139La NMR as a tool for kineic studies

✍ Scribed by Y. Ducommun; L. Helm; G. Laurenczy; A. E. Merbach

• Publisher: John Wiley and Sons
• Year: 1988
• Tongue: English
• Weight: 390 KB
• Volume: 26
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.1260261116

✦ Synopsis

The application of '39La NMR to study the kinetics of substitution reactions is described. Rate constants associated with fast substitution reactions on La3+ complexes in the presence of excess of the aqua-ion can be obtained by measuring the line widths of the corresponding signals. Measurements as a function of temperature allow the separation of the kinetic and quadrupolar relaxation effects. The rate of aquation of La(2,6-dicarboxy-4 hydroxypyridine)+ was measured in aqueous solution. The dissociation rate constant and the activation parameters obtained for this process are k:98 = 207 f 51 s-', AH: = 38.3 & 3.1 kJ mol-' and AS,' = -72 f 8 J K-' mol-'. The spin-spin relaxation rates of the lanthanum(II1) in the two environments are described by l/ci' = 550 f 83 s-' and EA = 26.4 f 5.8 kJ mol-' for the aqua-ion and by 1/32;' = (2.00 f 0.08) x lo's-' and EB = 16.3 f 1.6 kJ mol-' for the mono-complex.

KEY WORDS '39La NMR Kinetic studies La3 + complex La(2,6-dicarboxy-4-hydroxypyridine)'