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Double-rotation (DOR) solid-state NMR spectroscopy is a high-resolution technique developed in the late 1980s. Although multiple-quantum magic-angle spinning (MQMAS) became the most widely used high-resolution method for half-integer spin quadrupoles after 1995, development and application of DOR NMR to a variety of chemical and materials science problems has endured. This Trend article recapitulates the development of DOR NMR, discusses various applications, and describes possible future directions. The main technical limitations specific to DOR NMR are simply related to the size of the double rotor system. The relatively large outer rotor (and thus coil) used for most applications over the past 35 years translates into relatively low rotor spinning frequencies, a low filling factor, and weak radiofrequency powers available for excitation and for proton decoupling. Ongoing developments in NMR instrumentation, including ever-shrinking MAS rotors and spherical NMR rotors, could solve many of these problems and may augur a renaissance for DOR NMR. [Display omitted] • Advances in double-rotation solid-state NMR spectroscopy are reviewed. • DOR NMR provides high-resolution spectra of quadrupolar nuclei in one dimension. • Limitations include a poor filling factor, low spinning rates, and low rf powers. • New developments in magic angle spinning technology could reinvigorate DOR NMR. [ABSTRACT FROM AUTHOR]

A pair of novel polymorphic ionic cocrystals of 3,4‐dicyanotelluradiazole and tetraphenylphosphonium bromide are synthesized and are characterized by single‐crystal XRD. Strong and directional non‐covalent chalcogen bonds (ChB) between Te and Br are analyzed via solid‐state NMR to reveal large and anisotropic J(125Te,79/81Br) coupling tensors, providing unequivocal evidence for non‐Fermi contact contributions across ChBs. Along with large 79/81Br quadrupolar couplings for the Br− anions, these data provide new tools to characterize chalcogen bonds and to differentiate between ChB polymorphs. [ABSTRACT FROM AUTHOR]

A pair of novel polymorphic ionic cocrystals of 3,4‐dicyanotelluradiazole and tetraphenylphosphonium bromide are synthesized and are characterized by single‐crystal XRD. Strong and directional non‐covalent chalcogen bonds (ChB) between Te and Br are analyzed via solid‐state NMR to reveal large and anisotropic J(125Te,79/81Br) coupling tensors, providing unequivocal evidence for non‐Fermi contact contributions across ChBs. Along with large 79/81Br quadrupolar couplings for the Br− anions, these data provide new tools to characterize chalcogen bonds and to differentiate between ChB polymorphs. [ABSTRACT FROM AUTHOR]

The design and implementation of a software package for the analysis of single-crystal NMR data is presented. The SCFit software can treat spectra arising from various interactions: (i) chemical shift tensor only; (ii) chemical shift tensor and quadrupolar coupling tensor; (iii) dipolar and indirect nuclear spin-spin coupling tensors; (iv) all four interactions. The software is demonstrated on recently reported 17O and 31P single-crystal NMR data for triphenylphosphine oxide and for two of its halogen-bonded cocrystals. The 17O single-crystal NMR data represent a case where all four above-mentioned interactions simultaneously affect the spectra. SCFit can fit the chemical shift and quadrupolar coupling in two ways: (i) through an unconstrained fitting process where all tensor parameters are freely optimized or (ii) through a constrained fitting process where the principal components of the tensors may be fixed to values known previously with high precision via the analysis of powder samples. The second strategy is explored in an effort to reduce the number of unknowns in the fitting process; an improvement in the precision of the resulting tensor orientations is noted in some cases. Image 1 • SCFit software for analyzing single-crystal NMR data is described. • Chemical shift, quadrupolar, and spin-spin coupling interactions are treated. • The utility of fixing tensor magnitudes to known values is explored. [ABSTRACT FROM AUTHOR]

This article describes some highlights of the research which has been carried out in my laboratory at the University of Ottawa over the period covering 2005 to 2014. My research is in the general areas of solid-state NMR, applications of quantum chemistry, and biomolecular NMR. The format will follow that of my 2014 Canadian Society for Chemistry Keith Laidler Award presentation given in Vancouver in June 2014 at the 97th Canadian Chemistry Conference and Exhibition. Following a brief introduction, I will present some of our most interesting and exciting recent advances according to the following six themes: 1. Fundamental solid-state NMR. 2. Materials characterization and NMR crystallography. 3. Pharmaceuticals and polymorphism. 4. Non-covalent interactions: Halogen bonds. 5. Biomolecular NMR. 6. Software development. [ABSTRACT FROM AUTHOR]

Abstract: Residual dipolar couplings between spin-1/2 and quadrupolar nuclei are often observed and exploited in the magic-angle spinning (MAS) NMR spectra of spin-1/2 nuclei. These orientation-dependent splittings contain information on the dipolar interaction, which can be translated into structural information. The same type of splittings may also be observed for pairs of quadrupolar nuclei, although information is often difficult to extract from the quadrupolar-broadened lineshapes. Here, the complete theory for describing the dipolar coupling between two quadrupolar nuclei in the frequency domain by Hamiltonian diagonalization is given. The theory is developed under MAS and double-rotation (DOR) conditions, and is valid for any spin quantum numbers, quadrupolar coupling constants, asymmetry parameters, and tensor orientations at both nuclei. All terms in the dipolar Hamiltonian become partially secular and contribute to the NMR spectrum. The theory is validated using experimental 11B and 35/37Cl NMR experiments carried out on powdered B-chlorocatecholborane, where both MAS and DOR are used to help separate effects of the quadrupolar interaction from those of the dipolar interaction. It is shown that the lineshapes are sensitive to the quadrupolar coupling constant of both nuclei and to the J coupling (including its sign). From these experiments, the dipolar coupling constant for a heteronuclear spin pair of quadrupolar nuclei may be obtained as well as the sign of the quadrupolar coupling constant of the perturbing nucleus; these are two parameters that are difficult to obtain experimentally otherwise. [Copyright &y& Elsevier]

Abstract: Double-rotation (DOR) is the only technique generally capable of yielding high-resolution NMR spectra of half-integer quadrupolar nuclei in one dimension for solids without the need for sophisticated coherence pathway selection. Unfortunately, due to the low outer rotor spinning frequencies currently available, the spectra often contain a large number of spinning sidebands which may overlap with the resonances of interest. We implement a simple, robust, and easy to use family of pulse sequences, which in practice are fully analogous to the ‘total suppression of sidebands’ (TOSS) sequences, to suppress all sidebands arising from the spinning of the outer rotor in DOR experiments. By removing the rotor phase dependence of the evolution of the sidebands, the sidebands destructively interfere with one another during the course of signal averaging to yield ‘solution-like’ spectra of half-integer quadrupolar nuclei in solids. Advantages and shortcomings of the method compared to other DOR sideband suppression methods are explored with the aid of simulations. [Copyright &y& Elsevier]

The group 2 metal halides and corresponding metal halide hydrates serve as useful model systems for understanding the relationship between the electric field gradient (EFG) and chemical shift (CS) tensors at the halogen nuclei and the local molecular and electronic structure. Here, we present a 35/37Cl and 43Ca solid-state nuclear magnetic resonance (SSNMR) study of CaCl2. The 35Cl nuclear quadrupole coupling constant, 8.82(8) MHz, and the isotropic chlorine CS, 105(8) ppm (with respect to dilute NaCl(aq)), are different from the values reported previously for this compound, as well as those reported for CaCl2·2H2O. Chlorine-35 SSNMR spectra are also presented for CaCl2·6H2O, and when taken in concert, the SSNMR observations for CaCl2, CaCl2·2H2O, and CaCl2·6H2O clearly demonstrate the sensitivity of the chlorine EFG and CS tensors to the local symmetry and to changes in the hydration state. For example, the value of δiso decreases with increasing hydration. Gauge-including projector-augmented wave (GIPAW) density functional theory (DFT) calculations are used to substantiate the experimental SSNMR findings, to rule out the presence of other hydrates in our samples, to refine the hydrogen positions in CaCl2·2H2O, and to explore the isostructural relationship between CaCl2 and CaBr2. Finally, the 43Ca CS tensor span is measured to be 31(5) ppm for anhydrous CaCl2, which represents only the fifth CS tensor span measurement for calcium. [ABSTRACT FROM AUTHOR]

Group 16 chalcogens potentially provide Lewis‐acidic σ‐holes, which are able to form attractive supramolecular interactions with electron rich partners through chalcogen bonds. Here, a multifaceted experimental and computational study of a large series of novel chalcogen‐bonded cocrystals, prepared using the principles of crystal engineering, is presented. Single‐crystal X‐ray diffraction studies reveal that dicyanoselenadiazole and dicyanotelluradiazole derivatives work as promising supramolecular synthons with the ability to form double chalcogen bonds with a wide range of electron donors including halides and oxygen‐ and nitrogen‐containing heterocycles. Extensive 77Se and 125Te solid‐state nuclear magnetic resonance spectroscopic investigations of cocrystals establish correlations between the NMR parameters of selenium and tellurium and the local chalcogen bonding geometry. The relationships between the electronic environment of the chalcogen bond and the 77Se and 125Te chemical shift tensors were elucidated through a natural localized molecular orbital density functional theory analysis. This systematic study of chalcogen‐bond‐based crystal engineering lays the foundations for the preparation of the various multicomponent systems and establishes solid‐state NMR protocols to detect these interactions in powdered materials. [ABSTRACT FROM AUTHOR]

127I nuclear quadrupole resonance (NQR) spectroscopy is established as a rapid and robust method to indicate the formation of iodine–nitrogen halogen bonds in co‐crystalline powders. Once the relevant spectral frequency range has been established, diagnostic 127I NQR spectra can be acquired in seconds. The method is demonstrated for a series of co‐crystals of 1,4‐diiodobenzene. Changes in the 127I quadrupolar coupling constant (CQ) by up to 74.4 MHz correlate with the length of the C−I donor covalent bond and inversely with the I⋅⋅⋅N halogen‐bond length. The predictive power of this technique is validated on two previously unknown co‐crystalline powders prepared mechanochemically. Single‐crystal growth via co‐sublimation and structure determination by single‐crystal X‐ray diffraction cross‐validates the findings. Natural localized molecular‐orbital analyses provide insight into the origins of the quadrupolar coupling constants. [ABSTRACT FROM AUTHOR]

Halogen bonding to phosphorus atoms remains uncommon, with relatively few examples reported in the literature. Here, the preparation and investigation of the cocrystal bis(dicyclohexylphenylphosphine)(1,6‐diiodoperfluorohexane) by X‐ray crystallography and solid‐state multinuclear magnetic resonance spectroscopy is described. The crystal structure features two crystallographically unique C—I…P halogen bonds [dI…P = 3.090 (5) Å, 3.264 (5) Å] and crystallographic disorder of one of the 1,6‐diiodoperfluorohexane molecules. The first of these is the shortest and most linear I…P halogen bond reported to date. 13C, 19F, and 31P magic angle spinning solid‐state NMR spectra are reported. A 31P chemical shift change of −7.0 p.p.m. in the cocrystal relative to pure dicyclohexylphenylphosphine, consistent with halogen bond formation, is noted. This work establishes iodoperfluoroalkanes as viable halogen bond donors when paired with phosphorus acceptors, and also shows that dicyclohexylphenylphosphine can act as a practical halogen bond acceptor.The halogen‐bonded cocrystal bis(dicyclohexylphenylphosphine)(1,6‐diiodoperfluorohexane) is prepared mechanochemically and investigated by X‐ray crystallography and solid‐state NMR spectroscopy, revealing the presence of a rare C—I…P halogen bond. [ABSTRACT FROM AUTHOR]

Sodium valproate is a pharmaceutical with applications in the treatment of epilepsy, bipolar disorder, and other ailments. Sodium valproate can exist in many hydrated and acid-stabilized forms in the solid state, and it can be difficult to obtain precise structural information about many of these. Here, we present a 13C and 23Na solid-state NMR study of several forms of sodium valproate, only one of which has been previously structurally characterized by single-crystal X-ray diffraction. 23Na magic-angle spinning (MAS), double-rotation (DOR), and multiple-quantum magic-angle spinning (MQMAS) NMR spectra are shown to provide useful information on the number of molecules in the asymmetric unit, the local coordination geometry of the sodium cations, and the presence of amorphous phases. Two previously identified forms are shown to be highly similar, or identical, according to the 23Na NMR data. The utility of carrying out both DOR and MQMAS NMR experiments to identify all crystallographically unique sites is demonstrated. 13C cross-polarization MAS NMR spectra also provide complementary information on the number of molecules in the asymmetric unit and the crystallinity of the sample. [ABSTRACT FROM AUTHOR]

Field‐stepped NMR spectroscopy at up to 36 T using the series‐connected hybrid (SCH) magnet at the U.S. National High Magnetic Field Laboratory is demonstrated for acquiring ultra‐wideline powder spectra of nuclei with very large quadrupolar interactions. Historically, NMR evolved from the continuous‐wave (cw) field‐swept method in the early days to the pulsed Fourier‐transform method in the modern era. Spectra acquired using field sweeping are generally considered to be equivalent to those acquired using the pulsed method. Here, it is shown that field‐stepped wideline spectra of half‐integer spin quadrupolar nuclei acquired using WURST/CPMG methods can be significantly different from those acquired with the frequency‐stepped method commonly used with superconducting magnets. The inequivalence arises from magnetic field‐dependent NMR interactions such as the anisotropic chemical shift and second‐order quadrupolar interactions; the latter is often the main interaction leading to ultra‐wideline powder patterns of half‐integer spin quadrupolar nuclei. This inequivalence needs be taken into account to accurately and correctly determine the quadrupolar coupling and chemical shift parameters. A simulation protocol is developed for spectral fitting to facilitate analysis of field‐stepped ultra‐wideline NMR spectra acquired using powered magnets. A MATLAB program which implements this protocol is available on request. [ABSTRACT FROM AUTHOR]

Frontispiece: Double Chalcogen Bonds: Crystal Engineering Stratagems via Diffraction and Multinuclear Solid-State Magnetic Resonance Spectroscopy Keywords: chalcogen bonds; crystal engineering; dicyanoselenadiazole; dicyanotelluradiazole; molecular orbital analysis; solid-state NMR Chalcogen bonds, crystal engineering, dicyanoselenadiazole, dicyanotelluradiazole, molecular orbital analysis, solid-state NMR. [Extracted from the article]

We present herein an in‐depth study of complexes in which a molecule containing a boron‐boron triple bond is bound to tellurate cations. The analysis allows the description of these salts as true π complexes between the B−B triple bond and the tellurium center. These complexes thus extend the well‐known Dewar‐Chatt‐Duncanson model of bonding to compounds made up solely of p block elements. Structural, spectroscopic and computational evidence is offered to argue that a set of recently reported heterocycles consisting of phenyltellurium cations complexed to diborynes bear all the hallmarks of π‐complexes in the π‐complex/metallacycle continuum envisioned by Joseph Chatt. Described as such, these compounds are unique in representing the extreme of a metal‐free continuum with conventional unsaturated three‐membered rings (cyclopropenes, azirenes, borirenes) occupying the opposite end. [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]

Carboxylate paddlewheels and their oxo-bridged analogues constitute ideal building blocks for the assembly of two- and three-dimensional framework materials. Here, we present a multinuclear ( 1 H, 13 C, 93 Nb, 95 Mo) magnetic resonance study of solid samples of Nb 2 OCl 6 (O 2 Ph) 2 ( 1 ), Mo 2 (O 2 CMe) 4 ( 2 ), and Mo 2 (O 2 CCHF 2 ) 4 ( 3 ). High-resolution proton and 13 C CP/MAS NMR spectra provide valuable information on structure and crystal symmetry and on cocrystallized solvent. 93 Nb solid-state NMR spectra of 1 provide quadrupolar coupling constants and chemical shift tensors which are characteristic of the axially asymmetric Nb-O-Nb bridging environment. 95 Mo solid-state NMR spectra of 2 and 3 provide quadrupolar coupling constants and chemical shift tensors which are directly characteristic of the molybdenum-molybdenum quadruple bonds in these compounds. The quadruple bonds are characterized by particularly large 95 Mo chemical shift tensor spans on the order of 5500 ppm. Density functional theoretical computations provide good agreement with the 93 Nb and 95 Mo experimental data, with some exceptions noted. This work demonstrates possible NMR approaches to characterize more complex framework materials and provides key insight into the Mo-Mo quadruple bond. [ABSTRACT FROM AUTHOR]

The results of a 35/37Cl solid-state nuclear magnetic resonance (SSNMR) study of the 1-butyl-3-methylimidazolium chloride complex of meso-octamethylcalix[4]pyrrole ( 1) are reported. Line shapes obtained from magic-angle-spinning and stationary powder samples collected at 9.4 and 21.1 T are analyzed to provide the 35/37Cl quadrupolar tensor and chemical shift (CS) tensor and their relative orientation. The relatively high symmetry of the chloride ion coordination environment is manifested in the small value of the quadrupole coupling constant, CQ(35Cl) = 1.0 MHz. The isotropic chemical shift of 120 ppm (with respect to NaCl(s)) is at the upper edge of the typical range seen for organic hydrochlorides. Consideration of chemical shift anisotropy (span, Ω = 50 ppm) and non-coincidence of the quadrupolar and CS tensors were essential to properly simulate the experimental spectra. The utility of gauge-including projector-augmented wave density functional theory (GIPAW-DFT) calculations of chlorine quadrupolar and CS tensors in organic chlorides was explored by validation against available benchmark experimental data for solid amino acid hydrochlorides. The calculations are shown to systematically overestimate the value of the 35Cl quadrupole coupling constant. Additional calculations on various hydrated and solvated models of 1 are consistent with a structure in which solvent and water of hydration are absent. [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]