Tautomerism and Rotamerism of Favipiravir and Halogenated Analogues in Solution and in the Solid State

Favipiravir is an important selective antiviral against RNA-based viruses, and currently, it is being repurposed as a potential drug for the treatment of COVID-19. This type of chemical system presents different carboxamide-rotameric and hydroxyl-tautomeric states, which could be essential for interpreting its selective antiviral activity. Herein, the tautomeric 3-hydroxypyrazine/3-pyrazinone pair of favipiravir and its 6-substituted analogues, 6-Cl, 6-Br, 6-I, and 6-H, were fully investigated in solution and in the solid state through ultraviolet-visible, 1H nuclear magnetic resonance, infrared spectroscopy, and X-ray diffraction techniques. Also, a study of the gas phase was performed using density functional theory calculations. In general, the keto-enol balance in these 3-hydroxy-2-pyrazinecarboxamides is finely modulated by external and internal electrical variations via changes in solvent polarity or by replacement of substituents at position 6. The enol tautomer was prevalent in an apolar environment, whereas an increase in the level of the keto tautomer was favored by an increase in solvent polarity and, even moreso, with a strong hydrogen-donor solvent. Keto tautomerization was favored either in solution or in the solid state with a decrease in 6-substituent electronegativity as follows: H ≫ I ≈ Br > Cl ≥ F. Specific rotameric states based on carboxamide, "cisoide" and "transoide", were identified for the enol and keto tautomer, respectively; their rotamerism is dependent on the tautomerism and not the aggregation state.

Revealing the Elusive Structure and Reactivity of Iron Boride α-FeB

Crystal structures can strongly deviate from bulk states when confined into nanodomains. These deviations may deeply affect properties and reactivity and then call for a close examination. In this work, we address the case where extended crystal defects spread through a whole solid and then yield an aperiodic structure and specific reactivity. We focus on iron boride, α-FeB, whose structure has not been elucidated yet, thus hindering the understanding of its properties. We synthesize the two known phases, α-FeB and β-FeB, in molten salts at 600 and 1100 °C, respectively. The experimental X-ray diffraction (XRD) data cannot be satisfactorily accounted for by a periodic crystal structure. We then model the compound as a stochastic assembly of layers of two structure types. Refinement of the powder XRD pattern by considering the explicit scattering interference of the different layers allows quantitative evaluation of the size of these domains and of the stacking faults between them. We, therefore, demonstrate that α-FeB is an intergrowth of nanometer-thick slabs of two structure types, β-FeB and CrB-type structures, in similar proportions. We finally discuss the implications of this novel structure on the reactivity of the material and its ability to perform insertion reactions by comparing the reactivities of α-FeB and β-FeB as reagents in the synthesis of a model layered material: Fe₂AlB₂. Using synchrotron-based in situ X-ray diffraction, we elucidate the mechanisms of the formation of Fe₂AlB₂. We highlight the higher reactivity of the intergrowth α-FeB in agreement with structural relationships.

Reactivity of bi- and monometallic trifluoroacetates towards amorphous SiO2

The reactivity of alkali-manganese(II) and alkali trifluoroacetates towards amorphous SiO2 (a-SiO2) was studied in the solid-state. K4Mn2(tfa)8, Cs3Mn2(tfa)7(tfaH), KH(tfa)2, and CsH(tfa)2 (tfa = CF3COO-) were thermally decomposed under vacuum in fused quartz tubes. Three new bimetallic fluorotrifluoroacetates of formulas K4Mn3(tfa)9F, Cs4Mn3(tfa)9F, and K2Mn(tfa)3F were discovered upon thermolysis at 175 °C. K4Mn3(tfa)9F and Cs4Mn3(tfa)9F feature a triangular-bridged metal cluster of formula [Mn3(μ3-F)(μ2-tfa)6(tfa)3]4-. In the case of K2Mn(tfa)3F, fluoride serves as an inverse coordination center for the tetrahedral metal cluster K2Mn2(μ4-F). Fluorotrifluoroacetates may be regarded as intermediates in the transformation of bimetallic trifluoroacetates to fluoroperovskites KMnF3, CsMnF3, and Cs2MnF4, which crystallized between 250 and 600 °C. Decomposition of these trifluoroacetates also yielded alkali hexafluorosilicates K2SiF6 and Cs2SiF6 as a result of the fluorination of fused quartz. The ability to fluorinate fused quartz was observed for monometallic alkali trifluoroacetates as well. Hexafluorosilicates and heptafluorosilicates K3SiF7 and Cs3SiF7 were obtained upon thermolysis of KH(tfa)2 and CsH(tfa)2 between 200 and 400 °C. This ability was exploited to synthesize fluorosilicates under air by simply reacting alkali trifluoroacetates with a-SiO2 powder.

Expanding the synthetic toolbox to access pristine and rare-earth-doped BaFBr nanocrystals

A new synthetic route to access pristine and rare-earth-doped BaFBr nanocrystals is described. Central to this route is an organic-inorganic hybrid precursor of formula Ba₅(CF₂BrCOO)₁₀(H₂O)₇ that serves as a dual-halogen source. Thermolysis of this precursor in a mixture of high-boiling point organic solvents yields spherical BaFBr nanocrystals (≈20 nm in diameter). Yb:Er:BaFBr nanocuboids (≈26 nm in length) are obtained following the same route. Rare-earth-doped nanocrystals display NIR-to-visible photon upconversion under 980 nm excitation. The temperature-dependence of the green emission from Er³⁺ may be exploited for optical temperature sensing between 150 and 450 K, achieving a sensitivity of 1.1 × 10^-2 K^-1 and a mean calculated temperature of 300.9 ± 1.5 K at 300 K. The synthetic route presented herein not only enables access to unexplored upconverting materials but also, and more importantly, creates the opportunity to develop solution-processable photostimulable phosphors based on BaFBr.

Efficient Access to the Iboga Skeleton: Optimized Procedure to Obtain Voacangine from Voacanga africana Root Bark

Iboga alkaloids are a group of monoterpenoid indole alkaloids with promising and intriguing biological activities. Ibogaine is the representative member of the series and has become widely known as a potent atypical psychedelic with promising effects to treat substance use disorder. Nowadays, an efficient and scalable enantioselective total synthesis of ibogaine and related iboga alkaloids is still lacking, so direct extraction from natural sources or semi-synthetic schemes are the methods of choice to obtain them in a preparative scale. In particular, ibogaine can be obtained either by a low yielding direct isolation from Tabernanthe iboga or using a semi-synthetic procedure from voacangine, an iboga alkaloid occurring in a higher yield in the root bark of Voacanga africana. In this work, we describe an optimized process to obtain voacangine from V. africana root bark as a precursor of the iboga scaffold. Using a direct acetone-based extraction procedure (0.5 kg of root bark), voacangine was isolated in ∼0.8% of root bark dried weight, while the major alkaloids isolated from the bark were identified as iboga-vobasinyl dimers (∼3.7%) such as voacamine and voacamidine. Since these alkaloids contain the voacangine moiety in their structure, the cleavage of the dimers was further optimized, affording an extra amount of voacangine in ∼50% isolated molar yield. In this manner, the total amount of voacangine obtained by application of the whole procedure to the plant material (extraction and dimer cleavage) could almost duplicate the content originally found in the root bark.

Novel complexes with ONNO tetradentate coumarin schiff-base donor ligands: x-ray structures, DFT calculations, molecular dynamics and potential anticarcinogenic activity

The synthesis of eight novel Zn(II), Co(II), Cu(II), Ni(II) and Pt(II) complexes (2-9) derived from the ONNO tetradentate coumarin Schiff-Base donor ligands, L₁ and the novel L₂, was performed. All compounds were characterized by analytical, spectrometry and spectroscopy techniques. Complexes 2-4 were also characterized by DFT calculations and the structures of 5 and 6 were determined by single-crystal X-ray diffraction analysis. A cytotoxicity study was carried out through an MTT assay in the carcinogenic cell line HeLa and the noncarcinogenic cell lines HFF-1 and HaCaT. The results indicated that among all the evaluated compounds, 2 and 6 presented the best anticarcinogenic potential against HeLa cells with an IC₅₀ of 3.5 and 4.1 µM, respectively. In addition, classical molecular dynamics simulations were performed on the synthesized coordination compounds bound to G4 DNA architectures in the scope of shedding light on their inhibition mode and the most conserved interactions that may lead to the biological activity of the compounds.

Ln(iii)–Ni(ii) heteropolynuclear metal organic frameworks of oxydiacetate with promising proton-conductive properties

Heteropolynuclear metal organic frameworks (MOFs) of the general formula [Ln₂Ni₃(oda)₆(H₂O)₆]·xH₂O (oda = oxydiacetate, Ln = +3 rare earth ion) were synthesized and characterized.

Chemoenzymatic Total Synthesis and Structural Revision of Ampelomins B, D, E, and epi-Ampelomin B

Enantioselective synthesis of ampelomin B and epi-ampelomin B, D, and E was accomplished starting from toluene, through a chemoenzymatic sequence, in which stereoselective hydrogenation, Mitsunobu reaction, and regio- and stereoselective nucleophilic opening of an epoxide were used as the main transformations. Structural revision and absolute configuration of the natural compounds were carried out.

Crystal structure and Hirshfeld surface analysis of poly[tris-(μ4-benzene-1,4-di-carboxyl-ato)tetra-kis-(di-methyl-formamide)-trinickel(II)]: a two-dimensional coordination network

The structure of catena-[tris­(μ₄-benzene-1,4-di­carboxyl­ato)-tetra­kis­(μ₁– di­methyl­formamide-κ¹O)-trinickel(II)], C₃₆H₄₀N₄Ni₃O₁₆, has been determined in the monoclinic P2₁/n space group. The compound has a two-dimensional coordination network structure and it is of inter­est with respect to lithium-ion battery applications. Hirshfeld surface analysis was performed to characterize inter­planar inter­actions. The structure exhibits disorder of coordinated solvent mol­ecules.

The crystal structure of the title compound, [Ni₃(C₈H₄O₄)₃(C₃H₇NO)₄], is a two-dimensional coordination network formed by trinuclear linear Ni₃(tp)₃(DMF)₄ units (tp = terephthalate = benzene-1,4-di­carboxyl­ate and DMF = di­methyl­formamide) displaying a characteristic coordination mode of acetate groups in polynuclear metal–organic compounds. Individual trinuclear units are connected through tp anions in a triangular network that forms layers. One of the DMF ligands points outwards and provides inter­actions with equivalent planes above and below, leaving the second ligand in a structural void much larger than the DMF mol­ecule, which shows positional disorder. Parallel planes are connected mainly through weak C—H⋯O, H⋯H and H⋯C inter­actions between DMF mol­ecules, as shown by Hirshfeld surface analysis.

Crystal structure and Hirshfeld surface analysis of lapachol acetate 80 years after its first synthesis

Lapachol acetate [systematic name: 3-(3-methyl-but-2-en-yl)-1,4-dioxonaph-thalen-2-yl acetate], C17H16O4, was prepared using a modified high-yield procedure and its crystal structure is reported for the first time 80 years after its first synthesis. The full spectroscopic characterization of the mol-ecule is reported. The mol-ecular conformation shows little difference with other lapachol derivatives and lapachol itself. The packing is directed by inter-molecular π-π and C-H⋯O inter-actions, as described by Hirshfeld surface analysis. The former inter-actions make the largest contributions to the total packing energy in a ratio of 2:1 with respect to the latter.

Absolute structure of (3aS,5S,7aS,7bS,9aR,10R,12aR,12bS)-7b-hy-droxy-4,4,7a,9a,12a-penta-methyl-10-[(2'R)-6-methyl-heptan-2-yl]-2,8,9-trioxo-octa-deca-hydro-benzo[d]indeno-[4,5-b]azepin-5-yl acetate from 62-year-old crystals

The structure of the title compound was determined using single crystals obtained more than 60 years ago at the Facultad de Química, Universidad de la República. The chemical structure of the compound, now confirmed by X-ray diffraction, was determined spectroscopically and was relevant in the determination of the structure of lanosterol and other triterpenoids in the early 50′s.

The structure of the title compound, C₃₂H₅₁NO₆, was determined from 62-year-old crystals at room temperature and refined with 100 K data in a monoclinic (C2) space group. This compound with a triterpenoid structure, now confirmed by this study, played an important role in the determination of the structure of lanosterol. The mol­ecules pack in linear O—H⋯O hydrogen-bonded chains along the short axis (b), while parallel chains display weak van der Waals inter­actions that explain the needle-shaped crystal morphology. The structure exhibits disorder of the flexible methyl­heptane chain at one end of the main mol­ecule with a small void around it. Crystals of the compounds were resistant to data collection for decades with the available cameras and Mo Kα radiation single-crystal diffractometer in our laboratory until a new instrument with Cu Kα radiation operating at 100 K allowed the structure to be solved and refined.

Inhibition of C. albicans Dimorphic Switch by Cobalt(II) Complexes with Ligands Derived from Pyrazoles and Dinitrobenzoate: Synthesis, Characterization and Biological Activity

Seven cobalt(II) complexes of pyrazole derivatives and dinitrobenzoate ligands were synthesized and characterized. The single-crystal X-ray diffraction structure was determined for one of the ligands and one of the complexes. The analysis and spectral data showed that all the cobalt complexes had octahedral geometries, which was supported by DFT calculations. The complexes and their free ligands were evaluated against fungal strains of Candida albicans and emerging non-albicans species and epimastigotes of Trypanosoma cruzi. We obtained antifungal activity with a minimum inhibitory concentration (MIC) ranging from 31.3 to 250 µg mL-1. The complexes were more active against C. krusei, showing MIC values between 31.25 and 62.5 µg mL-1. In addition, some ligands (L1-L6) and complexes (5 and Co(OAc)2 · 4H2O) significantly reduced the yeast to hypha transition of C. albicans at 500 µg mL-1 (inhibition ranging from 30 to 54%). Finally, the complexes and ligands did not present trypanocidal activity and were not toxic to Vero cells. Our results suggest that complexes of cobalt(II) with ligands derived from pyrazoles and dinitrobenzoate may be an attractive alternative for the treatment of diseases caused by fungi, especially because they target one of the most important virulence factors of C. albicans.

Room-Temperature Broadband Light Emission from Hybrid Lead Iodide Perovskite-Like Quantum Wells: Terahertz Spectroscopic Investigation of Metastable Defects

The properties of mid-band-gap electronic states are central to the potential application of self-assembled, hybrid organic-inorganic perovskite-like quantum wells in optoelectronic technologies. We investigate broadband light emission from mid-band-gap states in fast-forming hybrid organic lead iodide quantum wells at room temperature. By comparing temperature- and intensity-dependent photoluminescence (PL) spectra emitted from butyl ammonium spaced inorganic layers, we propose that structural defects in a metastable material phase trap excitons and cause broadband light emission spanning wavelengths between 600 and 1000 nm. We use temperature-dependent terahertz time-domain spectroscopy to correlate changes in the subgap PL emission with changes in the chemical bonding of the inorganic octahedral layer. Our results provide new fundamental physical insights into the array of mechanisms capable of inducing broadband light emission from low-dimensional perovskite-like materials central to their application in future optoelectronic technologies and novel spectroscopic tools to characterize these states.

The first enantioselective strategy towards speciosins

We introduce chirality with a biotransformation and a side chain with a Sonogashira reaction, for the first enantioselective strategy for speciosins.

Four interpenetrating hydrogen-bonded three-dimensional networks in divanillin

The crystal structure of divainillin (systematic name: 6,6'-dihydroxy-5,5'-dimethoxy-[1,1'-biphenyl]-3,3'-dicarbaldehyde), C₁₆H₁₄O₆, was determined from laboratory powder X-ray diffraction data using the software EXPO2013 (direct methods) and WinPSSP (direct-space approach). Divanillin molecules crystallize in the orthorhombic space group Pba2 (No. 32), with two molecules per unit cell (Z' = 1/2). Each divanillin molecule, with twofold symmetry, is linked through strong alcohol-aldehyde hydrogen bonds to four equivalent molecules, defining a three-dimensional hydrogen-bonding network, with rings made up of six divanillin units (a diamond-like arrangement). Each molecule is also connected through π-π interactions to a translation-equivalent molecule along c. Four consecutive molecules stacked along [001] belong to four different three-dimensional hydrogen-bonding networks defining a quadruple array of interpenetrating networks. This complex hydrogen-bonding array is proposed as an explanation for the aging process experienced by divanillin powders.

Observation of an infrequent enantiomer/conformer substitutional disorder in ethyl 13-ethyl-4-oxo-8,13-dihydro-4H-benzo[5,6]azepino[3,2,1-ij]quinoline-5-carboxylate heptane hemisolvate

Considering the importance of quinolones due to their broad spectrum of biological activities, the crystal structure of the title compound, C₂₂H₂₁NO₃·0.5C₇H₁₆, has been determined. Two enantiomers of the benzazepinoquinoline molecule and one molecule of heptane form the asymmetric unit of this centrosymmetric triclinic (P-1) crystal. All the molecules in the crystal present disorder. Substitutional disorder is observed for the benzazepine molecules, where a minority conformer of the R enantiomer replaces the main conformer of the S enantiomer and vice versa. Positional disorder is found for the heptane solvent molecule, which occupies a void left by the independent enantiomers of both conformers.

General Method for the Synthesis of (-)-Conduritol C and Analogs from Chiral Cyclohexadienediol Scaffolds

An efficient and facile general method for the synthesis of conduritol C analogs, taking advantage of an enantioselective biocatalysis process of monosubstituted benzenes, is described. The absolute stereochemical patterns of the target molecules (−)-conduritol C, (−)-bromo-conduritol C, and (−)-methyl-conduritol C were achieved by means of chemoenzymatic methods. The stereochemistry present at the homochiral cyclohexadiene-cis-1,2-diols derived from the arene biotransformation and the enantioselective ring opening of a non-isolated vinylepoxide derivative permitted the absolute configuration of the carbon bearing the hydroxyl groups at the target molecules to be established. All three conduritols and two intermediates were crystallized, and their structures were confirmed by X-ray diffraction. The three conduritols and intermediates were isostructural. The versatility of our methodology is noteworthy to expand the preparation of conduritol C analogs starting from toluene dioxygenase (TDO) monosubstituted arene substrates.

Polymorphism and luminescence properties of heteropolynuclear metal–organic frameworks containing oxydiacetate as linker

A structural study concerning polymorphism control and the luminescence properties of lanthanide based MOFs.

Synthesis, structural characterization and scalable preparation of new amino-zinc borates

Zinc borates are very important industrial materials with applications that include fire retardants and preservatives in wood. In this work, we report the preparation of three novel zinc borates: [Zn(NH₃)₃B₄O₅(OH)₄]·H₂O (ZB1), Zn₃(H₂B₃O₇)₂·2NH₃·4H₂O (ZB2), and [Zn(NH₃)₄][B₄O₅(OH)₄]·4H₂O (ZB3). The solid phases were characterized by elemental analysis, X-ray diffraction, infrared and Raman spectroscopy, scanning electron microscopy and thermal analysis. The crystal structures of ZB1 (monoclinic, Cc, a = 12.1972(8), b = 7.8314(5), c = 12.1441(8) Å and β = 107.404(5)°) and ZB3 (orthorhombic, Pbca, a = 15.0796(9), b = 11.8853(5) and c = 16.7606(8) Å) were determined. They are novel neutral Zn-polyborate complexes [Zn(NH₃)₃B₄O₅(OH)₄] hydrate and [Zn(NH₃)₄][B₄O₅(OH)₄] tetrahydrate salt, respectively. The complete assignment of infrared and Raman spectra was performed theoretically using DFT calculations. For ZB2 (obtained as a polycrystalline phase), powder X-ray diffraction confirmed a single phase and allowed the determination of the unit cell parameters and lattice type (rhombohedral, a = 36.78076 (6), c = 12.20052 (3) Å) with an expected formula Zn₃(H₂B₃O₇)₂·2NH₃·4H₂O suggesting that this compound is a complex triborate. Furthermore, a low-cost scalable synthetic procedure for ZB1 starting from zinc oxide and boric acid in ammonia solution with a high yield is also reported.

Crystal structure and absolute configuration of (4S,5R,6S)-4,5,6-trihy-droxy-3-methyl-cyclo-hex-2-enone (gabosine H)

The mol-ecule of the title keto carbasugar, C₇H₁₀O₄, is formed by a cyclo-hexene skeleton with an envelope conformation, substituted by carbonyl, methyl and hydroxyl groups. The crystal structure is controlled mainly by a combination of strong O-H⋯O and weak C-H⋯O hydrogen bonds, forming nearly perpendicular chains running parallel to the [110] and [-110] directions. This perpendicularity is caused by a tetra-gonal pseudosymmetry influenced by the similarity between the a and b axes, the value of 90.9770 (10)° of the β angle and the action of a 2₁ screw axis, which transform each chain into its corresponding nearly orthogonal one.

Synthesis of bimetallic trifluoroacetates through a crystallochemical investigation of their monometallic counterparts: the case of (A, A')(CF3COO)2·nH2O (A, A' = Mg, Ca, Sr, Ba, Mn)

Owing to their potential as single-source precursors for compositionally complex materials, there is growing interest in the rational design of multimetallic compounds containing fluorinated ligands. In this work, we show that chemical and structural principles for a materials-by-design approach to bimetallic trifluoroacetates can be established through a systematic investigation of the crystal-chemistry of their monometallic counterparts. A(CF₃COO)₂·nH₂O (A = Mg, Ca, Sr, Ba, Mn) monometallic trifluoroacetates were employed to demonstrate the feasibility of this approach. The crystal-chemistry of monometallic trifluoroacetates was mapped using variable-temperature single-crystal X-ray diffraction, powder X-ray diffraction, and thermal analysis. The evolution with temperature of the previously unknown crystal structure of Mg(CF₃COO)₂·4H₂O was found to be identical to that of Mn(CF₃COO)₂·4H₂O. More important, the flexibility of Mn_x(CF₃COO)_2x·4H₂O (x = 1, 3) to adopt two structures, one isostructural to Mg(CF₃COO)₂·4H₂O, the other isostructural to Ca₃(CF₃COO)₆·4H₂O, enabled the synthesis of Mg-Mn and Ca-Mn bimetallic trifluoroacetates. Mg_0.45Mn_0.55(CF₃COO)₂·4H₂O was found to be isostructural to Mg(CF₃COO)₂·4H₂O and exhibited isolated metal-oxygen octahedra with Mg²⁺ and Mn²⁺ nearly equally distributed over the metal sites (Mg/Mn: 45/55). Ca_1.72Mn_1.28(CF₃COO)₆·4H₂O was isostructural to Ca₃(CF₃COO)₆·4H₂O and displayed trimers of metal-oxygen corner-sharing octahedra; Ca²⁺ and Mn²⁺ were unequally distributed over the central (Ca/Mn: 96/4) and terminal (Ca/Mn: 38/62) octahedral sites.

Enantioselective synthesis of new oxazolidinylthiazolidines as enzyme inhibitors

The synthesis of new oxazolidinylthiazolidines bicycles, oxygen analogues of bisthiazolidines, also known as metallo-β-lactamase inhibitors is described. The reaction of β-aminoalcohols and 2,5-dihydroxy-1,4-dithiane led to oxazolidinylthiazolidines and/or dithia-azabicycles as the main products. The distribution pattern depends mainly on the aminoalcohol substituents. In a one-pot reaction, four new bonds are formed in good yields and with high atom efficiency. When the oxazolidinylthiazolidines are formed, two stereogenic centres are generated with high enantiospecificity. The reaction mechanism is discussed based on crystallographic data and interconversion studies. Two oxazolidinylthiazolidines were evaluated as inhibitors of the potent lactamase NDM-1 and compound 4f displayed competitive inhibition with K_i = 1.6 ± 0.6 µM.

Crystal structure and absolute configuration of (3aR,3'aR,7aS,7'aS)-2,2,2',2'-tetra-methyl-3a,6,7,7a,3'a,6',7',7'a-octa-hydro-4,4'-bi[1,3-benzodioxol-yl], obtained from a Pd-catalyzed homocoupling reaction

The absolute configuration, i.e. (3aR,3'aR,7aS,7'aS), of the title compound, C18H26O4, synthesized via a palladium-catalyzed homocoupling reaction, was determined on the basis of the synthetic pathway and was confirmed by X-ray diffraction. The homocoupled mol-ecule is formed by two chemically identical moieties built up from two five- and six-membered fused rings. The supra-molecular assembly is controlled mainly by C-H⋯O inter-actions that lead to the formation of hydrogen-bonded chains of mol-ecules along the [001] direction, while weak dipolar inter-actions and van der Waals forces hold the chains together in the crystal structure.

Crystal structure of 1,3-bis-(1H-benzotriazol-1-yl-meth-yl)benzene

The mol-ecular structure of the title compound, C20H16N6, contains two benzotriazole units bonded to a benzene nucleus in a meta configuration, forming dihedral angles of 88.74 (11) and 85.83 (10)° with the central aromatic ring and 57.08 (9)° with each other. The three-dimensional structure is controlled mainly by weak C-H⋯N and C-H⋯π inter-actions. The mol-ecules are connected in inversion-related pairs, forming the slabs of infinite chains that run along the [-110] and [110] directions.

Crystal structures of five new substituted tetrahydro-1-benzazepines with potential antiparasitic activity

Tetrahydro-1-benzazepines have been described as potential antiparasitic drugs for the treatment of chagas disease and leishmaniasis, two of the most important so-called `forgotten tropical diseases' affecting South and Central America, caused by Trypanosoma cruzi and Leishmania chagasi parasites, respectively. Continuing our extensive work describing the structural characteristics of some related compounds with interesting biological properties, the crystallographic features of three epoxy-1-benzazepines, namely (2SR,4RS)-6,8-dimethyl-2-(naphthalen-1-yl)-2,3,4,5-tetrahydro-1H-1,4-epoxy-1-benzazepine, (1), (2SR,4RS)-6,9-dimethyl-2-(naphthalen-1-yl)-2,3,4,5-tetrahydro-1H-1,4-epoxy-1-benzazepine, (2), and (2SR,4RS)-8,9-dimethyl-2-(naphthalen-1-yl)-2,3,4,5-tetrahydro-1H-1,4-epoxy-1-benzazepine, (3), all C22H21NO, and two 1-benzazepin-4-ols, namely 7-fluoro-cis-2-[(E)-styryl]-2,3,4,5-tetrahydro-1H-1-benzazepin-4-ol, C18H18FNO, (4), and 7-fluoro-cis-2-[(E)-pent-1-enyl]-2,3,4,5-tetrahydro-1H-1-benzazepin-4-ol, C15H20FNO, (5), are described. Some peculiarities in the crystallization behaviour were found, involving significant variations in the crystalline structures as a result of modest changes in the peripheral substituents in (1)-(3) and the occurrence of discrete disorder due to the molecular overlay of enantiomers with more than one conformation in (5). In particular, an interesting phase change on cooling was observed for compound (5), accompanied by an approximate fourfold increase of the unit-cell volume and a change of the Z' value from 1 to 4. This transition is a consequence of the partial ordering of the pentenyl chains in half of the molecules breaking half of the -3 symmetry axes observed in the room-temperature structure of (5). The structural assembly in all the title compounds is characterized by not only (N,O)-H...(O,N) hydrogen bonds, but also by unconventional C-H...O contacts, resulting in a wide diversity of packing.

Open-Framework Structures of Anhydrous Sr(CF3COO)2 and Ba(CF3COO)2

Anhydrous Sr(CF3COO)2 and Ba(CF3COO)2 open-framework structures featuring three-dimensional connectivity of metal-oxygen polyhedra were crystallized from a mixture of water and CF3COOH. Crystallization was induced via evaporation of the solvent mixture under a dry nitrogen flow. This approach differs from that routinely employed for crystallization of metal trifluoroacetates, which achieves solvent evaporation by heating under air and yields hydrated salts. Thermogravimetric and differential thermal analysis as well as single-crystal and synchrotron powder X-ray diffraction were employed to characterize the alkaline-earth trifluoroacetate products. Neither thermal analysis nor single-crystal X-ray diffraction detected the presence of crystallization water molecules, demonstrating these trifluoroacetates can be obtained in anhydrous form. Single-crystal X-ray diffraction studies showed that Sr(CF3COO)2 and Ba(CF3COO)2 are isostructural and crystallize in the rhombohedral R3̅ space group. Both compounds belong to the class of organic-inorganic extended hybrids and exhibit an open-framework structural motif with three-dimensional connectivity of the metal-oxygen polyhedra and one-dimensional channels along the c axis. The channels are decorated with the trifluoromethyl groups of the trifluoroacetate ligands, and their average (minimum) diameters are ∼3.75 (2.60) and 3.45 (2.25) Å for Sr(CF3COO)2 and Ba(CF3COO)2, respectively. This size range is comparable to the kinetic diameter of small molecules such as hydrogen (2.3 Å). Chemical substitution of barium for strontium affects not only the diameter of the channels but also the spatial arrangement of the trifluoromethyl groups within the channels and the coordination environment of the metal atoms. The different coordination requirements of the strontium and barium atoms are accommodated through the displacement of one of the two chemically distinct trifluoroacetate ligands relative to the metal center.

Crystal structure and absolute configuration of (3aS,4S,5R,7aR)-2,2,7-trimethyl-3a,4,5,7a-tetra-hydro-1,3-benzodioxole-4,5-diol

The absolute configuration of the title compound, C10H16O4, determined as 3aS,4S,5R,7aR on the basis of the synthetic pathway, was confirmed by X-ray diffraction. The mol-ecule contains a five- and a six-membered ring that adopt twisted and envelope conformations, respectively. The dihedral angle between the mean planes of the rings is 76.80 (11)° as a result of their cis-fusion. In the crystal, mol-ecules are linked by two pairs of O-H⋯O hydrogen bonds, forming chains along [010]. These chains are further connected by weaker C-H⋯O inter-actions along [100], creating (001) sheets that inter-act only by weak van der Waals forces.