Speciation of chromium aqua and chloro complexes in hydrochloric acid solutions at 298 K

Abstract

The dissolution and speciation mechanism of the chromium aqua and chloro complex in hydrochloric acid solutions.

Analysis of the First Ion Coordination Sphere: A Toolkit to Analyze the Coordination Sphere of Ions

“…As expected, six water molecules coordinate to the Cr 3+ ion throughout the AIMD simulation. The results from the AFICS toolkit (Figure ) report the time-averaged Cr–O distance (the maximum of the first peak in the RDF; Figure A) to be 1.98 Å and a maximum threshold distance of 2.22 Å, which is consistent with the 1.96–2.0 Å distances measured experimentally. − The integral of the RDF (CN) at that threshold distance is 6.0, affirming that there are six waters coordinated and no change in coordination number during the simulation. The angle distribution function (Figure B) indicates two peaks at 89 and 175°, which are both near the ideal bond angles (90 and 180°) for an octahedral polyhedron.…”

“…In aqueous solution, the Cr 3+ ion is known to have six waters coordinate to the metal in an octahedral geometry. − The ion complex is fairly acidic and will typically have a coordinated water donate a proton to form [Cr­(H 2 O) 5 (OH)] 2+ , but for this model, we will focus on only the hexaaqua structure. To examine the dynamic structural properties of [Cr­(H 2 O) 6 ] 3+ , an ab initio molecular dynamics (AIMD) simulation was constructed for Cr 3+ (quartet spin state) within a periodic cube (cell length 12.42 Å) containing 64 water molecules (Figure S1).…”