Lanthanide azolecarboxylate compounds: Structure, luminescent properties and applications

The unique optical and magnetic properties of lanthanide ions (Ln), like a gem, need the right faceting and the right setting. Azole carboxylic acids provide a unique platform for driving the structure of complex compounds ranging in dimensions from 0-D (molecular complexes) to 1-D, 2-D polymers and 3-D MOF (Metal Organic Framework) structures. The peculiarity of azolecarboxylate ligands is that numerous possible coordination fashions, including both carboxyl groups and nitrogen atoms, on the one hand, open up almost unlimited possibilities for obtaining materials with desired properties, for example, luminescent sources and sensors, molecular magnets, catalysts and materials for gas sorption and separation. Several coordination modes, dependent on the reaction conditions, make the structural diversity of lanthanide carboxylates difficult to predict and require systematic analysis. Our analysis is critical to produce efficient and advanced materials. This review describes and systematizes data on both synthesis and structure and functional properties of pyrazole-, imidazole-, 1,2,3-triazole, 1,2,4-triazole- and tetrazole-carboxylates of lanthanide metals and evaluates the achievements in this area of coordination chemistry. The author's view on the future of the chemistry of lanthanides azole carboxylates and possible new applications in materials science is also presented.