Halogen Bond of Halonium Ions: Benchmarking DFT Methods for the Description of NMR Chemical Shifts.

Daniel Sethio,Gerardo Raggi,Roland Lindh,Máté Erdélyi

doi:10.1021/acs.jctc.0c00860

Daniel Sethio, Gerardo Raggi + Show 2 more

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https://doi.org/10.1021/acs.jctc.0c00860

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Abstract

Because of their anisotropic electron distribution and electron deficiency, halonium ions are unusually strong halogen-bond donors that form strong and directional three-center, four-electron halogen bonds. These halogen bonds have received considerable attention owing to their applicability in supramolecular and synthetic chemistry and have been intensely studied using spectroscopic and crystallographic techniques over the past decade. Their computational treatment faces different challenges to those of conventional weak and neutral halogen bonds. Literature studies have used a variety of wave functions and DFT functionals for prediction of their geometries and NMR chemical shifts, however, without any systematic evaluation of the accuracy of these methods being available. In order to provide guidance for future studies, we present the assessment of the accuracy of 12 common DFT functionals along with the Hartree–Fock (HF) and the second-order Møller–Plesset perturbation theory (MP2) methods, selected from an initial set of 36 prescreened functionals, for the prediction of 1H, 13C, and 15N NMR chemical shifts of [N–X–N]+ halogen-bond complexes, where X = F, Cl, Br, and I. Using a benchmark set of 14 complexes, providing 170 high-quality experimental chemical shifts, we show that the choice of the DFT functional is more important than that of the basis set. The M06 functional in combination with the aug-cc-pVTZ basis set is demonstrated to provide the overall most accurate NMR chemical shifts, whereas LC-ωPBE, ωB97X-D, LC-TPSS, CAM-B3LYP, and B3LYP to show acceptable performance. Our results are expected to provide a guideline to facilitate future developments and applications of the [N–X–N]+ halogen bond.

Highlights

Halogen bonding is the attractive interaction of the electrondepleted region of a halogen with a Lewis base.[1]
It is worth noting that HF and MP2 provide comparably accurate predictions to DFT for 1H and 13C but not for 15N NMR chemical shifts
We found that only six of the DFT functionals (M06, B3LYP, CAM-B3LYP, LC-ωPBE, ωB97X-D, and LC-TPSS) gave reasonably good accuracy at the prediction of 15N NMR chemical shifts for [N− I−N]+ halogen-bond complexes

Summary

INTRODUCTION

Halogen bonding is the attractive interaction of the electrondepleted region of a halogen with a Lewis base.[1]. We assessed B3LYP against B3LYP-D3, MP2, and M06-2X8 and compared the outcome to independent CCSD(T) calculations.[42] We have shown that the contribution of dispersion to the overall interaction energy of three-center halogen bonds, [D−X−D]+, is minor, in contrast to its major impact for conventional neutral and weak halogen bonds, D−X···D.8 This is due to the partial ionic character, unusual strength, and shortness of the halogen bonds of halonium ions.[3] we proved the influence of basis-set superposition error (BSSE) to be negligible.[5] we report the comprehensive assessment of the accuracy of DFT methods and two wave functions (HF and MP2) for the description of NMR chemical shifts of three-center, fourelectron halogen-bond systems, that is, the exceptionally strong halogen-bond complexes of halonium ions. As the counterion has previously been demonstrated to not influence [N−I−N]+ halogen bonds significantly, it was omitted in the current calculations.[9]

COMPUTATIONAL DETAILS

RESULTS AND DISCUSSION

SUMMARY

■ ACKNOWLEDGMENTS

■ REFERENCES