## 3 Results
### Thermal Decomposition under Nitrogen Atmosphere
After searching through the Cambridge Structural Database [28], several cobalt acetate structures with different water content were found. Between the starting Co(CH\({}_{3}\)COO)\({}_{2}\cdot\)4H\({}_{2}\)O (CSD-1491979 [29] and CSD-225647 [30]) and the anhydrous Co(CH\({}_{3}\)COO)\({}_{2}\) (CSD-715832 [31]), two intermediate crystalline phases--Co(CH\({}_{3}\)COO)\({}_{2}\cdot\)2H\({}_{2}\)O (CSD-138992 [32] and CSD-715831 [31]) and [Co(CH\({}_{3}\)COO)\({}_{2}\)]\({}_{5}\cdot\)H\({}_{2}\)O (CSD-1127997 [33])--have been described. Thus, from a chemical point of view, it would be reasonable to think that this could be the path of dehydration, but none of these phases were detected by XRD (although we were able to stabilize the dihydrate, crystalline Co(CH\({}_{3}\)COO)\({}_{2}\cdot\)2H\({}_{2}\)O under the experimental conditions described in Section I of Supporting Information). In addition, the hydration water could hydrolyze the acetates and both processes could occur simultaneously, giving rise to the formation of basic acetates. In this sense, intermediate phases of general formula Co(OH)\({}_{\rm x}\)(CH\({}_{3}\)COO)\({}_{2-\rm x}\) or CoO\({}_{\rm x}\)(CH\({}_{3}\)COO)\({}_{2-\rm 2x}\) could also be present as non-crystalline compounds, since none were detected by X-ray diffraction. From 200 to 275 \({}^{\circ}\)C, the sample quickly lost weight until a total \(\Delta\)W of \(\sim\)11.95%, indicating the partial decomposition of acetate groups. No significant change in the intensity of the diffraction lines (see Figure 3) up to a temperature close to 220 \({}^{\circ}\)C was observed; from this, the sample crystallinity increased, as evidenced by the presence of two well-defined lines at around 20 \(\approx\) 9-9.5\({}^{\circ}\). Finally, around 250 \({}^{\circ}\)C, a new crystalline phase appeared. Figure 5a-d shows the obtained XRD patterns for some selected temperatures in the 200-280 \({}^{\circ}\)C range. At 200 \({}^{\circ}\)C (Figure 5a), only a broad diffraction maximum centered at 20 \(\approx\) 9-9.5 \({}^{\circ}\) can be observed; this splits in two well-defined reflections at a temperature close to 230 \({}^{\circ}\)C, with a significant increase in the sample crystallinity (Figure 5b). At this stage of the decomposition process, following the previous dehydration step, it has been suggested that the formation of Co(OH)\({}_{\rm x}\)(CH\({}_{3}\)COO)\({}_{2-\rm x}\) or/and CoO\({}_{\rm x}\)(CH\({}_{3}\)COO)\({}_{2-\rm 2x}\)[24] occurs as intermediate phases that, according to our experimental data (\(\Delta\)W of \(\sim\)11.95%), should correspond to Co\({}_{2}\)(OH)(CH\({}_{3}\)COO)\({}_{3}\) and Co\({}_{5}\)O(CH\({}_{3}\)COO)\({}_{8}\). However, there are no data to support the possible stabilization of any of these phases, so the crystalline product emerging at 230 \({}^{\circ}\)C remains an unidentified phase (or phases). Figure 3: X-ray powder diffraction thermal evolution for cobalt (II) acetate tetrahydrate under N\({}_{2}\) between RT and 400 \({}^{\circ}\)C (heating) and then cooled down to 270 \({}^{\circ}\)C. Intensity scale as square root. _Note the presence of a width scattering bump around 20 = 7\({}^{\circ}\) coming out from the camera, as well as main platinum peaks around 41.0\({}^{\circ}\) and 47.7\({}^{\circ}\). 20 values (ICDD PDF card 01-087-0642) produced by the camera heating element are present in some scans._  
From 250 to 280 \({}^{\circ}\)C, the intensity of these maxima decreased, and the new emerging phase (Figure 5c) became the only crystalline one (Figure 5d). In previous works, this phase has been associated with the formation of different stable intermediate compounds. [PERSON] et al., [25] suggested that this intermediate product corresponds to Co(OH)\({}_{0.8}\)(CH\({}_{3}\)COO)\({}_{1.2}\), whereas [PERSON] et al. [24] identified it as an acetate oxide of composition Co\({}_{4}\)O(CH\({}_{3}\)COO)\({}_{6}\). However, our results indicate that the new phase did not correspond to either one of these.