Relativistic Effects on NMR Parameters of Halogen-Bonded Complexes.

Ibon Alkorta,M Merced Montero-Campillo,Manuel Yáñez,Otilia Mó,José Elguero

doi:10.3390/molecules24234399

Ibon Alkorta, M Merced Montero-Campillo + Show 3 more

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https://doi.org/10.3390/molecules24234399

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Abstract

Relativistic effects are found to be important for the estimation of NMR parameters in halogen-bonded complexes, mainly when they involve the heavier elements, iodine and astatine. A detailed study of 60 binary complexes formed between dihalogen molecules (XY with X, Y = F, Cl, Br, I and At) and four Lewis bases (NH3, H2O, PH3 and SH2) was carried out at the MP2/aug-cc-pVTZ/aug-cc-pVTZ-PP computational level to show the extent of these effects. The NMR parameters (shielding and nuclear quadrupolar coupling constants) were computed using the relativistic Hamiltonian ZORA and compared to the values obtained with a non-relativistic Hamiltonian. The results show a mixture of the importance of the relativistic corrections as both the size of the halogen atom and the proximity of this atom to the basic site of the Lewis base increase.

Highlights

The geometry of the complexes was optimized at the MP2 computational level [26] with the augaug-cc-pVTZ basis set [27,28]
The relationships for the complexes with iodine and astatine are depicted, showing a linear behavior with R2 > 0.99. These results strongly indicate that other component in addition to electrostatics should be taken into account for a fine-tuning of the estimation of the dissociation energies (De)
NMR and nuclear quadrupole coupling constants (NQCC) parameters, dissociation energies, and intermolecular distances were studied in detail for 60 halogen-bonded complexes between XY halogen molecules and a set of Lewis bases, namely NH3, PH3, SH2, and H2 O, taking into account relativistic effects

Summary

Introduction

Second in importance after hydrogen bonds, halogen bonds (XB) are widely present in many fields such as crystal engineering, biological systems, and the design of new materials, amongst others It is worth citing here the IUPAC definition of the halogen bond: “A halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity” [1]. A key feature of halogen molecules is the polar flattening of the electron density [4,5,6], known as σ-hole [6,7,8] This phenomenon is responsible for the directionality of the halogen bond when halogens interact with a Lewis base, a property with an enormous influence on the strength of non-covalent bonds. When combined with other bonds, the same or different, positive and negative cooperativity effects are observed [9,10,11,12]

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