The enanti­opure monopyrrolidine derivative (2S)-methyl (Z)-5-(2-tert-but­oxy-1-cyano-2-oxo­ethyl­idene)pyrrolidine-2-carboxyl­ate, C13H18N2O4, (1), represents a potential ligand and an attractive inter­mediate for the synthesis of chiral metal com­plexes. At the mol­ecular level, the com­pound features an intra­molecular N—H⋯O hydrogen bond; neighbouring mol­ecules inter­act via N—H⋯N contacts to form chains along [100]. Due to its elemental com­position, resonant scattering of the target com­pound is entirely insignificant for diffraction experiments with Mo Kα and small even for Cu Kα radiation. A preliminary study with the harder radiation type confirmed the chiral space group and the suitability of the single crystal chosen; as expected, the results concerning the absolute structure remained com­pletely inconclusive. A second data collection with the longer wavelength gave satisfactory quality indicators for the correct handedness of the mol­ecule, albeit with high standard uncertainties. The absolute configuration has been assessed independently: CD spectra for both enanti­omers of the target mol­ecule were calculated and the spectrum for the S-configured stereoisomer was in agreement with the experiment. The Cotton effect of (1) may be ascribed to π–π* transitions from HOMO to LUMO and from HOMO to LUMO+1. As both independent techniques agree with respect to the handedness of the target mol­ecule, the absolute structure may be assigned with a high degree of confidence.

The title com­pound, tetra­ethyl­ammonium tetra­thio­rhenate, [(C2H5)4N][ReS4], has, at room temperature, a disordered structure in the space group P63mc (Z = 2, α-phase). A phase transition to the monoclinic space group P21 (Z = 2, γ-phase) at 285 K leads to a pseudo-merohedral twin. The high deviation from the hexa­gonal metric causes split reflections. However, the different orientations could not be separated, but were integrated using a large integration box. Rapid cooling to 110–170 K produces a metastable β-phase (P63, Z = 18) in addition to the γ-phase. All crystals of the β-phase are contaminated with the γ-phase. Additionally, the crystals of the β-phase are merohedrally twinned. In contrast to the α-phase, the β- and γ-phases do not show disorder.

During investigations of the formation of hydrated magnesium carbonates, a sample of the previously unknown magnesium carbonate hexa­hydrate (MgCO3·6H2O) was synthesized in an aqueous solution at 273.15 K. The crystal structure consists of edge-linked isolated pairs of Mg(CO3)(H2O)4 octa­hedra and noncoordinating water mol­ecules, and exhibits similarities to NiCO3·5.5H2O (hellyerite). The recorded X-ray diffraction pattern and the Raman spectra confirmed the formation of a new phase and its transformation to magnesium carbonate trihydrate (MgCO3·3H2O) at room temperature.

An error in an equation in the paper by Song et al. [Acta Cryst. (2019), C75, 1353–1358] is corrected.

An efficient synthesis of 1-aryl­isochromeno[3,4-d][1,2,3]triazol-5(1H)-ones, involving the diazo­tization of 3-amino-4-aryl­amino-1H-isochromen-1-ones in weakly acidic solution, has been developed and the spectroscopic characterization and crystal structures of four examples are reported. The mol­ecules of 1-phenyl­isochromeno[3,4-d][1,2,3]triazol-5(1H)-one, C15H9N3O2, (I), are linked into sheets by a combination of C—H⋯N and C—H⋯O hydrogen bonds, while the structures of 1-(2-methyl­phen­yl)isochromeno[3,4-d][1,2,3]triazol-5(1H)-one, C16H11N3O2, (II), and 1-(3-chloro­phen­yl)isochromeno[3,4-d][1,2,3]triazol-5(1H)-one, C15H8ClN3O2, (III), each contain just one hydrogen bond which links the mol­ecules into simple chains, which are further linked into sheets by π-stacking inter­actions in (II) but not in (III). In the structure of 1-(4-chloro­phen­yl)isochromeno[3,4-d][1,2,3]triazol-5(1H)-one, (IV), isomeric with (III), a combination of C—H⋯O and C—H⋯π(arene) hydrogen bonds links the mol­ecules into sheets. When com­pound (II) was exposed to a strong acid in methanol, qu­anti­tative conversion occurred to give the ring-opened transesterification product methyl 2-[4-hy­droxy-1-(2-methyl­phen­yl)-1H-1,2,3-triazol-5-yl]benzoate, C17H15N3O3, (V), where the mol­ecules are linked by paired O—H⋯O hydrogen bonds to form centrosymmetric dimers.

An operationally simple and time-efficient approach has been developed for the synthesis of racemic N-substituted 3-(2-aryl-2-oxoeth­yl)-3-hy­droxy­indolin-2-ones by a piperidine-catalysed aldol reaction between aryl methyl ketones and N-alkyl­isatins. These aldol products were used successfully as strategic inter­mediates for the preparation of N-substituted (E)-3-(2-hetaryl-2-oxo­ethyl­idene)indolin-2-ones by a stereoselective dehydration reaction under acidic conditions. The products have all been fully characterized by 1H and 13C NMR spectroscopy, by mass spectrometry and, for a representative selection, by crystal structure analysis. In each of (RS)-1-benzyl-3-hy­droxy-3-[2-(4-meth­oxy­phen­yl)-2-oxoeth­yl]indolin-2-one, C24H21NO4, (Ic), and (RS)-1-benzyl-3-{2-[4-(di­methyl­amino)­phen­yl]-2-oxoeth­yl}-3-hy­droxy­indolin-2-one, C25H24N2O3, (Id), inversion-related pairs of mol­ecules are linked by O—H⋯O hydrogen bonds to form R22(10) rings, which are further linked into chains of rings by a combination of C—H⋯O and C—H⋯π(arene) hydrogen bonds in (Ic) and by C—H⋯π(arene) hydrogen bonds in (Id). The mol­ecules of (RS)-1-benzyl-3-hy­droxy-3-[2-oxo-2-(pyridin-4-yl)eth­yl]indolin-2-one, C22H18N2O3, (Ie), are linked into a three-dimensional framework structure by a combination of O—H⋯N, C—H⋯O and C—H⋯π(arene) hydrogen bonds. (RS)-3-[2-(Benzo[d][1,3]dioxol-5-yl)-2-oxoeth­yl]-1-benzyl-3-hy­droxy­indolin-2-one, C24H19NO5, (If), crystallizes with Z' = 2 in the space group Poverline{1} and the mol­ecules are linked into com­plex sheets by a combination of O—H⋯O, C—H⋯O and C—H⋯π(arene) hydro­gen bonds. In each of (E)-1-benzyl-3-[2-(4-fluoro­phen­yl)-2-oxo­ethyl­idene]indolin-2-one, C23H16FNO2, (IIa), and (E)-1-benzyl-3-[2-oxo-2-(thiophen-2-yl)ethylidene]indolin-2-one, C21H15NO2S, (IIg), the mol­ecules are linked into simple chains by a single C—H⋯O hydrogen bond, while those of (E)-1-benzyl-3-[2-oxo-2-(pyridin-4-yl)ethyl­idene]indolin-2-one, C22H16N2O2, (IIe), are linked by three C—H⋯O hydrogen bonds to form sheets which are further linked into a three-dimensional structure by C—H⋯π(arene) hydrogen bonds. There are no hydrogen bonds in the structures of either (E)-1-benzyl-3-[2-(4-meth­oxy­phen­yl)-2-oxo­ethyl­idene]indolin-2-one, C24H19NO3, (IIc), or (E)-1-benzyl-5-chloro-3-[2-(4-chloro­phen­yl)-2-oxo­ethyl­idene]indolin-2-one, C23H15Cl2NO2, (IIh), but the mol­ecules of (IIh) are linked into chains of π-stacked dimers by a combination of C—Cl⋯π(arene) and aromatic π–π stacking inter­actions.

The com­pound poly[2-hy­droxy-N-methyl­ethan-1-aminium [μ3-cyanido-κ3C:C:N-di-μ-cyanido-κ4C:N-dicuprate(I)]], {(C3H10NO)[Cu2(CN)3]}n or [meoenH]Cu2(CN)3, crystallizes in the tetra­gonal space group P43. The structure consists of a three-dimensional (3D) anionic CuICN network with noncoordinated protonated N-methyl­ethano­lamine cations providing charge neutrality. Pairs of cuprophilic Cu atoms are bridged by the C atoms of μ3-cyanide ligands, which link these units into a 43 spiral along the c axis. The spirals are linked together into a 3D anionic network by the two other cyanide groups. The cationic moieties are linked into their own 43 spiral via N—H⋯O and O—H⋯O hydrogen bonds, and the cations inter­act with the 3D network via an unusual pair of N—H⋯N hydrogen bonds to one of the μ2-cyanide groups. Thermogravimetric analysis indicates an initial loss of the base cation and one cyanide as HCN at temperatures in the range 130–250 °C to form CuCN. We show how loss of a specific cyanide group from the 3D CuCN structure could form the linear CuCN structure. Further heating leaves a residue of elemental copper, isolated as the oxide.

The monoclinic crystal structure of Na2SO3(H2O)7 is characterized by an alternating stacking of (100) cationic sodium–water layers and anionic sulfite layers along [100]. The cationic layers are made up from two types of [Na(H2O)6] octa­hedra that form linear 1∞[Na(H2O)4/2(H2O)2/1] chains linked by dimeric [Na(H2O)2/2(H2O)4/1]2 units on both sides of the chains. The isolated trigonal–pyramidal sulfite anions are connected to the cationic layers through an intricate network of O—H⋯O hydrogen bonds, together with a remarkable O—H⋯S hydrogen bond, with an O⋯S donor–acceptor distance of 3.2582 (6) Å, which is about 0.05 Å shorter than the average for O—H⋯S hydrogen bonds in thio­salt hydrates and organic sulfur com­pounds of the type Y—S—Z (Y/Z = C, N, O or S). Structural relationships between monoclinic Na2SO3(H2O)7 and ortho­rhom­bic Na2CO3(H2O)7 are discussed in detail.

The positional change of nitro­gen-7 of the RNA constituent guanosine to the bridgehead position-5 leads to the base-modified nucleoside 5-aza-7-de­aza­guanosine. Contrary to guanosine, this mol­ecule cannot form Hoogsteen base pairs and the Watson–Crick proton donor site N3—H becomes a proton-acceptor site. This causes changes in nucleobase recognition in nucleic acids and has been used to construct stable `all-purine' DNA and DNA with silver-mediated base pairs. The present work reports the single-crystal X-ray structure of 7-iodo-5-aza-7-de­aza­guanosine, C10H12IN5O5 (1). The iodinated nucleoside shows an anti conformation at the glycosylic bond and an N conformation (O4'-endo) for the ribose moiety, with an anti­periplanar orientation of the 5'-hy­droxy group. Crystal packing is controlled by inter­actions between nucleobase and sugar moieties. The 7-iodo substituent forms a contact to oxygen-2' of the ribose moiety. Self-pairing of the nucleobases does not take place. A Hirshfeld surface analysis of 1 highlights the contacts of the nucleobase and sugar moiety (O—H⋯O and N—H⋯O). The concept of pK-value differences to evaluate base-pair stability was applied to purine–purine base pairing and stable base pairs were predicted for the construction of `all-purine' RNA. Furthermore, the 7-iodo substituent of 1 was functionalized with benzo­furan to detect motional constraints by fluorescence spectroscopy.

Crystals of the rare earth metal polytelluride LaTe1.82(1), namely, lanthanum telluride (1/1.8), have been grown by molten alkali halide flux reactions and vapour-assisted crystallization with iodine. The two-dimensionally incommensurately modulated crystal structure has been investigated by X-ray diffraction experiments. In contrast to the tetra­gonal average structure with unit-cell dimensions of a = 4.4996 (5) and c = 9.179 (1) Å at 296 (1) K, which was solved and refined in the space group P4/nmm (No. 129), the satellite reflections are not compatible with a tetra­gonal symmetry but enforce a symmetry reduction. Possible space groups have been derived by group–subgroup relationships and by consideration of previous reports on similar rare earth metal polychalcogenide structures. Two structural models in the ortho­rhom­bic superspace group, i.e. Pmmn(α,β,1 over 2)000(−α,β,1 over 2)000 (No. 59.2.51.39) and Pm21n(α,β,1 over 2)000(−α,β,1 over 2)000 (No. 31.2.51.35), with modulation wave vectors q1 = αa* + βb* + 1 over 2c* and q2 = −αa* + βb* + 1 over 2c* [α = 0.272 (1) and β = 0.314 (1)], have been established and evaluated against each other. The modulation describes the distribution of defects in the planar [Te] layer, coupled to a displacive modulation due to the formation of different Te anions. The bonding situation in the planar [Te] layer and the different Te anion species have been investigated by density functional theory (DFT) methods and an electron localizability indicator (ELI-D)-based bonding analysis on three different approximants. The temperature-dependent electrical resistance revealed a semiconducting behaviour with an estimated band gap of 0.17 eV.

During evaporation of natural and synthetic K–Mg–Cl brines, the formation of almost square plate-like crystals of potassium carnallite (potassium chloride magnesium dichloride hexa­hydrate) was observed. A single-crystal structure analysis revealed a monoclinic cell [a = 9.251 (2), b = 9.516 (2), c = 13.217 (4) Å, β = 90.06 (2)° and space group C2/c]. The structure is isomorphous with other carnallite-type com­pounds, such as NH4Cl·MgCl2·6H2O. Until now, natural and synthetic carnallite, KCl·MgCl2·6H2O, was only known in its ortho­rhom­bic form [a = 16.0780 (3), b = 22.3850 (5), c = 9.5422 (2) Å and space group Pnna].

A new polymorph (form II) is reported for the 1:1 dimethyl sulfoxide solvate of 2,3,5,6-tetra­fluoro-1,4-di­iodo­benzene (TFDIB·DMSO or C6F4I2·C2H6SO). The structure is similar to that of a previously reported polymorph (form I) [Britton (2003). Acta Cryst. E59, o1332–o1333], containing layers of TFDIB mol­ecules with DMSO mol­ecules between, accepting I⋯O halogen bonds from two TFDIB mol­ecules. Re-examination of form I over the temperature range 300–120 K shows that it undergoes a phase transformation around 220 K, where the DMSO mol­ecules undergo re-orientation and become ordered. The unit cell expands by ca 0.5 Å along the c axis and contracts by ca 1.0 Å along the a axis, and the space-group symmetry is reduced from Pnma to P212121. Refinement of form I against data collected at 220 K captures the (average) structure of the crystal prior to the phase transformation, with the DMSO mol­ecules showing four distinct disorder com­ponents, corresponding to an overlay of the 297 and 120 K structures. Assessment of the inter­molecular inter­action energies using the PIXEL method indicates that the various orientations of the DMSO mol­ecules have very similar total inter­action energies with the molecules of the TFDIB framework. The phase transformation is driven by inter­actions between DMSO mol­ecules, whereby re-orientation at lower temperature yields significantly closer and more stabilizing inter­actions between neighbouring DMSO mol­ecules, which lock in an ordered arrangement along the shortened a axis.

Entangled embedded periodic nets and crystal frameworks are defined, along with their dimension type, homogeneity type, adjacency depth and periodic isotopy type.

The application of groupoids to modular crystal structures is presented.

Features of azimuthal plots for RHEED and its new counterpart, RHEPD, are discussed. The plots, for both electrons and positrons, are determined using dynamical diffraction theory.

A method is described for indexing grazing-incidence X-ray diffraction data of epitaxially grown thin films comprising various crystal orientations and/or polymorphs by measuring reciprocal-lattice vectors.

A method is adapted to generate a full rank realization of an abstract regular polyhedron with automorphism group H3.

Structure-mining finds and returns the best-fit structures from structural databases given a measured pair distribution function data set. Using databases and heuristics for automation it has the potential to save experimenters a large amount of time as they explore candidate structures from the literature.

To describe multiple Bragg reflection from a thick, ideally imperfect crystal, the transport equations are reformulated in three-dimensional phase space and solved by spectral collocation in the depth coordinate. Example solutions illustrate the orientational spread of multiply reflected rays and the distortion of rocking curves, especially for finite detectors.

Physical quantities in arbitrary dimensional space can be classified into 41 types using three antisymmetries within the framework of Clifford algebra.

A new type of X-ray LLL interferometer, a `hard' interferometer, which has both a base and a `ceiling', is tested for experimental investigations. The tested interferometer has no preliminary uncontrollable moiré and can be used for object and deformation investigations.

The Debye scattering equation (DSE) is generalized and augmented in order to account for moderate texture effects, yielding the differential cross section as a function of atomic coordinates and texture coefficients subject to symmetry constraints. Implications for the evaluation of the pair distribution function (PDF) as a direct transform of powder diffraction data from textured samples are also discussed.

Quaternion methods for obtaining solutions to the problem of finding global rotations that optimally align pairs of corresponding lists of 3D spatial and/or orientation data are critically studied. The existence of multiple literatures and historical contexts is pointed out, and the algebraic solutions of the quaternion approach to the classic 3D spatial problem are emphasized. The treatment is extended to novel quaternion-based solutions to the alignment problems for 4D translation and orientation data.

The inversion of X-ray reflectivity to reveal the topography of a one-dimensional interface is evaluated through model calculations.

A Landau theory for the wurtzite-based heterovalent ternary semiconductor ZnSnN2 is developed and a first-order reconstructive phase transition is proposed as the cause of observed crystal structure disorder. The model infers that the phase transition is paraelectric to antiferroelectric.

The analytical solution of the problem of X-ray spherical-wave Laue diffraction in a single crystal with a linear change of thickness on the exit surface is derived. General equations are applied to a specific case of plane-wave Laue diffraction in a thick crystal under the conditions of the Borrmann effect.

Using mineralogical data, it is demonstrated that chemical simplicity measured as an amount of Shannon information per atom on average corresponds to higher symmetry measured as an order of the point group of a mineral, which provides a modern formulation of the Fedorov–Groth law.

Combining sodium hydride with some solvents can be a bad idea, as a group of researchers from Corteva Agriscience and Dow Chemical remind the chemistry community in Organic Process Research & Development ,(2019, DOI: 10.1021/acs.oprd.9b00276). Reports of explosions from combining NaH with a polar aprotic solvent such as dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide […]

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Here’s what’s planned for chemical and laboratory safety at the ACS National Meeting in San Diego, which starts on Sunday. You can also take advantage of the Division of Chemical Health & Safety’s printer-friendly CHAS-At-A-Glance. Sunday, Aug. 25 Committee on Chemical Safety Open and Executive Subcommittee Meeting, 7:00–10:00 am, Marriott Marquis San Diego Marina, Marina […]

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Working in a lab is safe most of the time, “except when it isn’t, and that’s when being alone compounds the danger,” says a new lab safety video about working alone. You can watch it on YouTube or download it for offline viewing from the American Chemical Society’s Division of Chemical Health and Safety website. […]

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