Solvation structures in zirconium-amide interaction processes: A Raman spectroscopic study

Zr(IV)-protic amide interactions in solution were investigated for the first time by Raman spectroscopy. The dependence of the ZrCl4 concentration on the spectra of formamide (FA) and N-methylformamide (NMF) is evaluated and upshifts are observed for the νCO and νCN modes. These shifts are consistent with the stabilization of a neutral amide form, in which the O and N atoms can be employed in the coordination to the metal ion. Indeed, Zr(IV)–O and Zr(IV)–N vibrations were identified in the spectra. The carbonyl stretching region was used for the quantitative treatment and reveals that Zr(IV) is surrounded by 4 FA molecules, in a square prismatic arrangement, while 3 NMF molecules are around the metal in an equilibrium between octahedral and square prismatic geometries, where the counter-ion also takes part in the inner-sphere.