Weak Halogen Bonding in Solid Haloanilinium Halides Probed Directly via Chlorine-35, Bromine-81, and Iodine-127 NMR Spectroscopy

Abstract

A series of monohaloanilinium halides exhibiting weak halogen bonding (XB) has been prepared and characterized by 35 Cl, 81 Br, and 127 I solid-state nuclear magnetic resonance (SSNMR) spectroscopy in magnetic fields of up to 21.1 T. The quadrupolar and chemical shift (CS) tensor parameters for halide ions (Cl − , Br − , I − ) which act as electron density donors in the halogen bonds of these compounds are measured to provide insight into the possible relationship between halogen bonding and NMR observables. The NMR data for certain series of related compounds are strongly indicative of when such compounds pack in the same space group, thus providing practical structural information. Careful interpretation of the NMR data in the context of novel and previously available X-ray crystallographic data, and new gauge-including projector-augmented-wave density functional theory (GIPAW DFT) calculations has revealed several notable trends. When a series of related compounds pack in the same space group, it has been possible to interpret trends in the NMR data in terms of the strength of the halogen bond. For example, in isostructural series, the halide quadrupolar coupling constant was found to increase as the halogen bond weakens. In the case of a series of haloanilinium bromides, the 81 Br isotropic chemical shift and CS tensor span both decrease as the bromide−halogen XB is weakened. These trends were reproduced using both GIPAW DFT and cluster-model calculations of the bromide ion magnetic shielding tensor. Such trends are particularly exciting given the well-known role that NMR has played historically in the characterization of hydrogen bonding.

Natural Abundance 15N and 13C Solid‐State NMR Chemical Shifts: High Sensitivity Probes of the Halogen Bond Geometry

“…Selenocyanates were noted to show the opposite trends. Bryce and coworkers have used high-field SSNMR to directly probe weak XBs involving 35 Cl, 81 Br, and 127 I in various solid haloanilinium halides, 38 where the authors found interesting correlations between isostructural compounds. Widdifield et al have, instead, reported a multinuclear study on a series of decamethonium diiodide-dihalogenated benzene co-crystals.…”

Solid-State NMR Study of Halogen-Bonded Adducts

“…Clearly it would be advantageous to be able to probe directly the halogen bond donor itself using NMR spectroscopy. As mentioned, [40] the NMR spectroscopies of chlorine, bromine, and iodine are difficult, mainly due to the large quadrupole moments of their NMR-active isotopes and the resulting extremely broad powder patterns. Even for halide anions, where the closed-shell electronic configuration means that the EFG will be relatively low at the nucleus (zero in the limit of an isolated anion), powder patterns covering at least tens of kHz (for 35/37 Cl) and up to more than a MHz (for 127 I) in breadth are obtained.…”

“…One such class of compounds are the haloanilinium halides. Halogen bonding in these compounds has been discussed by Gray and Jones [54], Raatikainen et al [55], and Attrell et al [40]. The reduced distance parameter, R XB , varies from a minimum of 0.88 for 2-iodoanilinium bromide to a maximum of 1.03 in 3-chloroanilinium bromide, indicating that the halogen bonds are weak at best in such complexes.…”

“…Reproduced with permission of the American Chemical Society. Attrell et al [40] whether or not they packed in the same space group. In one isostructural series of compounds, the halide quadrupolar coupling constant was found to increase as the halogen bond weakens.…”

Rapid Identification of Halogen Bonds in Co‐Crystalline Powders via 127I Nuclear Quadrupole Resonance Spectroscopy

“…[24][25][26][27] Solid-state nuclear magnetic resonance (SSNMR) spectroscopy has been shown to be apowerful tool to characterize halogen-bonded adducts, [28,29] offering information on chemical shifts, [30,31] J-couplings, [32,33] dipolar coupling, [34] and quadrupolar coupling. [35][36][37][38] As ac rystal-engineering tool, 13 C chemical shifts were shown to be sensitive to the occurrence of ah alogen bond, [30,31] while the I···N halogen bond length has been measured using 15 N-127 Id ipolar coupling. [34] Re-cently,w eh ave applied 13 Ca nd 19 Fs olid-state NMR [39] to investigate the quality of samples prepared by alternative methods such as mechanochemistry [40] and co-sublimation.…”