IR fingerprints of U(VI) nitrate monoamides complexes: a joint experimental and theoretical study.

Infrared spectra of 0.5 mol·L(-1) uranium(VI) nitrate monoamide complexes in toluene have been recorded and compared with infrared spectra calculated by DFT. The investigated monoamides were N,N-dimethylformamide (DMF), N,N-dibutylformamide (DBF), and N,N-dicyclohexylformamide (DcHF). The validity of DFT calculations for describing uranium nitrate monoamide complexes has been confirmed as a fair agreement between experimental and calculated spectra was obtained. Furthermore, a topological analysis of the electron density has been carried out to characterize monoamide-uranium interactions. From this work, it appears that the increase of stability of uranylmonoamide complexes may be directly linked to the degree of polarization of the ligands in interaction with uranylnitrate. Among the investigated monoamides, the most stable complex is UO(2)(NO(3))(2)·2DcHF. This complex is characterized by a high positive charge delocalization in the outer part of the ligand molecule, which leads to a more concentrated positive charge close to the uranyl cation (UO(2)(2+)), thus strengthening the electrostatic interaction between the metal and the ligand.