Computational Modeling of Polyoxotungstates by Relativistic DFT Calculations of183W NMR Chemical Shifts

Computation of 31P NMR chemical shifts in Keggin-based lacunary polyoxotungstates

Density Functional Theory (DFT) calculations were employed to systematically study the accuracy of various exchange-correlation functionals in reproducing experimental 31P NMR chemical shifts, δExp(31P) for Keggin, [PW12O40]3- and corresponding lacunary clusters: [PW11O39]7-, [A-PW9O34]9-, and [B-PW9O34]9-. Initially, computed chemical shifts, δCalc(31P) were obtained with without neutralising their charge in which associated error, δError(31P), decreased as a function of Hartree-Fock (HF) exchange, attributed to constriction of the P-O tetrahedron. By comparison, δCalc(31P) performed with explicitly located counterions to render the system charge neutral, reduced discrepancies, δError(31P) by 1-2 ppm. However, uncertainties in δCalc(31P) remain, particularly for [B-PW9O34]9- anions attributed to direct electrostatic interactions between the counterions and the central tetrahedron. Optimal results were achieved using the PBE/TZP//PBE0/TZP method, achieving a mean absolute error (MAE) and a mean squared error (MSE) of 4.03 ppm. Our results emphasize that understanding the nature of the electrolyte and solvent environment is essential to obtaining reasonable agreement between theoretical and experimental results.

Aluminum-Substituted Keggin Germanotungstate [HAl(H2O)GeW11O39]4-: Synthesis, Characterization, and Antibacterial Activity

We report on the new monosubstituted aluminum Keggin-type germanotungstate (C₄H₁₂N)₄[HAlGeW₁₁O₃₉(H₂O)]·11H₂O ([Al(H₂O)GeW₁₁]^4–), which has been synthesized at room temperature via rearrangement of the dilacunary [γ-GeW₁₀O₃₆]^8– polyoxometalate precursor. [Al(H₂O)GeW₁₁]^4– has been characterized thoroughly both in the solid state by single-crystal and powder X-ray diffraction, IR spectroscopy, thermogravimetric analysis, and elemental analysis as well as in solution by cyclic voltammetry (CV) ¹⁸³W, ²⁷Al NMR and UV–vis spectroscopy. A study on the antibacterial properties of [Al(H₂O)GeW₁₁]^4– and the known aluminum(III)-centered Keggin polyoxotungstates (Al-POTs) α-Na₅[AlW₁₂O₄₀] (α-[AlW₁₂O₄₀]^5–) and Na₆[Al(AlOH₂)W₁₁O₃₉] ([Al(AlOH₂)W₁₁O₃₉]^6–) revealed enhanced activity for all three Al-POTs against the Gram-negative bacterium Moraxella catarrhalis (minimum inhibitory concentration (MIC) up to 4 μg mL^–1) and the Gram-positive Enterococcus faecalis (MIC up to 128 μg mL^–1) compared to the inactive Al(NO₃)₃ salt (MIC > 256 μg mL^–1). CV indicates the redox activity of the Al-POTs as a dominating factor for the observed antibacterial activity with increased tendency to reduction, resulting in increased antibacterial activity of the POT.

We report on the synthesis and thorough characterization of the new monosubstituted aluminum germanotungstate (C₄H₁₂N)₄[HAlGeW₁₁O₃₉(H₂O)]·11H₂O ([Al(H₂O)GeW₁₁]⁴⁻), which has been subjected to an antibacterial study including the previously reported α-Na₅[AlW₁₂O₄₀] and Na₆[Al(AlOH₂)W₁₁O₃₉]. All three aluminum-substituted polyoxotungstates (Al-POTs) revealed enhanced activity against Moraxella catarrhalis and Enterococcus faecalis compared to the inactive Al(NO₃)₃ salt. On the basis of cyclic voltammetry studies, the redox activity of the POTs is suggested to have an impact on their overall antibacterial activity.

An overview of selected current approaches to the characterization of aqueous inorganic clusters

This Perspective highlights several modern characterization techniques used to identify nanoscale inorganic clusters in the context of multiple case studies.

The calculation of 29Si NMR chemical shifts of tetracoordinated silicon compounds in the gas phase and in solution

²⁹Si NMR chemical shifts have been calculated for a variety of silicon-based species relevant in organic synthesis.

Structure, properties and reactivity of polyoxometalates: a theoretical perspective

In the thematic review dedicated to polyoxometalate (POM) chemistry published in Chemical Reviews in 1998, no contribution was devoted to theory. This is not surprising because computational modelling of molecular metal-oxide clusters was in its infancy at that time. Nowadays, the situation has completely changed and modern computational methods have been successfully applied to study the structure, electronic properties, spectroscopy and reactivity of POM clusters. Indeed, the progress achieved during the past decade has been spectacular and herein we critically review the most important papers to provide the reader with an almost complete perspective of the field.

Prediction of the 1H and 13C NMR Spectra of α-d-Glucose in Water by DFT Methods and MD Simulations

We have applied computational protocols based on DFT and molecular dynamics simulations to the prediction of the alkyl 1H and 13C chemical shifts of alpha-d-glucose in water. Computed data have been compared with accurate experimental chemical shifts obtained in our laboratory. 13C chemical shifts do not show a marked solvent effect. In contrast, the results for 1H chemical shifts provided by structures optimized in the gas phase are only fair and point out that it is necessary to take into account both the flexibility of the glucose structure and the strong effect exerted by solvent water thereupon. Thus, molecular dynamics simulations were carried out to model both the internal geometry as well as the influence of solvent molecules on the conformational distribution of the solute. Snapshots from the simulation were used as input to DFT NMR calculations with varying degrees of sophistication. The most important factor that affects the accuracy of computed 1H chemical shifts is the solute geometry; the effect of the solvent on the shielding constants can be reasonably accounted for by self-consistent reaction field models without the need of explicitly including solvent molecules in the NMR property calculation.

Computing the1H NMR Spectrum of a Bulk Ionic Liquid from Snapshots of Car–Parrinello Molecular Dynamics Simulations

We have investigated the performance of several computational protocols in predicting the NMR spectrum of a molecular ion in a complex liquid phase such as an ionic liquid. To do this, we computed the proton NMR chemical shifts of the 1-ethyl-3-methylimidazolium cation [emim](+) in [emim][Cl]. Environmental effects on the imidazolium ring proton chemical shifts are quite significant and must be taken into account explicitly. Calculations performed on the isolated imidazolium cation as well as on the [emim][Cl] ion pair grossly fail to reproduce the correct spacing between proton signals. In contrast, calculations performed on clusters extracted from the trajectory of a Car-Parrinello molecular dynamics simulation yield very good results.