetallic complexation of ligand with Pr(III)/Nd(III) and Zn(II).