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Chapter 5 Published Results Chapter V Non‐Lanthanide‐Containing POMS 5.A. Tellurium‐Containing POMs 5.A.1. Tellurium‐Containing Polyoxotungstates: The 20‐Tungsto‐4‐ Tellurate(IV) [H2Te4W20O80] 22− and the 15‐Tungstotellurate(IV) [NaTeW15O54] 13− A. H. Ismail, N. H. Nsouli, M. H. Dickman, U. Kortz, J. Clust. Sc. 2009, 20, 453 5.A.1.1. Introduction Polyoxometalates (POMs) represent a large class of nanosized metal-oxygen cluster anions. POMs are remarkable not only in terms of molecular and electronic structural versatility, but also due to their applications in many fields such as catalysis, medicine, electronics, multifunctional materials, and analytical chemistry. 1 In recent years there has been developing interest in these remarkable compounds of tungsten, molybdenum, vanadium, niobium, and tantalum. POM clusters have been known for a long time (first prepared in 1826 by Berzelius) but the mechanism of their formation is still not completely understood, and is often described as “self-assembly”. 1a POMs are formed through condensation reactions of metalate ions in acidified solutions (usually aqueous), through aggregation of octahedral [MO 6 ] building blocks sharing corners, edges, and rarely faces. Many of the reported POMs are based on the well-known Keggin ion ([XM 12 O 40 ] n– ), or lacunary fragments of that structure, where X is the central heteroatom and M the addenda atom. The heteroatom can be one of many elements of the periodic table, most commonly P, As, Si, Ge or B. 165
Chapter 5 Published Results Also tellurium can act as a heteroatom, but the number of such POMs is rather limited. In 1948 Evans reported the first structure of a tellurium containing polyanion, [TeMo 6 O 24 ] 6– . 2 Many other inorganic salts of the Anderson-Evans type molybdotellurate(VI) [TeMo 6 O 24 ] 6– have been reported meanwhile. 3 Molybdotellurates containing organic counter-cations have also been described. 4 The first examples of the Anderson-Evans type tungstotellurate [TeW 6 O 24 ] 6– were reported by Ganelina and Ripan. 5 Tungstotellurates with organic cations have also been reported. 6 Some examples of tellurium(IV) containing POMs are also known. In 1992, Yurchenko reported on a Cu-containing tungstotellurate(IV), but no XRD crystal structure was shown. 7 Between 1998 and 2003 Krebs’ group reported the transition metal containing derivatives [Mn 3 (H 2 O) 10 (β-TeW 9 O 33 ) 2 ] 8– , [Co 3 (H 2 O) 8 (WO 2 )(β-TeW 9 O 33 ) 2 ] 8– , [(V(H 2 O) 3 ) 2 (VO 2 )(WO 2 )(β- TeW 9 O 33 ) 2 ] 6– , [(Zn(H 2 O) 3 ) 2 (WO 2 ) 2 (β-TeW 9 O 33 ) 2 ] 8– , [Cu 3 (H 2 O)(-TeW 9 O 33 ) 2 ] 10– , [Pd 3 (- TeW 9 O 33 ) 2 ] 10– ) as well as several others. 8 In 2001 our group reported the structure of [Cu 3 (H 2 O) 3 (α-TeW 9 O 33 ) 2 ] 10– . 9 In the following year we reported on [Fe 4 (H 2 O) 10 (β- TeW 9 O 33 ) 2 ] 4– and isostructural derivatives of Cr III , Mn II , Co II , Ni II , Cu II , Zn II , Cd II and Hg II . 10 Finally, Pope and coworkers reported the synthesis and structural characterization of [UO 2 (H 2 O) 2 (TeW 9 O 33 ) 2 ] 12– . 11 In the same paper the synthesis of the tungstotellurate(IV) [TeW 9 O 33 ] 8– precursor was reported. This species was characterized by infrared spectroscopy, but no single-crystal X-ray structure was presented. The complete lack of structurally characterized tungstotellurates(IV) without any incorporated transition metals provides an impetus to prepare such species. 12 Herein we report on a novel tungstotellurate containing two pairs of face-shared WO 6 octahedra. 166
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