Sulfates ligand exchange

Cation exchange, solvent extraction and Raman spectroscopic studies of highly acidic zirconium sulfate solutions suggest that these solutions contain a mixture of solution species having from one to four sulfate ligands per Zr atom.153,351 The sulfato-zirconium complexes appear to be somewhat more stable than the analogous hafnium complexes.351... 

Phosphate, silicate, borate, arsenate, selenite, chromate, and fluoride are anions for which ligand exchange is important. Nitrate, chloride, bromide, and perchlorate are not held, while sulfate and selenate may be weakly held. As a consequence, leaching of nitrate and sulfate from soil in drainage water can be significant, but very little phosphate is lost in solution. Of the trace metals, Co, Cu, Ni, and Pb are strongly held on oxide surfaces by chemisorption, but the process is much less important for Cd and Zn. 

Type IV includes chiral phases that usually interact with the enantiomeric analytes through the formation of metal complexes. There are usually used to separate amino acid enantiomers. These types of phases are also called ligand exchange phases. The transient diastereomeric complexes are ternary metal complexes between a transitional metal (usually Cu +), an amino acid enantiomeric analyte, and another compound immobilized on the CSP which is able to undergo complexation with the transitional metal (see also the ligand exchange section. Section 22.5). The two enantiomers are separated based on the difference in the stability constant of the two diastereomeric species. The mobile phases used to separate such enantiomeric analytes are usually aqueous solutions of copper (II) salts such as copper sulfate or copper acetate. To modulate the retention, several parameters—such as the pH of the mobile phase, the concentration of the copper ion, or the addition of an organic modifier such as acetonitrile or methanol in the mobile phase—can be varied. 

Blackwell and Carr investigated the ligand exchange chromatography of free amino acids on copper-loaded zirconia. It was shown that the use of Lewis base buffers in this system improved the operating efficiency. Acetate, sulfate, fluoride, and phosphate are the effective competing ions. 

If ammonia is added to the light blue copper sulfate solution, then the color turns deep violet a ligand exchange takes place. However, the resulting complex is so stable that the equilibrium lies completely on the side of the ammine complexes. The color of the solution remains unchanged during the dilution with water the ammine complex is not destroyed during the process ... 

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