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Structural Chemistry of Akdalaite, Al10O14(OH)2, the Isostructural Aluminum Analogue of Ferrihydrite

1
Department of Geosciences, Stony Brook University, Stony Brook, NY 11794, USA
2
Department of Chemistry, Stony Brook University, Stony Brook, NY 11794, USA
3
Joint Photon Sciences Institute, Stony Brook University, Stony Brook, NY 11794, USA
4
Department of Physics, Farmingdale State College, Farmingdale, NY 11735, USA
5
EAG Laboratories, 625-B, Alfred Nobel Dr, Hercules, CA 94547, USA
6
Department of Materials Science and Chemical Engineering, Stony Brook University, Stony Brook, NY 11794, USA
7
Mineral Physics Institute, Stony Brook University, Stony Brook, NY 11794, USA
*
Author to whom correspondence should be addressed.
Crystals 2019, 9(5), 246; https://doi.org/10.3390/cryst9050246
Received: 21 April 2019 / Revised: 7 May 2019 / Accepted: 9 May 2019 / Published: 12 May 2019
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Abstract

As part of an effort to characterize clusters and intermediate phases likely to be encountered along solution reaction pathways that produce iron and aluminum oxide-hydroxides from Fe and Al precursors, the complete structure of Al10O14(OH)2 (akdalaite) was determined from a combination of single-crystal X-ray diffraction (SC-XRD) data collected at 100 K to define the Al and O positions, and solid-state nuclear magnetic resonance (NMR) and neutron powder diffraction (NPD) data collected at room temperature (~300 K) to precisely determine the nature of hydrogen in the structure. Two different synthesis routes produced different crystal morphologies. Using an aluminum oxyhydroxide floc made from mixing AlCl3 and 0.48 M NaOH, the product had uniform needle morphology, while using nanocrystalline boehmite (Vista Chemical Company Catapal D alumina) as the starting material produced hexagonal plates. Akdalaite crystallizes in the space group P63mc with lattice parameters of a = 5.6244(3) Å and c = 8.8417(3) Å (SC-XRD) and a = 5.57610(2) Å and c = 8.77247(6) Å (NPD). The crystal structure features Al13O40 Keggin clusters. The structural chemistry of akdalaite is nonideal but broadly conforms to that of ferrihydrite, the nanomineral with which it is isostructural. View Full-Text
Keywords: akdalaite; ferrihydrite; solution synthesis; X-ray diffraction; NMR spectroscopy; bond valence sums akdalaite; ferrihydrite; solution synthesis; X-ray diffraction; NMR spectroscopy; bond valence sums
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Parise, J.B.; Xia, B.; Simonson, J.W.; Woerner, W.R.; Plonka, A.M.; Phillips, B.L.; Ehm, L. Structural Chemistry of Akdalaite, Al10O14(OH)2, the Isostructural Aluminum Analogue of Ferrihydrite. Crystals 2019, 9, 246.

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