Synthesis, spectroscopic characterization, and theoretical studies on the substitution reaction of chromium(III) picolinate

Add time:09/03/2019    Source:sciencedirect.com

Chromium (III) picolinate, [Cr(pic)3], was synthesized and characterized by solid electron paramagnetic resonance (EPR) in both room and frozen temperatures. Broad EPR signals of the mer-[Cr(pic)3] complex were found for the solid with g values of 3.45 and 3.47 at room temperature and frozen at 100 K, respectively. This result indicates that the mer-[Cr(pic)3] system has a rhombic character and a large zero-field splitting D value. In addition, its purity was confirmed by elementary analysis, atomic absorption spectroscopy (AAS), HPLC, UV–Vis, ATR-FTIR, Raman spectroscopy, and ESI-mass spectrometry. DFT calculations reveal that the most likely pathway for the acid-catalyzed [Cr(pic)3] aquation is via a two-step mechanism, which is in excellent agreement with the experimental result. Furthermore, the importance of outer sphere solvation was investigated with the addition of up to three explicit water molecules in the second coordination sphere. The enthalpies of activation (ΔH‡) for water-water exchange on the D pathway of [Cr(pic)(H2O)4]2+… nH2O complexes are found to decrease for n = 0–3 (64, 58, 56, and 53 kJ mol−1, respectively).

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