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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