Tuning the topology of hybrid inorganic-organic materials based on the study of flexible ligands and negative charge of polyoxometalates: A crystal engineering perspective

Currently, the design and assembly of hybrid inorganic-organic compounds has become an area of rapid growth due to their structural diversities as molecular building blocks. Polyoxometalates (POMs) as a subset of metal oxides, that represent a tremendous range of inorganic clusters with unique physical and chemical performances, possess intriguing structures and abundant potential applications. In the self assembling process of POM-based architectures, in addition to the important role of POMs, the choice of adequate ligands is significant to modulate the properties of inorganic-organic hybrids. Moreover, flexible N-donor ligands, including imidazole, triazole, tetrazole, and pyridyl derivatives with strong coordination capacity have been used for construction of POM-based compounds with attractive topologies and different dimensionality. Thus, this review puts into perspective latest research on this topic focusing to the construction of hybrid inorganic-organic materials based on flexible ligands. Remarkably, they provide to POM-based systems the flexibility and conformational freedom necessary to satisfy the coordination environment of the metal centers creating fascinating structural topologies, such as entangled and other structures with various architectures. In addition, this review also describes recent work devoted to analyze how the negative charge of POMs influences the supramolecular assembly of hybrid inorganic-organic compounds. (C) 2015 Elsevier B.V. All rights reserved.