Advances and Challenges in Diethylenetriamine-Based Schiff Bases: Synthesis, Structural Diversity, Coordination Chemistry, and Emerging Applications

Schiff bases derived from diethylenetriamine (DETA) have attracted considerable attention due to their versatile coordination behavior and structural flexibility. The presence of multiple donor atoms within the diethylenetriamine framework enables the formation of a wide variety of mono- and polynuclear metal complexes with diverse geometries. Despite the extensive development of Schiff base chemistry, challenges remain in achieving controlled asymmetric synthesis and improving the stability of certain metal complexes, highlighting the need for continued investigation in this field. This review provides a comprehensive overview of the chemistry of diethylenetriamine-derived Schiff bases reported between 2000 and 2025, with emphasis on their synthetic strategies, structural characteristics, and metal complex formation. Various condensation approaches involving diethylenetriamine and different aldehydes or ketones are discussed, highlighting factors that influence ligand architecture and denticity. The structural diversity of these ligands, including tridentate, tetradentate, and higher denticity systems, is examined in relation to their coordination modes and chelating behavior toward transition metal ions. Reported metal complexes are analyzed in terms of coordination geometry, bonding features, and ligand–metal interactions as revealed by spectroscopic and crystallographic studies. Key trends identified in the literature include increasing interest in asymmetric ligand design, development of multinuclear coordination systems, and exploration of environmentally relevant catalytic processes such as carbon dioxide reduction. The review also identifies current trends and gaps in the literature, particularly regarding ligand design and coordination versatility. Future research is expected to focus on sustainable synthetic approaches, improved structural control, and the development of multifunctional complexes for applications in catalysis, sensing, and biomedical chemistry. Overall, this work provides a consolidated understanding of the development of diethylenetriamine-derived Schiff bases and outlines perspectives for future investigations in coordination chemistry.