35Cl Solid-State NMR and Computational Study of Chlorine Halogen Bond Donors in Single-Component Crystalline Chloronitriles

Abstract

Halogen bonding is a noncovalent interaction between the electrophilic region of a halogen (σ-hole) and an electron donor, which has gained popularity in the field of crystal engineering due to its strength and linearity. Here, we present a 35Cl solid-state NMR study of chlorine atoms as halogen bond donors, with interpretation aided by crystallographic symmetry and computational chemistry. In a series of chlorinated benzonitrile compounds, the magnitude of the 35Cl quadrupolar coupling constant (CQ) was found to increase, and the quadrupolar asymmetry parameter (η) was found to decrease upon halogen bonding. A natural localized molecular orbital (NLMO) analysis attributes these changes to an increase in the contribution from the lone pair NLMOs to |CQ|. This is distinguished from a short proton-chlorine contact, which causes an increase in the magnitude of the σ-bond contribution and a decrease in the lone pair contribution, resulting in an overall decrease in |CQ|. This first direct 35Cl solid-state NMR...