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

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 zerofield 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 twostep 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 (Delta H-double dagger) for water-water exchange on the D pathway of [Cr(pic)(H2O)(4)](2+)center dot center dot center dot nH(2)O complexes are found to decrease for n = 0-3 (64, 58, 56, and 53 kJ mol(-1), respectively). (C) 2019 Published by Elsevier B.V.