Bridgeman Adam J
Department of Chemistry, University of Hull, Kingston-upon-Hull, HU6 7RX (UK).
Chemistry. 2006 Feb 20;12(7):2094-102. doi: 10.1002/chem.200500802.
The structures and vibrational frequencies of the type II Anderson heteropolyanions [TeMo6O24]6- and [IMo6O24]5- have been calculated by using density functional theory using a number of common functionals and basis sets. For the first time, Raman intensities have been calculated and the effect of solvent on the modeling has been investigated. The calculated IR and Raman spectral traces are in good agreement with experiment allowing the characteristic group frequencies for this class of polyoxometalate to be identified. The stretching vibrations of the molybdenum-oxygen bonds are predicted to occur at somewhat lower frequencies than in the type I polyoxometalates. Stretching of the heteroatom-oxygen bonds occurs at significantly lower frequencies than in the Keggin anions as a simple consequence of the higher coordination number of the central heteroatom in the Anderson systems. For the [Mo2O7]2- and [Mo6O19]2- ions, the relatively low negative charge leads to small structural changes when solvent is included. In these systems, solvent leads to an increase in the bond polarity and a decrease in the covalent bond orders, resulting in decreases in the calculated frequencies. For the Anderson anions, the higher negative charges leads to greater solvent effects with contraction of the clusters and increases in the frequencies of bands due to stretching of the two, cis-related molybdenum-oxygen bonds.
通过使用多种常用泛函和基组的密度泛函理论，计算了II型安德森杂多阴离子[TeMo6O24]6-和[IMo6O24]5-的结构和振动频率。首次计算了拉曼强度，并研究了溶剂对建模的影响。计算得到的红外和拉曼光谱曲线与实验结果吻合良好，从而能够识别这类多金属氧酸盐的特征基团频率。预计钼 - 氧键的伸缩振动发生的频率比I型多金属氧酸盐略低。杂原子 - 氧键的伸缩发生的频率比Keggin阴离子中的显著更低，这是安德森体系中中心杂原子配位数较高的一个简单结果。对于[Mo2O7]2-和[Mo6O19]2-离子，相对较低的负电荷在包含溶剂时导致较小的结构变化。在这些体系中，溶剂导致键极性增加和共价键级降低，从而使计算频率降低。对于安德森阴离子，较高的负电荷导致更大的溶剂效应，伴随着簇的收缩以及由于两个顺式相关的钼 - 氧键的伸缩而使谱带频率增加。
