Adventures in the coordination chemistry of 2-pyridyl oximes: On the way to 3d/4f-metal coordination clusters

[Display omitted] •The 3d/4f-metal chemistry is rich and with many potential applications.•Synthetic strategies and routes for 3d/4f-metal complexes are described.•The use of 2-pyridyloximate ligands in 3d/4f metal chemistry is highlighted.•The properties of 3d/4f-metal complexes are briefly described. Molecular compounds containing both 3d- and 4f-metal ions have played an important role in the development of inorganic chemistry in the last 15 years or so because of their relevance to a number of interdisciplinary research fields, including Molecular Magnetism, Optics and Catalysis. The synthesis of such discrete (dinuclear and polynuclear) complexes is not straightforward. Simply mixing the starting 3d- and 4f-metal materials in the presence of an organic ligand, often results in homometallic 3d-metal complexes, the driving force for this being the ligand-field stabilization for compounds of the 3d-metal ions. For the synthesis of mixed 3d/4f-metal complexes, one route and one strategy are usually employed. The route consists of “one-pot’ procedures and the strategy is based on the “metal complexes as ligands” approach; in both, the choice of the primary organic ligand is of paramount importance. Ligands that simultaneously have soft or intermediate basic sites (HSAB model) for preferential binding of the 3d-metal ion (intermediate or soft acid) and hard basic sites for selective binding of the oxophilic (hard acid) lanthanoid(III) center are preferable. One family of such ligands consists of deprotonated 2-pyridyl oximes. This comprehensive review covers all aspects of synthetic chemistry that has led to discrete 3d/4f-metal complexes which contain 2-pyridyloximates as primary ligands; emphasis is given on the design principles. The ligands, whose 3d/4f-metal chemistry is described, are 2-pyridyl aldoxime, methyl 2-pyridyl ketoxime, phenyl 2-pyridyl ketoxime and di-2-pyridyl ketoxime. Complexes containing the metal combinations {NiIILnIII}, {FeIIDyIII}, {ZnIILnIII}, {CoIIIDyIII}, {NiII2Ln}, {CoIII2Ln}, {MIILnIII2}, {NiII2LnIII2}, {CoIII2LnIII2}, {FeII2DyIII2}, {CrIII2LnIII2}, {CoIII4DyIII2}, {NiII4LnIII4} and {NiII8LnIII8} have been isolated and studied (M = Ni, Cu; Ln = various lanthanoids). The molecular structures of the complexes, some of which are exciting, are discussed and the physical/spectroscopic properties of selected compounds are briefly described. The HSAB principles apply to most (but not all) of the reported complexes, giving a rational