Characterization of compounds derived from copper-oxamate and imidazolium by X-ray absorption and vibrational spectroscopies

• Salts of copper-oxamate anions and imidazolium cations were studied.
• Raman and IR band assignments were supported by DFT calculations.
• Electronic distribution around CuN sites is changed by anion–cation interaction.

In this work, compounds derived from copper-oxamate anions (ortho, meta, and para)-phenylenebis (oxamate) and imidazolium cations (1-butyl-3-methylimidazolium) were synthesized. The compounds were characterized by Raman and FTIR spectroscopies and the band assignments were supported by DFT calculations. Strong IR bands from 1610 to 1700 cm−1 dominated the spectra of the complex and can be assigned to νCO vibrations of the [Cu(opba)]2− anions by the comparison with the DFT data. In opposition to the FTIR spectra, the main vibrational bands in the Raman spectra are observed in the 1350–1600 cm−1 range. All bands in this region are associated to the modified benzene vibrations of the copper-phenylenebis(oxamate) anions. X-ray absorption near edge (XANES) at different energies (NK and Cu L2,3 edges) was also used to probe the interionic interactions. XANES data show that anion–cation interaction in the Cu-oxamate–imidazolium changes the electronic structure around the CuN sites in the oxamate anion.

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