Effect of Cations in Infrared and Computational Analysis of Vanadium-Containing Six-Coordinate Oxotungstates

Abstract

Complex salts of VW 5 O 19 3-, cis-V 2 W 4 O 19 , 4-, and W 6 O 19 2-anions have been investigated using Fourier transform infrared spectroscopy and density functional theory computational methods. The intensities of the infrared absorption bands commonly used to identify the bridge and terminal oxygen atoms in these hexametalate systems were found to depend drastically on the nature of the countercation and presence of water in the salts. Theoretical investigations suggest that the anions alone may not show significant absorption in the region commonly assigned to the M-O t vibrations (subscripts t and b denote terminal and bridged oxygen atoms, respectively). At the same time, the addition of even a single molecule of water or tetraalkylammonium into the calculation results in almost quantitative agreement between the theoretical and experimental spectra. The presence of vanadium has a profound effect both on M-O t and on M-O b -M vibrations.

A new model for the molecular structure of supported vanadium oxide catalysts

“…Harmonic frequencies were obtained from analytical hessian calculations. As is well known the frequencies resulting from B3LYP DFT calculations are slightly too high, compared with experiments [22]. Commonly a scaling factor around 0.95 is used to correct for this deficiency [23,24].…”

Molecular view of copper deposition chemistry: (Hexafluoroacetylacetonate)Cu(vinyltrimethylsilane) on a Si(100)-2×1 surface

“…It has been successfully utilized before in our group to investigate the structural properties of Keggin structure polyoxometalates [16] and to investigate countercation and water bonding in Lindqvist structure polyoxometalates [17]. Although commonly used in this type of investigations and inexpensive, this basis set is rarely used in investigation of hydrocarbons or their fragments.…”

Effect of positional isomerism and vanadium substitution on 51V magic angle spinning NMR Spectra Of Wells-Dawson polyoxotungstates

“…As we have reported previously for the 51 V NMR studies in Lindqvist and Keggin solids, both countercations and vanadium substitution modulates the electric field gradient of the vanadium center giving rise to substantial variations in the quadrupolar coupling parameters [40, 41]. The current and prior results make it clear that counter cations have to be explicitly included in computational models, which to the best of our knowledge has only been done in one study - our prior work on computing the vibrational frequencies in Lindqvist solids [16]. It will be interesting in the future to conduct these studies on Wells-Dawson series of compounds as well.…”

“…This understanding includes the knowledge of both the three-dimensional geometry of the extended solid (available from the single crystal X-ray diffraction in the cases where the solid can be crystallized) and the electronic structure of the anion and of vanadium center in particular. Advancements in theoretical quantum chemical methods have allowed for the investigations of Wells-Dawson (and generally polyoxometalate solids) [16–20], and these studies are expected to aid in the interpretation of the experimental structural and spectroscopic data. We and others have shown that 51 V solid-state NMR spectroscopy can be used as a sensitive reporter of the structural and electronic environment of vanadium sites in a wide variety of inorganic and bioinorganic solids [21–39] including polyoxometalates [40–42].…”

“…We and others have shown that 51 V solid-state NMR spectroscopy can be used as a sensitive reporter of the structural and electronic environment of vanadium sites in a wide variety of inorganic and bioinorganic solids [21–39] including polyoxometalates [40–42]. Specifically, in our previous MAS NMR studies on Lindqvist and Keggin polyoxotungstate solids, we have demonstrated that insights unavailable from X-ray diffraction and other structural methods could be gained, namely that counter cations and the degree of vanadium substitution modulate the electronic structure of the oxoanion as is evident in the 51 V magic angle spinning (MAS) NMR spectra [40, 41] as well as vibrational spectra [16]. Since Wells-Dawson polyoxometalates have been utilized for homogeneous and heterogeneous catalysis, characterization of the electronic and structural properties of these complexes in both liquid and solid phase is needed to investigate their catalytic activities, dependence on metal ion substitution, and redox properties.…”