Predicting ¹⁷O NMR chemical shifts of polyoxometalates using density functional theory

Abstract

We have investigated the computation of (17)O NMR chemical shifts of a wide range of polyoxometalates using density functional theory. The effects of basis sets and exchange-correlation functionals are explored, and whereas pure DFT functionals generally predict the chemical shifts of terminal oxygen sites quite well, hybrid functionals are required for the prediction of accurate chemical shifts in conjunction with linear regression. By using PBE0/def2-tzvp//PBE0/cc-pvtz(H-Ar), lanl2dz(K-) we have computed the chemical shifts of 37 polyoxometalates, corresponding to 209 (17)O NMR signals. We also show that at this level of theory the protonation-induced pH dependence of the chemical shift of the triprotic hexaniobate Lindqvist anion, [HxNb6O19]((8-x)), can be reproduced, which suggests that hypotheses regarding loci of protonation can be confidently tested.

Quantum chemical modeling of tri-Mn-substituted W-based Keggin polyoxoanions

“…The exchange-correlation approximation also hardly affects the Mn-O bonds, by 2-3 pm on average. Our findings agree with those of earlier studies on POMs [17,18] where similarly small variations of structure parameters had been determined for different exchange-correlation functionals. This similarity did not carry over to calculated chemical shifts [18] and energies of frontier molecular orbitals [17].…”

“…Previous studies found that experimental structural parameters of Keggin-type polyoxometalates are best reproduced in PBE0 calculations [17,18]. However, the average absolute errors of the functionals PBE0, B3LYP, and PBE, do not exceed 3 pm [17,18]. In conclusion, calculations with GGA and various hybrid func-tionals yield rather similar structural parameters, in contrast to the resulting energy characteristics [17,18].…”

“…However, the average absolute errors of the functionals PBE0, B3LYP, and PBE, do not exceed 3 pm [17,18]. In conclusion, calculations with GGA and various hybrid func-tionals yield rather similar structural parameters, in contrast to the resulting energy characteristics [17,18]. In consequence, we refrain from comparing here the structural results for the POMs calculated with hybrid methods; for details, see the SD.…”

“…PBE and B3LYP results are slightly longer, by 1-2 pm, than the results of PBE0 and TPSSh calculations. Previous studies found that experimental structural parameters of Keggin-type polyoxometalates are best reproduced in PBE0 calculations [17,18]. However, the average absolute errors of the functionals PBE0, B3LYP, and PBE, do not exceed 3 pm [17,18].…”

“…Computational chemistry offers an approach complimentary to experiment, for characterizing the (electrochemical) properties of POMs [17][18][19][20][21][22][23][24]; see also some reviews [25][26][27] and the references therein. Thus far, structural parameters, electronic properties, and the magnetism of POMs have been computationally examined [17,18,21,25]. Solvation effects on the properties of POMs were also explored in this way [28][29][30], including those of a surrounding electrolyte [29,30].…”