Synthesis and Structural Characterization of ... - Jacobs University

Chapter 5
Unpublished Results
5.A.2. Tellurium‐Containing Polyoxomolybdates:
The 44‐Molybdo‐24‐Tellurate(IV), [H2Te24Mo44O198] 34−
5.A.2.1. 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), via 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.
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 ever since. 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 Some examples of tellurium(IV)
containing polymolybdates are also known. The manganese derivative of the classical
184