Medium Effects on51V NMR Chemical Shifts: A Density Functional Study

Abstract

Car-Parrinello molecular dynamics simulations were performed for [H2VO4], [VO2(OH2)4]+, and [VO(O2)2(OH2)]- in periodic boxes with 30, 28, and 29 water molecules, respectively, employing the BLYP density functional. On the timescale of the simulations, up to 2 ps, well-structured first solvation spheres are discernible for [H2VO4]- and [VO(O2)2(OH2)]- containing, on average, eight and ten water molecules, respectively. One of the four water molecules directly attached to the metal in [VO2(OH2)4]+ is only loosely bound, and the average coordination number of vanadium in aqueous VO2+ is between five and six. 51V chemical shifts were evaluated at the B3LYP level for representative snapshots along the trajectories, including the water molecules of the solvent by means of point charges. The resulting averaged delta(51V) values are proposed to model the combined effects of temperature (dynamic averaging) and solvent (charge polarization). Both effects are shown to be rather small, of the order of a few dozen ppm. The observed shielding of 51V in the bis(peroxo) complex with respect to the vanadate species is not reproduced computationally.

Towards understanding the poor thermal stability of V5+ electrolyte solution in Vanadium Redox Flow Batteries

“…2, which is in good agreement with results of Bühl and Parrinello [15]. Hence, compound A is the plausible initial structure in the V 5+ electrolyte solution before the thermally induced structural transition.…”

“…It should be noted that experimental NMR chemical shifts observed during cooling cycle represents the averaged state of both compounds A and B. Hence more attention should be paid to the trends in the DFT calculated ı values between the compounds rather than to their actual values [15]. The DFT computed 51 V chemical shifts for compound A (ı ∼ −623 ppm) and compound B (ı ∼ −577 ppm) show that any transition from compounds A to B should induce a shift towards higher frequency (i.e.…”

Investigating the Vanadium Environments in Hydroxylamido V(V) Dipicolinate Complexes Using 51V NMR Spectroscopy and Density Functional Theory

“…It has been suggested that for vanadium complexes with weakly bound ligands, such as the H 2 O in these compounds, thermal and solvent effects are on the order of a few dozen ppm. 34 The pairs of compounds that have the same hydroxylamine ligand are illustrated using the same symbols in Figure 9. This plot clearly illustrates the small changes in the solution δ iso values when the dipic ligand is varied whereas the solid-state δ iso values are more sensitive to dipic substitution.…”

Density functional theory investigation of3dtransition metal NMR shielding tensors in diamagnetic systems using the gauge-including projector augmented-wave method

“…Several all-electron calculations of the 51 V and 49 Ti isotropic shielding values have been reported in the literature for organometallic systems. [78][79][80][81][82][83][84] Here, we have focused our investigations on the complexes presented in Tables II and III, which have been studied in recent works by Bühl et al. [83] Computation of the NMR shielding parameters within the GIPAW approach was investigated through the use of 3s P 3p 2×P 4s 2×P 3d 2×P and 3s P 3p 3×P 4s 2×P 3d 3×P ultrasoftpseudopotentials (see caption of Table I) which leads to different convergence levels.…”