Building polyoxometalates

Here we start to examine the pivotal role that polyoxometalate clusters can play in the development of nanoscale devices that utilize POM components, and start to conceptualize some example systems in which POM components could have a crucial role [13, 19]. This is because such functional nanosystems can exploit the building block principle already established in this area of chemistry, coupled with the range of physical properties, and the fact that POM systems can really be seen as molecular metal oxides [20]. To demonstrate this point, a number of examples have been selected across the area of POM chemistry, including our contributions, to help highlight new directions and concepts. It should also be noted that metal oxides already play an important role in the electronics and semiconductor industry today and their solid-state properties have been studied extensively [21, 22]. Many of these concepts are not new in isolation, but the possibility of using molecular design in metal oxides to produce... 

Polyoxometalates (POMs), also known as heteropolyacids (HPA),3 are a class of compounds formed from negatively charged inorganic metal-oxygen building blocks. When charge-balanced with cationic species, POMs self-assemble into unusual 3D structures with specific topological and electronic properties.214 POMs are commonly formed from polyanions of early transition metals such as W, Mo or V. These anions can be substituted with other transition metals. The diversities in POMs composition and structure make them attractive for many applications, particularly as Bronsted acid and redox catalysts. For example,... 

In the decade or so since the first edition of this encyclopedia, there has been a considerable growth in the synthesis and structural characterization of unusually large polyoxometalates. In most cases, these have stability in solution (NMR spectroscopy) as well as in the solid state, and can be considered as linked assemblies of polyoxoanion building blocks. 

Figure 5.16 The one-dimensional chain structure of [La(H20)7Al(OH)6Mo60ig] [54]. (Reprinted from V. Shivaiah, et al., A novel polyoxometalate chain formed from heteropolyanion building blocks and rare earth metal ion linkers [La(H2O)7Al(OH)6M06Ois] -4nH2O, Journal of the Chemical Society, Dalton Transactions, 3781-3782 (Figure 1), 2002, by permission of The Royal Society of Chemistry.)...

Figure 5.21 The one-dimensional chain in [Ce(H20)3(SiWn039)] [67b], (Reproduced with permission from M. Sadakane, et ai, Controlled assembly of polyoxometalate chains from lacunary building blocks and lanthanide-cation linkers, Angewandte Chemie International Edition, 2000, 39, no.l6, 2914-2916 (Figure 1). Wiley-VCH Verlag GmbH Co. KGaA.)...

Recent years have seen the reports of increasing numbers of very large polyoxometalate anions. These may be divided into two classes (i) composite anions constructed of assemblies of simpler, usually lacunary, polyanions and (ii) mixed-valence polymolybdate anions which comprise common building blocks, e.g., Mo8, Mo6, and Mo2 clusters that have no separate, stable existence. 

We shall define a composite polyoxometalate as one containing two or more polyoxoanion building blocks and linker atoms or groups. Although the stmctures of such composite species suggest that they can be rationally synthesized by combination of building block with linker, in many cases the complete structure is formed from mononuclear components in a one-pot reaction. ... 

Polyoxometalates can be versatile inorganic building blocks for construction of molecular-based materials. The use of polyoxometalates, in combination with inorganic or organic components has been realized in the construction of molecule-hased materials. Prominent examples of inorganic materials can he found in the work by Muller on giant molybdates.We have been interested in materials comprised of lanthanide polyoxoanion building blocks. We report herein our efforts in the studies of lanthanide complexes of [a-... 

I-P2W17O61] " and [a-2-P2Wi706i], isomers of the monovacant Wells-Dawson anion, and [a-B-PW9034] as building blocks to new lanthanide polyoxometalate materials. 

Lanthanide polyoxometalates can be used in conventional s)mtheses to build up two dimensional materials. Linking up lacunary subunits is accomplished by lanthanide binding to terminal oxygen atoms of an adjacent polyoxometalate, forming dimers. The appropriate cations can link the dimers into a lattice, as found in the case of At. ... 

J. -H. Son, H. Choi, Y. -U.Kwon, Porous crystal-formation from polyoxometalate building-blocks. Single-... 

J. L. Stark, A. L. Rheingold, E. A. Maatta, Polyoxometalate clusters as building-blocks. Preparation and structure ofbis (hexamolybdate) complexes covalently bridged by organodiimido ligands, J. 

The specific building blocks for type I polyoxometalate structures of interest are as follows ... 

Polyoxometalate systems provide excellent models for the study of unusual molecular growth processes based on Mon -type building motifs/blocks leading to unusual giant spherical and ring-shaped structures with stoichiometry Mon (n = 12, 14, 16)-a Pythagorean harmony. 

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