New Polymorph of Dehydroepiandrosterone Obtained via Cryomodification

A new anhydrous polymorph of dehydroepiandrosterone (DHEA) is detected in cryomodified powder samples and designated as form VII. The crystal structure of form VII is determined from multiphase X-ray powder diffraction (XRPD) data. Additionally, the unknown crystal structures of anhydrous form III and the new monohydrated DHEA form designated as form S5 are also determined from multiphase XRPD data. To validate the crystal structures III, VII, and S5, energy minimization with dispersion-corrected density functional theory is performed in VASP. An extended list of the DHEA forms with the known crystal structures, which now covers anhydrous forms I, II, III, VI, and VII and solvated forms S1, S2, S4 and S5, allows quantification of DHEA solid-state transformations to be carried out

Structural Properties and Phase Transition of Exfoliated-Restacked Molybdenum Disulfide

The product of exfoliation and restacking of MoS₂ in acidic conditions is studied in detail using X-ray powder diffraction, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The temperature dependence of powder patterns reveals that the heating of exfoliated-restacked MoS₂ is a way to a new nanostructured MoS₂-based layered material that remains nanosized even upon heating to 850 °C. Previously this material has been described as 2H-MoS₂, but according to the X-ray diffraction (XRD) data, its structure cannot be correctly described by any of the “usual” MoS₂ polytypes. A model of the structure of the material describing its XRD patterns and thermal behavior is discussed in detail

Synthesis of thiazolo[3,2-<i>a</i>]pyridines via an unusual Mannich-type cyclization

<p>The Mannich-type reaction of <i>N</i>-methylmorpholinium 4-aryl-3-cyano-6-oxo-1,4,5,6-tetrahydropyridine-2-thiolates with 3-(1,3-benzodioxol-5-yl)-2-methylpropanal (ocean propanal) and <i>p</i>-toluidine afforded 7-aryl-2-(1,3-benzodioxol-5-ylmethyl)-2-methyl-3-[(4-methylphenyl)amino]-5-oxo-2,3,6,7-tetrahydro-5<i>H</i>-thiazolo[3,2-<i>a</i>]pyridine-8-carbonitriles in modest (25–46%) yields. The structure of the key compound was confirmed by X-ray crystal structure analysis.</p> <p></p

Stabilization of 1T-MoS₂ Sheets by Imidazolium Molecules in Self-Assembling Hetero-layered Nanocrystals

We report a facile, room-temperature assembly of MoS₂-based hetero-layered nanocrystals (NCs) containing embedded monolayers of imidazolium (Im), 1-butyl-3-methyl­imid­azolium (BuMeIm), 2-phenyl­imid­azolium, and 2-methyl­benz­imid­azolium molecules. The NCs are readily formed in water solutions by self-organization of the negatively charged, chemically exfoliated 0.6 nm thick MoS₂ sheets and corresponding cationic imidazole moieties. As evidenced by transmission electron microscopy, the obtained NCs are anisotropic in shape, with thickness varying in the range 5–20 nm and lateral dimensions of hundreds of nanometers. The NCs exhibit almost turbostratic stacking of the MoS₂ sheets, though the local order is preserved in the orientation of the imidazolium molecules with respect to the sulfide sheets. The atomic structure of NCs with BuMeIm molecules was solved from powder X-ray diffraction data assisted by density functional theory calculations. The performed studies evidenced that the MoS₂ sheets of the NCs are of the nonconventional 1T-MoS₂ (metallically conducting) structure. The sheets’ puckered outer surface is formed by the S atoms and the positioning of the BuMeIm molecules follows the sheet nanorelief. According to thermal analysis data, the presence of the BuMeIm cations significantly increases the stability of the 1T-MoS₂ modification and raises the temperature for its transition to the conventional 2H-MoS₂ (semiconductive) counterpart by ∼70 °C as compared to pure 1T-MoS₂ (∼100 °C). The stabilizing interaction energy between inorganic and organic layers was estimated as 21.7 kcal/mol from the calculated electron density distribution. The results suggest a potential for the design of few-layer electronic devices exploiting the charge transport properties of monolayer thin MoS₂

Electrostatic Origin of Stabilization in MoS₂–Organic Nanocrystals

Negatively charged molybdenum disulfide layers form stable organic–inorganic layered nanocrystals when reacted with organic cations in solution. The reasons why this self-assembly process leads to a single-phase compound with a well-defined interlayer distance in given conditions are, however, poorly understood to date. Here, for the first time, we quantify the interactions determining the cation packing and stability of the MoS₂–organic nanocrystals and find that the main contribution arises from Coulomb forces. The study was performed on the series of new layered compounds of MoS₂ with naphthalene derivatives, forming several distinct phases depending on reaction conditions. Starting with structural models derived from powder X-ray diffraction data and TEM, we evaluate their cohesion energy by modeling layer separation with periodic PW-DFT-D calculations. The results provide a reliable approach for estimation of the stability of MoS₂-based heterolayered compounds

Stabilization of 1T-MoS₂ Sheets by Imidazolium Molecules in Self-Assembling Hetero-layered Nanocrystals

We report a facile, room-temperature assembly of MoS₂-based hetero-layered nanocrystals (NCs) containing embedded monolayers of imidazolium (Im), 1-butyl-3-methyl­imid­azolium (BuMeIm), 2-phenyl­imid­azolium, and 2-methyl­benz­imid­azolium molecules. The NCs are readily formed in water solutions by self-organization of the negatively charged, chemically exfoliated 0.6 nm thick MoS₂ sheets and corresponding cationic imidazole moieties. As evidenced by transmission electron microscopy, the obtained NCs are anisotropic in shape, with thickness varying in the range 5–20 nm and lateral dimensions of hundreds of nanometers. The NCs exhibit almost turbostratic stacking of the MoS₂ sheets, though the local order is preserved in the orientation of the imidazolium molecules with respect to the sulfide sheets. The atomic structure of NCs with BuMeIm molecules was solved from powder X-ray diffraction data assisted by density functional theory calculations. The performed studies evidenced that the MoS₂ sheets of the NCs are of the nonconventional 1T-MoS₂ (metallically conducting) structure. The sheets’ puckered outer surface is formed by the S atoms and the positioning of the BuMeIm molecules follows the sheet nanorelief. According to thermal analysis data, the presence of the BuMeIm cations significantly increases the stability of the 1T-MoS₂ modification and raises the temperature for its transition to the conventional 2H-MoS₂ (semiconductive) counterpart by ∼70 °C as compared to pure 1T-MoS₂ (∼100 °C). The stabilizing interaction energy between inorganic and organic layers was estimated as 21.7 kcal/mol from the calculated electron density distribution. The results suggest a potential for the design of few-layer electronic devices exploiting the charge transport properties of monolayer thin MoS₂

Electrostatic Origin of Stabilization in MoS₂–Organic Nanocrystals

Negatively charged molybdenum disulfide layers form stable organic–inorganic layered nanocrystals when reacted with organic cations in solution. The reasons why this self-assembly process leads to a single-phase compound with a well-defined interlayer distance in given conditions are, however, poorly understood to date. Here, for the first time, we quantify the interactions determining the cation packing and stability of the MoS₂–organic nanocrystals and find that the main contribution arises from Coulomb forces. The study was performed on the series of new layered compounds of MoS₂ with naphthalene derivatives, forming several distinct phases depending on reaction conditions. Starting with structural models derived from powder X-ray diffraction data and TEM, we evaluate their cohesion energy by modeling layer separation with periodic PW-DFT-D calculations. The results provide a reliable approach for estimation of the stability of MoS₂-based heterolayered compounds

Electronic Structure of Cesium Butyratouranylate(VI) as Derived from DFT-assisted Powder X‑ray Diffraction Data

Investigation of chemical bonding and electronic structure of coordination polymers that do not form high-quality single crystals requires special techniques. Here, we report the molecular and electronic structure of the first cesium butyratouranylate, Cs­[UO₂(<i>n</i>-C₃H₇COO)₃]­[UO₂(<i>n</i>-C₃H₇COO)­(OH)­(H₂O)], as obtained from DFT-assisted powder X-ray diffraction data because of the low quality of crystalline sample. The topological analysis of the charge distribution within the quantum theory of atoms-in-molecules (QTAIM) space partitioning and the distribution of electron localization function (ELF) is reported. The constancy of atomic domain of the uranium­(VI) atom at different coordination numbers (7 and 8) and the presence of three ELF maxima in equatorial plane of an uranyl cation attributed to the 6s and 6p electrons were demonstrated for the first time. Details of methodologies applied for additional verification of the correctness of powder XRD refinement (Voronoi atomic descriptors and the Morse restraints) are discussed

Electronic Structure of Cesium Butyratouranylate(VI) as Derived from DFT-assisted Powder X‑ray Diffraction Data

Investigation of chemical bonding and electronic structure of coordination polymers that do not form high-quality single crystals requires special techniques. Here, we report the molecular and electronic structure of the first cesium butyratouranylate, Cs­[UO₂(<i>n</i>-C₃H₇COO)₃]­[UO₂(<i>n</i>-C₃H₇COO)­(OH)­(H₂O)], as obtained from DFT-assisted powder X-ray diffraction data because of the low quality of crystalline sample. The topological analysis of the charge distribution within the quantum theory of atoms-in-molecules (QTAIM) space partitioning and the distribution of electron localization function (ELF) is reported. The constancy of atomic domain of the uranium­(VI) atom at different coordination numbers (7 and 8) and the presence of three ELF maxima in equatorial plane of an uranyl cation attributed to the 6s and 6p electrons were demonstrated for the first time. Details of methodologies applied for additional verification of the correctness of powder XRD refinement (Voronoi atomic descriptors and the Morse restraints) are discussed

Synthesis of Isomeric Isothiazolo[4′,3′:4,5]- and Isothiazolo[4′,5′:4,5]thieno[3,2‑<i>b</i>]pyrano[2,3‑<i>d</i>]pyridines by Combination of Domino Reactions

Isothiazolothienopyridines have been prepared by a domino reaction (the S_N2 reaction → the Thorpe–Ziegler reaction → the Thorpe–Guareschi reaction type) from disodium 4-cyanoisothiazole-3,5-dithiolate. By changing the order of addition of the alkylation reagents in the reaction with disodium 4-cyanoisothiazole-3,5-dithiolate both possible isomers of the isothiazolothienopyridines are synthesized. These isomers were further used in three-component domino reaction (the Knoevenagel reaction → the Michael reaction → the hetero-Thorpe–Ziegler reaction type) to obtain wide range of isomeric isothiazolothienopyranopyridines