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首页> 外文期刊>Chemistry: A European journal >Hydration of lanthanoid(III) ions in aqueous solution and crystalline hydrates studied by EXAFS spectroscopy and crystallography: The myth of the 'gadolinium break'
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Hydration of lanthanoid(III) ions in aqueous solution and crystalline hydrates studied by EXAFS spectroscopy and crystallography: The myth of the 'gadolinium break'

机译：通过EXAFS光谱学和晶体学研究水溶液和结晶水合物中镧系元素（III）的水合：“：断裂”的神话

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摘要

The structures of the hydrated lanthanoid(III) ions including lanthanum(III) have been characterized in aqueous solution and in the solid trifluoromethanesulfonate salts by extended X-ray absorption fine structure (EXAFS) spectroscopy. At ambient temperature the water oxygen atoms appear as a tricapped trigonal prism around the lanthanoid(III) ions in the solid nonaaqualanthanoid(III) trifluoromethanesulfonates. Water deficiency in the capping positions for the smallest ions starts at Ho and increases with increasing atomic number in the [Ln(H2O)(9-x)] (CF3SO3)(3) compounds with x = 0.8 at Lu. The crystal structures of [Ho(H2O)(8.91)](CF3SO3)(3) and [Lu(H2O)(8.2)](CF3SO3)(3) were re-determined by X-ray crystallography at room temperature, and the latter also at 100 K after a phase-transition at about 190 K. The very similar Ln K- and L-3-edge EXAFS spectra of each solid compound and its aqueous solution indicate indistinguishable structures of the hydrated lanthanoid(III) ions in aqueous solution and in the hydrated trifluoromethanesulfonate salt. The mean Ln-O bond lengths obtained from the EXAFS spectra for the largest ions, La-Nd, agree with estimates from the tabulated ionic radii for nine-fold coordination but become shorter than expected starting at samarium. The deviation increases gradually with increasing atomic number, reaches the mean Ln-O bond length expected for eightfold coordination at Ho, and increases further for the smallest lanthanoid(III) ions, Er-Lu, which have an increasing water deficit. The low-temperature crystal structure of [Lu(H2O)(8.2)](CF3SO3)(3) shows one strongly bound capping water molecule (Lu-O 2.395(4) angstrom) and two more distant capping sites corresponding to Lu-O at 2.56(1) angstrom, with occupancy factors of 0.58(1) and 0.59(1). There is no indication of a sudden change in hydration number, as proposed in the "gadolinium break" hypothesis.
机译：已通过扩展X射线吸收精细结构（EXAFS）光谱对水溶液和固体三氟甲磺酸盐中的水合镧系元素（III）离子的结构进行了表征。在环境温度下，水氧原子以固态三氟甲磺酸类非甲戊二烯酮（III）中的镧系元素（III）离子的形式出现，成为三棱三角棱镜。最小离子在封端位置的缺水现象从Ho开始，并随着Lu处x = 0.8的[Ln（H2O）（9-x）]（CF3SO3）（3）化合物中原子序数的增加而增加。 [Ho（H2O）（8.91）]（CF3SO3）（3）和[Lu（H2O）（8.2）]（CF3SO3）（3）的晶体结构在室温下通过X射线晶体学重新确定，并且后者在约190 K发生相变后也在100 K发生。每种固体化合物及其水溶液的非常相似的Ln K和L-3-edge EXAFS光谱表明，水合镧系元素（III）离子在水溶液中的结构难以区分溶液和水合三氟甲磺酸盐。从EXAFS光谱中获得的最大离子La-Nd的平均Ln-O键长与九个配位的列表离子半径的估计值相符，但比sa开始时要短。偏差随原子序数的增加而逐渐增加，达到在Ho处预期达到八重配位的平均Ln-O键长度，而对于最小的镧系元素（III）离子Er-Lu则进一步增加，后者的缺水率增加。 [Lu（H2O）（8.2）]（CF3SO3）（3）的低温晶体结构显示一个牢固结合的封端水分子（Lu-O 2.395（4）埃）和两个更远的对应于Lu-O的封端位在2.56（1）埃，占用因子分别为0.58（1）和0.59（1）。没有“ ga裂”假说中提出的水合数突然变化的迹象。

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