NMR Crystallography

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.

Solid-state NMR and short-range order in crystalline oxides and silicates: a new tool in paramagnetic resonances

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.

`NMR Crystallization': in-situ NMR techniques for time-resolved monitoring of crystallization processes

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.

Single-crystal X-ray diffraction and NMR crystallography of a 1:1 cocrystal of di­thia­non and pyrimethanil

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.

¹³C and ¹⁹F solid-state NMR and X-ray crystallographic study of halogen-bonded frameworks featuring nitro­gen-containing heterocycles

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.

Structure and physicochemical characterization of a naproxen–picolinamide cocrystal

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.

NMR crystallography to probe the breathing effect of the MIL-53(Al) metal–organic framework using solid-state NMR measurements of ¹³C–²⁷Al distances

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.

Structure determination of a partially ordered layered silicate material with an NMR crystallography approach

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.

The ambient hydration of the aluminophosphate JDF-2 to AlPO-53(A): insights from NMR crystallography

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.

Inter­molecular inter­actions in AST zeolites through ¹⁴N NMR and DFT calculations

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.

Insight into the local environment of magnesium and calcium in low-coordination-number organo-complexes using ²⁵Mg and ⁴³Ca solid-state NMR: a DFT study

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.

Solid-state NMR meets electron diffraction: determination of crystalline polymorphs of small organic microcrystalline samples

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

Ab initio crystal structure prediction of magnesium (poly)sulfides and calculation of their NMR parameters

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.

A ¹³C solid-state NMR investigation of four cocrystals of caffeine and theophylline

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.

Crystal structure of guanidinium hexa­fluorido­vanadate(III), (CN₃H₆)₃[VF₆]: an unusual hybrid compound related to perovskite

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

Syntheses and structures of two new coordination polymers generated from a 4-amino­triazole-bridged organic ligand and Co^II salts

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 Co^II coordination polymers, under solvothermal conditions, both featuring two-dimensional networks. The amino­triazole functions as a bidentate cis-conformation ligand linking the Co^II ions in one complex, while it functions as a tridentate trans-conformation linker binding Co^II ions in the other complex.

Structural study of the novel deuterated calix[4]pyrrole complex d₁₂-meso-tetra­kis­(4-meth­oxy­phenyl)-meso-tetra­methyl­calix[4]pyrrole–pyridine N-oxide–aceto­nitrile (1/1/1)

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.

Supra­molecular hydrogen-bonding patterns in 1:1 cocrystals of 5-fluoro­uracil with 4-methyl­benzoic acid and 3-nitro­benzoic acid

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 [(8) homosynthon]. Similarly, the 5FU mol­ecules form two types of base pair via a pair of N—H⋯O hydrogen bonds [(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 (8) ring motif (heterosynthon).

Structure of salts of lithium chloride and lithium hexa­fluoro­phosphate as solvates with pyridine and vinyl­pyridine and structural comparisons: (C₅H₅N)LiPF₆, [p-(CH₂=CH)C₅H₄N]LiPF₆, [(C₅H₅N)LiCl]_n, and [p-(CH₂=CH)C₅H₄N]₂Li(μ-Cl)₂Li[p-(CH₂=CH)C₅H₄N]₂

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.

Structure of a penta­manganese(II)–phenoxide cluster with a central five-coordinate oxide: Mn^II₅(μ-OPh)₆(μ₃-OPh)₂(μ₅-O)(Py)₆·Py (Py is pyridine)

We report here the structure of the Mn^II₅(μ-OPh)₆(μ₃-OPh)₂(μ₅-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.

Crystal structure of a fluorescent C-shaped mol­ecule containing closely stacked bi­thio­phene-substituted quinoxaline rings

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.

Synthesis, crystal structure, DFT studies and photophysical properties of a copper(I)–tri­phenyl­phosphane complex based on trans-(±)-2,4,5-tris­(pyridin-2-yl)-2-imidazoline

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.

Extensive analysis of N—H⋯O hydrogen bonding in four classes of phosphorus compounds: a combined experimental and database study

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.

Three closely related 4,5,6,7-tetra­hydro-1H-pyrazolo­[4,3-c]pyridines: synthesis, mol­ecular conformations and hydrogen bonding in zero, one and two dimensions

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.