Keggin silicotungstate

The di-copper-substituted y-Keggin silicotungstate [y-H2SiWio036Cu2( j,-l, 1-N3)2]4- could act as an effective homogeneous catalyst for the oxidative homocoupling of various kinds of alkynes, including aromatic, aliphatic and heteroatom-containing ones (6.8) [108] ... 

Y. Goto, K. Kamata, K. Yamaguchi, K. Uehara, S. Hikichi, N. Mizuno, Synthesis, structural characterization, and catalytic performance of dititanium-substituted y-Keggin silicotungstate, Inorg. Chem. 45 (2006) 2347. 

Evidence supporting the Bohlmann mechanism was provided by the direct involvement of a dicopper(II)-substituted y-Keggin silicotungstate (1), shown in Fig. 1, in catalytic oxidative alkyne-coupling reactions the catalyst was shown to give excellent yields of the expected conjugated diynes using a wide variety of alkynes, an example is shown in Scheme 10 [89]. 

The possibilities of POMs compositions and structures are virtually enormous, and the number of these molecules actually prepared and characterized continues to grow unabated. However, examination of their short electrochemical studies, which are becoming a usual part of their characterization, shows that a limited selection of representative groups of POMs is sufficient for a description of the main electrochemical behaviors of this class of chemicals. Therefore, a-Keggin- and Dawson-type heteropolyanions of phosphotungstate, silicotungstate, phosphomolybdate, and silicomolybdate mixed addenda heteropolyanions, and transition-metal substituted heteropolyanions including sandwich-type derivatives were selected for the present article. 

The y-isomer Keggin-type silicodecatungstate [y-SiWio036]8- has been used as a structural motif for di-metal-substituted POMs with bis- i-oxo(or hydroxo)-dimetal cores [97-102]. The di-iron-substituted silicotungstate [y-SiWi0 Fe(OH2) 2O3g]6 was synthesized by the reaction of [y-SiWi0O36]8- with Fe(N03)3 in acidic aqueous... 

Figure 14. Polyhedral representation of diiron-substituted Keggin-type silicotungstate.

Fig. 1 Heteropoly acid structures (a) Ball and stick model of the silicotungstic Keggin anion (SiWi2O40 " ). (b) Space filling model of the secondary crystalline structure of Keggin HPA with base-centered cubic arranged cavities containing H502 cations (red = O, gray = W, blue = H, purple = P or Si)...

---