NMR Spectroscopic Studies on Interactions of Tripositive Ions of Cobalt(III) and Chromium(III) Complexes in Micellar Solutions

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Abstract

Interactions between micelles and tripositive ions of metal complexes such as [M(en)3]3+ (M = Co or Cr, en = ethylenediamine), [M(chxn)3]3+ (chxn = (R,R)-1,2-cyclohexanediamine), and [M(phen)3]3+ (phen = 1,10-phenanthroline), were studied using 59Co NMR spectroscopies and paramagnetic Cr(III)-induced 13C NMR relaxations of the surfactants. The magnitudes of the changes in 59Co chemical shifts and relaxation rates for [Co(en)3]3+ (= en complex) and [Co(chxn)3]3+ (= chxn complex) were dependent on the type of the head group: The carboxylate and alaninate surfactants caused larger changes in the 59Co NMR parameters than the sulfonate and sulfate ones did. The 59Co longitudinal and transverse relaxation rates were measured for the typical systems; these results gave effective 59Co electric field gradients (efgs) and effective correlation times for the three complex ions in the micellar solutions. The effective 59Co efgs obtained for the en and chxn complexes were larger in the carboxylate micelles than in the sulfonate and sulfate micelles. This result is in accord with the larger changes in the 59Co chemical shifts. The paramagnetic Cr(III)-induced 13C relaxation studies for each carbon of the surfactants suggest that [Cr(chxn)3]3+ is located at the micelle−water interface as well as the en complex. The correlation times and their activation energies also gave useful information on the selective interactions of the metal complex ions in the micellar solutions.

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