Vibrational investigations of polyoxometalates. 2. Evidence for anion-anion interactions in molybdenum(VI) and tungsten(VI) compounds related to the Keggin structure

Abstract

A systematic study of the cation-size effect on the vibrational spectra of a-and ß-^ ^"" polyoxoanions has been performed (X = Bnl, SiIV, GeIV, Pv, Asv; M = MoVI, WVI). The M-Od stretching frequencies decrease as the cation size increases. This is attributed to a weakening of anion-anion interactions of the electrostatic type. These interactions vanish for only interanionic oxygen-oxygen distances as long as 6 Á (tetrabutylammonium (TBA) salts). For these polyanions, the approximation for the isolated anion strictly holds with large counterions such as TBA. In addition, some preparations of polyanions are described for the first time.

Influence of peroxometallic intermediaries present on polyoxometalates nanoparticles surface on the adipic acid synthesis

“…3 compiles the comparison among both spectra (obtained from fresh and used CsPMo). The Raman spectra indicate that the catalyst structure before and after the reaction is the same, characteristic of the Keggin structure [28,29].…”

Luminescent Polyoxotungstoeuropate Anion‐Pillared Layered Double Hydroxides

“…The intercalation of polyoxoanions into the layered double hydroxide was clearly shown by the presence in the infrared and Raman spectra of several bands in the range 700-1200 cm -1 , on top of the lattice vibrations of the host ( Figure 2, Table 3), assigned to X-O stretch (X = B or P), the terminal W=O stretch (918-989 cm -1 ), and the W-O-W corner or edge-shared stretching modes (700-900 cm -1 ). [38,39] 3 ], gives rise to a much broader peak (fwhm 440 Hz) at 0.1 ppm (Figure 3). [31] As described in ref.…”

The structure of molybdenum-heteropoly acids under conditions of gas-phase selective oxidation catalysis: a multi-method in situ study

“…IR spectroscopy was chosen as the method of analysis, because unlike calorimetry or TPD, it gives information on the nature of the sites and with the right probes is fairly sensitive to small energetic differences between sites. IR spectroscopy has been applied extensively for the structural characterization of heteropoly compounds at various temperatures and degrees of dehydration [62,63,64,65,66,67,68,69]. This method in addition delivers information on the structure of a sample after each treatment by investigating the lowfrequency range of the IR spectrum.…”