POM clusters

The preparation of solids with covalently attached POM complexes is a serious and worthwhile research target because these materials might be expected to be rather stable to POM leaching in solutions. Many new materials of this type have been reported in the literature [16,49,74,137-143] however, catalytic studies on covalently boimd POMs still remain a rare event. In 1992, Judeinstein reported the first POM-polymer hybrid where a lacunary Keggin POM cluster was covalently linked to polystyrene or polymethacrylate backbone through Si-0 bonds [137]. This approach has been further developed by several research groups. 

The POM clusters tend to be anionic in nature, being based upon metal oxide building blocks with a general formula of MO (where M is Mo, W, V and sometimes Nb and x can be 4, 5, 6 or 7). POM-based materials have a large range of interesting physical properties [6-10] which result from their many structures, the ability to delocalize electrons over the surface of the clusters, and the ability... 

Figure 2.1 Representations of the structures of some Mo-based POM clusters (nuclearity given in subscript), all synthesized under...

The challenge now is to design individual POM cluster molecules that can interact both with each other and with the macroscale (as shown in Figure 2.12), in a desired fashion in response to inputs and environmental effects, so that a functioning molecular system is really constructed. 

Ce(IV)03)3(H20)2(A-a-PW9034)2] [23] is an example of sandwich type RE-POM clusters with three central RE atoms. The structure is composed of two trivacant Keggin anions [A-a-PW9034] and a central belt of three cerium atoms alternating with three oxygen atoms. Three cerium atoms have two types of coordination one is six-coordinated while... 

RE-POM clusters with a large size are normally composed of several equivalent or nonequivalent POM building units (for example, XW9 and XWio in a large RE-tungstate cluster, M07 and Mog in a large RE-molybdate cluster) with RE atoms as linkers or decorate groups. 

At the end of this section, there are two points that should be stated, (i) The RE-POM clusters described here are mainly those with complete structural characterization among a... 

Various POM clusters can act as building units and are connected by RE linkers into one-, two-, three-dimensional structural RE-POM complexes. In reported extending structural RE-POMs complexes, various POM building blocks participate in the structural construction as discrete clusters, whereas RE linkers participate in the structural construction as diverse modes, including hydrated RE ions, discrete RE-organo clusters, and one-, two-, three-dimensional structural RE-organopolymers. 

As depicted in Fig. 4, a POM cluster consisting of 6 unit cells along the b axis is chosen to test the effect of the size of starting cluster. The deviation percentage of the (hyper)polarizabilities between elg-FF and conventional are listed in Table 4 with respect to the size of the starting cluster, N, . It is also found as expected that the (hyper)polarizability values converge nicely... 

Table 4 Effect of the size of the starting cluster in the elg-FF calculations in the (hyper)po-larizabilities of a POM cluster... 

Using Dye/amine/alkyl bromide, iridium-containing photoluminescent polyacrylate films have also been manufactured. Polyoxometallate (POM)/polymer hybrid materials exhibiting modified mechanical properties (polymerized EPOX/TMPTA matrix with inserted POM clusters [XIA 15]) were synthesized in a one-step process using a silicon or phosphor polyoxomolybdate/iodonium salt/silane system. 

Jahier, C., Cantuel, M., McClenaghan, N., et al. (2009). Enantiopure Dendritic Polyoxometalates Chirality Transfer from Dendritic Wedges to a POM Cluster for Asymmetric Sulfide... 

Fig. 5.3 A representation of the building blocks available from the simple [M0O4P precursor and representations of the crystal structures of some of the POM clusters isolated to date. These clusters represent some of the largest molecules yet isolated. For instance the Mosss cluster is about the same size as the protein hemoglobin [34]...

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