Controllable growth of polyoxometalate based building blocks : towards the construction of clusters, arrays and nanostructures

• Main Author: Abbas, Hamera
• Published: University of Glasgow 2006
• Subjects: 541.2242; QD Chemistry
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.479050

The work presented in this thesis describes routes to the controlled growth of small polyoxometalate clusters achieved by utilising a range of organic counterions in conjunction with electrophilic Ag(I) ions. The subsequent isolation of a new building block; {Ag(β-Mo8O26)Ag} has demonstrated how subtle control can be achieved through the use of bulky and flexible counterions and by solvent. Within most structures the electrophilic ions form {Ag2} dimer groups that link together β-octamolydbdate anions to produce a family of structurally related architectures ranging from isolated units, one- and two-dimensional architectures. Each of the architectures contain {Ag(β-Mo8O26)Ag} based building blocks that can be controlled in their self-assembly by cation and solvent interaction in the solid state. This set of architectures differ in the coordination modes of the linker {Ag2} groups and in the nature of the Ag.Ag interactions that are present in most structures. Furthermore, the isolation of polymeric structures exclusively through solvent ligation has yielded one- and two-dimensional architectures where acetonitrile molecules in particular have formed pseudo cations around the {Ag(β-Mo8O26)Ag} based building blocks. The above synthetic strategy was also extended to other metals to yield some additional structures. Several of the silver polyoxomolybdate compounds have been further investigated on silicon substrates using Scanning Electron Microscope (SEM), and in some instance with Energy Dispersive X-ray (EDX), Transmission Electron Microscopy (TEM) and Selective Area Electron Diffraction (SAED). These techniques have revealed the growth of nanostructure on multiple length scales. Knowledge of the molecular architecture has given a unique understanding of the assembly of these nanostructures including various one-dimensional assemblies (nanorods and nanowires), that have been obtained through different, efficient and inexpensive synthetic methods. The structures have been identified and a hypothetical mechanism for the growth of Ag(0) based nanowires has been correlated to the partial oxidation of methanol and the reduction of Ag(I).