Synthesis and Structural Characterization of ... - Jacobs University

Chapter 5
Published Results
5.B.5. Conclusions
We have prepared the three dimeric, sandwich-type tungstogermanates [Cu 3 (H 2 O)(B-β-
GeW 9 O 33 (OH))(B-β-GeW 8 O 30 (OH))] 12– (29), [Co(H 2 O) 2 {Co 3 (B-β-GeW 9 O 33 (OH))(B-β-
GeW 8 O 29 (OH) 2 )} 2 ] 20– (30) and [Mn(H 2 O) 2 {Mn 3 (H 2 O)(B-β-GeW 9 O 33 (OH))(B-β-
GeW 8 O 30 (OH))} 2 ] 22– (31) in simple, one-pot reactions using aqueous, buffered pH 4.8
medium. All three polyanions 29-31 have been fully characterized by single-crystal X-ray
diffraction, FTIR, elemental analysis, and thermogravimetric analysis. The magnetic
properties of K-29, K-30 and K-31 have been also studied. We used Cu 2+ , Co 2+ or Mn 2+ to [γ-
GeW 10 O 36 ] 8– ratios of 1.5:1 for the synthesis of 29-31. Our results demonstrate that the
reactivity of [γ-GeW 10 O 36 ] 8– with 3d metal ions in an aqueous acidic medium is similar to that
of its silicon analogue [γ-SiW 10 O 36 ] 8– . Both species can easily rearrange to different isomers
of trilacunary “XW 9 ” and tetralacunary “XW 8 ” fragments which coordinate to the d-block
metal ions, resulting in sandwich-type assemblies. We have shown that [γ-GeW 10 O 36 ] 8– is a
highly flexible lacunary POM precursor which can adjust to the specific coordination
requirements of the respective type of transition metal ion (e.g. Cu 2+ vs Co 2+ ). We believe that
29-31 could also be interesting for homogeneous or heterogeneous oxidation catalysis
applications. Currently, we are exploring the reactivity of [γ-GeW 10 O 36 ] 8– with other d- and f-
block metal ions.
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