Self-Assembly of Anionic Polyoxometalate-Organic Architectures Based on Lacunary Phosphomolybdates and Pyridyl Ligands.

The development of novel systems for metal-organic architectures is an attractive research field because they are fascinating materials with unexplored functions. Lacunary polyoxometalates (POMs) offer structurally well-defined coordination sites with various coordination directions and numbers in addition to the designable properties; thus, lacunary POMs are ideal building blocks for inorganic-organic architectures. However, their utilization is currently limited by their low stability and difficulty in controlling the reactivity. Here, we report the successful self-assembly of anionic POM-organic architectures comprising multivacant lacunary POMs and pyridyl ligands. By introducing pyridine moieties to its vacant sites, the trivacant lacunary phosphomolybdate [A-α-PMo9O34]9- is significantly stabilized in organic solvents. Furthermore, the resultant structure can be utilized as a stable and reactive building block to synthesize a dimer pillared by 4,4'-bipyridyl and a tetramer bridged by two cofacial porphyrin ligands, which can intercalate aromatic molecules.