Descrição
Novel luminescent polyoxometalate anion-pillared layered
double hydroxides (LDHs) were prepared by aqueous ion exchange
of a Zn–Al LDH precursor in nitrate form with the
europium-containing polyoxotungstate anions [EuW10O36]9–,
[Eu(BW11O39)(H2O)3]6– and [Eu(PW11O39)2]11–. The host–
guest interaction has a strong influence on the nature of the
final intercalated species, as evidenced by elemental analy-
Introduction
Layered double hydroxides are an important class
of ionic lamellar solids with the general formula
[M2+
1–xM3+
x(OH)2](Am–)x/m·nH2O (M2+ = Mg2+, Zn2+,
Ni2+ etc., M3+ = Al3+, Cr3+, Ga3+ etc).[1] The positively
charged layers, containing divalent and trivalent cations in
octahedral positions, are separated by charge balancing
anions and water molecules. The water molecules are connected
to both the metal hydroxide layers and the interlayer
anions through extensive hydrogen bonding. A range of organic
or inorganic guests may be incorporated into LDHs
by either ion exchange, direct synthesis or hydrothermal reconstruction
of calcined precursors.[2,3] In particular, intercalation
chemistry has been explored with the aim of introducing
catalytically active sites and photo- and electroactive
species. Many different types of metal coordination compounds
and oxometalates have been immobilized in LDHs,
including phthalocyanines, cyanocomplexes, oxalate complexes
and polyoxometalates (POMs).[4]
The first report of LDHs containing polyoxometalates
concerned their use as exhaust gas and hydrocarbon conversion
catalysts.[5] Since then, a variety of iso- and heteropolyanions
with different nuclearities and structures (Keggin,
Dawson, Preyssler, Finke) have been incorporated into the
interlayer space of these materials.[6–18] Two factors assume
considerable importance for the successful intercalation of
polyoxometalates into an LDH compound. First, the heteropoly
species should carry sufficient charge in order to be
[a] Department of Chemistry, CICECO, University of Aveiro,
3810-193 Aveiro, Portugal
E-mail: helena@dq.ua.pt
[b] Department of Physics, CICECO, University of Aveiro,
3810-193 Aveiro, Portugal
© 2006 Wiley-VCH Verlag 726 GmbH & Co. KGaA, Weinheim Eur. J. Inorg. Chem. 2006, 726–734
sis, powder X-ray diffraction (XRD), infra-red (IR) and Raman
spectroscopy, solid state magic-angle spinning (MAS) 11B
and 31P NMR spectroscopy, and photoluminescence spectroscopy. FCT - POCTI
; Pillinger, Martyn 
