Mechanistic study of the aquation of nutritional supplement chromium chloride and other chromium(III) dihalides

Abstract

The mechanism for aquation of dihalotetraaquachromium(III) complexes (trans-[Cr(H 2 O) 4 TX] + , where X or T = Cl, Br, or I), including a common component of many nutritional supplements (X, T = Cl) has been investigated using density functional theory. A number of mechanistic pathways were explored including associative interchange (I a), and dissociative (D) mechanisms. The overall activation enthalpy for the D pathway of the dichloro (trans-[Cr (H 2 O) 4 Cl 2 ]) system calculated at the PBE0/cc-pVDZ level, with inclusion of an explicit outer sphere water molecule and in aqueous solution (PCM), is in excellent agreement with the experimental result. The results provide a detailed understanding of the mechanism for the hydrolysis of trans-Cr(III) complexes, which could be useful in understanding the speciation of Cr(III) complexes in physiological environments.