Investigation of mono-, bis- and tris-glycinatochromium(III): Comparisons of computational and experimental results

Abstract

The synthesis and characterization of mono-, bis- and tris-glycinatochromium(III) complexes by elemental analysis, UV–Vis, electron paramagnetic resonance (EPR), ATR-FTIR and Raman spectroscopy has been performed in this work. IR stretching bands obtained from DFT calculations of the mono-, bis- and tris-glycinatochromium(III) complexes are in good agreement with experimental data. Different mechanistic pathways were explored for the water exchange reactions of [Cr(+NH3CH2COO−)(H2O)5]3+ and its conjugate base species including, associative interchange (Ia), and dissociative (D) mechanisms. The lowest activation enthalpies for the mono- and bis-complexes are obtained for the Ia pathways with explicit outer sphere solvation (88 and 76kJmol−1), which are in good agreement with the experimental values (87 and 75kJmol−1). In comparison, tris-glycinatochromium(III) undergoes aquation via the dissociative (D) mechanism. Investigation of these systems in the pH range ∼3.0 to ∼8.5 by UV–Vis monitoring, helps identify the speciation of these complexes in physiological environments.