Study of the histidine complex of uranium(IV): synthesis, spectrophotometric, magnetic and electrochemical properties

Abstract

We synthesized the novel histidine complex of uranium(IV). A 1:3 mole ratio was found between metal and ligand by the mole ratio method, while –NH2 and –COO– groups of histidine behave as coordinating sites. The IR spectra confirmed the lone pair donating or coordinating sites. The elemental analysis confirmed the stoichiometry. The bathochromic shift with an increase in the optical density in the UV-Visible range indicated that the compound and its central metal ion hold uniform electronic charge distribution. The electrochemical results indicated a quasi-reversible (neither completely reversible nor completely irreversible) oxidation of the complex to its uranium(V) product at the platinum working electrode. The quasi-reversible process shows a comparatively slow electron transfer (ET) rate with the heterogeneous electron transfer rate constant ‘ks’ (3.4 ×  10–4 cm s-1) at 50 mV s-1 and 305 ± 0.5 K. The kinetics such as diffusion and charge transfer lead the reaction with an ECE (electrochemical–chemical–electrochemical) mechanism. The thermodynamic parameters of activation such as ΔH*; 4.257 kJ mol–1, ΔS*; -2.519 × 10–3 J mol–1 K–1 and ΔG* 4.26 kJ mol–1 helped to propose an associative mechanism of the electron transfer at the platinum working electrode.                     KEY WORDS: Uranium, Histidine, Spectroscopy, Electrochemistry, Kinetics   Bull. Chem. Soc. Ethiop. 2020, 34(3), 557-569.  DOI: https://dx.doi.org/10.4314/bcse.v34i3.11