A Nuclear Magnetic Relaxation of <SUP>139</SUP>La in Ionic Aqueous Solutions
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概要
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The nuclear magnetic relaxation rates of the <SUP>139</SUP>La ion in aqueous solutions of halides, nitrate, sulfate, and perchlorate have been measured. The observed relaxation rates increased as the concentration of the salts increased. However, in the low concentration range, the relaxation rate divided by the relative viscosity, <I>Δv</I>/η<I><SUB>r</SUB></I> increased only in the cases of nitrate and sulfate, while it decreased in the cases of halides and perchlorate. It was found that the formation of inner-sphere complexes is a satisfactory explanation of the increase in the <I>Δv</I>/η<I><SUB>r</SUB></I> of nitrate and sulfate solutions in the low to middle concentration range. With the fact, proved by various authors, that the lanthanide ions have several coordination numbers, the decrease in the <I>Δv</I>/η<I><SUB>r</SUB></I> of halide and perchlorate solutions in the same concentration range can be explained in terms of the existence of an equilibrium between two hydrated species, such as:<BR>La(H<SUB>2</SUB>O)<SUB>9</SUB><SUP>3+</SUP>\rightleftharpoonsLa(H<SUB>2</SUB>O)<SUB>8</SUB><SUP>3+</SUP>+H<SUB>2</SUB>O<BR>and the symmetrical species, La(H<SUB>2</SUB>O)<SUB>8</SUB><SUP>3+</SUP>, contributes to the decrease in <I>Δv</I>/η<I><SUB>r</SUB></I>. At a high nitrate concentration, after reaching the maximum value <I>Δv</I>/η<I><SUB>r</SUB></I> decreases, demonstrating that a symmetrical trinitrato species may be formed in the solution.
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