*3.2. Thermogravimetric Analysis and Powder XRD*

All the products of reaction (1) were thermally stable solids, indicating a strong metal– ligand bonding. Figure 5 shows DTA and TG curves with endo- and exothermic peaks of complex I and the oligomer based on it. The thermal behavior of the free molecules of aminoacids, including tyrazine, has been well studied. According to the results found by the authors of [34,35], the first endothermic stage of tyrazine decomposition occurs in the temperature range of 276–322 ◦C and corresponds to the reactions of its decarboxylation and deamination. Further, in the temperature range of 322–350 ◦C, the resulting intermediate product is relatively stable. The second stage of tyrazine decomposition occurs at 350–355 ◦C and involves oxidation of the phenolic fragment. At the same time, the porphyrin macrocycles in the general case [36], particularly the Sn(IV)-porphyrins [37], are highly resistant to thermal oxidative destruction.

As Figure 4 shows, the decomposition of complex I consisted of four stages. At the first stage, in the temperature range up to 100 ◦C, the complex thermal dehydration occurred. The loss of 9.45% of the sample mass corresponded to water evaporation as the sample itself was not subjected to preliminary drying. At the second stage, in the temperature range of 217–441 ◦C, the loss of 15.8% of the sample mass indicates partial axial ligand decomposition. The third stage, in the temperature range of 518–727 ◦C, the loss of 29.2% of the sample mass corresponded to the detaching of four sulfo groups from the porphyrin aryl fragments. The fourth stage consisted of the removal of the phenyl fragments, both of the porphyrin and axial ligands (15.5% of the sample mass). The residue mass (30% of the sample mass) indicates that the tetrapyrrole macrocycle containing the Sn(IV) cation in the coordination center was not destroyed. Similar data on the thermal decomposition of Sn(IV)-porphyrins have been described by the authors of [37]. The first stage of decomposition of the tyrazine fragments in porphyrin complex I begins at lower temperatures than that of the free aminoacid ligand, whereas the second stage (phenyl fragment oxidation), on the contrary, occurs at a higher temperature.

**Figure 5.** Differential thermal analysis (dashed line, DTA) and thermogravimetric analysis (solid line, TG) curves with endo- and exothermic peaks for thermal decomposition of I (red line) and Cu-[I-Cu]6 (green line).

A thermal analysis of the hexamers shows that decomposition of this compound consists of more stages. The first stage (up to 100 ◦C), as in the case of monomeric complex I, was associated with thermal dehydration. The second stage, in the temperature range of 100–136 ◦C, consisted of the dehydration of the water molecules located in the coordination bis-chelate center of Cu2+. The third stage of destruction, in the temperature range of 213–351 ◦C, corresponded to the destruction stage of the tyrazine fragments of the chelate

cycles. At the next stage, in the temperature range of 434–605 ◦C, the porphyrin macrocycle sulfo groups were eliminated. The last stage, in the temperature range of 736−925 ◦C, was probably associated with the processes of removal of the phenyl fragments of the porphyrin macrocycle and axial ligands. The residue mass (33% of the initial sample mass) indicates that the residue contains Sn(IV)-porphyrin and CuO. Similar results were obtained for the [I-Cu]n polymer. The data for the II and its hexamers are depicted in Table 3.


**Table 3.** Thermogravimetric analysis data of the II and its hexamer.

Powder X-ray diffraction (PXRD) was performed to verify the purity of [I-Cu]n and [II-Cu]n. The PXRD curve of [II-Cu]n, shown in Figure 6 as an example, indicates a diffuse large steam bun peak. The PXRD curve of [I-Cu]n looks similar. The absence of other obvious sharp peaks in the corresponding curves indicates that the polymers wereamorphous, with random growth during the self-assembly [38].

**Figure 6.** Powder X-ray diffraction XRD (PXRD) of the [I-Cu]n (**a**) and [II-Cu]n (**b**).
