Preparation and Structural Characterization of Copper(II) Complex with Maltol

Maltol (3-hydroxy-2-methyl-4H-pyran-4-one) is a bidentate ligand that coordinates transition metal ions via its hydroxyl and carbonyl groups. Copper(II) forms stable complexes with oxygen-donor ligands due to its flexible coordination geometry and biological relevance. This study investigates the complexation of copper(II) nitrate trihydrate with maltol, forming a stable complex with distinct structural characteristics. The copper(II)–maltol complex was synthesized by reacting copper(II) nitrate trihydrate with maltol in aqueous solution under ambient conditions. The resulting solid was characterized using FT-IR, PXRD, and TGA/DSC to evaluate coordination modes, structure, thermal stability, and solution behavior. FT-IR analysis showed the absence of the C–OH stretching vibration at 3255 cm⁻¹, indicating deprotonation of maltol and coordination to the copper ion. The C=O stretching vibration shifted from 1616 cm⁻¹ in free maltol to 1568 cm⁻¹ in the complex, confirming chelation. A weak Cu–O band at 719 cm⁻¹ was observed, with no nitrate ions detected. Thermal analysis revealed a single-step degradation, with 70% mass loss attributed to the removal of maltol, and a sharp exothermic peak at 220°C in the DSC curve, consistent with CuO. X-ray diffraction confirmed the monoclinic crystal system (space group C2/c) with square-planar coordination around the copper ion, exhibiting Jahn–Teller distortion. This study successfully synthesized and characterized the copper(II)–maltol complex. FT-IR confirmed maltol coordination with copper, forming a stable chelate. Thermal analysis indicated good stability, and X-ray diffraction revealed a monoclinic structure with Jahn–Teller distortion. These findings enhance understanding of copper(II) coordination chemistry with maltol.

This research was funded by the European Union—NextGenerationEU Project “Advanced Interdisciplinary Approaches to Environmental Chemistry: From Materials to Sustainable Solutions for Pollution” (Grant number: 581-UNIOS-101).