Recent developments in penta-, hexa- and heptadentate Schiff base ligands and their metal complexes

•Coordination chemistry of penta-, hexa- and heptadentate Schiff base ligands.•Penta-, hexa- and heptadentate Schiff base ligands with donor sets combining N, O, S or P donors.•Structural aspects of their transition metal, main group, lanthanide and actinide complexes.•Linear and macrocyclic pentadentate Schiff bases and their metal complexes.•Discussion of structures and physico-chemical properties of SB metal complexes. Novel ligand platforms that promote reactivity are of long standing and continued interest in coordination chemistry, with Schiff base ligands and their metal complexes representing one of the most versatile and long standing topics of interest. The synthesis and structure of polydentate Schiff bases and their metal complexes is fascinating, because it reveals a great richness of structural, physico-chemical and catalytic properties. Given the simplicity and ease of access to multidentate Schiff bases and their metal complexes, investigation of such compounds is essential to precise and understand structure–property relationships in order to optimize and improve their use in a wide range of fields, including catalysis, supramolecular chemistry, magnetism, electrochemistry, nanoscience, energy materials, and biological applications. This review highlights the recent developments of pentadentate, hexadentate, heptadentate and macrocyclic Schiff base ligands containing various donor sets made of different combinations of N, O, S or P donor atoms and their metal complexes (essentially mononuclear), as well as presenting synthetic methods and interesting structures of complexes formed by first-to-third row transition metals (from group 4–12), main group elements, lanthanides and actinides. This review is divided into three main sections, each of them corresponding to one type of denticity of the Schiff base under consideration. Each category is described with representative examples according to a periodic order, and emphasis is given to the coordination aspects. Their catalytic, magnetic and biological properties are also outlined. This review that contains 359 references should act as a source of information to researchers interested to work in this domain and stimulate further investigation in this fascinating area of Schiff base coordination compounds.