The solution chemistry of aluminum has long interested scientists due to its relevance to materials chemistry and geochemistry. The dynamic behavior of large aluminum-oxo-hydroxo clusters, specifically [Al O (OH) (H O) ] (Al ), is the focus of this paper. Al NMR, H NMR, and H DOSY techniques were used to follow the isomerization of the ϵ-Al in the presence of glycine and Ca at 90 °C. Although the conversion of ϵ-Al to new clusters and/or Baker-Figgis-Keggin isomers has been studied previously, new H NMR and H DOSY analyses provided information about the role of glycine, the ligated intermediates, and the mechanism of isomerization. New H NMR data suggest that glycine plays a critical role in the isomerization. Surprisingly, glycine does not bind to Al clusters, which were previously proposed as an intermediate in the isomerization. Additionally, a highly symmetric tetrahedral signal (δ=72 ppm) appeared during the isomerization process, which evidence suggests corresponds to the long-sought α-Al isomer in solution.
One-dimensional Al,Na Magic-Angle-Spinning (MAS) NMR and Al Multiple-Quantum Magic-Angle-Spinning NMR (MQMAS) measurements are reported for the δ-isomer of the Al Keggin structure at high spinning speed and 14.1 T field. Values for the C and η parameters are on the same scale as those seen in other isomers of the Al structure. Density functional theory (DFT) calculations are performed for comparison to the experimental fits using the B3PW91/6-31+G* and PBE0/6-31+G* levels of theory, with the Polarizable Continuum Model (PCM).
What was the initial goal of this collaborative project?Our group wanted to understand the role of glycine in the isomerization of the Al 13 Keggin clusters. This goal was accomplished using diffusiono rdered spectroscopy to monitor the size of the species to which glycine was bound. Glycine not only gave a 1 HNMR signal, but some collaborators previously showed that it enhances formation of the rotated-cap isomers.What is the most significant result of this research?An ew tetrahedral 27 Al NMR signal was uncovered that was assigned to the long-sought a-isomer of the Al 13 Keggin ion series.Only the e-a nd a-isomers can produce such as harp signal, because it requires high symmetry in the central Al(O) 4 site. The intermediate isomers do not have such symmetry.T he result matches predictions and is consistent with the mineral form, zunyite.
Who designed the cover and what was the inspiration?The cover was designed and created by the first author,D r. Anna F. Oliveri. She has recently begun creating structural images of clusters in solution by using layered tissue paper.A lthough art has always been ah obby for Anna, she has only recently begun creating table-of-content and cover images.
This artwork depicts an artist's rendition of the α‐AlO4Al12(OH)24(H2O)127+ Keggin cluster with glycine molecules ligating the surface. The artist depicts aluminum ions as silver spheres, oxygen atoms as red spheres, carbon as black spheres, and nitrogen as green spheres (hydrogen atoms were omitted for clarity). More information, including insight on the other aluminum clusters that glycine stabilizes, can be found in the Communication by P. H.‐Y. Cheong, L. Pan, W. H. Casey et al. on page 18682 ff.
Invited for the cover of this issue are Anna Oliveri from Southern Oregon University, USA, and co-workers. The cover image shows the outer surface of a nanoscale U 28 cage cluster.
The Front Cover shows an artistic representation of the outer surface of a nanoscale U28 cage cluster. Three uranyl moieties connected by phosphonic bridges (μ3‐HPO3) can be seen in the image, which depicts μ3‐HPO3 conformations with and without an associated cation directly inside the cage. 1H NMR spectroscopy provides a direct way to monitor this conformational change as cations like sodium are introduced into the solution. Yellow, red, green, white, and purple spheres represent uranium, oxygen, phosphorus, hydrogen, and sodium, respectively. (Artist: Dr. Anna F. Oliveri). More information can be found in the https://doi.org/10.1002/ejic.201701074 For more on the story behind the cover research, see the https://doi.org/10.1002/ejic.201701349.
The conformational dynamics of nanometer-sized actinide ions are exceptionally sensitive to the choice of countercations. A new means of following these dynamics in solution is presented that follows 1 H NMR signals. The direct bond between hydrogen and phosphorus atoms in the bridging phosphonic groups of the [(UO 2 ) 28 (O 2 ) 20 (PHO 3 ) 24 (H 2 O) 12 ] 32-(U 28 ) cluster allows unparalleled recording of the orientations of these bridges in situ. The μ 3 -PHO 3 bridges are organized into two supersets of conformers (facing inward vs. outward from the cluster), but each of these supersets additionally have four [a]
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