In-Situ Spectroscopic Studies of Aqueous Cu(II)-Organic Complexes.

Chemical speciation of metals in the environment is vital in assessing their toxicity, reactivity, and mobility.  Most important reactions of metals occur at the interface between the aqueous phase and both mineral and organic solids.  This presentation will focus on the role of copper(II) organic complexation in solutions as this important interaction can determine the environmental fate of copper in surface waters, soils, and sediments.  Aqueous solutions containing copper-organic mixtures were measured in-situ using X-ray Absorption Near Edge Structure (XANES) spectroscopy at the Cu L-edge at the Spherical Grating Monochromator (SGM) of the Canadian Light Source.  Measurements at the Cu(II) L-edge were chosen for this study as they provide direct, core-level access to the bonding orbitals in metal-ligand complexes.  High resolution XANES data can be obtained in relatively low concentrations (10 mM) using a silicon drift detector array.  Distinct shifts can be seen at the L₃-edge that corresponds to changes in the ligand field of the metal-ligand complexes.  Ligands in this study were systematically chosen to explore how structure and functional groups of environmentally important ligand classes (carboxylic, alcohol, and amine) affect the ligand field. The role of Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) investigations of aqueous complexes will also be discussed as a complementary in-situ spectroscopic method capable of providing structural information on the local bonding environment and symmetry of the aqueous copper-ligand complexes. The need for aqueous measurements will be highlighted via comparison with dried samples and powders where changes in the chemical structure of Cu-ligand complexes and radiation damage can both occur.