Polyoxomolybdate clusters and copper-organonitrogen complexes as building blocks for the construction of composite solids

The influences of ligand coordination modes on the oxide microstructures in the copper molybdate system were investigated. Rigid bridging ligands such as 4,4'-bypyridine (4,4'-bpy) and 2,4,6-tripyridyltriazine (tptz) afford polymeric cationic substructures with Cu(I) which provide scaffoldings for the entrainment and modification of the molybdenum oxide microstructure. These structural influences are manifested in [{Cu(4,4'-bpy)}₂Mo₂O₇] (MOXI-45) and [{Cu(tpt)}₂Mo₆O₁₉] (MOXI-46). In contrast, ligands such as pyridine (py) which do not effect the construction of polymeric substructures provide molecular building blocks which combine with the molybdenum oxide motifs in a less predictable fashion. Thus, [{Cu(py)}₄Mo₈O₂₆] (MOXI-47) is constructed from octamolybdate clusters linked by {Cu(py)}⁺¹ fragments into a virtual two-dimensional network. The interplay of ligand geometry and bonding mode and of metal coordination preferences plays an important role in the structure of [{Cu₂(tpypz)(H₂O)₂}Mo₈O₂₆] (MOXI-44), the unique example of a Cu(II)-containing material, with the binucleating tetrapyridylpyrazine ligand (tpypz) providing the organic building unit. The overall structure reflects the binucleating role of the ligand and the distorted octahedral geometry of the Cu(II) centers. The importance of hydrothermal techniques in effecting the syntheses of such composite materials is also discussed. (C) 2000 Elsevier Science S.A.