## 3 Results and Discussion  
### Synthesis of the Nanocomposite with ReNSs  
According to the route displayed in Figure 1, synthesis of the Re@NCat involved at first the production of anion exchange resins containing functionalities derived from CIM. Afterwards, the relevant polymer was employed to adsorb ReO\({}_{4}\)\({}^{-}\) ions, and it was further reduced on amino ligands by NaBH\({}_{4}\). To verify this protocol, each stage of the above-mentioned synthesis was monitored by recording ATR FT-IR spectra. The collected data are displayed in Figure 2.  
Figure 1: A simplified scheme of Re@NCat synthesis. The structure of the CIM functionality is proposed, based on the FT-IR analysis.  
The polymeric base used for synthesis of the Re-based nanocomposite (CIM-functionalized copolymer) revealed the presence of a series of bands attributed to the amino ligands derived from CIM. This included vibration bands at 3394 cm\({}^{-1}\), 1540 cm\({}^{-1}\), and 1357 cm\({}^{-1}\) attributed, respectively, to the N-H stretching, the C=N aromatic ring deformation, and the N-C-N stretching (Figure 2, Table 1) [28]. All these identified moieties were consistent with the structure of CIM (see Figure 1) and pointed out that the relevant anion exchange resin was successfully synthesized. The ATR FT-IR spectrum of the CIM-functionalized VBC-co-DVB copolymer also indicated that the CIM functionality was attached to the polymeric matrix. Accordingly, C=O stretching vibrations at 1681 cm\({}^{-1}\), as well as at 1648 cm\({}^{-1}\) for R-N-CO-N-R bonds were identified as well (see Figure 2). Simultaneously, the presence of C-O-C stretching vibrations at 1143, 1014, and 906 cm\({}^{-1}\) and N\({}^{+}\)-H aromatic stretching vibration at 2472 cm\({}^{-1}\)[28] were noted. This indicated that the CIM functionality was likely attached to the polymeric matrix, by either the -N\({}^{+}\)-moiety in the aromatic ring as well as through the C=O group. The latter one was selected to be displayed in Figure 1 as a simplified representation.  
Figure 2: ATR FT-IR spectra recorded for the anion exchange resin (CIM-functionalized VBC-co-DVB copolymer), the ReO\({}_{4}\)– loaded anion exchange resin, and the resultant Re@NCat.  
Then, FT-IR analysis was repeated for the CIM-functionalized resin loaded with ReO4-ions, and again when oxyanions were reduced, leading to synthesis of the Re@NCat. The data indicating changes in the resin's structure are summarized in Table 1. After adsorption of ReO4- ions on the CIM functionality (see Section 2.2 for details), the above-discussed bands (attributed to the amino group) gradually shifted (see Table 1). After reduction of oxyanions, these shifts further increased their magnitude to achieve the effect in which the following transitions were observed: from 3394 to 3297 cm\({}^{-1}\) (a 97 cm\({}^{-1}\) shift), from 1540 to 1546 cm\({}^{-1}\) (a 6 cm\({}^{-1}\) shift), from 1648 to 1658 cm\({}^{-1}\) (a 10 cm\({}^{-1}\) shift), and from 1357 to 1349 cm\({}^{-1}\) (8 cm\({}^{-1}\) shift). This suggested a primary role of the CIM functionality in the capping and stabilization of the resultant ReNSs [29; 30]. It was also noticed that the vibration band at 2472 cm\({}^{-1}\), attributed to the N+-H aromatic stretching, faded, and a new one at 2796 cm\({}^{-1}\), attributed to the H-bridge in the NH chelating group, appeared. This suggested the chelation of ReO4- ions on CIM through both amino and carbonyl functionalities [31; 32].  
These results proved that the synthesis of the polymeric base was successful. In addition, they proved that ReNSs were effectively formed and stabilized with the aid of the CIM functionality.