Preyssler Polyoxometalate (POM) is a
doughnut shaped heteropolytungstate constructed from
five PW6O22 units, each of which is derived from the
lacunary fragment of Keggin anion, α-[PW12O40]3-.
They are the first examples of POMs with an internal
cavity within which remains encrypted a sodium cation.
This sodium cation can be replaced for trivalent
lanthanide cations and other cations of similar size.
Hence, Preyssler POM is also called inorganic crown
ethers or inorganic cryptrates. Preyssler POM is a redox
active cluster which is active over a wide range of pH
from 0 to 10. As said, the encrypted lanthanide is usually
in +III oxidation state. However, Europium and Cerium
encrypted POMs shows certain behaviour that lead the
chemists to predict +II and +IV Oxidation states
respectively . However, XANES, EXAFS, CV confirmed
an oxidation state of +III in the above cases. Cyclic
voltammetry reveals an extensive redox chemistry of the
lanthanide encrypted POMs. Dyprosium and Holmiun
encrypted POMs are found to exhibit single molecular
magnetism. The study on the surface of Preyssler POM
is highly explored and has ruled almost a decade.
Various reseachers employed various techniques like
layer-by-layer mechanism and Ionic self-Assembly
process for the construction of multilayer composites
and nanostructures and subjected them to the study of
electrochromism. Preyssler POM has been for lesser
number of times employed as a building block for the
construction of extended strutures, owing to the
discrepancy in obtaining single crystal. A handful of
examples have been elucidated below. The example of
the lacunary Preyssler POM and an extended structure
based on it have also been set up. Preyssler POM has
been observed to make its most remarkable contribution
in the field of catalysis. Preyssler POM is found to be a
green catalyst and has efficiently catalysed a huge
number of organic reactions. The medicinal value of
Preyssler POM has also been established. A number of
theoretical studies have also been performed.
Keywords :
Preyssler, Polyoxometalates, Cryptohydration, Hysterysis, Electrochromism
