Coordination chemistry of pyrazolone-based ligands and applications of their metal complexes

Pyrazolone-based ligands are rapidly becoming popular for use in catalysis, in biological applications, in sensors, in functional materials and as pigments for dyes. Many metal complexes with pyrazolonebased ligands have been reported since 80s of the last century, and several of them were found to possess interesting features, such as catalytic activity, anticancer, antioxidant, antifungal and anti-microbial activity, and enhanced NLO, photoluminescence and optical properties with respect to simple pyrazolone-based ligands. Some metal complexes display mesomorphic behavior, others have been investigated as dyes for leather and some also as models for metalloproteins on the basis of their metal environment and spectral features characteristic of important metalloenzymes. Depending on the nature of pyrazolone moieties condensing with primary amine, different classes of pyrazolone-based ligands can be created and used toward metal acceptors. This review provides an overview of this field, with the aim of highlighting both ligand design, synthetic methodology development and relevant applications of the metal complexes.