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Weak hydrogen bonds are important structure-directing elements in supramolecular chemistry and biochemistry. We consider here weak CH⋯O hydrogen bonds in a series of cocrystals of theophylline and caffeine and assess to what extent the CH⋯O distance and angle govern the observed 13C and 1H isotropic chemical shifts. Gauge-including projector-augmented wave density functional theory (GIPAW DFT) calculations consistently predict a decrease in the 13C and 1H magnetic shielding constants upon hydrogen bond formation on the order of 2–5 ppm (13C) and 1–2 ppm (1H). These trends are reproduced using the machine-learning approach implemented in ShiftML. Experimental 13C and 1H chemical shifts obtained for powdered samples using one-dimensional NMR spectroscopy as well as heteronuclear correlation (HETCOR) spectroscopy correlate well with the GIPAW DFT results. However, the experimental 13C NMR response only correlates moderately well with the hydrogen bond length and angle, while the experimental 1H chemical shifts only show very weak correlations to these local structural elements. DFT computations on isolated imidazole-formaldehyde models show that the 13C and 1H chemical shifts generally decrease with the C⋯O distance but show no clear dependence on the CH⋯O angle. These results demonstrate that the 13C and 1H response to weak CH⋯O hydrogen bonding is influenced significantly by additional weak contacts within cocrystal heterodimeric units. [Display omitted] • Weak CH⋯O hydrogen bonds involving the methine group of imidazole ring fragments are investigated. • Experimental 13C and 1H chemical shifts for solid cocrystals of caffeine and theophylline are assessed. • GIPAW-DFT, ShiftML machine learning, and cluster model calculations show the impact of hydrogen bond geometry on chemical shift response. • The most robust correlation is noted between the 13C isotropic chemical shift and the hydrogen bond length. [ABSTRACT FROM AUTHOR]

Group 16 chalcogen atoms may exhibit Lewis acidic σ-holes which are able to form attractive supramolecular interactions with Lewis bases via chalcogen bonds (ChB). Interest in ChB is increasing rapidly; however, the potential for anion binding has not been fully explored. Herein we report on the application of chemically robust and stable benzylic selenocynates (1 and 2) for halide ion recognition in the solid state and in solution. Single crystal X-ray structural analysis of various cocrystals reveals structurally important Se…X− (X = Cl, Br, I) chalcogen bonds. Changes in the 13C and 77Se chemical shifts via NMR spectroscopy show how halide ion recognition influences the local electronic environment of the selenium atoms in solution. Deviations of the interaction from the extension of the C–Se covalent bond are quantified and assessed with the aid of computational chemistry. [ABSTRACT FROM AUTHOR]

The halogen bond has previously been explored as a versatile tool in crystal engineering and anion coordination chemistry, with mechanochemical synthetic techniques having been shown to provide convenient routes towards cocrystals. In an effort to expand our knowledge on the role of halogen bonding in anion coordination, here we explore a series of cocrystals formed between 3‐iodoethynylpyridine and 3‐iodoethynylbenzoic acid with halide salts. In total, we report the single‐crystal X‐ray structures of six new cocrystals prepared by mechanochemical ball milling, with all structures exhibiting C≡C−I⋅⋅⋅X− (X=Cl, Br) halogen bonds. Whereas cocrystals featuring a pyridine group favoured the formation of discrete entities, cocrystals featuring a benzoic acid group yielded an alternation of halogen and hydrogen bonds. The compounds studied herein were further characterized by 13C and 31P solid‐state nuclear magnetic resonance, with the chemical shifts offering a clear and convenient method of identifying the occurrence of halogen bonding, using the crude product obtained directly from the mechanochemical ball milling. Whereas the 31P chemical shifts were quickly able to identify the occurrence of cocrystallization, 13C solid‐state NMR was diagnostic of both the occurrence of halogen bonding and of hydrogen bonding. [ABSTRACT FROM AUTHOR]

Abstract: Halogen bonding is an increasingly important tool in crystal engineering, and measuring its influence on the local chemical and electronic environment is necessary to fully understand this interaction. Here, we present a systematic crystallographic and solid‐state NMR study of self‐complementary halogen‐bonded frameworks built from the halide salts (HCl, HBr, HI, HI3) of 2‐iodoethynylpyridine and 3‐iodoethynylpyridine. A series of single crystal X‐ray structures reveals the formation of discrete charged dimers in the solid state, directed by simultaneous X−⋅⋅⋅H−N+ hydrogen bonds and C−I⋅⋅⋅X− halogen bonds (X=Cl, Br, I). Each compound was studied using multinuclear solid‐state magnetic resonance spectroscopy, observing 1H to investigate the hydrogen bonds and 13C, 35Cl, and 79/81Br to investigate the halogen bonds. A natural localized molecular orbital analysis was employed to help interpret the experimental results. 1H SSNMR spectroscopy reveals a decrease in the chemical shift of the proton participating in the hydrogen bond as the halogen increases in size, whereas the 13C SSNMR reveals an increased 13C chemical shift of the C−I carbon for C−I⋅⋅⋅X− relative to C−I⋅⋅⋅N halogen bonds. Additionally, 35Cl and 79/81Br SSNMR, along with computational results, have allowed us to compare the C−I⋅⋅⋅X− halogen bond involving each halide in terms of NMR observables. Due to the isostructural nature of these compounds, they are ideal cases for experimentally assessing the impact of different halogen bond acceptors on the solid‐state NMR response. [ABSTRACT FROM AUTHOR]

2-Iodoethynylpyridine and 2-iodoethynyl-1-methyl-imidazole self-assemble under halogen-bonding control into discrete macrocycles, viz. supramolecular triangles. [ABSTRACT FROM AUTHOR]

Halogen bonding has been shown to be a versatile interaction for crystal engineering purposes, with characteristics that parallel those of hydrogen bonding. Here, we explore the potential of a new halogen bond donor, 3-iodoethynylbenzoic acid (1), which is functionalized with both halogen bond donor and hydrogen bond donor groups. We explore its crystal engineering potential by cocrystallizing it with a series of nitrogen-containing heterocycles, namely 2,3,5,6-tetramethylpyrazine, 1,4-diazabicyclo[2.2.2]octane, piperazine, and hexamethylenetetramine. In total, we report six new single-crystal X-ray diffraction structures, including those of 1 and five of its halogen-bonded cocrystals. The halogen-bonded cocrystals are further investigated using 13C magic-angle spinning solid-state NMR spectroscopy and the observed changes in chemical shifts are attributed to particular structural or crystallographic features. The 13C chemical shift of the ethynyl carbon bonded to the aromatic ring consistently decreased by several ppm upon halogen bond formation while that of the ethynyl carbon bonded to iodine increased. Furthermore, we show that these cocrystals are also readily prepared by mechanochemical ball milling, allowing for the rapid screening of cocrystal formation based on this halogen bond donor. [ABSTRACT FROM AUTHOR]

17O solid-state NMR studies of waters of hydration in crystalline solids are presented. The 17O quadrupolar coupling and chemical shift (CS) tensors, and their relative orientations, are measured experimentally at room temperature for α-oxalic acid dihydrate, barium chlorate monohydrate, lithium sulfate monohydrate, potassium oxalate monohydrate, and sodium perchlorate monohydrate. The 17O quadrupolar coupling constants ( CQ) range from 6.6 to 7.35 MHz and the isotropic chemical shifts range from -17 to 19.7 ppm. The oxygen CS tensor spans vary from 25 to 78 ppm. These represent the first complete CS and electric field gradient tensor measurements for water coordinated to metals in the solid state. Gauge-including projector-augmented wave density functional theory calculations overestimate the values of CQ, likely due to librational dynamics of the water molecules. Computed CS tensors only qualitatively match the experimental data. The lack of strong correlations between the experimental and computed data, and between these data and any single structural feature, is attributed to motion of the water molecules and to the relatively small overall range in the NMR parameters relative to their measurement precision. Nevertheless, the isotropic chemical shift, quadrupolar coupling constant, and CS tensor span clearly differentiate between the samples studied and establish a 'fingerprint' 17O spectral region for water coordinated to metals in solids. [ABSTRACT FROM AUTHOR]

A series of monohaloanilinium halides exhibiting weakhalogen bonding(XB) has been prepared and characterized by 35Cl, 81Br, and 127I solid-state nuclear magnetic resonance(SSNMR) spectroscopy in magnetic fields of up to 21.1 T. The quadrupolarand chemical shift (CS) tensor parameters for halide ions (Cl–, Br–, I–) whichact as electron density donors in the halogen bonds of these compoundsare measured to provide insight into the possible relationship betweenhalogen bonding and NMR observables. The NMR data for certain seriesof related compounds are strongly indicative of when such compoundspack in the same space group, thus providing practical structuralinformation. Careful interpretation of the NMR data in the contextof novel and previously available X-ray crystallographic data, andnew gauge-including projector-augmented-wave density functional theory(GIPAW DFT) calculations has revealed several notable trends. Whena series of related compounds pack in the same space group, it hasbeen possible to interpret trends in the NMR data in terms of thestrength of the halogen bond. For example, in isostructural series,the halide quadrupolar coupling constant was found to increase asthe halogen bond weakens. In the case of a series of haloaniliniumbromides, the 81Br isotropic chemical shift and CS tensorspan both decrease as the bromide–halogen XB is weakened. Thesetrends were reproduced using both GIPAW DFT and cluster-model calculationsof the bromide ion magnetic shielding tensor. Such trends are particularlyexciting given the well-known role that NMR has played historicallyin the characterization of hydrogen bonding. [ABSTRACT FROM AUTHOR]

• Solid-state NMR provides a nuclear site specific probe of non-covalent bonds. • Applications to hydrogen bonds, halogen bonds, tetrel bonds, and pnictogen bonds are discussed. • NMR parameters correlate with structural features of the non-covalent bonds. • Dynamic processes may be probed through relaxation time constant measurements. We review applications of solid-state NMR spectroscopy for the analysis of element-based non-covalent interactions, with an emphasis on developments since 2009. The review is presented in five parts: 1. General Introduction; 2. Basic Principles of Solid-State NMR; 3. Applications to Hydrogen Bonding; 4. Applications to Halogen Bonding; 5. Applications to Other Element-Based Interactions (Tetrel, Pnictogen, Chalcogen). Chemical shifts, quadrupolar couplings, dipolar couplings, and J couplings are the main NMR parameters used to study non-covalent interactions in solids. Correlations with structural features are described. The utility of relaxation time constants in probing dynamic processes is discussed. In addition to covering standard solid-state NMR studies of powdered samples, applications of nuclear quadrupole resonance NQR and single-crystal NMR are discussed. It is clear that the vast array of magnetic resonance techniques available affords numerous important insights into a wide range of non-covalent interactions in solids. [ABSTRACT FROM AUTHOR]

Keywords: halogen bonding; hydrogen bonding; solid-state NMR; crystal engineering; X-ray crystallography The identity and phase purity of this and five related anion-coordinated architectures based on 3-iodoethynylpyridine and 3-iodoethynylbenzoic acid halogen bond donors are established with powder X-ray diffraction and multinuclear solid-state magnetic resonance spectroscopy. Halogen bonding, hydrogen bonding, solid-state NMR, crystal engineering, X-ray crystallography. [Extracted from the article]