Organic-inorganic hybrid materials: From 'simple' coordination polymers to organodiamine-templated molybdenum oxides

The vast range of solid-state properties exhibited by the oxides is a result of their diversity of chemical composition and structure type. However, while many naturally occurring oxides and minerals possess complex crystal structures, the majority are of simple composition and have highly symmetrical structures with rather small unit cells. Most silicates, important ores, gems, and many rocks and soils are examples of these materials. Although such simple oxides can possess unique and specific properties - such as piezoelectricity, ferromagnetism, or catalytic activity - as a general rule there is a correlation between the complexity of the structure of a material and its functionality. One approach to the design of novel oxide materials mimics nature's use of organic molecules to modify inorganic microstructures. In this instance, the inorganic oxide contributes to the increased functionality by assimilation as one component in a hierarchical structure where there is a synergistic interaction between organic material and the inorganic oxide. Synthetic studies of materials that possess such an interface, coupled with the acquisition of the appropriate structural information, should contribute to the development of an increased understanding of methods to control the structure -property relationships within these hybrid materials. While the organic component may assume a variety of structural or functional roles in the design of novel oxide-based composite materials, the extensive contemporary interest in framework solids suggested their use as ligands in a polymeric coordination complex cation which provides not only charge compensation for the anionic oxide substructure but also a rigid framework for entraining and, to a degree, for controlling the surface of the growing oxide microstructure. These framework solids are particularly attractive from several perspectives: 1) They are accessible by self-assembly under exceedingly mild conditions which allows retention of the structural integrity of the starting materials and the isolation of kinetic, rather than exclusively thermodynamic, products; 2) they possess a remarkable chemical and structural diversity; and 3) the numerous examples described in recent years demonstrate that some control is achievable in defining their architectures. Consequently, by appropriate selection of ligand types and through exploitation of the coordination preferences of the metal, one-, two-, or three-dimensional coordination complex cations may be constructed to provide a scaffolding for the entraining of the oxide substructure. Application of this strategy to the study of the molybdenum oxide/organodiamine - metal complex interface has produced a wealth of organic - inorganic hybrid materials of the MOXI family. These materials demonstrate not only the complexity of the organic-inorganic synthetic interface in the construction of such materials but also provide evidence of a powerful tool for the low-temperature synthesis of new materials endowed with structural complexity.