Composition of aluminum phosphate solutions. Evidence from aluminum-27 and phosphorus-31 nuclear magnetic resonance spectra

• Published in: Analytical chemistry (Washington) Vol. 61; no. 11; pp. 1253 - 1259
• Main Authors: Wilson, Michael A, Collin, Philip J, Akitt, J. W
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.06.1989
• Subjects: 400201 - Chemical & Physicochemical Properties; ALUMINIUM 27; ALUMINIUM CHLORIDES; ALUMINIUM COMPOUNDS; ALUMINIUM ISOTOPES; ALUMINIUM PHOSPHATES; AQUEOUS SOLUTIONS; Chemistry; CHLORIDES; CHLORINE COMPOUNDS; DISPERSIONS; Exact sciences and technology; HALIDES; HALOGEN COMPOUNDS; Inorganic chemistry and origins of life; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ISOTOPES; LIGHT NUCLEI; MAGNETIC RESONANCE; MEASURING METHODS; MIXTURES; NUCLEAR MAGNETIC RESONANCE; NUCLEI; ODD-EVEN NUCLEI; OXYGEN COMPOUNDS; PHOSPHATES; PHOSPHORUS 31; PHOSPHORUS COMPOUNDS; PHOSPHORUS ISOTOPES; Preparations and properties; RESONANCE; Salts; SOLUTIONS; STABLE ISOTOPES; Cationic complex; Phosphates; Aluminium III Chlorides; Low field; Trivalent metal Complexes; Inorganic polymer; Metal Complexes; Chemical equilibrium; Hydroxo complex; Aqua complex; Preparation; High field; Polynuclear complex; Aluminium «III» Complexes; Aqueous solution; Chemical reactivity; NMR spectrum
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/ac00186a016

Low- (2.11 T) and high-field (9.4 T) {sup 27}Al and {sup 31}P 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{sup {minus}}, H{sub 3}PO{sub 4}, H{sub 2}PO{sub 4}{sup {minus}}, HPO{sub 4}{sup 2{minus}}, and PO{sub 4}{sup 3{minus}} species. Evidence is presented for the existence of higher molecular weight complexes than the (AlO{sub 4}Al{sub 12}(OH){sub 24}(H{sub 2}O){sub 12}){sup 7+} cation in the presence of hydroxide ion. At high field, at least five types of complexed aluminum are observed by {sup 27}Al NMR in the presence of phosphate species. Three species at {minus}3.6, {minus}6.2, and {minus}7.6 ppm are observed in solutions containing predominantly H{sub 3}PO{sub 4}, and two species are observed in the presence of H{sub 2}PO{sub 4}{sup {minus}} at {minus}3.6 and {minus}7.6 ppm. It is proposed that the species at {minus}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 {sup 31}P NMR. It is shown that principal differences in chemical shift are due to the nature of the ligand (L = H{sub 3}PO{sub 4}, H{sub 2}PO{sub 4}{sup {minus}}, HPO{sub 4}{sup 2{minus}}) rather than the number of ligands (L{sub 1}, L{sub 2}, L{sub 3}, L{sub n}, etc.) in the complexes.