Synthesis and Structural Characterization of ... - Jacobs University

Chapter 3
Published Results
Chapter III
Lanthanide‐Containing POMs
3.A. Lanthanide‐Containing Isopolytungstates:
3.A.1. The 22‐Isopolytungstate Fragment [H2W22O74] 14− Coordinated to
Lanthanide Ions
A. H. Ismail, M. H. Dickman, U. Kortz, Inorg. Chem. 2009, 48, 1559
3.A.1.1. Introduction
Polyoxometalates (POMs) represent a large class of nanosized metal-oxo anions. POMs are
remarkable not only in terms of molecular and electronic structural versatility but also
because of their reactivity and relevance in fields such as photochemistry, analytical
chemistry, clinical chemistry, magnetism, catalysis, biology, medicine, and materials science. 1
Polyoxoanions which result from the condensation of metalate anions in acidified solutions
(usually aqueous) can efficiently absorb light in the near UV-vis region and can therefore be
used as photocatalysts. 2 The intrinsic chemical properties of POMs as electron acceptors or as
very strong Brønsted acids (in their protonated form) make them useful as catalysts in organic
transformations, and their abilities to form peroxo complexes or to serve as supports for
catalytically active metal ions in high oxidation states are particularly useful in oxidation
reactions. 1b,3
Although the first POM was synthesized already in 1826 by Berzelius, 1a the mechanism of
POM formation is still not completely understood and is often described as a self-assembly.
POMs can usually be isolated from aqueous solution as solid salts with appropriate counter
cations which may be alkali metal cations (e.g., Li + , Na + , K + , Rb + , Cs + ) or organic cations
(e.g., guanidinium, alkylamines). Two main types of POMs are known, based on their
chemical composition: isopoly and heteropoly anions. Isopolyanions are represented by the
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