Synchrotron radiation X-ray absorption spectroscopic studies in solution and electrochemistry of a nitroimidazole conjugated heteroscorpionate copper(II) complex

Synchrotron radiation X-ray absorption spectroscopy has been used to determine the solution structure of the nitroimidazole conjugated heteroscorpionate copper(II) complex {[(LMN)2Cu]Cl2} (LMN = 2,2-bis(3,5-dimethyl-1H-pyrazol-1-yl)-N-(2-(2-methyl-5-nitro-1H-imidazol-1-yl)ethyl)acetamide) at three different pH values. The strategy used for the XAS data analysis for a straightforward data interpretation is presented. The copper center is coordinated by two molecules of ligands, describing a quasi-octahedral figure, in all investigated solutions, demonstrating the stability of the complex in solution. The copper complex displays a pH dependence where the Cu–O first shell distance (from the carbonyl) lengthens at acid pH; the Cu–N equatorial distances are almost the same. XANES spectroscopy also indicates structural rearrangements occurring in solution at various pH, where the spectrum at pH 4.4 displays the largest differences from the other ones. The cyclic voltammetry curves obtained on the same solutions show an irreversible peak due to the reduction of Cu(II) → Cu(I), which falls at potential of about 0.4–0.5 V versus SCE, and it is found to be depending on pH. The potentiality of the joint XAS and electrochemical approach in the determination of the structural characteristics of the solutions is highlighted.

Structure of nitroimidazole conjugated heteroscorpionate copper(II) complex {[(LMN)2Cu]Cl2} at three different pH values by X-ray absorption spectroscopic studies (EXAFS and XANES).Figure optionsDownload as PowerPoint slideHighlights
► Copper is found to be coordinated by two molecules of scorpionate ligands, describing a quasi-octahedral environment.
► XANES spectra have evidenced a change of the local octahedral symmetry around the Cu site at acidic pH.
► Agreement cyclic voltammetry – XAS studies.