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Matere bonds (MaB) to rhenium in a set of organic perrhenates are probed via185/187Re solid-state NMR in applied magnetic fields of up to 35.2 T, and via185/187Re NQR. 185/187Re quadrupolar couplings distinguish between MaB samples and control samples, and their precise values are governed by shear strain of the ReO4− anions. [ABSTRACT FROM AUTHOR]

The first example of a binary cocrystal, comprised of SnPh3Cl and PPh3, whose components are organized via short and directional tetrel bonds (TtB) between tin and phosphorus, is described. DFT elucidates, for the first time, the factors influencing the strength of TtBs involving heavy pnictogens. A CSD survey reveals that such TtBs are also present and determinative in single component molecular systems, highlighting their significant potential as tuneable structure-directing elements. [ABSTRACT FROM AUTHOR]

We report a multifaceted experimental and computational study of three self-complementary chalcogen-bond donors as well as a series of seven chalcogen bonded cocrystals. Bis(selenocyanatomethyl)benzene derivatives were cocrystallized with various halide salts (Bu4NCl, Bu4NBr, Bu4NI) and nitrogen-containing Lewis bases (4,4′-bipyridine and 1,2-di(4-pyridyl)ethylene). Three new single-crystal X-ray structures are reported. 77Se solid-state nuclear magnetic resonance spectroscopic study of a series of cocrystals establishes correlations between the NMR parameters of selenium and the local ChB geometry. For example, the 77Se isotropic chemical shift generally decreases on cocrystal formation. Diagnostic 13C chemical shifts are also described. In addition, all the chalcogen bonded cocrystals and pure tectons are investigated by Raman and IR spectroscopy techniques. Characteristic red shifts of the NC–Se stretching band upon cocrystal formation on the order of 10 to 20 cm−1 are observed, which provides a distinct signature of the chalcogen bond involving selenocyanates. The 125Te chemical shift tensor and X-ray structure of chalcogen-bonded tellurocyanatomethylbenzene are also reported. Insights into the connection between the electronic structure of the chalcogen bond and the experimentally measured 77Se chemical shift tensors are afforded through a natural localized molecular orbital density functional theory analysis. For the systems studied here, the lack of a very strong a correlation between experimental and DFT-computed 77Se chemical shift tensors leads to the conclusion that many structural features likely influence their ultimate values; however, computations on model systems reveal that the ChB alone produces consistent and predictable effects (e.g., the chalcogen chemical shift decreases as the chalcogen bond is shortened). [ABSTRACT FROM AUTHOR]

Selected highlights of the recent literature on solid-state NMR of some of the lesser studied nuclei are provided. The roles of ultrahigh magnetic fields, radiofrequency pulse sequences, dynamic nuclear polarization, isotopic enrichment, and nuclear quadrupole resonance in opening up the periodic table to in-depth study are discussed. [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]

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]

The feasibility and value of 207Pb solid-state NMR experiments on compounds featuring lead tetrel bonds is explored. Although the definition remains to be formalized, lead tetrel bonds may be qualitatively described as existing when there is evidence of a net attractive interaction between an electrophilic region associated with lead in a molecular entity and a nucleophilic region in another, or the same, molecular entity. Unambiguous identification of lead tetrel bonds can be challenging due to the hypervalent tendency of lead. We report here a series of 207Pb solid-state NMR experiments on five metal–organic frameworks featuring lead coordinated to hydrazone-based ligands. Such frameworks may be held together in part by lead tetrel bonds. The acquisition of 207Pb solid-state NMR spectra for such materials is feasible and is readily accomplished using a combination of magic-angle spinning and Carr–Purcell–Meiboom–Gill methods in moderate to low applied magnetic fields. The lead centres are characterized by 207Pb isotropic chemical shifts ranging from −426 to −2591 ppm and chemical shift tensor spans ranging from 910 to 2681 ppm. Careful inspection of the structures of the compounds and the literature 207Pb NMR data may suggest that a tetrel bond to lead results in chemical shift parameters which are intermediate between those which are characteristic of holodirected and hemidirected lead coordination geometries. Challenges associated with DFT computations of the 207Pb NMR parameters are discussed. In summary, the 207Pb data for the compounds studied herein show a marked response to the presence of non-coordinating electron-rich moieties in close contact with the electrophilic surface of formally hemidirectionally coordinated lead compounds. [ABSTRACT FROM AUTHOR]

In situ31P solid-state NMR studies of halogen bond formation between triphenylphosphine oxide and para-diiodotetrafluorobenzene provide insights into the cocrystallisation process and provide an estimate of the activation energy. The effects of temperature, magic-angle spinning speed, and initially added liquid on the reaction rate and mechanism have been investigated. [ABSTRACT FROM AUTHOR]

We report the preparation and characterisation of a cocrystal of triphenylphosphine with 1,3,5-trifluoro-2,4,6-triiodobenzene. The structure features a rare example of phosphorus acting as a halogen bond acceptor. [ABSTRACT FROM AUTHOR]

Studies of three related CdII systems (a discrete [CdII2] unit, a one-dimensional [CdII2]n coordination polymer and a CdII-based MOF) all derived from the ligand 2,4,6-tris(2-pyrimidyl)-1,3,5-triazine, reveal an exceptionally rare example of 113Cd–113Cd J coupling in the polymer that is detectable by solid-state NMR (2JCd–Cd = ∼65 Hz). [ABSTRACT FROM AUTHOR]

An overview of the role of solid-state nuclear magnetic resonance (SSNMR) spectroscopy in the field of crystal engineering is provided. NMR methodologies often provide insights into the structure and dynamics of solid materials which would otherwise be unavailable by X-ray diffraction. More generally, NMR crystallographic structure solutions or refinement approaches seek to incorporate available data from all sources, including the results of density functional theory calculations and diffraction data. This Highlight article discusses the state of the field through a recapitulation of relevant theory and selected applications from the literature. Specific topics covered include NMR structure refinement, polymorph identification and differentiation, non-covalent interactions, and the role of dynamics. [ABSTRACT FROM AUTHOR]

2D polymeric water–chloride/bromide sheets comprising a unique pentagon-like dichloride/dibromide-trihydrate cluster in the solid state have been observed as [Co(bpca)2]+ (bpca = bis(2-pyrimidylcarbonyl)amidate anion) counterions. Both compounds were obtained by the reaction of 2,4,6-tris(2-pyrimidyl)-1,3,5-triazine (TPymT) with CoX2 (X = Cl, Br) in water. Solid-state multinuclear magnetic resonance spectroscopy and XRD provide insight into the structures. [ABSTRACT FROM AUTHOR]

Advances in solid-state nuclear magnetic resonance (SSNMR) methods, such as dynamic nuclear polarization (DNP), intricate pulse sequences, and increased applied magnetic fields, allow for the study of systems which even very recently would be impractical. However, SSNMR methods using certain quadrupolar probe nuclei (i.e., I ＞ 1/2), such as 185/187Re remain far from fully developed due to the exceedingly strong interaction between the quadrupole moment of these nuclei and local electric field gradients (EFGs). We present a detailed high-field (B0 = 21.1 T) experimental SSNMR study on several perrhenates (KReO4, AgReO4, Ca(ReO4)2·2H2O), as well as ReO3 and Re2(CO)10. We propose solid ReO3 as a new rhenium SSNMR chemical shift standard due to its reproducible and sharp 185/187Re NMR resonances. We show that for KReO4, previously poorly understood high-order quadrupole-induced effects (HOQIE) on the satellite transitions can be used to measure the EFG tensor asymmetry (i.e., ηQ) to nearly an order-of-magnitude greater precision than competing SSNMR and nuclear quadrupole resonance (NQR) approaches. Samples of AgReO4 and Ca(ReO4)2·2H2O enable us to comment on the effects of counter-ions and hydration upon Re(vii) chemical shifts. Calcium-43 and 185/187Re NMR tensor parameters allow us to conclude that two proposed crystal structures for Ca(ReO4)2·2H2O, which would be considered as distinct, are in fact the same structure. Study of Re2(CO)10 provides insights into the effects of Re–Re bonding on the rhenium NMR tensor parameters and rhenium oxidation state on the Re chemical shift value. As overtone NQR experiments allowed us to precisely measure the 185/187Re EFG tensor of Re2(CO)10, we were able to measure rhenium chemical shift anisotropy (CSA) for the first time in a powdered sample. Experimental observations are supported by gauge-including projector augmented-wave (GIPAW) density functional theory (DFT) calculations, with NMR tensor calculations also provided for NH4ReO4, NaReO4 and RbReO4. These calculations are able to reproduce many of the experimental trends in rhenium δiso values and EFG tensor magnitudes. Using KReO4 as a prototypical perrhenate-containing system, we establish a correlation between the tetrahedral shear strain parameter (☋φ☋) and the nuclear electric quadrupolar coupling constant (CQ), which enables the refinement of the structure of ND4ReO4. Shortcomings in traditional DFT approaches, even when including relativistic effects via the zeroth-order regular approximation (ZORA), for calculating rhenium NMR tensor parameters are identified for Re2(CO)10. [ABSTRACT FROM AUTHOR]

Halogen bonds constitute an important and topical class of non-covalent interaction. We report a combined X-ray diffraction, multinuclear (77Se, 31P, 13C) solid-state magnetic resonance, and computational study of a series of crystalline triphenylphosphine selenide-iodoperfluorobenzene complexes which feature P=Se⋯I-C halogen bonds. Selenium-77 chemical shifts increase due to halogen bonding with iodine and correlate with the P=Se distance, which in turn correlates with the strength of the halogen bond. (77Se, 31P) coupling constants increase in magnitude as the halogen bond weakens. This observation is understood a natural localized molecular orbital (NLMO) DFT approach which shows that contributions from the selenium lone pair orbital tend to dominate both the magnitude and trends in (77Se, 31P), with the selenium-phosphorus bonding orbital being the second largest contributor. This work suggests that couplings measured NMR spectroscopy may play an important role in the characterization of halogen bonds, in clear analogy with their role in the characterization of hydrogen bonds. [ABSTRACT FROM AUTHOR]

Calcium is the 5th most abundant element on earth, and is found in numerous biological tissues, proteins, materials, and increasingly in catalysts. However, due to a number of unfavourable nuclear properties, such as a low magnetogyric ratio, very low natural abundance, and its nuclear electric quadrupole moment, development of solid-state 43Ca NMR has been constrained relative to similar nuclides. In this study, 12 commonly-available calcium compounds are analyzed via43Ca solid-state NMR and the information which may be obtained by the measurement of both the 43Ca electric field gradient (EFG) and chemical shift tensors (the latter of which are extremely rare with only a handful of literature examples) is discussed. Combined with density functional theory (DFT) computations, this ‘tensor interplay’ is, for the first time for 43Ca, illustrated to be diagnostic in distinguishing polymorphs (e.g., calcium formate), and the degree of hydration (e.g., CaCl2·2H2O and calcium tartrate tetrahydrate). For Ca(OH)2, we outline the first example of 1H to 43Ca cross-polarization on a sample at natural abundance in 43Ca. Using prior knowledge of the relationship between the isotropic calcium chemical shift and the calcium quadrupolar coupling constant (CQ) with coordination number, we postulate the coordination number in a sample of calcium levulinate dihydrate, which does not have a known crystal structure. Natural samples of CaCO3 (aragonite polymorph) are used to show that the synthetic structure is present in nature. Gauge-including projector augmented-wave (GIPAW) DFT computations using accepted crystal structures for many of these systems generally result in calculated NMR tensor parameters which are in very good agreement with the experimental observations. This combination of 43Ca NMR measurements with GIPAW DFT ultimately allows us to establish clear correlations between various solid-state 43Ca NMR observables and selected structural parameters, such as unit cell dimensions and average Ca–O bond distances. [ABSTRACT FROM AUTHOR]

Reaction of 2,4,6-tris(2-pyrimidyl)-1,3,5-triazine (TPymT) with Pb(NO3)2 in aqueous medium leads to the formation of a mixture of two pseudopolymorphs, {[Pb2(TPymT)(H2O)(NO3)4]·H2O}n, 1 and [Pb2(TPymT)(NO3)4]n, 2, where TPymT molecules are coordinated with two PbII ions in a bridging bis-terpyridine fashion. We demonstrate that fast evaporation of the solvent leads exclusively to the formation of 1, while 2 was formed upon slow evaporation. The two pseudopolymorphs can be interconverted by dissolving in water upon heating and controlling the evaporation rate. [ABSTRACT FROM AUTHOR]

The crystal structures of two sodium diphosphates (Na4P2O7 and Na3HP2O7·H2O) that were solved using diffraction methods are refined with the use of 23Na and 31P NMR data in conjunction with projector-augmented-wave density functional theory (DFT) calculations. The sodium cations' NMR parameters are shown to be particularly well suited for the investigation of crystalline structures as they are largely dictated by the crystalline network instead of local directional bonding interactions. High-resolution spin-diffusion 23Na correlation spectra were acquired with the use of double rotation (DOR) and the spin diffusion build-up curves were modeled with the use of the rate matrix method. The availability of dipolar-based information from these measurements is important in validating the assignment of the resonances prior to performing structural refinements using the 23Na EFG tensor parameters. The NMR-refined structures of Na4P2O7 and Na3HP2O7·H2O are then cross-validated with the use of diffraction and magnetic shielding tensor information and are compared to the pure DFT and X-ray diffraction structures. A new crystal structure of Na3HP2O7·9H2O is solved using single-crystal X-ray diffraction and is compared to the refined crystal structures of Na3HP2O7·H2O. The combination of methods used in this work ensures consistency of the final structures with all available data. [ABSTRACT FROM AUTHOR]

Rhenium-185/187 solid-state nuclear magnetic resonance (SSNMR) experiments using NaReO4and NH4ReO4powders provide unambiguous evidence for the existence of high-order quadrupole-induced effects (HOQIE) in SSNMR spectra. Fine structure, not predicted by second-order perturbation theory, has been observed in the 185/187Re SSNMR spectrum of NaReO4at 11.75 T, where the ratio of the Larmor frequency (ν0) to the quadrupole frequency (νQ) is ∼2.6. This is the first experimental observation that under static conditions, HOQIE can directly manifest in SSNMR powder patterns as additional fine structure. Using NMR simulation software which includes the quadrupole interaction (QI) exactly, extremely large 185/187Re nuclear quadrupole coupling constants (CQ) are accurately determined. QI parameters are confirmed independently using solid-state 185/187Re nuclear quadrupole resonance (NQR). We explain the spectral origin of the HOQIE and provide general guidelines that may be used to assess when HOQIE may impact the interpretation of the SSNMR powder pattern of any spin-5/2 nucleus in a large, axially symmetric electric field gradient (EFG). We also quantify the errors incurred when modeling SSNMR spectra for any spin-5/2 nucleus within an axial EFG using second-order perturbation theory. Lastly, we measure rhenium chemical shifts in the solid state for the first time. [ABSTRACT FROM AUTHOR]

Calcium is an important component of materials, metalloproteins, minerals, glasses, and small inorganic and organic complexes. However, NMR spectroscopy of the quadrupolar 43Ca nuclide remains difficult primarily due to its low natural abundance and low resonance frequency. In this Perspective, experimental challenges and recent successes in the field are highlighted, with a focus on solid-state 43Ca NMR spectroscopy. Solution 43Ca NMR studies of calcium-binding biomolecules are also presented. The structural insights afforded from quadrupolar and chemical shift parameters are examined. For example: isotropic chemical shifts have been shown to correlate with the mean Ca–O distance and also with calcium coordination number; quadrupolar coupling constants and chemical shift tensor spans have been shown to be useful probes of polymorphism; and, distance measurements involving 43Ca have been recently demonstrated. Lastly, challenges and opportunities for the future are considered. [ABSTRACT FROM AUTHOR]

A series of four anhydrous group 13 chloride salts has been studied by 35/37Cl solid-state NMR spectroscopy and complementary quantum chemical calculations. Due to the large 35/37Cl quadrupolar interactions in these salts, a high magnetic field (21.1 T) and the variable-offset QCPMG technique was used to obtain full chlorine central transition (m= −1/2 ↔ 1/2) NMR spectra. Analyses of the NMR spectra of the synthetically important Lewis acid trichlorides of aluminium, gallium, and indium, as well as gallium dichloride, allowed for characterisation of the chlorine electric field gradient (EFG) tensors and, in three cases, the chlorine chemical shift (CS) tensors. The quadrupolar interaction was found to dominate the central transition chlorine NMR spectrum in all cases, with chlorine-35 quadrupolar coupling constants (CQ) ranging in magnitude from 22.45 ± 2.00 to 40.44 ± 2.00 MHz, and the spectral breadths ranging from approximately 1.0 to 2.5 MHz. For the trichloride salt of gallium, it was confirmed that the terminal chlorine sites exhibit larger chlorine CQvalues than do the bridging chlorines. The isotropic chemical shifts range from 150 ± 100 to 375 ± 100 ppm while the largest CS tensor span is 500 ± 200 ppm, for InCl3. The chlorine chemical shift was found to increase with increasing M–Cl distance in all cases. Quantum chemical calculations of the EFG and magnetic shielding tensors, performed using the gauge-including projector-augmented-wave (GIPAW) method as implemented in the CASTEP program, were found to be in excellent agreement with the experimentally determined values, reproducing CQ(35Cl) to within 7% in all cases. The agreement between experiment and theory substantiates the accuracy of the NMR parameters. Solid-state NMR spectra of the cation species (aluminium-27, gallium-69/71 and indium-113/115) were also collected, and the EFG and CS parameters were determined in some cases. The study demonstrates the utility of multinuclear solid-state magnetic resonance studies of half-integer spin quadrupolar nuclei in ionic systems when the central transition is broadened greatly by the quadrupolar interaction, and in particular contributes to our understanding of the relationship between solid-state structure and chlorine NMR interaction tensors. [ABSTRACT FROM AUTHOR]

Solid-state NMR spectroscopy and GIPAW DFT calculations reveal the pronounced sensitivity of 79/81Br and 25Mg quadrupolar coupling constants to subtle aspects of solid state structure which were not previously detected by pXRD methods. [ABSTRACT FROM AUTHOR]

Reaction of 2,4,6-tris(2-pyrimidyl)-1,3,5-triazine (TPymT) with Pb(NO3)2 in aqueous medium leads to the formation of a mixture of two pseudopolymorphs, {[Pb2(TPymT)(H2O)(NO3)4]·H2O}n, 1 and [Pb2(TPymT)(NO3)4]n, 2, where TPymT molecules are coordinated with two PbII ions in a bridging bis-terpyridine fashion. We demonstrate that fast evaporation of the solvent leads exclusively to the formation of 1, while 2 was formed upon slow evaporation. The two pseudopolymorphs can be interconverted by dissolving in water upon heating and controlling the evaporation rate. [ABSTRACT FROM AUTHOR]