Foreword to the special virtual issue on Modern approaches and tools for teaching crystallography

A compilation of articles with a strong teaching element published since 2018 is presented alongside an overview of the articles in the special issue on this topic.

Diastereotopic groups in two new single-enanti­omer structures (R₂)P(O)[NH-(+)CH(C₂H₅)(C₆H₅)] (R = OC₆H₅ and C₆H₅)

Two new single-enanti­omer phospho­rus structures were studied. Their geometries, conformations and NMR features are discussed.

Crystal structure and Hirshfeld surface analysis of 7-[(6-hy­droxy-5,5,8a-tri­methyl-2-methylene­deca­hydro­naphthalen-1-yl)meth­oxy]-2H-chromen-2-one

Crystal structure of bis­(3,5-di­chloro-2-hydroxybenzyl)(2-methoxyethyl)amine

The title compound was prepared via a modified Mannich reaction between 2-meth­oxy­ethyl­amine, 2,4-di­chloro­phenol, and aqueous formaldehyde. The resulting amine bis­(phenol) provides an inter­esting comparison to related species as a result of the electron-withdrawing substituents on the phenol rings, in combination with similar steric parameters.

Structures of rac-2,4:3,5-di­methyl­ene xylitol derivatives

The crystal structures of three xylitol derivatives prepared directly from commercially available xylitol by treatment with formalin and acid followed by subsequent derivatization of the primary hydroxyl group of the bis-methyl­ene ketal with mesyl chloride, benzyl bromide or phenyl iso­cyanate are reported.

A nickel(II) complex with an unsymmetrical tetra­dentate chelating ligand derived from pyridine-2,6-dicarbaldehyde and 2-amino­thio­phenol

[(2-{[6-(1,3-Benzo­thia­zol-2-yl)pyridin-2-yl]carbonyl­aza­nid­yl}phen­yl)sulfanido]nickel(II) crystallizes in the centrosymmetric monoclinic space group P2₁/n. Both arms of the expected bis-Schiff base ligand based on pyridine-2,6-dicarbaldehyde and 2-amino­thio­phenol had oxidized; one by cyclization to a benzo­thia­zole, the other by oxidation of its imine linkage to the corresponding amide.

Synthesis, crystal structure and Hirshfeld surface analysis of 5-[2-(di­cyano­methyl­idene)hydrazin-1-yl]-2,4,6-tri­iodo­isophthalic acid ethanol monosolvate

In the crystal, pairs of mol­ecules are linked by O—H⋯O and N—H⋯O hydrogen bonds forming dimers with (14) motifs. These dimers are connected by O—H⋯O hydrogen bonds into chains along the a-axis direction, forming (16) ring motifs. Further O—H⋯O inter­actions involving the ethanol solvent mol­ecule connect the chains into a three-dimensional network.

Crystal structure of a (carb­oxy­meth­yl)tri­ethyl­aza­nium bromide–2-(tri­ethyl­aza­nium­yl)acetate (1/1) hydrogen-bonded dimer

The crystal structure of a hydrogen-bonded dimer of (tri­ethyl­azaniumyl)­acetic acid and (tri­ethyl­azaniumyl)­acetate bromide features a carb­oxy­lic acid hydrogen atom that is engaged in an asymmetric hydrogen bond with the carboxyl­ate oxygen. The crystal also features intra­molecular C—H hydrogen bonds and a layer of bromide ions that is surrounded by alkyl groups.

Synthesis, crystal structure and Hirshfeld surface analysis of a copper(II) complex involving 3-methyl­benzoate and 2,2′-bi­pyridine ligands

A new copper(II) complex with 3-methyl­benzoate and 2,2′-bi­pyridine synthesized displays chains of hydrogen-bonded complex units along the b axis. Hirshfeld surface analysis indicates that H⋯H and H⋯C/C⋯H contacts are the most important inter­actions.

Crystal structure and Hirshfeld surface analysis of 2-amino-5-{(1E)-1-[(carbamo­thioyl­amino)­imino]eth­yl}-4-methyl-1,3-thia­zol-3-ium chloride monohydrate

In the crystal, the 2-amino-5-{(1E)-1-[(carbamo­thioyl­amino)­imino]­eth­yl}-4-methyl-1,3-thia­zol-3-ium cations are linked by O—H⋯Cl, N—H⋯Cl, N—H⋯O, N—H⋯S and C—H⋯S hydrogen bonds, forming a tri-periodic network.

Crystal structure and Hirshfeld surface analysis of 3-(bromo­meth­yl)-2-[1,2-di­bromo-2-(6-nitro­benzo[d][1,3]dioxol-5-yl)eth­yl]-1-(phenyl­sulfon­yl)-1H-indole chloro­form 0.585-solvate

The title indole derivative crystallizes with a partial occupancy [0.585 (4)] CHCl₃ solvent mol­ecule. The dihedral angles between the indole ring system and pendant nitro­benzodioxolane rings system and phenyl­sulfonyl ring are 4.81 (14) and 72.24 (19)°, respectively. In the crystal, the indole mol­ecules are linked to each other and to the chloro­form mol­ecule by weak C—H⋯O, C—H⋯Cl, C—H⋯π, C—Br⋯π and C—Cl⋯π and aromatic π–π stacking inter­actions.

Crystal structure of 2-{[5-(methyl­sulfan­yl)-4-phenyl-4H-1,2,4-triazol-3-yl]meth­yl}benzo[d]thia­zole

In the crystal structure of the title compound, the triazole ring exhibits inter­planar angles of ca 64 and 77° with the phenyl and benzo­thia­zole planes, respectively. The packing involves three borderline C—H⋯N contacts and a pairing of the triazole rings across an inversion centre.

Crystal structures of the complexes containing macrocyclic cations [M(cyclam)]²⁺ (M = Ni, Zn) and tetra­iodido­cadmate(2–) anion

The isostructural compounds I and II are composed of planar macrocyclic cations [M(cyclam)]²⁺ and the tetra­hedral anion [CdI₄]²⁻, which plays a purely charge-compensation function in the Ni^II complex I and is axially coordinated via the iodide atom in the Zn^II complex II. In both complexes, as a result of N–H⋯I hydrogen bonding, the alternating cations and anions form chains running along the b-axis direction that are arranged into di-periodic sheets oriented parallel to the (101) and (01) planes.

Crystal structure studies and Hirshfeld surface analysis of 4-(di­methyl­aza­nium­yl)-2-hy­droxy­anilinium dichloride monohydrate at 90 K

The low-temperature (90 K) crystal structure of 4-(di­methyl­aza­nium­yl)-2-hy­droxy­anilinium dichloride monohydrate is presented along with a Hirshfeld surface analysis of the organic cation.

Spectroscopic, crystallographic, and Hirshfeld surface characterization of nine-membered-ring-containing 9-meth­oxy-3,4,5,6-tetra­hydro-1H-benzo[b]azonine-2,7-dione and its parent tetra­hydro­car­bazole

9-Meth­oxy-3,4,5,6-tetra­hydro-1H-benzo[b]azonine-2,7-dione and 6-meth­oxy-1,2,3,4-tetra­hydro­car­ba­zole represent the structures of a benzoazonine that contains a nine-membered ring and its parent tetra­hydro­car­ba­zole. The mol­ecules of the former pack together via strong amide N—H⋯O hydrogen bonding and weak C—H⋯O inter­actions, whereas the parent tetra­hydro­car­ba­zole packs with C/N—H⋯π inter­actions, as visualized by Hirshfeld surface characterization.

The unusual (syn-/anti-)₂ conformation of a di­meth­oxy­pyrimidyl-based tennimide

The tennimide macrocycle (I) resides on a twofold axis and adopts an alternate (syn/anti)₂ conformation with no inner cavity (niche), unlike all previously reported (syn)₄ tennimide conformations. A partial occupancy water mol­ecule (with 0.167 site occupancy) at hydrogen-bonding distances to two symmetry-related carbonyl O atoms (as O—H⋯O=C) resides on the twofold axis in a mol­ecular niche between two of the pyridine rings. Macrocycle aggregation occurs as one-dimensional chains along the (010) direction.

Synthesis, characterization and crystal structure of methyl 2-(2-oxo-2H-chromen-4-yl­amino)­benzoate

A new coumarin derivative, methyl 2-(2-oxo-2H-chromen-4-yl­amino)­benzoate, has been synthesized and characterized.

Crystal structure and Hirshfeld surface analysis of (2E)-1-(4-bromo­phen­yl)-3-(2-methyl­phen­yl)prop-2-en-1-one

In the crystal of (2E)-1-(4-bromo­phen­yl)-3-(2-methyl­phen­yl)prop-2-en-1-one, the mol­ecules are linked into chains by weak C—H⋯O inter­actions along the b axis. Successive chains form a zigzag structure along the c axis, and these chains are connected to each other by face-to-face π–π stacking inter­actions along the a axis, forming layers parallel to the (001) plane. The crystal structure maintains its stability via van der Waals inter­actions between the layers.

Crystal structure of the nucleoside 2′-de­oxy­guanosine di­methyl sulfoxide disolvate

The first high-quality crystal structure of unmodified 2′-de­oxy­guanosine is reported. The isolated crystals are the dimethyl sulfoxide disolvate.

Crystal structure and Hirshfeld surface analysis of 8-aza­niumylquinolinium tetra­chlorido­zincate(II)

The organic–inorganic hybride salt (C₉H₁₀N₂)[ZnCl₄] consists of a planar 8-aza­niumylquinolinium dication and a tetra­hedral tetra­chlorido­zincate(II) dianion, held together by N—H⋯Cl and C—H⋯Cl hydrogen bonds, and π—π inter­actions.

Synthesis, structure and Hirshfeld surface analysis of a coordination compound of cadmium acetate with 2-amino­benzoxazole

The mol­ecular and crystal structures of a cadmium acetate coordination compound with 2-amino­benzoxazole were studied, and the Hirshfeld surfaces and fingerprint plots were generated to investigate various inter­molecular inter­actions.