Comparative absorption spectroscopy involving 4f–4f transitions to explore the kinetics of simultaneous coordination of uracil with Nd(III) and Zn(II) and its associated thermodynamics

The interaction of uracil with Nd(III) has been explored in presence and absence of Zn(II) using the comparative absorption spectroscopy involving the 4f–4f transitions in different solvents. The complexation of uracil with Nd(III) is indicated by the change in intensity of 4f–4f bands expressing in terms of significant change in oscillator strength and Judd–Ofelt parameters. Intensification of this bands became more prominent in presence of Zn(II) suggesting the stimulative effect of Zn(II) towards the complexation of Nd(III) with uracil. Other spectral parameters namely Slator–Condon (Fk's), nephelauxetic effect (β), bonding (b1/2) and percent covalency (δ) parameters are computed to correlate their simultaneous binding of metal ions with uracil. The sensitivities of the observed 4f–4f transitions towards the minor coordination changes around Nd(III) has been used to monitor the simultaneous coordination of uracil with Nd(III) and Zn(II). The variation of intensities (oscillator strengths and Judd–Ofelt parameters) of 4f–4f bands during the complexation has helped in following the heterobimetallic complexation of uracil. Rate of complexation with respect to hypersensitive transition was evaluated. Energy of activation and thermodynamic parameters for the complexation reaction were also determined.

Graphical abstractTime-dependant absorption spectra for Nd(III):uracil:Zn(II) at 25 °C at (A) 0, (B) 0.5, (C) 1, (D) 2, (E) 4, (F) 6, (G) 8, (H) 12, (I) 14 h in DMF.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights• 4f–4f transition spectra as a probe in coordination of uracil with Nd(III) and Zn(II). • Sensitivity of all the five bands of Nd(III). • Stimulative effect of Zn(II) towards Nd(III)–uracil. • Intensity changes with time. • Spontaneity of the heterobimetallic complexation of uracil with Nd(III) and Zn(II).