A Raman study on the coordination sites and stability of the [Al(formamide)5]Cl3 complex

Raman experiments of aluminum chloride and formamide (FA) solutions in different compositions and temperatures were carried out. Spectral changes provoked by the increase of the salt concentration were observed in different regions. The νCO and νCN modes of FA upon complexation were upshifted and suggest that the CONH hybrid (II) is stabilized by Al(III). Bands at 547 and 295 cm−1, which are assigned to the νAlO and νAlN vibrations, respectively, evidence coordination through both O and N atoms of FA. The quantitative analysis performed at the carbonyl stretching region found 5 FA molecules around this cation, resulting in the formation of the [Al(FA)5]Cl3 complex. Its stability is maintained by whole studied concentration range and up to around 100 °C. At higher temperatures, distortions in the FA shell begin occurring and a new component at 356 cm−1 is then observed and assigned to the [AlCl4]− complex.