19F NMR study of the equilibria and dynamics of the Al3+/F- system

被引:59
作者
Bodor, A
Tóth, I
Bányai, I
Szabó, Z
Hefter, GT
机构
[1] Univ Debrecen, Dept Inorgan & Analyt Chem, KLTE, H-4010 Debrecen, Hungary
[2] Univ Debrecen, Dept Phys Chem, KLTE, H-4010 Debrecen, Hungary
[3] Royal Inst Technol, Dept Chem, KTH, S-10044 Stockholm, Sweden
[4] Murdoch Univ, Dept Chem, Murdoch, WA 6150, Australia
关键词
D O I
10.1021/ic991248w
中图分类号
O61 [无机化学];
学科分类号
070301 ; 081704 ;
摘要
A careful reinvestigation by high-field F-19 NMR (470 MHz) spectroscopy has been made of the Al3+/F- system in aqueous solution under carefully controlled conditions of pH, concentration, ionic strength (I), and temperature. The F-19 NMR spectra show five distinct signals at 278 K and I = 0.6 M (TMACl) which have been attributed to the complexes AlFi(3-i)+(aq) with i less than or equal to 5. There was no need to invoke AlFi(OH)(j)((3-i-j)+) mixed complexes in the model under our experimental conditions (pH less than or equal to 6.5), nor was any evidence obtained for the formation of AlF63-(aq) at very high ratios of F-/Al3+. The stepwise equilibrium constants obtained for the complexes by integration of the F-19 signals are in good agreement with literature data given the differences in medium and temperature. In I = 0.6 M TMACl at 278 K and in I = 3 M KCl at 298 K the log K-i values are 6.42, 5.31, 3.99, 2.50, and 0.84 (for species i = 1-5) and 6.35, 5.25, and 4.11 (for species i = 1-3), respectively. Disappearance of the F-19 NMR signals under certain conditions was shown to be due to precipitation. Certain 19F NMR signals exhibit temperature- and concentration-dependent exchange broadening. Detailed line shape analysis of the spectra and magnetization transfer measurements indicate that the kinetics are dominated by F- exchange rather than complex formation. The detected reactions and their rate constants are AlF22+ + *F- reversible arrow AIF*F2+ + F- (k(02) = (1.8 +/- 0.3) x 10(6) M-1 s(-1)), AlF30 + *F- reversible arrow (AlF2F0)-F-* + F- (k(03) = (3.9 +/- 0.9) x 10(6) M-1 s(-1)), and AlF30 + H*F reversible arrow AlF2*F-0 + HF (k(03)(H) = (6.6 +/- 0.5) x 10(4) M-1 s(-1)). The rates of these exchange reactions increase markedly with increasing F- substitution. Thus, the reactions of AlF2+(aq) were too inert to be detected even on the T-1 NMR time scale, while some of the reactions of AlF30(aq) were fast, causing large line broadening. The ligand exchange appears to follow an associative interchange mechanism. The cis-trans isomerization of AlF2+(aq), consistent with octahedral geometry for that complex, is slowed sufficiently to be observed at temperatures around 270 R. Difference between the Al3+/F- system and the much studied Al3+/OH- system are briefly commented on.
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页码:2530 / 2537
页数:8
相关论文
共 37 条
[1]  
AKITT JW, 1989, PROG NMR SPECTROSC, V21, P41
[2]  
ANTHONY L, 1970, ANAL CHEM, V42, P679
[3]  
Baes C.F., 1976, HYDROLYSIS CATIONS, P112
[4]   RATES OF SUBSTITUTION OF HYDRATED BERYLLIUM CATION BY HYDROGEN FLUORIDE AND FLUORIDE ION [J].
BALDWIN, WG ;
STRANKS, DR .
AUSTRALIAN JOURNAL OF CHEMISTRY, 1968, 21 (09) :2161-+
[5]   EQUILIBRIUM DYNAMICS IN THE THALLIUM(III)-CHLORIDE SYSTEM IN ACIDIC AQUEOUS-SOLUTION [J].
BANYAI, I ;
GLASER, J .
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 1989, 111 (09) :3186-3194
[6]  
BOND AM, 1980, IUPAC CHEM DATE SERI, V27
[7]  
BROSSET C, 1943, J SVENSK KEM TIDSKR, V5, P101
[8]  
BUSLAEV YA, 1979, KOORDINATS KHIM, V5, P163
[9]  
Corain B, 1996, COORDIN CHEM REV, V149, P11, DOI 10.1016/0010-8545(95)01211-7