Vibrational spectroscopic study of the complexation of mercury(II) by substituted acetates in aqueous solutions

Attenuated total reflectance infrared (ATR-IR) and Raman spectroscopies are used to identify the complexed species of mercury(II) with acetate and som e aliphatic derivatives in aqueous solutions, as a function of pH and metal -to-acetate ratio. The spectra of the free carboxylate ions, in their sodiu m salt solutions, and of the protonated molecules are shown for comparison and assigned below 1800 cm(-1). Whatever the stoichiometries assumed [HgCH3 COO+ up to Hg(CH3COO)(4)(2-)], one structure is observed, principally via t he stretching modes nu(CO2) and nu(CC), although two strong bands have a nu (s)(CO2) character owing to an accidental coupling of this mode with delta( s)(CH3) in all the acetate complexes. This coupling is demonstrated with th e isotopic ligand CD3COO, which displays only one nu(s)(CO2) band on accoun t of the separation of this mode from delta(s)(CD3). The splitting between nu(a)(CO2) and nu(s)(CO2) increases up to about 260 cm(-1) for all the carb oxylates under study, the value pointing to a hydrated monodentate form.