The totally symmetric stretching mode $$\nu_{1}$$ ν 1 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 $$\nu_{1}$$ ν 1 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 $$\nu_{1}$$ ν 1 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.

中文翻译：

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稀土离子在水溶液中的水合作用

在稀高氯酸盐水溶液中测量了从镧到镥的所有稀土 (RE) 离子的第一个水合壳层的完全对称拉伸模式 $$\nu_{1}$$ ν 1 Ln–(OH 2 )室温下的溶液。已发现 $$\nu_{1}$$ ν 1 Ln–(OH 2 ) 峰位置与镧系元素 (III) 水离子的 Ln–(OH 2 ) 键距之间存在 S 形关系。轻稀土离子形成九水合物，重离子形成八水合物，系列中间的稀土离子显示9到8之间的非整数水合数。 波数位置之间的关系$$\nu_{1 }$$ ν 1 Ln–(OH 2 ) 和稀土水合物的Ln–(OH 2 ) 键距已经给出。最近的量子力学计算支持给定的解释。