Using IR spectroscopy and multivariate curve resolution to elucidate mechanism of heat-induced decomposition of an organic complex

Many practically important processes occur upon elevated temperatures, and the induced chemical transformations are accompanied by gases evolution: heat-induced degradation of plastics, conversion of acrylic fibers into carbon ones, and fossil fuels pyrolysis – to name just a few. Generally, the evolved compounds structure is relatively similar, and therefore their analysis by means of vibrational spectroscopy is a convenient approach towards elucida- tion of the underlying reactions mechanism as well as optimization of the pro- cess conditions. Modern analytical instruments provide the opportunity to carry out simultaneous thermogravimetry/differential scanning calorimetry analysis and IR/Raman/mass spectrometry investigation of the evolving gaseous products. However, elucidation of the mechanism of the reactions occurring upon heat- ing is not completely straightforward, due to a number of experimental limita- tions. They include, for instance, poor resolution of the spectral bands, their overlap with these of traces of water and carbon dioxide in the atmosphere, the lag between the TGA/DSC signal and the spectra registration, and the specimen inhomogeneity.

In this contribution we present and discuss the results of TGA-DSC-IR study of heat-induced decomposition of tris(acetylacetonato)manganese(III) complex. Using this process as an example, we have indicated the complications of the evolved gas analysis and demonstrated that they can be partially overcome taking advantage of multivariate curve resolution methods. Moreover, we have shown that the conventional methods based on TGA and IR analysis of the solid decomposition products produce incomplete data that is not enough for reliable elucidation of the decomposition mechanism. Finally, we have de- veloped a workflow to extract the meaningful information from the set of the evolved gas spectra. The elaborated approach is fairly general and applicable for study of a variety of the processes accompanied by evolution of gaseous products.