Groenewold Gary S, Gianotto Anita K, McIlwain Michael E, Stipdonk Michael J Van, Kullman Michael, Moore David T, Polfer Nick, Oomens Jos, Infante Ivan, Visscher Lucas, Siboulet Bertrand, Jong Wibe A de
Idaho National Laboratory, Idaho Falls, Idaho, USA.
J Phys Chem A. 2008 Jan 24;112(3):508-21. doi: 10.1021/jp077309q. Epub 2007 Dec 29.
The Free-Electron Laser for Infrared Experiments (FELIX) was used to study the wavelength-resolved multiple photon photodissociation of discrete, gas-phase uranyl (UO22+) complexes containing a single anionic ligand (A), with or without ligated solvent molecules (S). The uranyl antisymmetric and symmetric stretching frequencies were measured for complexes with general formula [UO2A(S)n]+, where A was hydroxide, methoxide, or acetate; S was water, ammonia, acetone, or acetonitrile; and n = 0-3. The values for the antisymmetric stretching frequency for uranyl ligated with only an anion ([UO2A]+) were as low or lower than measurements for [UO2]2+ ligated with as many as five strong neutral donor ligands and are comparable to solution-phase values. This result was surprising because initial DFT calculations predicted values that were 30-40 cm(-1) higher, consistent with intuition but not with the data. Modification of the basis sets and use of alternative functionals improved computational accuracy for the methoxide and acetate complexes, but calculated values for the hydroxide were greater than the measurement regardless of the computational method used. Attachment of a neutral donor ligand S to [UO2A]+ produced [UO2AS]+, which produced only very modest changes to the uranyl antisymmetric stretch frequency, and did not universally shift the frequency to lower values. DFT calculations for [UO2AS]+ were in accord with trends in the data and showed that attachment of the solvent was accommodated by weakening of the U-anion bond as well as the uranyl. When uranyl frequencies were compared for [UO2AS]+ species having different solvent neutrals, values decreased with increasing neutral nucleophilicity.
用于红外实验的自由电子激光（FELIX）被用于研究含有单个阴离子配体（A）、有或没有连接的溶剂分子（S）的离散气相铀酰（UO22+）配合物的波长分辨多光子光解离。对于通式为[UO2A(S)n]+的配合物，测量了铀酰的反对称和对称伸缩频率，其中A为氢氧化物、甲醇盐或乙酸盐；S为水、氨、丙酮或乙腈；n = 0 - 3。仅与阴离子配位的铀酰（[UO2A]+）的反对称伸缩频率值与与多达五个强中性供体配体配位的[UO2]2+的测量值一样低或更低，并且与溶液相值相当。这一结果令人惊讶，因为最初的密度泛函理论（DFT）计算预测的值要高30 - 40 cm(-1)，这符合直觉但与数据不符。基组的修改和替代泛函的使用提高了甲醇盐和乙酸盐配合物的计算精度，但无论使用何种计算方法，氢氧化物的计算值都大于测量值。向[UO2A]+附着中性供体配体S产生了[UO2AS]+，这对铀酰反对称伸缩频率仅产生了非常适度的变化，并且并没有普遍地将频率移至更低值。[UO2AS]+的DFT计算与数据趋势一致，并且表明溶剂的附着通过铀 - 阴离子键以及铀酰的减弱来适应。当比较具有不同溶剂中性体的[UO2AS]+物种的铀酰频率时，值随着中性亲核性的增加而降低。
