Azapropanedithiolate (adt)-bridged model complexes of [FeFe]-hydrogenase bearing a carboxylic acid functionality have been designed with the aim of decreasing the potential for reduction of protons to hydrogen. Protonation of the bisphosphine complexes 4–6 has been studied by in situ IR and NMR spectroscopy, which revealed that protonation with triflic acid most likely takes place first at the N-bridge for complex 4 but at the FeFe bond for complexes 5 and 6. Using an excess of acid, the diprotonated species could also be observed, but none of the protonated species was sufficiently stable to be isolated in a pure state. Electrochemical studies have provided an insight into the catalytic mechanisms under strongly acidic conditions, and have also shown that complexes 3 and 6 are electro-active in aqueous solution even in the absence of acid, presumably due to hydrogen bonding. Hydrogen evolution, driven by visible light, has been observed for three-component systems consisting of [Ru(bpy)₃]²⁺, complex 1, 2, or 3, and ascorbic acid in CH₃CN/D₂O solution by on-line mass spectrometry.

Investigations of reaction mixtures RE_x(Au_0.79Si_0.21)_100–x (RE = Y and Gd) yielded the compounds REAu₃Si which adopt a new structure type, referred to as GdAu₃Si structure (tP80, P4₂/mnm, Z = 16, a = 12.8244(6)/12.7702(2) Å, and c = 9.0883(8)/9.0456(2) Å for GdAu₃Si/YAu₃Si, respectively). REAu₃Si was afforded as millimeter-sized faceted crystal specimens from solution growth employing melts with composition RE₁₈(Au_0.79Si_0.21)₈₂. In the GdAu₃Si structure, the Au and Si atoms are strictly ordered and form a framework built of corner-connected, Si-centered, trigonal prismatic units SiAu₆. RE atoms distribute on 3 crystallographically different sites and each attain a 16-atom coordination by 12 Au and 4 Si atoms. These 16-atom polyhedra commonly fill the space of the unit cell. The physical properties of REAu₃Si were investigated by heat capacity, electrical resistivity, and magnetometry techniques and are discussed in the light of theoretical predictions. YAu₃Si exhibits superconductivity around 1 K, whereas GdAu₃Si shows a complex magnetic ordering, likely related to frustrated antiferromagnets exhibiting chiral spin textures. GdAu₃Si-type phases with interesting magnetic and transport properties may exist in an extended range of ternary RE–Au–Si systems, similar to the compositionally adjacent cubic 1/1 approximants RE(Au,Si)_∼6.

In the title compound, C₃₀H₃₁NO₆S, the plane of the N-phthalimido group is nearly orthogonal to the least-squares plane of the sugar ring (defined by atoms C2, C3, C5 and O5 using standard glucose nomenclature), making a dihedral angle of 72.8 (1)°. The thioethyl group has the exo-anomeric conformation. The hydroxy group forms an intermolecular hydrogen bond to the O atom in the sugar ring, generating [100] chains. There are four close - contacts with centroid-centroid distances less than 4.0 Å, all with dihedral angles between the interacting systems of only 8°, supporting energetically favourable stacking interactions

The structure of the O-methyl glycoside of the naturally occurring 6-O-[(R)-1-carboxyethyl]-alpha-D-galactopyranose, C10H18O8, has been determined by X-ray crystallography at 100 K, supplementing the previously determined structure obtained at 293 K (Acta Crystallogr. 1996, C52, 2285-2287). Molecular dynamics simulations of this glycoside were Performed in the crystal environment with different numbers of units cells included in the primary simulation system at both 100 and 293 K. The Calculated unit cell Parameters and the intramolecular geometries (bonds, angles, and dihedrals) agree well with experimental results. Atomic fluctuations, including B-factors and anisotropies, are in good agreement with respect to the relative values on an atom-by-atom basis. In addition, the fluctuations increase with increasing simulation system size, with the simulated values converging to values lower than those observed experimentally indicating that the simulation model is not accounting for all possible contributions to the experimentally observed B-factors, which may be related to either the simulation time scale or size. In the simulation's, the hydroxyl group of O7 is found to from bifurcated hydrogen bonds with O6 and O8 of an adjacent molecule, with the interactions dominated by the interaction HO7-O6 interaction. Quantum mechanical calculations support this observation.

A broad range of aliphatic, aromatic, and heterocyclic boronic acids were successfully homologated using trifluorodiazoethane in the presence of BINOL derivatives to provide the corresponding chiral trifluoromethyl containing boronic acid derivatives in high yields and excellent enantioselectivity. The in situ conversion of the chiral transient boronic acids to the corresponding alcohols or β-CF3 carboxylates are also demonstrated. 

A new asymmetric catalytic propargyl- and allylboration of hydrazonoesters is reported. The reactions utilize allenyl- and allylboronic acids in the presence of the inexpensive parent BINOL catalyst. The reactions can be performed under mild conditions (0 degrees C) without any metal catalyst or other additives affording sterically encumbered chiral -amino acids. This is the first metal-free method for the asymmetric propargyl- and allylboration of hydrazonoesters.

Chiral α-substituted allylboronic acids were synthesized by asymmetric homologation of alkenylboronic acids using CF3/TMS-diazomethanes in the presence of BINOL catalyst and ethanol. The chiral α-substituted allylboronic acids were reacted with aldehydes or oxidized to alcohols in situ with a high degree of chirality transfer. The oxygen-sensitive allylboronic acids can be purified via their isolated diaminonaphthalene (DanH)-protected derivatives. The highly reactive purified allylboronic acids reacted in a self-catalyzed reaction at room temperature with ketones, imines, and indoles to give congested trifluoromethylated homoallylic alcohols/amines with up to three contiguous stereocenters.

The title compound, C₁₇H₂₂O₆, having an ester group at O4 of the hexopyranosyl sugar residue shows for the exo-cyclic C=O bond a conformation that is eclipsed to the C4-H4 bond. The two related torsion angles are denoted by syn and cis conformations. The q₁ torsion angle (H4-C4-O4-C10) is indicated to have a similar conformation in solution as analyzed by NMR spectroscopy and a Karplus-type relationship.

This study explores first-year university students' reasoning as they learn to draw Lewis structures. We also present a theoretical account of the formal procedure commonly taught for drawing these structures. Students' discussions during problem-solving activities were video recorded and detailed analyses of the discussions were made through the use of practical epistemology analysis (PEA). Our results show that the formal procedure was central for drawing Lewis structures, but its use varied depending on situational aspects. Commonly, the use of individual steps of the formal procedure was contingent on experiences of chemical structures, and other information such as the characteristics of the problem given. The analysis revealed a number of patterns in how students constructed, checked and modified the structure in relation to the formal procedure and the situational aspects. We suggest that explicitly teaching the formal procedure as a process of constructing, checking and modifying might be helpful for students learning to draw Lewis structures. By doing so, the students may learn to check the accuracy of the generated structure not only in relation to the octet rule and formal charge, but also to other experiences that are not explicitly included in the formal procedure.

A highly efficient iridium N,P-ligand-catalyzed asymmetric hydrogenation of functionalized tetrasubstituted olefins lacking a directing group has been developed. Various structural diverse chiral succinate derivatives were obtained in high yields and excellent enantio- and diastereoselectivities (up to 99% ee) using 0.5-1.0 mol % catalyst loadings. This stereoselective reaction is applicable for the synthesis of chiral acyclic molecules (up to >99% ee) having two contiguous stereogenic centers and is compatible with various aromatic, aliphatic, and heterocyclic systems, a variety of functional groups of different electronic nature. Furthermore, this asymmetric protocol allows a short enantioselective route to the butyrolactone building block, an intermediate in the synthesis of anticancer agent BMS-871 and pharmaceuticals (2S)-(-)-Verapamil and (2S)-(-)-Gallopamil.

A new tungsten bronze in the Sb-W-O system has been prepared in a solid state reaction from Sb2O3, WO3 and W metal powder. The average structure was determined by single crystal X-ray diffraction. SbxWO3+y (x similar to 0.11) crystallizes in the orthorhombic space group Pm2(1)n (no. 31), a = 27.8135(9) angstrom, b = 7.3659(2) angstrom and c = 3.8672(1) angstrom. The structure belongs to the (n)-ITB class of intergrowth tungsten bronzes. It contains slabs of hexagonal channels formed by six WO6 octahedra. These slabs are separated by three layers of WO6 octahedra that are arranged in a WO3-type fashion. The WO6 octahedra share all vertices to build up a three-dimensional framework. The hexagonal channels are filled with Sb atoms to similar to 80% and additional 0 atoms. The atoms are shifted out of the center of the channels. Exit-wave reconstruction of focal series of high resolution-transmission-electron-microscope (HRTEM) images combined with statistical parameter estimation techniques allowed to study local ordering in the channels. Sb atoms in neighbouring channels tend to be displaced in the same direction, which is in agreement with total energy calculations on ordered structure models, but the ratio of the occupation of the two possible Sb sites varies from channel to channel. The structure of SbxWO3+y exhibits pronounced local modulations.

Liquid chromophores constitute a rare but intriguing class of molecules that are in high demand for the design of luminescent inks, liquid semiconductors, and solar energy storage materials. The most common way to achieve liquid chromophores involves the introduction of long alkyl chains, which, however, significantly reduces the chromophore density. Here, strategy is presented that allows for the preparation of liquid chromophores with a minimal increase in molecular weight, using the important class of perylenes as an example. Two synergistic effects are harnessed: (1) the judicious positioning of short alkyl substituents, and (2) equimolar mixing, which in unison results in a liquid material. A series of 1-alkyl perylene derivatives is synthesized and it is found that short ethyl or butyl chains reduce the melting temperature from 278 degrees C to as little as 70 degrees C. Then, two low-melting derivatives are mixed, which results in materials that do not crystallize due to the increased configurational entropy of the system. As a result, liquid chromophores with the lowest reported molecular weight increase compared to the neat chromophore are obtained. The mixing strategy is readily applicable to other pi-conjugated systems and, hence, promises to yield a wide range of low molecular weight liquid chromophores.

The band gap in semiconducting Mg2NiH4 was found to be dependent on subtle structural differences. This was discovered when investigating if thin film samples of Mg2NiH4 could be used in a switchable mirror or window device by utilizing a high to low temperature transition at about 510K. In powder samples; this transition between an FCC high temperature phase, with dynamically disordered NiH4-complexes, and a monoclinic distorted low temperature phase, with ordered Mg2NiH4-complexes, has been demonstrated in a mechanical reversible conductor-insulator transition (Blomqvist and Noreus (2002) [7]). Black monoclinic Mg2NiH4 powders were found to have a band gap of 1.1 eV. Pressed tablets of black monoclinic Mg2NiH4 powders are conductive, probably from doping by impurities or non-stoichiometry. Thin film Mg2NiH4 samples were produced by reacting hydrogen with magnetron sputtered Mg2Ni films on quartz glass or CaF2 substrates. The Mg2NiH4 films on the other hand were orange, transparent with a band gap of 2.2 eV and a cubic unit cell parameter almost identical to the disorder HT phase but with lower symmetry. If black Mg2NiH4 powder is heated above the phase transition at 510K and subsequently cooled down, the conductivity is lost and the powder turns brown. After this heat treatment TEM pictures revealed a multiple stacking fault having a local pseudo-cubic arrangement separating regions of monoclinic symmetry. The loss of conductivity and colour change is attributed to a higher band gap in the strained areas. The structure on each side of the stacking fault is related by a mirror plane as a consequence of the possibility for the NiH4-complexes to order with different orientations. This leads to a mismatch in the long range ordering and strain is probably creating the stacking faults. Strain is important for forming the cubic modification. A severely strained film was revealed with optical microscopy in reflected light, indicating that strain prevents it from relaxing back into the monoclinic structure. This was supported by multiple twinned red translucent Mg2NiH4 crystals grown with cubic symmetry at elevated temperatures in a LiH flux. When cooled to ambient conditions, the ""crystals"" had the same cubic symmetry as the films, probably held together by their neighbours. When they were ground to a fine powder to prepare TEM samples, they relaxed and reverted back to the conventional monoclinic unit cell. This interesting nanoscale modulated resistance could possibly be developed into novel memory devices if properly controllable.

A two-step synthesis of structurally diverse pyrrole-containing bicyclic systems is reported. ortho-Nitro-haloarenes coupled with vinylic N-methyliminodiacetic acid (MIDA) boronates generate ortho-vinyl-nitroarenes, which undergo a metal-free nitrene insertion, resulting in a new pyrrole ring. This novel synthetic approach has a wide substrate tolerance and it is applicable in the preparation of more complex drug-like molecules. Interestingly, an ortho-nitro-allylarene derivative furnished a cyclic beta-aminophosphonate motif.

Here we present a two-step diastereoselective methodology building on a multicomponent aza-Diels-Alder reaction. Using previously unexplored cyclic ketones, heterocyclic amines and cyclopentadiene derivatives, we obtained novel spiro-heterocyclic frameworks at the interphase between drug-like molecules and natural products.

Crystallographic investigations of eight homoleptic N,N '-dimethylpropyleneurea (dmpu) coordinated metal ions in the solid state, [Mg(dmpu)(5)]I-2 (1), [Ca(dmpu)(6)]I-2 (2), [Ca(dmpu)(6)](ClO4)(2) (3), [Ca(dmpu)(6)](CF3SO3)(2) (4), [Sr(dmpu)(6)](CF3SO3)(2) (5), [Ba(dmpu)(6)](CF3SO3)(2) (6), [Sc(dmpu)(6)]I-3 (7), and [Pr(dmpu)(6)]I(I-3)(2) (8), and the complex [CoBr2(dmpu)(2)] (9) as well as the structures of the dmpu coordinated calcium, strontium, barium, scandium(III) and cobalt(II) ions and the cobalt(II) bromide complex in dmpu solution as determined by EXAFS are reported. The methyl groups in the dmpu molecule are close to the oxygen donor atom, causing steric restrictions, and making dmpu space-demanding at coordination to metal ions. The large volume required by the dmpu ligand at coordination contributes to crowdedness around the metal ion with often lower coordination numbers than for oxygen donor ligands without such steric restrictions. The crowdedness is seen in M & ctdot;H distances equal to or close to the sum of the van der Waals radii. To counteract the space-demand at coordination, the dmpu molecule has an unusual ability to increase the M-O-C bond angle to facilitate as large coordination numbers as possible. M-O-C bond angles in the range of 125-170 degrees are reported depending on the crowdedness caused by the coordination figure and the M-O bond distance. All reported structures of dmpu coordinated metal ions in both the solid state and dmpu solution are summarized to study the relationship between the M-O-C bond angle and the crowdedness around the metal ion. However, highly symmetric complexes seem to be favoured in the solid state due to favourable lattice energies. As a result, the dmpu coordinated lanthanoid(III) ions are octahedral in the solid state, while they, except lutetium, are seven-coordinate in the dmpu solution.

The structures of the N,N'-dimethylpropyleneurea (dmpu) solvated lanthanoid(III) ions have been studied in dmpu solution (La-Nd, Sm-Lu) and in solid iodide salts (La-Nd, Sm, Gd-Lu) by extended X-ray absorption fine structure (EXAFS), and single crystal X-ray diffraction (La, Pr, Nd, Gd, Tb, Er, Yb, and Lu); the EXAFS studies were performed on both K and L-III absorption edges. Because of the space-demanding properties of dmpu upon coordination, dmpu solvated metal ions often show coordination numbers lower than those found in corresponding hydrates and solvates of oxygen donor solvents without steric requirements beyond the size of the donor atom. All lanthanoid(III) ions are seven-coordinate in solution, except lutetium(III) which is six-coordinated in regular octahedral fashion, whereas in the solid iodide salts the dmpu solvated lanthanoid(III) ions are all six-coordinate in regular octahedral fashion, A comparison of Ln-O bond lengths in a large number of lanthanoid(III) complexes with neutral oxygen donor ligands and different configurations shows that the metal ion-oxygen distance is specific for each coordination number with a narrow bond distance distribution. This also shows that the radius of the coordinated oxygen atom in these compounds can be assumed to be 1.34 angstrom as proposed for coordinated water, while for ethers such as tetrahydrofuran (thf) it is somewhat larger. Using this atomic radius of oxygen in coordinated water molecules, we have calculated the ionic radii of the lanthanoid(III) ions in four- to nine-coordination and evaluated using the bond lengths reported for homo- and heteroleptic complexes in oxygen donor solvates in solution and solid state. This yields new and revised ionic radii which in some instances are significantly different from the ionic radii normally referenced in the literature, including interpolated values for the elusive promethium(III) ion.

XRD measurements of RaCO3 revealedthat it isnot isostructural with witherite, and direct-space ab initio modeling showed that the carbonate oxygens are highly disordered.It was found that the solubility of RaCO3 is unexpectedlyhigher than the solubility of witherite (log(10) K (sp) (0) = -7.5 and -8.56,respectively), supporting the disordered nature of RaCO3. EXAFS data revealed an ionic radius of Ra2+ of 1.55 & ANGS;. Radium is the only alkaline-earth metal which forms disorderedcrystals in its carbonate phase. Radium-226 carbonate was synthesized from radium-bariumsulfate ((Ra0.76Ba0.24SO4)-Ra-226) at room temperature and characterized by X-ray powder diffraction(XRPD) and extended X-ray absorption fine structure (EXAFS) techniques.XRPD revealed that fractional crystallization occurred and that twophases were formed the major Ra-rich phase, Ra(Ba)CO3, and a minor Ba-rich phase, Ba(Ra)CO3, crystallizingin the orthorhombic space group Pnma (no. 62) thatis isostructural with witherite (BaCO3) but with slightlylarger unit cell dimensions. Direct-space ab initio modeling shows that the carbonate oxygens in the major Ra(Ba)CO3 phase are highly disordered. The solubility of the synthesizedmajor Ra(Ba)CO3 phase was studied from under- and oversaturationat 25.1 & DEG;C as a function of ionic strength using NaCl as thesupporting electrolyte. It was found that the decimal logarithm ofthe solubility product of Ra(Ba)CO3 at zero ionic strength(log(10) K (sp) (0)) is-7.5(1) (2 & sigma;) (s = 0.05 g & BULL;L-1). This is significantly higher than the log(10) K (sp) (0) of witheriteof -8.56 (s = 0.01 g & BULL;L-1), supporting the disordered nature of the major Ra(Ba)CO3 phase. The limited co-precipitation of Ra2+ within witherite,the significantly higher solubility of pure RaCO3 comparedto witherite, and thermodynamic modeling show that the results obtainedin this work for the major Ra(Ba)CO3 phase are also applicableto pure RaCO3. The refinement of the EXAFS data revealsthat radium is coordinated by nine oxygens in a broad bond distancedistribution with a mean Ra-O bond distance of 2.885(3) & ANGS;(1 & sigma;). The Ra-O bond distance gives an ionic radius ofRa(2+) in a 9-fold coordination of 1.545(6) & ANGS; (1 & sigma;).

The present study examines a series of six biologically-active flavonoid and chromanone derivatives by X-ray crystal structure analysis: (E)-3-benzyl­idene-2-phenyl­chroman-4-one, C₂₂H₁₆O₂, I, (E)-3-(4-methyl­benzyl­idene)-2-phenyl­chroman-4-one, C₂₃H₁₈O₂, II, (E)-3-(3-methyl­benzyl­idene)-2-phenyl­chroman-4-one, C₂₃H₁₈O₂, III, (E)-3-(4-meth­oxy­benzyl­idene)-2-phenyl­chroman-4-one, C₂₃H₁₈O₃, IV, (E)-3-benzyl­idenechroman-4-one, C₁₆H₁₂O₂, V, and (E)-3-(4-meth­oxy­benzyl­idene)chroman-4-one, C₁₇H₁₄O₃, VI. The cytotoxic activities of the presented crystal structures have been determined, together with their inter­molecular inter­action preferences and Hirshfeld surface characteristics. An inverse relationship was found between the contribution of C⋯C close contacts to the Hirshfeld surface and cytotoxic activity against the WM-115 cancer line. Dependence was also observed between the logP value and the percentage contribution of C⋯H contacts to the Hirshfeld surface.

DNA adducts can be formed from covalent binding of electrophilic reactive compounds to the nucleophilic Nand O-atoms of the biomolecule. The O-sites on DNA, with nucleophilic strength (n) of ca. 2, is recognized as a critical site for mutagenicity. Characterization of the reactivity of electrophilic compounds at the O-sites can be used to predict their mutagenic potency in relative terms. In the present study, reaction kinetic experiments were performed for butadiene monoxide (BM) in accordance with the Swain-Scott relation using model nucleophiles representing N- and O-sites on DNA, and earlier for glycidamide (GA) using a similar approach. The epoxide from the kinetic experiments was trapped by cob(I)alamin, resulting in formation of an alkylcobalamin which was analyzed by liquid chromatography tandem mass spectrometry. The Swain-Scott relationship was used to determine selectivity constant (s) of BM and GA as 0.86 and 1.0, respectively. The rate constant for the reaction at n of 2 was extrapolated to 0.023 and 0.038M(-1) h(-1) for BM and GA, respectively, implying a higher mutagenic potency per dose unit of GA compared to BM. The reaction kinetic parameters associated with mutagenic potency were also estimated by a density functional theory approach, which were in accordance to the experimental determined values. These types of reaction kinetic measures could be useful in development of a chemical reactivity based prediction tool that could aid in reduction of animal experiments in cancer risk assessment procedures for relative mutagenicity.

At elevated pressures (above 1.5 GPa) dihydrogen bonded ammonia borane, BH3NH3, undergoes a solid-solid phase transition with increasing temperature. The high pressure, high temperature (HPHT) phase precedes decomposition and evolves from the known high pressure, low temperature form with space group symmetry Cmc2(1) (Z = 4). Structural changes of BH3NH3 with temperature were studied at around 6 GPa in a diamond anvil cell by synchrotron powder diffraction. At this pressure the Cmc2(1) phase transforms into the HPHT phase at around 140 degrees C. The crystal system, unit cell, and B and N atom position parameters of the HPHT phase were extracted from diffraction data, and a hydrogen ordered model with space group symmetry Pnma (Z = 4) subsequently established from density functional calculations. However, there is strong experimental evidence that HPHT-BH3NH3 is a hydrogen disordered rotator phase. A reverse transition to the Cmc2(1) phase is not observed. When releasing pressure at room temperature to below 1.5 GPa the ambient pressure (hydrogen disordered) I4mm phase of BH3NH3 is obtained. 

An intermolecular cyclization of alkynyl enones with cyclic ketones for the synthesis of bicyclo[3.n.1]alkenones is reported. This protocol exhibits a high functional group tolerance and provides access to a variety of bicyclic systems found as skeletons in many natural products.

A highly selective Lewis acid catalyzed annulation of three-membered heterocycles with nitrones has been developed. Oxiranes, aziridines, and thiiranes were used as substrates for the synthesis of various six-membered heterocycles using Al or In catalysts. This catalytic protocol demonstrates a broad substrate scope and provides access to new structural motifs in high yields and in excellent selectivity under mild reaction conditions.

A diastereoselective three-component reaction between alkynyl enones, aldehydes and secondary amines is reported. With the aid of a benign indium catalyst, a range of highly substituted cyclopenta[c]furan derivatives can be obtained in a single-step procedure. The formation of the stereodefined heterocyclic motifs takes place via in situ generation of enamines followed by two sequential cyclization steps.

The structure of the solvated mercury(II) ion in aqueous and dimethyl sulfoxide solution has been studied by means of large angle X-ray scattering (LAXS) and EXAFS tech¬niques. The distribution of the Hg-O bond distances is unusually wide and asymmetric in both solvents. In aqueous solution hexahydrated [Hg(OH2)6]2+ ions in distorted octahedral configuration, with the centroid of the Hg-O bond distances at 2.38(1) Å, are surrounded by a diffuse second hydration sphere, with HgOII distances around a mean value of 4.20(2) Å. In dimethyl sulfoxide solution the six Hg-O and HgS distances of the hexasolvated Hg(OS(CH3)2)6]2+ complex are centered around 2.38(1) and 3.45(2) Å, respectively. The crystal structure of hexakis¬(pyridine-1-oxide)mercury(II) perchlorate has been re-determi¬ned at 100 K. The space group R implies six equal Hg-O bond distances of 2.3416(7) Å for the Hg(ONC5H5)62+ complex, as also for the hexaaquamercury(II) perchlorate and hexakis(dimethyl sulfoxide)mercury(II) trifluoro¬methanesulfonate compounds, according to previous crystallographic results. However, EXAFS results for those compounds in all cases reveal strongly asymmetric Hg-O bond distance distributions. Vibronic coupling of close valence states in a so-called Pseudo Jahn-Teller Effect probably induces the distorted configurations.

The coordination chemistry of lead(II) in the oxygen donor solvents water, dimethylsulfoxide (dmso, Me(2)SO), N,N-dimethylformamide (dmf), N,N-dimethylacetamide (dma), N,N'-dimethylpropyleneurea (dmpu), and 1,1,3,3-tetramethylurea (tmu), as well as in the sulfur donor solvent N,N-dimethylthioformamide (dmtf), has been investigated by extended X-ray absorption fine structure (EXAFS) and/or large angle X-ray scattering (LAXS) in solution, and by single crystal X-ray diffraction and/or EXAFS of solid hydrates and solvates. Lead(II) may either form hemidirected complexes with large bond distance distribution and an apparent gap for excess electron density, or holodirected ones with a symmetric coordination sphere with normal bond distance distribution, depending on the strength of antibonding lead 6s/ligand np molecular orbital interactions and ligand-ligand interactions. The crystallographic data show that the solid lead(II) perchlorate and trifluoromethanesulfonate hydrate structures are hemidirected, while the solid lead(II) solvates of dma and dmpu have regular octahedral configuration with holodirected geometry and mean Pb-O bond distances in the range 2.50-2.52 A. EXAFS data on the hydrated lead(II) ion in aqueous solution show broad bond distance distribution and a lack of inner-core multiple scattering contributions strongly indicating a hemidirected structure. The Pb-O bond distances found both by EXAFS and LAXS, 2.54(1) angstrom, point to a six-coordinate hydrated lead(II) ion in hemidirected fashion with an unevenly distributed electron density. The results obtained for the dmso solvated lead(II) ion in solution are ambiguous, but for the most part support a six-coordinate hemidirected complex. The mean Pb-O bond distances determined in dmf and dma solution by LAXS, 2.55(1) and 2.48(1) angstrom, respectively, indicate that in both solvate complexes lead(II) binds six solvent molecules with the former complex being hemidirected whereas the latter is holodirected. The dmpu and tmu solvated lead(II) ions have a regular holodirected octahedral configuration, as expected given their space-demanding characteristics and ligand-ligand intermolecular interactions. The dmtf solvated lead(II) ion in solution is most likely five-coordinate in a hemidirected configuration, with a mean Pb-S bond distance of 2.908(4) angstrom. New and improved ionic radii for the lead(II) ion in 4-8-coordination in hemi and holodirected configurations are proposed using crystallographic data.

A number of cyclic dienes containing the allylsilane moiety were prepared via Birch reduction and subjected to iridium-catalyzed regioselective and asymmetric hydrogenation, which provided chiral allylsilanes in high conversion and enantiomeric excess (up to 99 % ee). The compounds were successively used in the Hosomi-Sakurai allylation with various aldehydes employing TiCl4 as Lewis acid, providing adducts with two additional stereogenic centers in excellent diastereoselectivity.

A partially protected C-5C-5a unsaturated carbasugar with α-lyxo configuration is synthesised in five steps and 26% overall yield from a known mannose-derived hemiacetal, using ring-closing metathesis as a key step. This carbasugar is converted into valienamine derivatives with β-lyxo (i.e., corresponding to β-manno at C-1–C-4), α-lyxo (i.e., corresponding to α-manno at C-1–C-4) and β-2-acetamido-2-deoxy-xylo (i.e., corresponding to β-GlcNAc at C-1–C-4) configurations. This is the first report of the synthesis of the β-lyxo compound, 1,2-bis-epi-valienamine, which was found to inhibit Cellulomonas fimi β-mannosidase (CfMan2A) with K_i 140 μM. We report the crystal structures of three protected C-5C-5a unsaturated carbasugars with lyxo configuration.

Sulfur K-edge X-ray absorption near-edge structure (XANES) spectra have been recorded and the S(1s) electron excitations evaluated by means of density functional theory−transition potential (DFT−TP) calculations to provide insight into the coordination, bonding, and electronic structure. The XANES spectra for the various species in sulfur dioxide and aqueous sodium sulfite solutions show considerable differences at different pH values in the environmentally important sulfite(IV) system. In strongly acidic (pH < 1) aqueous sulfite solution the XANES spectra confirm that the hydrated sulfur dioxide molecule, SO₂(aq), dominates. The theoretical spectra are consistent with an OSO angle of 119° in gas phase and acetonitrile solution, while in aqueous solution hydrogen bonding reduces the angle to 116°. The hydration affects the XANES spectra also for the sulfite ion, SO₃^2-. At intermediate pH (4) the two coordination isomers, the sulfonate (HSO₃^-) and hydrogen sulfite (SO₃H^-) ions with the hydrogen atom coordinated to sulfur and oxygen, respectively, could be distinguished with the ratio HSO₃^-:SO₃H^- about 0.28:0.72 at 298 K. The relative amount of HSO₃^- increased with increasing temperature in the investigated range from 275 to 343 K. XANES spectra of sulfonate, methanesulfonate, trichloromethanesulfonate, and trifluoromethanesulfonate compounds, all with closely similar S−O bond distances in tetrahedral configuration around the sulfur atom, were interpreted by DFT−TP computations. The energy of their main electronic transition from the sulfur K-shell is about 2478 eV. The additional absorption features are similar when a hydrogen atom or an electron-donating methyl group is bonded to the −SO₃ group. Significant changes occur for the electronegative trichloromethyl (Cl₃C−) and trifluoromethyl (F₃C−) groups, which strongly affect the distribution especially of the π electrons around the sulfur atom. The S−D bond distance 1.38(2) Å was obtained for the deuterated sulfonate (DSO₃^-) ion by Rietveld analysis of neutron powder diffraction data of CsDSO₃. Raman and infrared absorption spectra of the CsHSO₃, CsDSO₃, H₃CSO₃Na, and Cl₃CSO₃Na·H₂O compounds and Raman spectra of the sulfite solutions have been interpreted by normal coordinate calculations. The C−S stretching force constant for the trichloromethanesulfonate ion obtains an anomalously low value due to steric repulsion between the Cl₃C− and −SO₃ groups. The S−O stretching force constants were correlated with corresponding S−O bond distances for several oxosulfur species.

The lateral habit, unit cell structure and melting behaviour of single crystals of poly(epsilon-caprolactone) (PCL) prepared by the rapid expansion of a supercritical solution technique was studied by AFM at ambient and higher temperatures and by grazing-incident X-ray scattering using a synchrotron source. After dissolving PCL in a solution of supercritical CO2 and 0.1 vol.% chloroform, an extremely fast phase transfer from a supercritical to a gas-like state occurred during expansion into atmospheric conditions, leading to a temporary temperature drop to below -;50 degrees C at the silica surface where the crystals were deposited. Single crystals of a hitherto unreported rectangular lateral habit were observed. Six-sided crystals were also observed, but they were fewer than the rectangular crystals and in addition the angles between the lateral faces were different from the theoretical angles between adjacent {110} faces and {110} and {100} faces. X-ray scattering indicated a polymorphic structure also including the orthorhombic (110) and (200) diffraction peaks. Distinct low angle peaks essentially along the c-axis indicated a stacking on a very fine scale (3.7-4.7 nm) within the crystals. The equatorial diffraction peaks indicated a less dense packing of the PCL stems. Rectangular single crystals with a height according to AFM of 11-27 nm melted between 40 and 45 degrees C, which is lower than the melting points (55 degrees C) recorded for the distorted six-sided crystals. The unusual conditions for crystallisation used gave the polymer molecules a severe limitation to rearrange from the initial random coil state. The facetted crystals consisted of a stack of 4 nm thick blocks; these blocks most probably constituted a regular variation in molecular packing, i.e. molecular order. The pronounced changes in the angles between adjacent faces from those observed in mature PCL crystals and the wide-angle X-ray scattering data indicated the presence of conformational disorder in the crystals.

Reaction of Pd(dba)(2) and P(OPh)(3) shows a unique equilibrium where the Pd[P(OPh)(3)](3) complex is favored over both Pd(dba)[P(OPh)(3)](2) and Pd[P(OPh)(3)](4) complexes at room temperature. At a lower temperature, Pd[P(OPh)(3)](4) becomes the most abundant complex in solution. X-ray studies of Pd[P(OPh)(3)](3) and Pd(dba)[P(OPh)(3)](2) complexes show that both complexes have a trigonal geometry with a Pd-P distance of 2.25 angstrom due to the pi-acidity of the phosphite ligand. In solution, pure Pd(dba)[P(OPh)(3)](2) complex equilibrates to the favored Pd[P(OPh)(3)](3) complex, which is the most stable complex of those studied, and also forms the most active catalytic species. This catalyst precursor dissociates one ligand to give the reactive Pd[P(OPh)(3)](2), which performs an oxidative addition of nonmanipulated allyl alcohol to generate the pi-allyl-Pd[P(OPh)(3)](2) intermediate according to ESI-MS

The title compound, tricalcium oxynitride silicate, with composition Ca(3-x)Si(2)N(2-2x)O(4+2x) (x similar or equal to 0.12), is a perovskite-related calcium oxynitrido silicate containing isolated oxynitrido silicate 12-rings. The N atoms are statistically disordered with O atoms (occupancy ratio N:O = 0.88:0.12) and occupy the bridging positions in the 12 ring oxynitrido silicate anion, while the remaining O atoms are located at the terminal positions of the Si(O,N)(4) tetrahedra. The majority of the Ca(2+) cations fill the channels along [100] in the packing of the 12-ring anions. The rest of these cations are located at several positions, with partial occupancy, in channels along the body diagonals.

Resolving the problem! The conformationally chiral bistridentate [Ru(dqp)₂]²⁺ complex (dqp=2,6-di(quinolin-8-yl)pyridine) was resolved by selective precipitation using [Δ-TRISPHAT]⁻ (tris(tetrachlorocatecholate)phosphate) as the chiral auxiliary. The X-ray crystal structure of one diastereomer has been solved (see picture). No evidence for racemization was observed either at elevated temperature or with visible light.

The highly active ruthenium-based water oxidation catalyst [Ru-X(mcbp)(OHn)(py)(2)] [mcbp(2-)=2,6-bis(1-methyl-4-(carboxylate)benzimidazol-2-yl)pyridine; n=2, 1, and 0 for X=II, III, and IV, respectively], can be generated in a mixture of Ru-III and Ru-IV states from either [Ru-II(mcbp)(py)(2)] or [Ru-III(Hmcbp)(py)(2)](2+) precursors. The precursor complexes are isolated and characterized by single-crystal X-ray analysis, NMR, UV/Vis, EPR, and FTIR spectroscopy, ESI-HRMS, and elemental analysis, and their redox properties are studied in detail by electrochemical and spectroscopic methods. Unlike the parent catalyst [Ru(tda) (py)(2)] (tda(2-)=[2,2:6,2-terpyridine]-6,6-dicarboxylate), for which full transformation into the catalytically active species [Ru-IV(tda)(O)(py)(2)] could not be carried out, stoichiometric generation of the catalytically active Ru-aqua complex [Ru-X(mcbp)(OHn)(py)(2)] from the Ru-II precursor was achieved under mild conditions (pH7.0) and short reaction times. The redox properties of the catalyst were studied and its activity for electrocatalytic water oxidation was evaluated, reaching a maximum turnover frequency (TOFmax) of around 40000s(-1) at pH9.0 (from foot-of-the-wave analysis), which is comparable to the activity of the state-of-the-art catalyst [Ru-IV(tda)(O)(py)(2)].

Biphenyl-2,2′-dithiolate (bpdt) bridged Fe₂(bpdt)(CO)₆ (1) undergoes two sequential electrochemically quasi-reversible reductions. The one-electron reduction product 1⁻ is unusually stable against irreversible structural changes and could be characterized by IR and EPR spectroscopy supported by computational methods. Reduction to the (I,0) state does not trigger bridging coordination of CO but partial deligation of the dithiolate in 1⁻ that ultimately forms a diamagnetic dimerization product.

The title compound, barium niobium titanium oxide, is isostructural with BaNb₄O_6, i.e. it contains alternating NbO and perovskite-type single slabs. The NbO slabs can alternatively be described as layers of Nb₆O₁₂ clusters, condensed via corner sharing among the central Nb₆ octahedra.

Single crystals of SrNb4O6 were obtained by heat treatment of a pelleted mixture of Sr5Nb4O15, Nb2O5, and Nb at 1670 degrees C in sealed Nb tubes. High-resolution electron microscopy (HREM) studies showed the structure to be an intergrowth of alternating slabs of SrNbO3 (perovskite-type structure) and NbO (ordered deficient NaCl-type structure), both two unit cells wide. SrNb4O6 has a tetragonal unit cell with a = 4.1655(3) Angstrom and c = 16.223(1) Angstrom and space group P4/mmm, Z = 2. The structure model obtained from the HREM images was refined, using single-crystal diffraction data, to R(f) = 3.0%

The structure of Ba₂Nb₅O₉ can be described as an intergrowth between perovskite- (BaNbO₃) and NbO-type slabs. The substitution of Ti for Nb according to the formula Ba₂Nb_5−xTi_xO₉ (0.00≤x≤1.75) has been investigated. The decrease in unit cell parameters as a function of overall composition determined by microanalysis shows the maximum value of x to be around 0.9. At higher x values increasing amounts of BaNb_1−xTi_xO₃ and Nb were found. Rietveld refinements of the structure using X-ray powder diffraction data show Ti to prefer Nb positions in the perovskite slab (NbO₆ octahedra) and the Nb positions in the NbO slab closest to the perovskite slabs. This latter Nb is five-fold coordinated by oxygen atoms, forming a square pyramid. The third Nb position, in the middle of the NbO slab with a square planar coordination of oxygen atoms, remains undoped.

The electrical resistivity and magnetic susceptibility of the x = 0.0, 0.25, 0.50 and 0.75 samples were measured. All samples were found to be metallic conductors and temperature-independent paramagnetic.