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We describe a new quadrupolar NMR crystallography guided crystal structure prediction (QNMRX-CSP) protocol for the prediction and refinement of crystal structures, including its design, benchmarking, and application to seven organic HCl salts. Five HCl salts with a limited number of low-energy conformations were chosen as model systems for benchmarking: betaine HCl, glycine HCl, D -alanine HCl, guanidine HCl, and aminoguanidine HCl; two were chosen for blind tests: N,N′-dimethylglycine HCl and metformin HCl. The QNMRX-CSP protocol uses experimental 35Cl solid-state NMR (SSNMR) spectra and X-ray diffraction (XRD) data in tandem with Monte Carlo simulated annealing and dispersion-corrected plane-wave density functional theory (DFT-D2*) calculations. The protocol comprises three modules: (i) the assignment of motion groups, (ii) a Monte Carlo simulated annealing algorithm for generating tens of thousands of candidate structures, and (iii) DFT-D2* geometry optimizations of structural models and concomitant computation of 35Cl EFG tensors. Key benchmarked metrics are used for retaining the best candidate structures, including unit cell parameters, static lattice energies, and EFG distances (ΓEFG). The protocol is shown to generate structural models that are excellent matches with experimental crystal structures that have been DFT-D2* geometry optimized, as validated by crystallographic R-factors (R) and root-mean squared distances (RMSDs) of atomic positions that are well below 10% and 0.2 Å, respectively. Finally, consideration is given to the use of the QNMRX-CSP protocol as a standalone technique or in concert with other NMRX methods and Rietveld refinements, and possible applications employing other quadrupolar nuclei (i.e., 14N and 17O). [ABSTRACT FROM AUTHOR]

Correlating data from optical, structural, and theoretical methods allows the properties of highly faceted Cd2SnO4 (CTO) inverted spinel plasmonic semiconductor nanocrystals (PSNCs) to be fully evaluated. The use of Sn(II) in the colloidal reaction for CTO results in reproducible octahedral PSNCs with an aspect ratio of 1.30. Correlating extinction spectra with magnetic circular dichroism yields a carrier density (n = 5.19 × 1019 cm−3) and carrier effective mass (m* = 0.022me) respectively. 113Cd and 119Sn solid‐state NMR experiments show clear evidence of metallic‐like carriers in CTO NCs based upon the observation of Knight shifts. These data suggest that carrier formation in CTO arises from Sn antisite occupation of octahedral Cd sites (SnCd). From a broader perspective, the results point to wide‐bandgap spinels as being an important but understudied class of plasmonic PSNCs. [ABSTRACT FROM AUTHOR]

This study describes the discovery of a unique ionic cocrystal of the active pharmaceutical ingredient (API) ponatinib hydrochloride (pon·HCl), and characterization using single-crystal X-ray diffraction (SCXRD) and solid-state NMR (SSNMR) spectroscopy. Pon·HCl is a multicomponent crystal that features an unusual stoichiometry, with an asymmetric unit containing both monocations and dications of the ponatinib molecule, three water molecules, and three chloride ions. Structural features include (i) a charged imidazopyridazine moiety that forms a hydrogen bond between the ponatinib monocations and dications and (ii) a chloride ion that does not feature hydrogen bonds involving any organic moiety, instead being situated in a "square" arrangement with three water molecules. Multinuclear SSNMR, featuring high and ultra-high fields up to 35.2 T, provides the groundwork for structural interpretation of complex multicomponent crystals in the absence of diffraction data. A 13C CP/MAS spectrum confirms the presence of two crystallographically distinct ponatinib molecules, whereas 1D 1H and 2D 1H–1H DQ–SQ spectra identify and assign the unusually deshielded imidazopyridazine proton. 1D 35Cl spectra obtained at multiple fields confirm the presence of three distinct chloride ions, with density functional theory calculations providing key relationships between the SSNMR spectra and H⋯Cl− hydrogen bonding arrangements. A 2D 35Cl → 1H D-RINEPT spectrum confirms the spatial proximities between the chloride ions, water molecules, and amine moieties. This all suggests future application of multinuclear SSNMR at high and ultra-high fields to the study of complex API solid forms for which SCXRD data are unavailable, with potential application to heterogeneous mixtures or amorphous solid dispersions. [ABSTRACT FROM AUTHOR]

Accurate measurements of longitudinal relaxation time constants (T1) in solid-state nuclear magnetic resonance (SSNMR) experiments are important for the study of molecular-level structure and dynamics. Such measurements are often made under magic-angle spinning conditions; however, there are numerous instances where they must be made on stationary samples, which often give rise to broad powder patterns arising from large anisotropic NMR interactions. In this work, we explore the use of wideband uniform-rate smooth-truncation pulses for the measurement of T1 constants. Two experiments are introduced: (i) BRAIN-CPT1, a modification of the BRAIN-CP (BRoadband Adiabatic-INversion-Cross Polarization) sequence, for broadband CP-based T1 measurements and (ii) WCPMG-IR, a modification of the WURST-CPMG sequence, for direct-excitation (DE) inversion-recovery experiments. A series of T1 constants are measured for spin-1/2 and quadrupolar nuclei with broad powder patterns, such as 119Sn (I = 1/2), 35Cl (I = 3/2), 2H (I = 1), and 195Pt (I = 1/2). High signal-to-noise spectra with uniform patterns can be obtained due to signal enhancements from T2eff-weighted echo trains, and in favorable cases, BRAIN-CPT1 allows for the rapid measurement of T1 in comparison to DE experiments. Protocols for spectral acquisition, processing, and analysis of relaxation data are discussed. In most cases, relaxation behavior can be modeled with either monoexponential or biexponential functions based upon measurements of integrated powder pattern intensity; however, it is also demonstrated that one must interpret such T1 values with caution, as demonstrated by measurements of T1 anisotropy in 119Sn, 2H, and 195Pt NMR spectra. [ABSTRACT FROM AUTHOR]

Multinuclear solid-state nuclear magnetic resonance (SSNMR) experiments have been performed on cisplatin and four related square-planar compounds. The wideband uniform rate smooth truncation--Carr-Purcell-Meiboom-Gill (WURST-CPMG) pulse sequence was utilized in NMR experiments to acquire [sup.195]Pt, [sup.14]N, and [sup.35]Cl ultra- wideline NMR spectra of high quality. Standard Hahn-echo and magic-angle spinning [sup.195]Pt NMR experiments are also performed to refine extracted chemical shielding (CS) tensor parameters. Platinum magnetic shielding (MS) tensor orientations are calculated using both plane-wave density functional theory (DFT) and standard DFT methods. The tensor orientations are shown to be highly constrained by molecular symmetry elements, but also influenced to some degree by intermolecular interactions. [sup.14]N WURST-CPMG experiments were performed on three compounds and electric field gradient (EFG) parameters (the quadrupolar coupling constant, [C.sub.Q], and the asymmetry parameter, i]q) are reported. First principles calculations of the [sup.14]N EFG tensor parameters and orientations and affirm their dependence on the local hydrogen bonding environment. [sup.35]Cl WURSTCPMG experiments on cisplatin and transplatin are reported, using two different static magnetic fields to extract EFG and CS tensor parameters, and [sup.35]Cl EFG tensor magnitudes and orientations are predicted using first principles calculations. Transverse ([T.sub.2]) relaxation data for all nuclei are used to investigate heteronuclear dipolar relaxation mechanisms, as well as the nature of the local hydrogen bonding environments. Key words: platinum NMR, [sup.195]Pt NMR, [sup.14]N NMR, [sup.35]Cl NMR, cisplatin, transplatin, carboplatin, solid- state NMR, wideline NMR, WURST-CPMG, electric field gradient tensors, chemical shift tensors. On a effectue des experiences de resonance magnetique nucleaire a l'etat solide (RMN-ES) sur le cisplatine et sur quatre composes apparentes plan carres. Dans les experiences de RMN, on a utilise la sequence de pulsation << wideband uniform rate smooth truncation--Carr-Purcell-Meiboom-Gill (WURST-CPMG) >> pour acquerir des spectres RMN du [sup.195]Pt, du [sup.14]N et du [sup.35]Cl avec des raies ultra-larges et de grande qualite. On a aussi effectue des experiences de RMN du [sup.195]Pt en echo de Hahn standard ainsi qu'al'angle magique de rotation afin d'affiner les parametres de tenseur du blindage chimique (BC). On a calcule les orientations du tenseur du blindage magnetique (BM) du platine en faisant appel aux methodes de la theorie de la fonctionnelle de la densite standard (TFD) ainsi qu' avec une onde plane. On a montre que les orientations du tenseur sont grandement contraintes par les elements de symetrie moleculaire, mais qu'ils sont aussi influences jusqu'a un certain point par les interactions intermoleculaires. Les experiences utilisant la sequence de pulsation << WURST-CPMG >> pour le [sup.14]N ont ete effectuees sur trois composes et on rapporte les parametres du gradient du champ electrique (GCE; la constante de couplage quadripolaire, [C.sub.Q] et le parametre d'asymetrie, [η.sub.Q]). Des calculs sur la base de premiers principes des parametres de tenseur du GCE et des ses orientations confirment leur dependance sur l'environnement local des liaisons hydrogenes. Operant sur le cisplatine et le transplatine, a deux champs magnetiques differents, on a aussi realise des experiences utilisant la sequence de pulsation << WURST-CPMG >> pour le [sup.35]Cl afin d'extraire les parametres de tenseur du GCE et du blindage chimique (BC); les amplitudes du tenseur GCE du [sup.35]Cl et ses orientations peuvent etre calculees correctement a partir de premiers principes. On a utilise les donnees de relaxation transversale ([T.sub.2]) de chacun des noyaux pour etudier les mecanismes de relaxation dipolaire heteronucleaire ainsi que la nature des environnements des liaisons hydrogenes locales. Mots-cles : RMN du platine, RMN du [sup.195]Pt, RMN du [sup.14]N, RMN du [sup.35]Cl, cisplatine, transplatine, carboplatine, RMN a l'etat solide, WURST-CPMG, tenseurs du gradient du champ electrique, tenseurs du deplacement chimique. [Traduit par la Redaction], Introduction Cancer is a class of diseases that affects people around the world, and in 2008 was responsible for an estimated 7.6 million deaths globally. (1) The treatment of cancer [...]

A preliminary study involving solid-state [sup.77.Se] NMR spectroscopy and first principles calculations of [sup.77.Se] NMR parameters in Se--N heterocycles is reported. [sup.77.Se] CP/MAS NMR spectra of the ring systems reveal expansive selenium chemical shift (CS) tensors, which are extremely sensitive to molecular geometry, symmetry, ligand substitution, and intermolecular contacts. For systems with known crystal structures, hybrid density functional theory (DFT) calculations of selenium nuclear magnetic shielding (NMS) tensors were carried out, and tensor orientations in the molecular frames examined. Additional DFT calculations of selenium NMS tensors are presented, along with a detailed analysis of pairs of occupied and virtual molecular orbitals that give rise to the Se NMS tensors. A new naturalized local molecular orbital (NLMO) analysis under the same DFT framework is also discussed. Collectively, the NMR data and first principles calculations provide understanding of the influences of electronic structure, bonding, and intermolecular interactions on the selenium NMS tensors, allowing for (i) prediction of unknown molecular structures and (ii) insight into the positions of the stereochemically active selenium lone pairs. Key words: solid-state NMR, [sup.77.Se] NMR, ab initio calculations, chemical shielding, main-group inorganic chemistry, heterocycles, DFT calculations, MO analysis, Gaussian 03, ADF. On rapporte les resultats d'une etude preliminaire de spectroscopie RMN du [sup.77.Se] a l'etat solide et de calculs a partir de principes fondamentaux des parametres RMN du [sup.77.Se] dans des heterocycles Se-N. Les spectres RMN des systemes cycliques par la technique de la rotation a l'angle magique avec polarisation croisee (RAMPC) mettent en evidence l'existence d'un large eventail de tenseurs du deplacement chimique (DC) du selenium qui sont extremement sensibles a la geometrie moleculaire, a la substitution par des ligands et aux contacts intermoleculaires. Pour les systemes dont on connait les structures cristallines, on a effectue des calculs des tenseurs de blindage magnetique nucleaire (BMN) du selenium avec la theorie de la fonctionnelle de la densite (TFD) hybride et on a examine les orientations des tenseurs dans des cadres moleculaires. On rapporte les resultats de calculs effectues sur la base de la TFD des tenseurs de blindage magnetique nucleaire ainsi qu'une analyse detaillee des paires d'orbitales moleculaires occupees et virtuelles qui donnent lieu aux tenseurs de blindage magnetique nucleaire du selenium. On discute aussi d'une nouvelle analyse de l'orbitale moleculaire naturalisee (OMLN) dans le meme cadre de la TFD. Pris collectivement, les donnees de la RMN et les calculs a partir de principes fondamentaux permettent de comprendre les influences de la structure electronique, des liaisons et des interactions intermoleculaires sur les tenseurs de BMN et aussi (i) de faire des predictions pour 15 structures moleculaires inconnues et (ii) de se faire une idee sur les positions des paires d'electrons libres du selenium qui sont actives d'un point de vue stereochimique. Mots-cles : RMN a l'etat solide, RMN du [sup.77.Se], calculs ab initio, blindage chimique, chimie inorganique du groupe principal, heterocycles, calculs TFD, analyse des OM, gaussienne 03, fonctionnelle de la densite d'Amsterdam (FDA). [Traduit par la Redaction], Introduction Carbenes are known to be important reaction intermediates, and there is an enormous amount of literature reporting their syntheses, structures, and reactivities. (1-7) Since the first report of the [...]

Mechanochemical synthesis provides new pathways for the rational design of multi-component crystals (MCCs) involving anionic or cationic components that offer molecular-level architectures unavailable to MCCs comprising strictly neutral components. Structural characterization of the products of mechanochemical syntheses is essential for divining clear relationships between the nature of coformers, milling conditions, reaction mechanisms, and intermolecular bonding. Notably, when powder X-ray diffraction and solid-state NMR (SSNMR) are combined with plane-wave density functional theory (DFT) calculations, they offer opportunities for NMR crystallographic solutions and structural refinements. Herein, we report mechanochemical syntheses of five urea-containing MCCs of the form NR4Cl:xUrea·yH2O (R = H, Et, n-Pr; x = 1, 2, 3; y = 0, 2), which can be made in high yields (> ca. 99%) and great rapidity (<40 minutes). We demonstrate the utility of 35Cl SSNMR for providing distinct fingerprints for each urea MCC and detecting chlorine-containing impurities. Dispersion-corrected plane-wave DFT-D2* calculations are used for structural refinement and relating 35Cl electric field gradient (EFG) tensors and chloride ion hydrogen bonding environments. Finally, ab initio molecular dynamics calculations are used to study the impact of molecular motions on 35Cl EFG tensors, and their concomitant use for site assignment and NMR crystallography. Together, these techniques show great promise for future development of crystal structure prediction protocols using NMR of quadrupolar nuclei. [ABSTRACT FROM AUTHOR]

A study was conducted to determine the effects of varying the [sigma]-electron donor ability of pyridine Lewis-base ligands on the coordination environment of lead(II) in bis-thiolate complexes. The results indicate that lead-nitrogen bond distances is reduced when [sigma]-electron donor ability of the 4-substituted pyridine ligand is increased.

Solid-state [.sup.45.Sc] NMR spectroscopy, ab initio calculations, and X-ray crystallography are applied to examine the relationships between [.sup,45Sc] NMR interactions and molecular structure and symmetry. [.sup.45Sc] NMR quadrupolar coupling constants ([C.sub.o]) range from 3.9 to 13.1 MHz and correlate directly with the symmetry of the scandium coordination environment.

Solid-state (super 93) Nb NMR spectroscopy and (super 13)C NMR experiments are show to be very sensitive and rapid probe of molecular structure and purity in half-sandwich metallocenes. Relationships between tensor orientations the principal components and molecular structures are determined by theoretically calculating CS and electric field gradient (EFG) tensors.

The first solid-state (super 39)K NMR spectra of organometallic complexes cyclopentadienyl potassium (CpK) and pentamethylcyclopentadienyl potassium (Cp*K) is presented. A high S/N (super 39)K spectrum of broad central transition of Cp*K with a breadth of ca. 200 kHz is acquired with the help of piecewise quadrupolar Carr-Purcell Meiboom-Gill (QCPMG) NMR techniques.