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Journal logoSTRUCTURAL
CHEMISTRY
ISSN: 2053-2296

March 2017 issue

Special issue on NMR crystallography

Guest Editors: David Bryce (University of Ottawa, Canada) and Francis Taulelle (Université de Versailles Saint Quentin en Yvelines, France)

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Cover illustration: The term `crystallography', in its broadest sense, refers to obtaining structural information on crystals and related solids. Diffraction-based methods continue to play an enormous role in this area of research. Nuclear magnetic resonance (NMR) spectroscopy has, however, from its earliest days, also provided structural information on both crystalline and amorphous samples. The contributions to this special issue serve as an excellent introduction to the power and scope of NMR crystallographic methods and applications.

editorial


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David Bryce and Francis Taulelle introduce this special issue of Acta Crystallographica Section C on `NMR Crystallography' where the contributions serve as an excellent introduction to the power and scope of NMR crystallographic methods and applications.

topical reviews


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In many oxide and silicate materials containing paramagnetic components at the hundreds of ppm to many percent level, high-resolution solid-state NMR spectra can provide important new types of information about short-range cation order/disorder, through often-large effects of unpaired electron spins on nuclear spins.

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A number of technical challenges are associated with adapting solid-state NMR spectroscopy for in-situ studies. Recently, an in-situ solid-state NMR strategy for monitoring the evolution of crystallization processes has been developed and has proven to be a promising approach for identifying the sequence of distinct solid forms present as a function of time during crystallization from solution, and for the discovery of new polymorphs. The latest development of this technique, called `CLASSIC' NMR, allows the simultaneous measurement of both liquid-state and solid-state NMR spectra as a function of time, thus yielding complementary information on the evolution of both the liquid phase and the solid phase during crystallization from solution.

nmr crystallography


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A combined single-crystal X-ray diffraction and NMR crystallography study of a 1:1 cocrystal of two fungicides, namely di­thia­non and pyrimethanil, is presented. Specifically, the role of hydrogen bonding and C—H⋯π and S⋯O inter­molecular inter­actions is qu­anti­tatively investigated.

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A crystallographic and structural analysis of halogen-bonded compounds by applying a combined X-ray diffraction (XRD) and solid-state nuclear magnetic resonance (SSNMR) approach is reported. 13C and 19F solid-state magic-angle spinning (MAS) NMR is shown to be a convenient method to characterize the structural features of the halogen-bond donor and acceptor, with chemical shifts attributable to cocrystal formation observed in the spectra of both nuclides.

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The crystal structure is reported of a new 1:1 cocrystal of naproxen with picolinamide, and the pharmaceutically relevant properties are investigated. An NMR crystallography approach is used to distinguish between two crystallographically unique COOH–CONH hydrogen-bonded dimers and to confirm the location of the H atoms in the two dimers.

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We show how 13C–27Al solid-state NMR experiments distinguish between the large and narrow pore structures of MIL-53(Al). These experiments also prove the rigidity of these structures and provide an estimate of the average distance between the free ligand and the framework in the as-synthesized MIL-53(Al) material.

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A structural model for the cetyltri­methyl­ammonium surfactant-templated layered silicate material, which lacks full three-dimensional crystallinity, is reported based an NMR crystallography approach which combines structural information obtained from powder X-ray diffraction and solid-state nuclear magnetic resonance spectroscopy.

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Using multinuclear solid-state NMR spectroscopy and first-principles DFT calculations, we examine the slow ambient hydration of the AEN-type aluminophosphate, JDF-2, to AlPO-53(A). We propose a modified version of the published structure of AlPO-53(A), with reorientation of the methyl­ammonium cations and partial occupancy of the water sites.

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The reinvestigation of silica AST zeolite by 14N NMR and DFT calculations allows the highlighting of inter­molecular inter­actions involving the tetra­methyl­ammonium cations and fluoride anions (hydrogen and tetrel bonds) that strengthen the stability of the whole structure.

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DFT calculations of 25Mg and 43Ca NMR parameters were performed on the crystal structures of organomagnesium and organocalcium complexes involving low coordination numbers and N-bearing ligands. It is shown how these spectroscopies may be used for these systems for NMR crystallography approaches.

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A combined approach of solid-state NMR and electron diffraction are demonstrated to determine the crystalline form of polycrystalline organic materials.

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Experimentally observed crystalline forms of MgS were successfully predicted from first principles and an inter­esting hypothetical structure of MgS2 was identified. For all these forms, 25Mg NMR parameters (chemical shifts and quadrupolar coupling constants) were calculated.

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This work reports an analysis of the 13C solid-state NMR chemical shifts for a series of four homologous cocrystals. The isotropic chemical shifts and shift tensors are compared.

research papers


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(CN3H6)3[VF6] has a cubic structure containing isolated VF6 octa­hedra and exhibiting structural relationships to perovskite.

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The multidentate 4-amino­triazole-bridged organic ligand 4-amino-3,5-bis­(4,3′-bipyridyl-5′-yl)-4H-1,2,4-triazole has been prepared and used to synthesize two CoII coordination polymers, under solvothermal conditions, both featuring two-dimensional networks. The amino­triazole functions as a bidentate cis-conformation ligand linking the CoII ions in one complex, while it functions as a tridentate trans-conformation linker binding CoII ions in the other complex.

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A novel complex based on d12-meso-tetra­kis­(4-meth­oxy­phen­yl)-meso-tetra­methyl­calix[4]pyrrole has been assembled using an excess of pyridine N-oxide. A single-crystal X-ray study shows that the receptor adopts a cone conformation with the N-oxide fragment encapsulated deep within the cavity. 1H NMR spectroscopy was used to probe the mol­ecular binding formation in CD3CN and confirms the X-ray results.

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Two cocrystals of 5-fluoro­uracil (5FU) cocrystallizing with 4-methyl­benzoic acid (MBA) and 3-nitro­benzoic (NBA) acid have been prepared. In the former, the MBA mol­ecules form carb­oxy­lic acid dimers [R_{2}^{2}(8) homosynthon]. Similarly, the 5FU mol­ecules form two types of base pair via a pair of N—H⋯O hydrogen bonds [R_{2}^{2}(8) homosynthon]. In the latter cocrystal, 5FU inter­acts with the carb­oxy­lic acid group of NBA via N—H⋯O and O—H⋯O hydrogen bonds, generating an R_{2}^{2}(8) ring motif (heterosynthon).

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Dissolution of LiCl or LiPF6 in pyridine or vinyl­pyridine and slow vapor diffusion of this solution with diethyl ether gives solvates of the lithium salts coordinated by pyridine ligands. In the case of the hexa­fluorophosphate salts, the chemical species formed are similar, namely binary salts with hexa­fluoro­phosphate counter-ions. In contrast, the solvates with LiCl are structurally dissimilar, with one forming a one-dimensional ionic polymer of fused LiCl rhombs and the other crystallizing as an isolated mol­ecular unit with a complex array of van der Waals inter­actions of neighboring mol­ecules.

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We report here the structure of the MnII5(μ-OPh)63-OPh)25-O)(Py)6 mol­ecular cluster containing an unusual central trigonal bipyramidal oxide, and compare its geometry to three analogous metalloclusters. While the structures are similar overall, the apical metal site shows the greatest contrast with the other reported first-row transition metal systems, having a larger bond distance than the Ti system, and a shorter contact than the Fe system.

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The structural characterization of a C-shaped mol­ecule with closely stacked bi­thio­phene-substituted quinoxaline rings revealed π-stacking inter­actions between the quinoxaline rings that are responsible for some of its photophysical properties.

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The mononuclear copper(I) compound, [Cu(L)(P)2]PF6, where L is trans-(±)-2,4,5-tris­(pyridin-2-yl)-2-imidazoline and P is tri­phenyl­phosphane, shows inter­esting photophysical properties, which were evaluated experimentally and theoretically.

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The positive or negative charge-assisted N—H⋯O hydrogen bonds in two new phospho­rus-based salts are compared with the neutral hydrogen bonds in two neutral mol­ecules. The study was completed by considering analogous structures from the Cambridge Structural Database.

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Three closely related 3-aryl-4,5,6,7-tetra­hydro­pyrazolo­[4,3-c]pyridine derivatives exhibit two quite distinct mol­ecular conformations, and all three show differing patterns of inter­molecular hydrogen bonding.

Special and virtual issues

Acta Crystallographica Section C has recently published special issues on

NMR Crystallography (March 2017)

Scorpionates: a golden anniversary (November 2016)

Full details are available on the special issues page.

The latest virtual issue features Coordination polymers, with an introduction by Len Barbour.

What are the 'most read' articles from the recent special issues?

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