Vibrational Spectroscopic Study of the Complexation of Mercury(II) by Substituted Acetates in Aqueous Solutions

Abstract

Attenuated total reflectance infrared (ATR-IR) and Raman spectroscopies are used to identify the complexed species of mercury(II) with acetate and some aliphatic derivatives in aqueous solutions, as a function of pH and metal-to-acetate ratio. The spectra of the free carboxylate ions, in their sodium salt solutions, and of the protonated molecules are shown for comparison and assigned below 1800 cm⁻¹. Whatever the stoichiometries assumed [HgCH₃COO⁺ up to Hg(CH₃COO)₄^2-], one structure is observed, principally via the stretching modes ν(CO₂) and ν(CC), although two strong bands have a ν_s(CO₂) character owing to an accidental coupling of this mode with δ_s(CH₃) in all the acetate complexes. This coupling is demonstrated with the isotopic ligand CD₃COO, which displays only one ν_s(CO₂) band on account of the separation of this mode from δ_s(CD₃). The splitting between ν_a(CO₂) and ν_s(CO₂) increases up to about 260 cm⁻¹ for all the carboxylates under study, the value pointing to a hydrated monodentate form.

Keywords

Infrared Raman Vibrational spectra Mercuric acetates Aqueous solutions Carboxylate complexation Monochloroacetic acid Propionic acid Trimethylacetic acid

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