## 3 Results and Discussion
The band intensities at 3375, 1646, 1608, and 1157 cm\({}^{-1}\) were smaller and, finally, in the case of sample MOC 350, the band assignments to the stretching modes of H-O-H in H\({}_{2}\)O were missing. The series of modes in the range of 1000-400 cm\({}^{-1}\) resulted from the lattice translation modes (Mg-OH) and vibrational modes of Mg-O/Mg\({}^{2+}\) and O/O-Mg-O/O-Mg\({}^{2+}\)-O bonds [32]. Lattice vibration modes of Mg-O/Mg-Cl bonds can be observed around 500 cm\({}^{-1}\). Simultaneous thermal analysis combined with mass spectroscopy (STA-MS) was used to analyze the thermal stability of the material under study (see Figure 7). The sample was gradually decomposed, and the final products were magnesium oxide, water, and hydrochloric acid, where H\({}_{2}\)O and HCl molecules were released in a gaseous form. According to the heat flow signal, five main endothermic effects accompanied by weight loss (seen on thermogravimetric curve) were detected. \begin{table}
\begin{tabular}{c c} \hline \hline
**Wave Number (cm\({}^{-1}\))** & **Assignment** \\ \hline
3696, 3631, 3612, 3565 & stretching modes (\(\
u\)) of O–H in Mg(OH)\({}_{2}\) \\
3375 & stretching modes (\(\
u\)) of H–O–H in H\({}_{2}\)O \\
1646, 1608, 1157 & bending (\(\delta\)) vibration of H–O–H in MgCl\({}_{2}\)-8H\({}_{2}\)O \\
1623, 1558, 1520, 1475, 1442 & stretching modes (\(\
u\)) of Mg–O in MgCl\({}_{2}\)-8H\({}_{2}\)O \\
845 & stretching vibration (\(\
u\)) of Mg–O cubic structure \\
668, 634 & stretching (\(\
u\)) vibrations of Mg–O \\
579 & deformation (\(\delta\)) and stretching (\(\
u\)) lattice vibrations of Mg–Cl/Mg–O \\
515 & translation vibrations of Mg/Mg–O, Mg–OH \\
420 & vibrational modes of the lattice showing the Mg–O/Mg\({}^{2+}\), \\  & O/O–Mg–O/O–Mg\({}^{2+}\)–O bonds \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Assignments of the major absorption bands of MOC 5-1-8 phase—reference sample. Figure 6: The Fourier-transform infrared (FT-IR) spectrum of MOC 5-1-8 phase in the range of 400–4000 cm\({}^{-1}\). The first endothermic effect with a maximum at 145 \({}^{\circ}\)C was attributed to the release of six molecules of water. This process was also confirmed by MS and TG curves (Equation (2)). Step 1:  
\[5\text{Mg}(\text{OH})_{2}\text{-MgCl}_{2}\text{-8H}_{2}\text{O}\to 5\text{Mg}( \text{OH})_{2}\text{-MgCl}_{2}\text{-2H}_{2}\text{O}\ +\ 6\text{H}_{2}\text{O}. \tag{2}\]  
The second effect (maximum at 205 \({}^{\circ}\)C) can be attributed to the release of two water molecules. Step 2:  
\[5\text{Mg}(\text{OH})_{2}\text{-MgCl}_{2}\text{-2H}_{2}\text{O}\to 5\text{Mg}( \text{OH})_{2}\text{-MgCl}_{2}\ +\ 2\text{H}_{2}\text{O}. \tag{3}\]  
The third effect (maximum at 335 \({}^{\circ}\)C) can be attributed to the release of two water molecules. Step 3:  
\[5\text{Mg}(\text{OH})_{2}\text{-MgCl}_{2}\to 2\text{Mg}_{2}(\text{OH})_{3} \text{Cl}\ +\ \text{MgO}\ +\ 2\text{H}_{2}\text{O}. \tag{4}\]  
The fourth effect (maximum at 370 \({}^{\circ}\)C) can be attributed to the release of one water molecule. Step 4:  
\[2\text{Mg}_{2}(\text{OH})_{3}\text{Cl}\to 2\text{Mg}(\text{OH})\text{Cl}\ +\ \text{Mg}( \text{OH})_{2}\ +\ \text{MgO}\ +\ \text{H}_{2}\text{O}. \tag{5}\]  
The last effect (maximum at 435 \({}^{\circ}\)C) can be attributed to two simultaneous effects, where one water molecule and two hydrochloric acids were released. Step 5:  
\[\text{Mg}(\text{OH})_{2}\to\text{MgO}\ +\ \text{H}_{2}\text{O}, \tag{6}\]  
\[2\text{Mg}(\text{OH})\text{Cl}\to 2\text{MgO}\ +\ 2\text{HCl}. \tag{7}\]  
Let us note that the ratio of the released molecules of water in the overlapping peaks was determined by peak deconvolution. The final ratio of the individual steps was evaluated according to the ratio of surface areas of the deconvoluted peaks, as well as with regard to the TG curves. According to the literature, the mechanism for the last step of decomposition was described differently. [PERSON] et al. [17] reported that only hydrochloric acid is released; however, we clearly proved using MS that water is also released in this step.