REDUCED MOLYBDENUM PHOSPHATES - OCTAHEDRAL TETRAHEDRAL FRAMEWORK SOLIDS WITH TUNNELS, CAGES, AND MICROPORES

The exquisite shape-selective absorptivities of the zeolites have inspired areas of research ranging from topological theories for filling space to novel hydrothermal experimental techniques to important petrochemical processes. However, the closed shell nature of these silicoaluminates renders them ineffective for many of the types of reactions that the d-block elements are capable of such as atom abstractions and redox chemistries. If one could prepare a heat-stable oxide with shape-selective access to large internal micropore volumes combined with the reactivity of a transition element, then the possibilities of observing new types of shape-selective catalysis could be enhanced. The molybdenum phosphates (MoPO) discussed here represent the beginning steps toward materials of this type. These MoPO's are synthesized hydrothermally in aqueous H3PO4 in the presence of a cationic template and contain anionic octahedral-tetrahedral frameworks with the Mo in an oxidation state of less-than-or-equal-to 5+. Almost all contain Mo-Mo bonds. The discussion will focus mainly on the synthesis, structures, and properties of molecular, large ionic aggregates, one-dimensional polymeric and two-dimensional layered MoPO's culminating in three-dimensional microporous solids, some of which contain nearly 40 vol % accessible internal void space.