*3.2. Infrared Spectroscopy*

The spectrum of FeCl3 × 6H2O (Figure 2A) displays small peaks of deformation vibrations of crystallized water at 1600 cm−<sup>1</sup> and stretching vibrations of free water at 3530 cm<sup>−</sup>1. A wide double band of stretching vibrations of crystallized water exhibits two pronounced maxima at 3000 and 3220 cm<sup>−</sup>1, while coordinated water deformation vibration bands arise at 840, 680, 600, 540 cm<sup>−</sup>1. The spectrum of FeCl3 × 6H2O also displays stretching vibration bands attributed to Fe–Cl (360 cm<sup>−</sup>1) and Fe–O (420 cm<sup>−</sup>1) vibrations [36].

**Figure 2.** IR spectrum of FeCl3×6H2O (**A**); IR spectrum of chitosan (**B**); IR spectrum of POX-1 (**C**); IR spectrum of deferoxamine (**D**); IR spectrum of POX-3 (**E**); IR spectrum of POX-2 (**F**).

The spectrum of chitosan (Figure 2B) shows a wide band of O–H and N–H stretching (3440–3100 cm<sup>−</sup>1), C–H stretching (2870 cm<sup>−</sup>1) and bending (1460, 1420, 1380 cm<sup>−</sup>1) vibrations, and N–H deformation vibrations (1590-1650 cm<sup>−</sup>1). Absorption bands in the range of 900–1200 cm−<sup>1</sup> are due to C–O–C, C–C and N–H deformation vibrations [37].

The spectrum of deferoxamine (Figure 2D) exhibits absorption bands of C=O, =O-H, -CONHR, -CH2 stretching vibrations (2840–3240 cm<sup>−</sup>1), peaks at 1620 cm<sup>−</sup><sup>1</sup> and 1560 cm−<sup>1</sup> of stretching =N-CO and deformation NH vibration bands. Peaks of stretching vibrations -CH2-CO are located in the interval 1400–1440 cm<sup>−</sup>1, while deformation aliphatic amine vibration peaks are found at 1030–1220 cm<sup>−</sup>1. In the range of 1040–500 cm<sup>−</sup>1, we observe deformation vibrations -(CH2)x-, -NH2.

The spectrum of POX-1 (Figure 2C) displays the C–H stretching vibration band at cm<sup>−</sup>1, which is shifted to 2890 cm−<sup>1</sup> as compared to the starting chitosan. The spectrum shows a wide band of O–H and N–H stretching (3440–3100 cm<sup>−</sup>1), C–H stretching (2890–2870 cm<sup>−</sup>1) and bending (1460, 1420, 1380 cm<sup>−</sup>1) vibrations and characteristic bands due to C–O–C and C–C deformation vibrations (900–1200 cm<sup>−</sup>1). The N–H deformation vibration band is shifted to 1560–1520 cm−<sup>1</sup> in comparison with the chitosan.

The spectrum of POX-2 (Figure 2E) exhibits stretching vibration bands characteristic of POX-1 (Figure 2C), i.e., O–H and N–H peaks (3440–3100 cm<sup>−</sup>1) and a characteristic band at 2360 cm<sup>−</sup>1. C–H stretching vibration bands are located at 2920–2840 cm<sup>−</sup><sup>1</sup> and slightly shifted in comparison to POX-1. The spectrum of POX-2 exhibits stretching vibration bands characteristic of deferoxamine (Figure 2D), i.e., peaks of stretching =N–CO (1620 cm<sup>−</sup>1) and deformation N–H (1560 cm<sup>−</sup>1) vibration bands, stretching vibrations CH2–CO (1400–1440 cm<sup>−</sup>1) and a characteristic peak at 520–580 cm<sup>−</sup>1.

The spectrum of POX-2 (Figure 2E) is identical to the spectrum of POX-3 (Figure 2F). This confirms our assumptions about their identical structures.
