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8412288 
Journal Article 
Composition of aluminum phosphate solutions. Evidence from Aluminum-27 and Phosphorus-31 nuclear magnetic resonance spectra 
Wilson, MA; Collin, PJ; Akitt, JW 
1989 
Yes 
Analytical Chemistry
ISSN: 0003-2700
EISSN: 1520-6882 
61 
11 
1253-1259 
English 
Low- (2.11 T) and high-field (9.4 T) 27Al and 31P nuclear magnetic resonance (NMR) spectrometry has been used to study the structure and reactivity of aluminum chloride solutions in the presence and absence of OH−, H3PO4, H2PO4−, HPO42-, and PO43- species. Evidence is presented for the existence of higher molecular weight complexes than the [AlO4Al12(OH)24(H2O)12]7+ cation in the presence of hydroxide ion. At high field, at least five types of complexed aluminum are observed by 27Al NMR in the presence of phosphate species. Three species at -3.6, -6.2, and -7.6 ppm are observed In solutions containing predominantly H3PO4, and two species are observed in the presence of H2PO4− at -3.6 and -7.6 ppm. It is proposed that the species at -3.6 ppm has a Al:P ratio of 1. At least 11 resonances from different complexes in aluminum phosphate solutions can be observed by 31P NMR. It is shown that principal differences in chemical shift are due to the nature of the ligand (L = H3PO4, H2PO4−, HPO42-) rather than the number of ligands (L1, L2, L3, Ln, etc.) in the complexes. High-temperature (up to 95 °C) studies show that the complexes can exchange ligand without equilibrating with uncomplexed aluminum. It is also shown that the acidities of the complex solutions are greater than those of the unmixed solutions alone. This acidity mainly results from dissociation of water molecules in the coordination sphere of aluminum. © 1989, American Chemical Society. All rights reserved.