DFT Calculations of the Molecular Force Field of Vanadyl Nitrate, VO(NO₃)₃

Abstract

A structural and vibrational theoretical study for vanadyl nitrate was carried out. The Density Functional Theory (DFT) has been used to study vibrational properties. The structures were fully optimized at the B3LYP/6‐31G*, B3LYP/6‐311G*, and B3LYP/6‐311+G* levels of theory and the harmonic vibrational frequencies were evaluated at the same level. The calculated harmonic vibrational frequencies for vanadyl nitrate are consistent with their experimental IR and Raman spectra in gas and liquid phases. Through these calculations a precise knowledge of the normal modes of vibration was obtained, considering the coordination mode adopted by the nitrate group in the mirror plane as monodentate and bidentate. A total assignment of the observed bands in the vibrational spectra for vanadyl nitrate is proposed in this work. The nature of the V–O and V ← O bonds in the compound was systematically and quantitatively investigated by means of the Natural Bond Order (NBO) analysis. The topological properties of the electronic charge density were analyzed employing Bader's Atoms in Molecules theory (AIM).

Theoretical structural and experimental vibrational study of niobyl nitrate

“…For niobyl nitrate the calculated force constants expressed in terms of simple valence internal coordinates appearing in Table 4 were comparable with those calculated for vanadyl nitrate [6]. In both compounds the force constants related to a single nitrate group that lies in the mirror plane, and with the MAO bond localized in that plane, vary slightly when the coordination mode changes.…”

“…This BCP has the typical properties of the closed-shell interaction and for this, the value of q(r) is relatively low, the relationship |k 1 |/k 3 is <1 and r 2 q(r) is positive indicating that the interaction is dominated by the charge contraction away from the interatomic surface toward each nucleus. Here, there are two important observations, in one case, only the Nb1 O10 bond critical point has the typical properties of the closed-shell interaction [6] and in the other, the topological properties of the two pairs of bond critical points, Nb1AO2 with Nb1AO9 and Nb1AO5 with Nb1AO6 are the same, as shown in Table S6. The seven critical points and the three ring points of the electron density obtained by AIM analysis reveal that the mode of coordination adopted by the nitrate groups in niobyl nitrate is bidentate.…”

“…4 shows the Raman spectra of the solid compound. Vibrational assignments were made on the basis of the PED/B3LYP/6-31G ⁄ level in terms of symmetry coordinates and by comparison with molecules that contain similar groups [1,[5][6][7][28][29][30][31]. The vibrational frequencies observed in the infrared and Raman spectra and the assignments of the vibrational normal modes of the molecule taking into account the two types of coordination are shown in Table 3.…”

“…As VO(NO 3 ) 3 , this compound has nitrate ligands that can act as monodentate and bidentate [2][3][4][5][6]. Hence, the study of this compound is very important in our laboratory since the coordination modes adopted by nitrate groups are important in relation to vibrational and chemical properties [6,7]. This white, solid compound can be obtained by the method reported by Field and Hardy [1].…”

“…Methods and basis sets are very important to evaluate the best level of theory and the best basis set to reproduce experimental geometry and frequencies. Smart et al [3] have predicted the final structure of the vanadyl nitrate using the B3LYP method while in different compounds that contain transition metals the HF and MP2 methodologies are much less satisfactory than the DFT techniques [6][7][8][9][10][11]. Bell and Dines [12] have found that the B3LYP/ Lanl2DZ combination gives the best fit for the geometries and observed vibrational spectra of chromium oxo anions and oxyhalides compounds.…”