Pillaring of layered double hydroxides with polyoxometalates in aqueous solution without use of preswelling agents

Luminescent Polyoxotungstoeuropate Anion‐Pillared Layered Double Hydroxides

“…The decay curves are well reproduced by a single exponential function from which the 5 D 0 lifetime was extracted (Table 4). For the [EuW 10 O 36 ] 9-anion the decay curve was also monitored for an excitation wavelength within the large broad band in the PLE spectrum, revealing a 5 D 0 lifetime value similar to that obtained for direct excitation in the 5 L 6 Eu 3+ level. In order to further investigate the number of distinct Eu 3+ local coordination sites in each material the PL and the lifetimes of the 5 D 0 excited state were acquired at lowtemperature for the same excitation wavelengths used to record the room-temperature emission.…”

“…The spectra are mainly composed of a series of straight lines ascribed to intra-4f 6 transitions. Only the spectrum of Na 9 [EuW 10 O 36 ] presents a large broad band in the UV spectral region with two main peaks around 270 and 320 nm. The origin of the PLE components may be related to ligand-to-europium charge-transfer (LMCT) transitions resulting from the interaction between the europium ion and the POM, in particular LMCT states associated with O Ǟ Eu and O ǞW transitions as already reported for other polyoxometalates containing Eu 3+ ions.…”

“…The spectra shown in Figure 6 were obtained for different excitation wavelengths, selected according to the excitation spectra in Figure 5, namely direct excitation into the Eu 3+ intra-4f 6 levels ( 5 L 6 , 395 nm), and within the UV band, at 320 nm for K 11 (3 and 4 lines, respectively), suggests that the metal ion local structure is characterized by a low symmetry group without an inversion centre according to the higher intensity of the 5 D 0 Ǟ 7 F 2 transition. The spectrum of Na 9 [EuW 10 O 36 ] has already been reported. [45] The compound prepared by us revealed a different spectrum with singular features, in particular the absence of the 5 D 0 Ǟ 7 F 0 transition and an abnormally high intensity for the 5 D 0 Ǟ 7 F 4 transition.…”

“…[24][25][26][27][28][29][30][31][32] Francesconi and co-workers recently described Mg-Al LDHs intercalated by luminescent polyoxometalate anions with Dawson-like [Eu(H 2 O) 3 [32] In the present work, new polyoxotungstoeuropate anion-pillared layered double hydroxides were prepared by anion exchange reactions of a Zn-Al LDH precursor in nitrate form. Reaction of the wet precursor with the species [EuW 10 O 39 ) 2 ] 11-gave the final materials, which were characterized by powder X-ray diffraction, solid state NMR ( 11 B, 27 Al, 31 P), infrared and Raman spectroscopy. The luminescence properties of the pillared LDHs were investigated in detail and are compared with those of the precursor polyoxotungstoeuropate anions.…”

“…These results show that, regardless of the initial polyoxometalate species in solution, the nature of the final intercalated species can be different, presumably due to the strong host-guest interaction(s). This was especially evident for the anion [EuW 10 O 36 ] 9-, which gave rise to a material containing intercalated anions with a quite different and, as yet, unknown structure. The observed basal spacing was only compatible with the presence of anions smaller than the decatungstometalate species, and the photoluminescence studies reveal the presence of more than one first coordination sphere for the lanthanide ions.…”