XAFS Studies On The Geometrical Structure Of Cobalt Ions In Ammonia Solution

As properties indeed depend on structure, the coordination chemistry of metal ions plays a vital role in their chemical reaction process in solution. Therefore, it is mandatory to identify the geometrical structure around metal ions in solution.In this dissertation, we will discuss the geometrical structure of Co2+/Co3+in ammonia solution by means of a combination of X-ray absorption fine structure spectroscopy (XAFS) and multiple scattering theory calculation method. This dissertation includes:1. We investigated the geometry structure of Co2+ in ammonia solution, via extended x-ray absorption fine structure (EXAFS) and full multiple-scattering theoretical (MXAN) analysis of the Co K-edge XANES (X-ray absorption near edge structure).Data show that Co2+ ions are coordinated by six NH3 ligands arranged in a Jahn-Teller (JT) distorted octahedral (DT Oc) geometrical configurationwithfour long Co-Neq bonds (2.17 A) and two short Co-Nax bonds (2.03 A).The JT effect is originated from the high-spin Co(II) center.2.We investigated the influence of addition of the activated carbons in the the oxidation reaction processof Co2+ to Co3+.We found that Co3+ ionsmay appear either [Co(NH3)6]3+ or [Co(NH3)5Cl]2+ clusters depending on the presence of charcoal catalystin the reaction process,.Wwith the help of calculation procedure (MXAN) analysis, we found that [Co(NH3)e]3+ is characterized by a regular octahedron with a 1.91 A Co-N distance while the [Co(NH3)5Cl]2+ has a distorted octahedral structure with four Co-Neq bonds (1.94 A), a shorter Co-Nax bond (1.91 A) and a Co-Cl bond (2.12 A).