Synthesis and Structural Characterization of ... - Jacobs University

Chapter 5
Published Results
5.B. Transition Metal‐Containing Heteropolytungstates:
Copper‐, Cobalt‐, and Manganese‐Containing 17‐Tungsto‐2‐Germanates
N. H. Nsouli, A. H. Ismail, I. S. Helgadottir, M. H. Dickman, J. M Clemente-Juan, U. Kortz, Inorg. Chem. 2009, 48, 5884
5.B.1. Introduction
Polyoxometalates (POMs) are metal-oxide clusters formed of early d-block elements in high
oxidation states (e.g., W 6+ , V 5+ ), and they constitute a unique class of inorganic compounds.
POMs were discovered in 1826 by Berzelius when he noted the formation of a yellow
precipitate after the reaction of ammonium molybdate with phosphoric acid. 1 The chemistry
of POMs is a rapidly growing field because they exhibit a combination of tunable properties,
including composition, size, shape, charge density, redox potentials, and solubility. 2 As a
result, POMs have potential applications in many fields such as catalysis, medicine,
photochemistry, electrochemistry, and magnetism. 3
The mechanism of formation of
polyanions is not well understood and is usually described as self-assembly. One important
goal in POM synthesis is the incorporation of transition metals, lanthanides, organometallic
entities, or any other functional unit(s) into lacunary (i.e., vacant) polyanion precursors,
leading to a tremendous diversity of structures. In particular, polytungstates are of importance
in this respect, as a large number of stable lacunary precursors are known (as opposed to
polymolybdates or polyvanadates).
From a magnetic point of view, POMs containing more than one paramagnetic transition
metal ion in close proximity may exhibit exchange-coupled spins. Polyanions with high-spin
ground states and magnetic anisotropy are of technical interest in areas such as data storage
and magnetic switches and so on. 4 In the past decades, much attention has been devoted to the
synthesis of transition-metal substituted POMs with multiple, spin-coupled magnetic centers
in the area known as molecular magnetism. 5
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