On the Hydration of the Rare Earth Ions in Aqueous Solution
Wolfram W. Rudolph, G. Irmer
Abstract
Abstract The totally symmetric stretching mode $$\nu_{1}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>ν</mml:mi><mml:mn>1</mml:mn></mml:msub></mml:math> Ln–(OH 2 ) of the first hydration shells of all the rare earth (RE) ions across the series from lanthanum to lutetium has been measured on dilute aqueous perchlorate solutions at room temperature. An S-shaped relationship has been found between the $$\nu_{1}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>ν</mml:mi><mml:mn>1</mml:mn></mml:msub></mml:math> Ln–(OH 2 ) peak positions and the Ln–(OH 2 ) bond distances of the lanthanide(III) aqua ions. While the light rare earth ions form nona-hydrates, the heavy ones form octa-hydrates and the rare earth ions in the middle of the series show non integer hydration numbers between 9 and 8. A relationship between wavenumber positions $$\nu_{1}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>ν</mml:mi><mml:mn>1</mml:mn></mml:msub></mml:math> Ln–(OH 2 ) and the Ln–(OH 2 ) bond distances of the RE hydrates has been given. Recent quantum mechanical calculations support the given interpretation.