Preyssler structures

Figure 1 Representative POM structures in polyhedral notation. Top left the common Keggin structure top right the hexametalate structure bottom left the Wells-Dawson structure bottom right the Pope-Jeannin-Preyssler structure. In polyhedral notation, the center of each M06 unit is a metal nucleus and each...

Pyrazolo[3,4-d]pyrimidines are of considerable chemical and pharmacological importance as purine analogues [75], Various compounds with related structures also possess antitumor and antileukemia activities [76]. Therefore, the investigation about new methods and synthesis of new derivatives of these compounds attracted considerable amount of interest. Reaction of 5-amino-l-phenyl-l/7-pyrazolo-4-carboxamide with aromatic aldehyde in the presence of HPAs, HjPWjjO q and Hj [NaP5W29MoO,jJ, gave derivatives of 6-aryl-l//-pyrazolo[3,4-r ]pyrimidin-4[5//]-ones. It was confirmed that HPA with Preyssler structure shows higher activity and yields due to the higher number of acidic protons (Scheme 3.29) [77]. 

Figure 2.1 Structure of (a) terbium phthalocyaninato derivative, (b) [Ln(W5018)2]9 ion, (c) [Ln(P2-SiW11039)2]13 ion and (d) Preyssler anion [l nP5W30O110]12-.

Figure 5.10 The structure of [ Ce(H20)s 4 Na(H20)P5W3oOno ] cluster [35]. (Reprinted from Inorganica Chimica Acta, 360, no. 6, Y. Lu, Y.G. Li, et al., A new family of polyoxometalate compounds built up of Preyssler anions and trivalent lanthanide cations, 2063-2070 (Figure 1), 2007, with permission from Elsevier.)...

Nd2(H20)i4 Na(H20)P5W3oOiio ] shows a one-dimensional chain structure built from Preyssler anions [Na(H20)P5W3oOno] " linked by neodymium cations. In the complex, the adjacent [Na(H20)P5W3oOno] clusters are linked to each other about a center of symmetry... 

Four of the possible six possible skeletal isomers having the Wells-Dawson structure, as exemplified by [EgWigOgz] (E = P or As), have been structurally identified. The so-called Preyssler anion was structurally identified as [ Na(H2 0) P5W3oOiio] , itbeing shown that the Na(H2 0)+ group was tightly bound in the center of the cluster. However, under forcing conditions, the aqua-sodium cation could be replaced by Ca +, trivalent lanthanide cations and some tetravalent actinide cations, all of which have similar ionic radii... 

FIGURE 4 Structures of a-Keggin (A)-, Wells-Dawson (B)-, and Preyssler (C)-typed frameworks. Eu is co-ordinated by oxygen atoms of mono-lacunary ligands for a-Keggin and Wells-Dawson frameworks, in contrast with the case of the Preyssler framework where Eu is encapsulated in the centre of the anion. 

The efficiency of Preyssler nanoparticles, Hj [NaP5W3Q0jjJ/Si02, is attributed to the nanoporous structure of this solid acid catalyst, whicli could act as a nanoreactor (Fig. 3.2). 

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