Phenolic pyrazoles: Versatile polynucleating ligands

The proximity of the donor atoms in phenolic pyrazoles and the ability to function in neutral and in singly and doubly deprotonated forms allows them to form a diverse range of metal complexes. The complexes in this review are classified on the basis of the nuclearity and the number of phenolic pyrazole units present in structures that have been determined by X-ray crystallography. Mononuclear complexes can contain one, two, or three phenolic pyrazoles or polydentate ligands where two phenolic pyrazoles are linked by an organic spacer. Six different coordination modes of the phenolic pyrazole have been identified in single crystal X-ray structure determinations with the ligand providing between one and four lone pairs from its oxygen and nitrogen atoms. Dinuclear complexes feature metals bridged by a phenolate or a pyrazolate unit, by other ligands, or by polydentate systems containing linked phenolic pyrazoles. Polynuclear complexes with up to 21 metal atoms have been reported.

Six different modes of coordination allow phenolic pyrazoles to form complexes containing up to 21 metal atoms.Figure optionsDownload high-quality image (177 K)Download as PowerPoint slide