Anderson heteropolyanions

FIGURE 42. Linking the Anderson heteropolyanion via O-H O hydrogen bonds that involve solvent waters including water trimer (shown in violet) (a) ball-and-stick representation and (b) polyhedral representation. Color code Al, cyan Mo, yellow O, red H, white. (Reprinted with permission from ref. 52.)... 

FIGURE 53. The side view of the water tube (white sticks) in between the Anderson heteropolyanions (polyhedral representation, red color). The copper dimeric complex cation is not shown for clarity. 

The repeating arrangement of the (H20)i3 cluster leads to the construction of a new type of waterpipe, as shown in Figure 52. The inner diameter dimensions of the water tube were found to be 8.527 x 8.061 A. The existence of such unstable pipe (vide supra) has been made possible by interactions with its surroundings, including an Anderson heteropolyanion and a dimeric copper complex cation. 

Figure 16 The structure of [TeMo6024]6 ( Anderson ) anion Table 9 Anderson and Related Heteropolyanions...

Several heteropolyanion structures accommodate central octahedral heteroatoms an especially widespread type is the Dm Anderson structure (Figure 11 and Table 2). Note that two versions of the structure are known with or without protonation of the central XOe octahedron, depending upon the oxidation state of X. Although the heptametalate anions, [M7O24] (Figure 5), can be considered to be Ci, isomers of the Anderson anions, few heteropolyanions have so far been shown to adopt the former structure. 

The Anderson-type heteropolyanions in the synthesis of alumina-and zeolite-supported HDS oxidic precursors... 

This study is aimed at using and identifying Al- and Co-containing Anderson-type heteropolyanions in the synthesis of (Co)Mo/alumina and (Co)Mo/zeolite HDS catalysts oxidic precursors. Various techniques such as Raman spectroscopy, NMR and EXAFS are used to show the apparition of the AlMo6024H6 entity upon impregnation of an alumina or a zeolite with an ammonium heptamolybdate solution. The question of the Mo-Co interaction in the promoted precursors is also tackled through the use of the CoMo6024H6 entity. 

Synthesis and characterisation of ammonium and exchanged salts of anderson-t3rpe heteropolyanions... 

This study enables us to draw a parallel between the behaviours of alumina and HY zeolite upon impregnation with oxomolybdate entities. In some conditions, when the buffer effect of the alumina is avoided, both supports see extraction of aluminium atoms and their inclusion in an Anderson-type heteropolyanion, AIMo6024H6. This entity is well dispersed on the alumina support whereas it appears as a bulk compound located in the macropores of the HY zeolite. However, it is still unknown whether the formation of this species is to be favoured. For promoted samples, a significant difference exists between both supports, since CoMo6024H6 can be preserved upon impregnation on a zeolite. Yet, the preparation of the catalysts has to be controlled the final calcination-rehydration steps tend to level the various synthesis and lead to the presence of AIMo6024H6. ... 

The ammonium salt of Rh(III) Anderson type heteropolymolybdate [RhMo6024H6] has been prepared and characterized by powder X-ray diffraction, spectroscopic [FTIR-Raman, DRS (UV-visible)] and SEM-EDAX electron microscopy techniques. The water soluble salts were used in the design and preparation of Y-AI2O3 supported catalysts. The varied Mo Rh ratio of both olution and solid samples was measured by AAS technique. The supported oxidic system was characterized by DRS spectroscopy and SEM-EDAX microscopy. The HDS and HYD activity for different bimetallic catalysts was measured in a high-pressure reactor. In addition, some conventional catalysts and some C0M06 and combined supported systems [(RhMoe + AIM06)] have been tested for comparative purposes. The discussion about the performance of the new catalysts is made on the basis of the structural and physicochemical heteropolyanion properties as well as the preparation conditions. 

Our recent research on a large series of hexametallates named Anderson [XM6024H6] , [1] [with M = Mo W or Mo(6-x)Wx and X = Co(III) Cr(III) Rh(III) Fe(III) Ni(II) Cu(II) Te(VI) etc.] [5,6,7] enabled the design and preparation of a variety of mixed bi- or tri-metallic phases which show interesting structural and redox properties, and can be used especially in heterogeneous catalysis. These planar heteropolyanions are precursors that provide well-dispersed bi- or tri-metallic ensembles on supports and have been proved successfully on some catalytic processes such as hydrotreating, ammoxidation, etc. [3,8,9]. 

In the present study a well defined inorganic cluster, hexamolybdoplatinate(IV) heteropolyanion, was employed as a bimetal ensemble precursor, which has a plane Anderson structure. The [PtMoej/MgO catalyst prepared by supporting the hexamolybdoplatinate(IV) heteropliyanion on MgO, followed by calculation at 773K, showed a unique surface structure and better catalytic performance for the alkane-to-alkene conversion than a conventional coimpregnation catalyst.[15]... 

From a catalytic point of view 0.5 is the optimum value [6] whereas the former one (0.17) is the ratio corresponding to the stoechiometry of the Anderson molybdocobaltate or Anderson molybdonickelate [XMoeHeOaJ heteropolyanion. Figure 1 shows the Raman spectra of these CoMo and NiMo solutions before precipitation. They exhibit the characteristic lines of the heptamolybdate anions in solution with the main lines at 942, 895 and 364 cm the line at 1050 cm" corresponding to nitrate anions. Whereas the Mo and CoMo solutions are relatively stable without any precipitation before several hours, a precipitation is rapidly observed for the NiMo based solutions, whatever the metal loading and the Ni/Mo ratio. 

During the past several years we have been working on an Anderson-type heteropolyanion, [Al(OH)6Mo60i8] and exploiting its linking propensity with metal ions-metal complex cations to obtain extended structures of new metal oxide based materials. We have demonstrated a chain-like extended structure based on an Anderson-type polyanion and a lanthanide cation linker in the compound [La(H20)7Al(OH)6Mo60i8] 4 H20." The structure of this... 

Thus far, it has been demonstrated that Anderson-type POM anions can support d-block transition metal coordination complexes that result in both discrete entities and infinite chain-like arrangements and f-block complex cations form versatile one-dimensional chains. S block metal cation (e.g., Na can also serve as a potential linker for assembling Anderson-type heteropolyanions, as described next. 

---