Cover Picture: Angew. Chem. Int. Ed. 19/2002

Abstract

The cover picture shows a novel hierarchic endohedral clusterization of H 2 O molecules in the form of a dodecahedron ((H 2 O) 20 , red), a further ™mounted∫ dodecahedron (green), and a rhombicosidodecahedron ((H 2 O) 60 , yellow). The shell/host (Mo atoms blue, O red) is built up by 12 pentagonal {(Mo)Mo 5 } type building blocks (one is highlighted as a blue ring),which are connected by 30 Mo V 2 linkers with the consequence that 20 nanosized Mo 9 O 9 pores/rings of classical crown ether quality are formed in which 20 guanidinium cations are encapsulated (C black, N green). The Mo V 2 type linkers are stabilized by PO 2 H 2 À /SO 4 2À ligands (P/S purple). As the clusterization in the cavity takes place after filling the receptors/pores at the cluster surface with guests, a process is modeled by which a cell converts an extracellular molecular signal into a response. The representative red ring below the blue ring is marked out by the 60 H 2 O ligands coordinated to the pentagonal Mo units, which altogether form a rhombicosidodecahedron (not shown completely). As the geometric forms described are those of Platonic and Archimedean solids Plato and Archimedes feel involved. Further details are reported by A. M¸ller et al. on p. 3756 ff.

Preparation of Phase-Pure M1 MoVTeNb Oxide Catalysts by Hydrothermal Synthesis—Influence of Reaction Parameters on Structure and Morphology

“…2c) showing a band at 450 nm and absorption below 300 nm, could therefore also be interpreted in terms of the formation of molybdenum-blue-type clusters. The latter interpretation would be in agreement with the existence of the band at 874 cm -1 in the Raman spectrum, which is also characteristic for such clusters [38]. Finally, the peak at 644 cm -1 indicates the presence of free telluric acid in the MoVTe filtrate.…”

“…The band at 1010 cm -1 may indicate partial substitution of Mo by V in the Anderson anion [42], which is also supported by a shift of the absorption maximum in the UV/Vis spectrum to lower energies (Fig. 2c) [38]. The spectrum of the MoVTe filtrate (Fig.…”

“…The bands due to ammonium heptamolybdate are reduced in intensity and two new bands at 824 and 874 cm -1 appear. The band at 874 cm -1 is reminiscent of the peaks observed in Raman spectra of supra-molecular polyoxomolybdates or mixed molybdenum-vanadium clusters [38,39]. Such clusters are composed of {(Mo)Mo 5 } structural units, which can be regarded as structural building block of the M1 structure.…”

Monitoring the Growth of Polyoxomolybdate Nanoparticles in Suspension by Flow Field-Flow Fractionation

“…In general, reduced molybdates assemble into nanometric species (Figure 1a). Light-scattering, small-angle X-ray scattering (SAXS), and microscopy show slow aggregation of Na 15 The key methodology of our study is field-flow fractionation (FFF), a flow-based, chromatography-like separation and sizing technique that can monitor changes in the particle-size distribution of a suspension in situ. FFF is conducted in a thin, empty channel, with separation based on relative hydrodynamic behavior.…”

“…24 We used FlFFF to monitor the evolution of molybdate nanoparticles in a {Mo 132 } suspension prepared by Müller's procedure. 7,15,16 Under our FlFFF conditions, 25 soluble species and particles smaller than 3 nm are swept to the waste stream by the cross-flow, while larger particles are separated and eluted through a UV-visible detector. FlFFF fractograms monitoring the absorbance of the eluate at 455 nm are shown in Figure 1b.…”