Computational modeling of polyoxotungstates by relativistic DFT calculations of 183W NMR chemical shifts
Computational modeling of polyoxotungstates by relativistic DFT calculations of 183W NMR chemical shifts
复制标题
DOI：
10.1002/chem.200600488
复制
发表时间：
2006-11-15
影响因子：
4.3
通讯作者：
Autschbach, Jochen
中科院分区：
文献类型：
--
作者：
Bagno, Alessandro;Bonchio, Marcella;Autschbach, Jochen
利用零级规则近似(ZORA)和溶剂效应的密度泛函理论，采用类导体屏蔽模型(COSMO)方法，对不同形状和电荷的钨多金属氧酸盐(POM)(Lindqvist，Anderson，Decatungate，Keggin)中的W-183核屏蔽进行了密度泛函理论模拟。提出了电荷/表面积比(Q1a)作为电荷密度的指标，所有POM的溶剂化能与电荷密度的关联令人满意。在所测试的各种理论水平(Zora标量或自旋轨道，冻结核或全电子基组，气相或连续溶剂中的几何优化等)中，当同时考虑溶剂和自旋轨道屏蔽中的几何优化时(Delta的平均绝对误差=35ppm)，获得了最好的结果。计算的化学位移的质量系统地依赖于Q/A所表示的电荷密度，因此，低Q/A比的POMS表现出与实验数据最好的一致性。这种方法的性能是这样的：计算值可以帮助指认多氧钨酸盐的W-183核磁共振谱，如α-[PW11TiO40](5-)的情况，其六个信号经过计算排序，即使信号的间距只有5ppm，也几乎重现了实验排序。
The W-183 nuclear shielding in a variety of tungsten polyoxometalates (POM) (Lindqvist, Anderson, decatungstates, Keggin) of different shapes and charges has been modeled by DFT calculations that take into account relativistic effects, by means of the zeroorder regular approximation (ZORA), and solvent effects, by the conductor-like screening model (COSMO) continuum method. The charge/surface area ratio (q1A) is proposed as an indicator of the charge density to which the solvation energies of all POMs are correlated in a satisfactory way. Among the various theoretical levels tested (ZORA scalar or spin-orbit, frozen-core or all-electron basis set, geometry optimization in the gas phase or in the continuum solvent, etc.), the best results are obtained when both geometry optimization in solvent and spin-orbit shielding are included (mean absolute error of delta = 35 ppm). The quality of the computed chemical shifts depends systematically on the charge density as expressed by q/A; thus, POMs with low q/A ratios display the best agreement with experimental data. The performance of the method is such that computed values can aid the assignment of the W-183 NMR spectra of polyoxotungstates, as shown by the case of alpha-[PW11TiO40](5-), whose six signals are ranked computationally so as to almost reproduce the experimental ordering even though the signals are spaced by as little as 5 ppm.