Multinuclear magnetic resonance studies of the hydrolysis of aluminium(III). Part 8. Base hydrolysis monitored at very high magnetic field

Abstract

New studies of base-hydrolysed aluminium(iii) solutions were made using high-field 'H and n.m.r. spectroscopy. The increased sensitivity of the modern equipment has allowed data t o be obtained at concentrations as l o w as 1 x 1 0-3 rnol dm-3, some of it quantitative, and the 'H n.m.r. spectra of solutes transferred to non-aqueous solvents has provided new structural data. The results enable it t o be stated quite unequivocally that the tridecameric cation [AIO,AI,,(OH),,( H,0),,I7+ is the principal species formed at lower concentrations, and is virtually the only one formed below 20 x 1 0-3 rnol dm-3. A t concentrations higher than this, and at intermediate levels of hydrolysis, an oligomeric mixture is formed with a stoicheiometry close t o {[AI(OH),~,]~f}, and which could be composed of species such as {AI,(OH),] +, [AI,(OH),] +, [A1,(0H),,]'+, and [AI,(OH),,I2+. Partial deuteriation produces isotopic splitting of the proton resonances of bound water which allows these t o be distinguished from the resonances of OH-bridge protons. A n indication of fine structure due t o hydrogen-deuterium substitution o n AIO, fragments is also obtained which favours the more condensed structures and this is in accord with the ease with which the oligomer is converted into the tridecamer o n simple dilution. It is now certain that the dihydroxo-bridged dimer found in the solid state is not a significant constituent of these solutions. Oxygen-I 7 n.m.r. data are also briefly reported.

The Al Pillaring of Clays. Part I. Pillaring with Dilute and Concentrated Al Solutions

“…It leads to a small increase of octahedral AI (0 ppm), but a drastic increase of the concentration of NMRsilent A1. Presumably, NMR-silent oligomeric complexes are formed, composed of [AI(OH)2.5] ~247 units (Akitt and Elders, 1988), the average positive charge per AI being very close to that of A1 in the Keggin ion (+0.54). The structure of these polymeric species cannot be elucidated on the basis of NMR results alone.…”

“…NMR spectroscopy usually detects three lines: monomeric, octahedral AP + at 0 ppm, dimeric to pentameric (oligomeric) AI 3+ at around 5 ppm, and tetrahedral AP § at 62.5 ppm (Akitt et al, 1972;Akitt and Elders, 1988). The latter is ascribed to the Keggin ion, A major part of the Al is, however, NMR-silent (Sterte, 1988).…”

Aluminum speciation of coagulants with low concentration: Analysis by electrospray ionization mass spectrometry

“…Many analytical methods have been used to characterize and quantify aluminum species. Traditional methods include potentiometric titration [4], Al-Ferron timed spectrophotometric assay [5,6] and 27 Al nuclear magnetic resonance ( 27 Al NMR) spectroscopy [7,8]. In addition, X-ray diffraction [9], Raman spectroscopy [10] and X-ray photoelectron spectroscopy [11] are used as aluminum speciation analysis.…”

Ispitivanje reakcija hidrolize i kompleksiranja u rastvorima aluminijum(III)-jona i nekih fluorohinolona metodom elektrosprej-tandem masene spektrometije

“…Мали пик на 0,34 ppm се уочава у pH опсегу од 3 до 5 и приписује се моно хидролизованим врстама Al(OH)(H 2 O) 5 2+ формираним у првој фази хидролизе, док се широки пик нижег интензитета јавља на 4,5 ppm, за pH>4,0 и приписује се врстама мале молекулске масе Al 2 (OH) 2 . Сходно литературиним подацима [120][121][122][123][124][125] могуће је наћи мономере до 9 ppm. У овим експериментима нису нађени сигнали за однос S/N већи од 3, где је S/N однос сигнала и шума (signal to noise).…”

“…У исто време већа вредност радијуса повећава гасно фазну концентрацију површински активних комплекса и смањује површински неактивне комплексе. Поређењем резултата ESI MS, NМR и потенциометријских мерења закључује се да се најбоље слагање [112,121,132] добија код хидролитичких врста мале молекулске масе, што је последица чињенице да густина и вискозност у растворима полимеризованог алуминијума расту, што за последицу има пораст површинског напрезања капљице. Зато су више енергије потребне за одвајање врста више молекулске масе из капљице.…”