Lead Hydro Sodalite [Pb2(OH)(H2O)3]2[Al3Si3O12]2: Synthesis and Structure Determination by Combining X-ray Rietveld Refinement,1H MAS NMR FTIR and XANES Spectroscopy

Abstract

Ion exchange of the sodium hydro sodalites [Na3(H2O)4]2-[Al3Si3O12]2 [Na4(H3O2)]2[Al3Si3O12]2 and [Na4(OH)]2[Al3Si3O12]2 with aqueous Pb(NO3)2 solutions yielded, whichever reactant sodalite phase was used, the same lead hydro sodalite, [Pb2(OH)-(H2O)3]2[Al3Si3O12]2. Thus, in the case of the non-basic reactant [Na3(H2O)4]2-[Al3Si3O12]2 an overexchange occurs with respect to the number of nonframework cationic charges. Rietveld structure refinement of the lead hydro sodalite based on powder X-ray diffraction data (cubic, a = 9.070 A, room temperature, space group P43n) revealed that the two lead cations within each polyhedral sodalite cage form an orientationally disordered dinuclear [Pb2(micro-OH)(micro-H2O)(H2O)2]3+ complex. Due to additional lead framework oxygen bonds the coordination environment of each metal cation (CN 3+3) is approximately spherical, and clearly the lead 6s electron lone pair is stereochemically inactive. This is also suggested by the absence of a small peak at 13.025 keV, attributed in other Pb2+-O compounds to an electronic 2p-6s transition, in the PbL3 edge XANES spectrum. 1H MAS NMR and FTIR spectra show that the hydrogen atoms of the aqua hydroxo complex (which could not be determined in the Rietveld analysis) are involved in hydrogen bonds of various strengths.

Confinement of Highly Luminescent Lead Clusters in Zeolite A

“…Each Pb c is coordinated to ca. 2.5 water molecules at a distance of 2.64 Å, which is in agreement with the Pb–OH 2 distances reported elsewhere. , Upon dehydration at 200 °C, a part of the Pb 4 (OH 2 ) x clusters swaps their water ligands for hydroxyl groups, since we found a shorter average Pb c –oxygen distance (Pb c –Ox) of 2.59 Å. This is in line with previously reported Pb–OH distances (2.50 Å). , The alteration from water to hydroxyl ligands may result from a hydrolysis reaction of the zeolitic water in the presence of metal ions, as described in the literature .…”

“…2.5 water molecules at a distance of 2.64 Å, which is in agreement with the Pb–OH 2 distances reported elsewhere. , Upon dehydration at 200 °C, a part of the Pb 4 (OH 2 ) x clusters swaps their water ligands for hydroxyl groups, since we found a shorter average Pb c –oxygen distance (Pb c –Ox) of 2.59 Å. This is in line with previously reported Pb–OH distances (2.50 Å). , The alteration from water to hydroxyl ligands may result from a hydrolysis reaction of the zeolitic water in the presence of metal ions, as described in the literature . In Pb 0.5 -LTA samples heat-treated at 200 °C, 17% of Pb atoms are now forming a combination of the aforementioned Pb 4 (OH 2 ) x ( x = 2 to 4) and Pb 4 (OH) y ( y = 2 to 4) tetrahedral clusters, with each Pb atom coordinated to 2 OH groups.…”

“…The tetrahedral Pb 4 clusters formed inside the sodalite cages of the Pb-exchanged LTA zeolites are all coordinated at their faces to 2-to-4 extra-framework O-based ligands (Figure ). Even though the occurrence of stable cubane-like Pb clusters has been claimed in computational studies on Pb clusters in the gas , and liquid phase and experimentally characterized in similar zeolite systems, − their interatomic distances significantly differ from the Pb clusters described in this work. In particular, larger Pb–Pb distances in the range of 3.3 Å were always observed, and the photoluminescence properties of such Pb species were not addressed.…”

“…EXAFS Pb L 3 -edge k 3 -weighted data of Pb 0.5 -LTA having different hydration states and their phase-corrected Fourier transforms (FTs), depicted in Figures A and 4B, show two main peaks in the range of 1.5–4 Å in the FT profiles (Figure B). The first peak (1.5–2.9 Å) can mainly be attributed to several oxygen neighbors, whereas the second multipeak (3.0–4.0 Å) corresponds to a mixed contribution of Si/Al and Pb neighbor atoms. ,− Whereas the intensities of the two peaks remain rather constant up to 200 °C, a sharp inversion of their relative intensities is observed at 450 °C, suggesting that significant structural changes are occurring upon dehydration. This is corroborated by the XANES analysis (Pb-L 3 ) (Figure S13), which shows that only the Pb 0.5 -LTA dehydrated at 450 °C has a small shoulder at 13 027 eV on top of the 13 037 eV present in the sample at all hydration states (hydrated and dehydrated at 200 and 450 °C).…”

Spatial Distribution and Speciation of Lead around Corroding Bullets in a Shooting Range Soil Studied by Micro-X-ray Fluorescence and Absorption Spectroscopy

“…Further, a pre-edge feature is clearly visible at 13 029 eV. Bargar et al (31), Eiden-Assmann et al (33), and Rao and Wong (32) assigned it to the electronic transition 2p f 6s. If Pb is tetravalent, 6s is a free electronic orbital and this peak always occurs (31).…”