Complexes of aluminium with aminopolycarboxylic acids: ²⁷Al NMR and potentiometric studies

Abstract

The reactions of A13+ ion with a series of aminopolycarboxylic acids containing coordinating sites (denticity, n) ranging from 3 to 8 were studied by potentiometric and "A1 NMR methods. Hydrolysis constants of the complexes were determined by potentiometry. The 27Al {'H} NMR data indicate a nearly linear relationship between the 27Al chemical shift of the normal complex and denticity of the ligand up to n = 6. Hydroxo complexes form in all systems, and at high pH (ca. 10) aluminate forms. Protonated complexes were formed in some cases. Diprotonated complexes of EDTA and PDTA have been identified by "A1 NMR spectroscopy. Maximum deshielding of the 27Al resonance was observed for the octahedral [Al(EDTA)I-complex. The Al-NTA complex appears to be the most symmetric of the complexes.

19F and 27Al NMR Study on the Formation of Al-EDTA-Fluoride Complex in Aqueous Solution

“…In the 27 Al NMR spectrum of a sample solution with a F/Al-EDTA molar ratio of zero (without fluoride), only a peak at 37 ppm appeared. 5 The 27 Al NMR peak width gradually increased from 470 to 690 Hz with an increase in the pH of the sample solution (from pH 3 to pH 6), indicating that Al-EDTA-OH was formed according to the following reaction, as previously described by Toth et al 6 In this paper the charge numbers of all complexes are omitted due to uncertainty.…”

27Al and 31P NMR Study on the Formation of Al-NTA-(Phosphate)n (n=1 or 2) Complexes in Aqueous Solution

“…According to an investigation by Iyer et al 10 , equilibrium is reached between Al-NTA-(H 2 O) 2 and the hydrolyzed complex, Al-NTA-H 2 O-OH, above pH 3.8. Figure 1 shows the 27 Al NMR spectrum of sample solutions of pH 4.5 with different phosphate contents (P/Al-NTA molar ratio).…”

“…On the other hand, although the peak intensities of 21 and 17 ppm increased complementarily, other peaks did not appear. A peak at -1 ppm may be due to an aluminum phosphate complex 10 which was formed by decomposition of the Al-NTA complex, because peaks due to free NTA appeared on the 13 C NMR spectrum of a sample solution with P/Al-NTA=3. Figure 2 shows the corresponding 31 P NMR spectra of solutions with P/Al-NTA=1 and 2.…”

Complexation Properties of Ethylenediaminetetramethylenephosphonic Acid (EDTMP) with AlIII and VIVO

“…In the case of a rigid dimer, at least three different P resonances should occur in the spectra: (i) the P atoms of the two CH 2 PO 3 2Ϫ arms at the coordinating side of the molecule, (ii) the coordinated P of the partially bound side of the molecule, and (iii) the P of the non-coordinating CH 2 PO 3 2Ϫ arm of this side. On the other hand, in the case of a flexible dimer the methylene protons in the N-attached phosphonate arms should become equivalent resulting in the appearance of a high-intensity doublet in the 1 H NMR spectra, which is not observed, instead rather complicated spectra are obtained (see Figure 4) were suggested by Westerback et al [7] and by Motekaitis et al, [10] and partly confirmed by Jarvis et al [11] [22,24] The pK a calculated from the data in Table 3 for the deprotonation of [AlLH] 4Ϫ to produce [AlL] 5Ϫ is 6.26, significantly lower than the pK a of the free ligand with the same number of protons, HL (pK a ഠ 13; see Table 2). This considerable decrease in the pK a of the HL 7Ϫ proton due to the coordination of Al III indicates the high stability of the hexadentate coordinated complex [AlL] 5Ϫ .…”

“…A similar hexadentate coordination mode was assumed for the carboxylate analogue EDTA in its [AlL] Ϫ complex. [22,24] This structure is rather rigid, accounting for the narrow peaks in the NMR spectra obtained, and has a C 2 symmetry axis so that the phosphorus atoms and the protons are equivalent in a pairwise manner. The CH 2 PO 3 2Ϫ arms bound to the same N atom are not equivalent; for this reason two 31 P signals of equal intensity are observed.…”