Coordiantion Assembly, Structure, And Properties Of Transition-metal Modified Heteropolymolybdate

In this paper, using different kinds of N-containing ligands and transition metal ions, a series of solid state functional polymolybdates have been synthesized under hydrothermal conditions, in which the secondary transition-metal building blocks presented various structures and served as modified or bridging groups. The controllable syntheses have been performed by various pH, counter ions, and ligands with different electron density of coordination atoms. By the concept of molecular design, we have also investigated the modification of secondary transition-metal building blocks to the polymolybdate structures together with their synergic effects. These results extend our understanding of the relationship between the structure and function of polyoxometalate materials; thus provide significant theoretical and experimental foundations for the syntheses and application of new kinds of polyoxometalat-based materials.In our experiments, using pyridine or amine organic ligands, transition-metal cations, and molybdate as starting materials, we have successfully synthesized new eighteen polymolybdates. These complexes have been investigated by IR and XPS spectra, elemental, electrochemical, and X-ray diffractometer analyses.1. Using diethylenetriamine and 2,2'-bipyridine organic ligands, four transition-metal modifiedε-Keggin molybdogermanates (1-4) have been synthesized.Compounds 1 to 4 contain similar four-electron reduced [GeMo12O40]8- polyoxoanions, in which polyanionic clusters covalently coordinate to the transition-metal ions. Due to the coordination by different transition-metal ions, the separation of Mo???Mo and the positions of reduced MoV ions in the polyanionic clusters are different.2. Using 1,2-diaminopropane, 4,4'-bipyridine and 4,4'-bispyridylethane organic ligands via reaction with simple molybdate, four Ni2+ ions capped 1D or 2Dε-Keggin molybdogermanates (5-8) have been synthesized. Compound 5 is composed of [GeMo12O40]8- polyoxoanion, capped {Ni(C4H13N3)} or {Ni(C4H13N3)(H2O)} groups, Ni2+ complex cations, and water molecules. Compounds 6 and 7 contain [GeMo12O40]8- polyoxoanion, capped {Ni(C4H13N3)}, {Ni(C4H13N3)(H2O)}, or {Ni(C4H13N3)(C12H12N2)} groups, Ni2+ complex cations, and water molecules. While compound 8 is composed of [GeMo12O40]8- polyoxoanion, capped {Ni(C4H13N3)} and {Ni(C4H13N3)(C10H8N2)} groups, Ni2+ complex cations, and water molecules.For compounds 5 and 6, two neighboring cluster link each other by four O?Ni?O bridging units to form a 1D chain. Due to the four Ni2+ in each cluster located in the cavities of each polyoxoanion, the chain is in a zigzag type. Compound 7 also forms 1D zigzag chain but only by two O?Ni?O bridging units. While in compound 8, one of the 4,4'-bpy ligands coordinates to two Ni2+ form different polyoxoanions; thus the neighboring chains are further connected to form 2D layered structure.3. Using Sb2O3 and molybdate starting materials in mixed pyridine/H2O (v:v = 1:1) solvent, five Sb cappedα-Keggin molybdoantimonates (9-13) have been synthesized.Compounds 9, 10, 12 and 13, contain the similarα?Keggin polyoxoanions as [BMo12O40]10-, [SiMo12O40]9-, [PMo12O40]8-, and [AsMo12O40]8-, respectively. By the linkage of Sb atoms, these polyoxoanions form 2D layered structure. While in compound 11, besides the similarα?Keggin type [SiMo12O40]9- anion, there exists copper complex cation, in which Cu2+ ions coordinate to three 2,2'-bpy ligands. However, compound 11 does not form the 2D structure.4. Under hydrothermal conditions, five compounds (14-18) have been synthesized by self-assembly of organic ligand, transition-metal ion, and molybdate as starting materials. In compound 14, the anion is the rare exmple ofβ?Keggintype [SiMo12O40]6- polyoxoanion. The organic ligand, 1,2,3,4-(4-pyridinium)butane, located in compound 14, was not added as the starting materials; thus it must be generated in the self-assembly process by virtue of the recombination of two 4,4'-bipyridyl-(1,2)-ethane ligands. Compound 15 is composed ofα?Keggin type [SiMo12O40]4- polyoxoanion, Ni(II)-organic complexes, and water molecules. By linkage of one Ni(II)-organic complex, the polyoxoanions in compund15 are connected to form 1D chain structure. Compound 16 contains [Mo4O13]2- polyoxoanion and Cu(I)-4,4'-bpy complex component, where the Cu(I)-4,4'-bpy subunits link the polyoxoanions to form the 2D layers. Compound 17 is composed ofα?[Mo8O26]2- anion and Cu(I)-4,4'-bpy subunits, in which the terminal oxygen atoms from the polyoxoanions link with Cu(I)-4,4'-bpy subunits to form 3D framework. Compound 18 also forms a 3D framework by way of linkage ofα?Keggin type [GeMo12O40]4- polyoxoanions and Cu(I/II)-organic subunits, among which the Cu(I)-bpy subunits link with Cu(II)-organic components to form the interesting meso-helical chains.