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Hydrogenolysis of alkyl-substituted cyclopentadienyl (CpR ) ligated thorium tribenzyl complexes [(CpR )Th(p-CH2 -C6 H4 -Me)3 ] (1-6) afforded the first examples of molecular thorium trihydrido complexes [(CpR )Th(μ-H)3 ]n (CpR =C5 H2 (t Bu)3 or C5 H2 (SiMe3 )3 , n=5; C5 Me4 SiMe3 , n=6; C5 Me5 , n=7; C5 Me4 H, n=8; 7-10 and 12) and [(Cp# )12 Th13 H40 ] (Cp# =C5 H4 SiMe3 ; 13). The nuclearity of the metal hydride clusters depends on the steric profile of the cyclopentadienyl ligands. The hydrogenolysis intermediate, tetra-nuclear octahydrido thorium dibenzylidene complex [(Cpttt )Th(μ-H)2 ]4 (μ-p-CH-C6 H4 -Me)2 (Cpttt =C5 H2 (t Bu)3 ) (11) was also isolated. All of the complexes were characterized by NMR spectroscopy and single-crystal X-ray analysis. Hydride positions in [(CpMe4 )Th(μ-H)3 ]8 (CpMe4 =C5 Me4 H) were further precisely confirmed by single-crystal neutron diffraction. DFT calculations strengthen the experimental assignment of the hydride positions in the complexes 7 to 12.

The observation of an unusual crystal habit in the common diuretic drug hydrochlorothiazide (HCT), and identification of its subtle conformational chirality, has stimulated a detailed investigation of its crystalline forms. Enantiomeric conformers of HCT resolve into an unusual structure of conjoined enantiomorphic twin crystals comprising enantiopure domains of opposite chirality. The purity of the domains and the chiral molecular conformation are confirmed by spatially revolved synchrotron micro-XRD experiments and neutron diffraction, respectively. Macroscopic inversion twin symmetry observed between the crystal wings suggests a pseudoracemic structure that is not a solid solution or a layered crystal structure, but an unusual structural variant of conglomerates and racemic twins. Computed interaction energies for molecular pairs in the racemic and enantiopure polymorphs of HCT, and the observation of large opposing unit-cell dipole moments for the enantiopure domains in these twin crystals, suggest a plausible crystal nucleation mechanism for this unusual crystal habit.

The solid-state structure of a discrete chloride monohydrate species, [Cl(H2O)]-, is reported for the first time. It was isolated as a salt of the tris(dipropylamino)cyclopropenium cation and has been structurally characterized by X-ray and neutron diffraction. Infrared (IR), far-infrared, and Raman spectroscopic studies were also carried out. Additionally, the D2O and HDO isotopomers were investigated. Of the six fundamental vibrational modes, only the out-of-plane bend ν3 was not observed as it forms an IR- and Raman-inactive local mode phonon.

The factors affecting the accuracy of structural refinements from image-plate neutron Laue diffractometers are analysed. From this analysis, an improved data-processing method is developed which optimizes the intensity corrections for exposure scaling, wavelength distribution, absorption and extinction corrections, and the wavelength/spatial/time dependence of the image-plate detector efficiencies. Of equal importance is an analysis of the sources of uncertainty in the final corrected intensities, without which bias of the merged intensities occurs, due to the dominance of measurements with small statistical errors though potentially large systematic errors. A new aspect of the impact of detector crosstalk on the counting statistics of area detectors is reported and shown to be significant for the case of neutron Laue diffraction. These methods have been implemented in software which processes data from the KOALA instrument at ANSTO and the now decommissioned VIVALDI instrument at ILL (Grenoble, France). A comparison with earlier data-analysis methods shows a significant improvement in accuracy of the refined structures.

Advanced organic nonlinear optical (NLO) materials have attracted increasing attention due to their multitude of applications in modern telecommunication devices. Arguably the most important advantage of organic NLO materials, relative to traditionally used inorganic NLO materials, is their short optical response time. Geminal amido esters with their donor-π-acceptor (D-π-A) architecture exhibit high levels of electron delocalization and substantial intramolecular charge transfer, which should endow these materials with short optical response times and large molecular (hyper)polarizabilities. In order to test this hypothesis, the linear and second-order nonlinear optical properties of five geminal amido esters, (E)-ethyl 3-(X-phenylamino)-2-(Y-phenylcarbamoyl)acrylate (1, X = 4-H, Y = 4-H; 2, X = 4-CH3, Y = 4-CH3; 3, X = 4-NO2, Y = 2,5–OCH3; 4, X = 2-Cl, Y = 2-Cl; 5, X = 4-Cl, Y = 4-Cl) were synthesized and characterized, whereby NLO structure–function relationships were established including intramolecul...

An overview is presented of an integrated software package for the processing of Laue data from reactor and other continuous neutron sources. LaueG appears to the user as a graphical user interface with interactive graphic modes that depend on the task being performed: simple image display, cell indexing and refinement, peak integration, wavelength normalization and intensity corrections, or identification of statistical outliers. Other capabilities under development, though still usable, include satellite spots and modulated structures, twinned crystal analysis, and ab initio indexing of unit cells. The emphasis is on accurate intensities for structure refinement using an integrated graphical approach.

International audience; The coupling of the crystallographic refinement technique Hirshfeld atom refinement (HAR) with the recently constructed libraries of extremely localized molecular orbitals (ELMOs) gives rise to the new quantum-crystallographic method HAR-ELMO. This method is significantly faster than HAR but as accurate and precise, especially concerning the free refinement of hydrogen atoms from X-ray diffraction data, so that the first fully quantum-crystallographic refinement of a protein is presented here. However, the promise of HAR-ELMO exceeds large molecules and protein crystallography. In fact, it also renders possible electron-density investigations of heavy elements in small molecules and facilitates the detection and isolation of systematic errors from physical effects.

Tris(acetylacteonate) iron(III) is a relatively ubiquitous mononuclear inorganic coordination complex. The bidentate nature of the three acetylacteonate ligands coordinating around a single centre inevitably leads to structural isomeric forms, however whether or not this relates to chirality in the solid state has been questioned in the literature. Variable temperature neutron diffraction data down to T = 3 K, highlights the dynamic nature of the ligand environment, including the motions of the hydrogen atoms. The Fourier transform of the molecular dynamics simulation based on the experimentally determined structure was shown to closely reproduce the low temperature vibrational density of states obtained using inelastic neutron scattering.

The anisotropy of the magnetic properties of molecular magnets is a key descriptor in the search for improved magnets. Herein, we prove how a novel analysis approach using single crystal polarized neutron diffraction (PND) provides direct access to atomic magnetic susceptibility tensors. The technique has been applied for the first time to two Dy-based single molecule magnets, showing clear axial atomic susceptibility for both Dy(III)-ions. For the triclinic system, bulk magnetization methods are not symmetry-restricted, and the experimental magnetic easy axes from both PND, angular-resolved magnetometry (ARM) and theoretical approaches all match reasonably well. ARM curves simulated from the molecular susceptibility tensor determined with PND show strong resemblance with the experimental ones. For the monoclinic compound, a comparison can only be made with the theoretically calculated magnetic anisotropy, and in this case PND yields an easy-axis direction that matches that predicted via electrostatic methods. Importantly, this technique allows the determination of all elements of the magnetic susceptibility tensor and not just the easy-axis direction as is available from electrostatic predictions. Furthermore, it has the capacity to provide each of the anisotropic magnetic susceptibility tensors for all independent magnetic ions in a molecule, thus allowing for studies of poly-nuclear complexes and compounds of higher crystalline symmetry than triclinic.

Boron hydride clusters are an extremely diverse compound class, which are of enormous importance to many areas of chemistry. Despite this, stable aluminium hydride analogues of these species have remained staunchly elusive to synthetic chemists. Here, we report that reductions of an amidinato-aluminium(III) hydride complex with magnesium(I) dimers lead to unprecedented examples of stable aluminium(I) hydride complexes, [(ArNacnac)Mg]2[Al6H6(Fiso)2] (ArNacnac = [HC(MeCNAr)2]−, Ar = C6H2Me3-2,4,6 Mes; C6H3Et2-2,6 Dep or C6H3Me2-2,6 Xyl; Fiso = [HC(NDip)2]−, Dip = C6H3Pri2-2,6), which crystallographic and computational studies show to possess near neutral, octahedral hypercloso-hexaalane, Al6H6, cluster cores. The electronically delocalised skeletal bonding in these species is compared to that in the classical borane, [B6H6]2−. Thus, the chemistry of classical polyhedral boranes is extended to stable aluminium hydride clusters for the first time., While polyhedral boron hydride complexes have found application in a number of diverse fields, the isolation of stable aluminium analogues remains highly challenging. Here, Jones and colleagues demonstrate that reduction of an amidinato-aluminum(III) hydride complex with magnesium(I) dimers affords stable aluminium(I) hydride compounds.

The 1H and 13C NMR spectra in methylammonium lead halide perovskites, CH3NH3PbX3 (X = I, Br and Cl) show that the CH3NH3+ units undergo dynamic reorientation, as the organic component tumbles in the perovskite cage. In addition, the differences in the anomalously long relaxation times of the protons associated with the CH3 and not the NH3 groups indicate that only the amine end of the CH3NH3+ group is interacting with the inorganic network. Using this information, we have refined some single crystal X-ray and neutron diffraction data to probe their unusual structures in more detail. Furthermore, impedance spectroscopy has been used to monitor the high-temperature phase transition of CH3NH3PbI3, which confirms a significant increase in conductivity, when it is in its high temperature and higher symmetry structural regime. The optical band-gaps of each halide perovskite were determined using UV-visible spectroscopy and are consistent with previous reports. NRF (Natl Research Foundation, S’pore) Accepted version

Lead-containing (Pb-B-X)-2Hapatites encompass a number of [AF]4[AT]6[(BO4)6]X2compounds used for waste stabilization, environmental catalysis and ion conduction, but the influence of the stereochemically active lone-pair electrons of Pb2+on crystal chemistry and functionality is poorly understood. This article presents a compilation of existing structural data for Pb apatites that demonstrate paired electrons of Pb2+at both theAFandATresults in substantial adjustments to the PbFO6metaprism twist angle, φ. New structure refinements are presented for several natural varieties as a function of temperature by single-crystal X-ray diffraction (XRD) of vanadinite-2H(ideally Pb10(VO4)6Cl2), pyromorphite-2H(Pb10(PO4)6Cl2), mimetite-2H/M(Pb10(As5+O4)6Cl2) and finnemanite-2H(Pb10(As3+O3)6Cl2). A supercell for mimetite is confirmed using synchrotron single-crystal XRD. It is suggested the superstructure is necessary to accommodate displacement of the stereochemically active 6s2lone-pair electrons on the Pb2+that occupy a volume similar to an O2−anion. We propose that depending on the temperature and concentration of minor substitutional ions, the mimetite superstructure is a structural adaptation common to all Pb-containing apatites and by extension apatite electrolytes, where oxide ion interstitials are found at similar positions to the lonepair electrons. It is also shown that plumbous apatite framework flexes substantially through adjustments of the PbFO6metaprism twist-angles (φ) as the temperature changes. Finally, crystalchemical [100] zoning observed at submicron scales will probably impact on the treatment of diffraction data and may account for certain inconsistencies in reported structures.

The molecular and supramolecular origins of the superior nonlinear optical (NLO) properties observed in the organic phenolic triene material, OH1 (2-(3-(4-hydroxystyryl)-5,5-dimethylcyclohex-2-enylidene)malononitrile), are presented. The molecular charge-transfer distribution is topographically mapped, demonstrating that a uniformly delocalized passive electronic medium facilitates the charge-transfer between the phenolic electron donor and the cyano electron acceptors which lie at opposite ends of the molecule. Its ability to act as a “push–pull” π-conjugated molecule is quantified, relative to similar materials, by supporting empirical calculations; these include bond-length alternation and harmonic-oscillator stabilization energy (HOSE) tests. Such tests, together with frontier molecular orbital considerations, reveal that OH1 can exist readily in its aromatic (neutral) or quinoidal (charge-separated) state, thereby overcoming the “nonlinearity-thermal stability trade-off”. The HOSE calculation also re...

To better understand the oxide ion conduction mechanism of rare earth silicate apatites as intermediate temperature electrolytes for solid oxide fuel cells (SOFC), the effect of lower valent metal doping on the performance of Nd(28+x)/3AlxSi6-xO26 (0 ≤ x ≤ 2) single crystals has been examined. The measurement of ionic conductivity via AC impedance spectroscopy showed that the conductivities were anisotropic and superior along the c direction. An interesting aspect from the impedance studies was the identification of a second semicircle with capacitance similar to that of a grain boundary component, despite the fact that polarized optical microscopy and electron backscattered diffraction showed that the single crystals consisted of a single grain. This semicircle disappeared after long-term (up to 3 months) annealing of the single crystals at 950 °C, also leading to a reduction in the bulk conductivity. In order to explain these observations, single-crystal X-ray diffraction studies were performed both before and after annealing. These studies found the undoped crystal conformed to P63/m, but with the O(3) oxygen positions, that participate in conduction, split nonstatistically across two sites with a shortened Si–O(3) bond. Consequently, the bond valence sum (BVS) of the Si (4.20) is larger than the formal valence. Fourier difference maps of the Al-doped crystals contain regions of excess scattering, suggesting the possible lowering of symmetry or creation of superstructures. After long-term annealing, the single crystal structure determinations were of higher quality and the experimental and nominal compositions were in better agreement. From these observations, we propose that in the as-prepared single crystals there are regions of high and low interstitial content (e.g., Nd9.67Si6O26.5 and Nd9.33Si6O26), and the second semicircle relates to the interface between such regions. On annealing, Nd redistribution and homogenization removes these interfaces and also reduces the number of interstitial oxide ions, hence eliminating this second semicircle while reducing the bulk conductivity. The results therefore show for the first time that the conductivity of apatite materials containing cation vacancies is affected by the thermal history. ASTAR (Agency for Sci., Tech. and Research, S’pore) MOE (Min. of Education, S’pore) Accepted version

et al., Rare earth silicate apatites are one-dimensional channel structures that show potential as electrolytes for solid oxide fuel cells (SOFC) due to their high ionic conductivity at intermediate temperatures (500-700 °C). This advantageous property can be attributed to the presence of both interstitial oxygen and cation vacancies, that create diffusion paths which computational studies suggest are less tortuous and have lower activation energies for migration than in stoichiometric compounds. In this work, neutron diffraction of NdAlSiO (0 ≤ x ≤ 1.5) single crystals identified the locations of oxygen interstitials, and allowed the deduction of a dual-path conduction mechanism that is a natural extension of the single-path sinusoidal channel trajectory arrived at through computation. This discovery provides the most thorough understanding of the O transport mechanism along the channels to date, clarifies the mode of interchannel motion, and presents a complete picture of O percolation through apatite. Previously reported crystallographic and conductivity measurements are re-examined in the light of these new findings., We are pleased to acknowledge the Agency for Science, Technology and Research (A*STAR) PSF grant 082 101 0021 “Optimization of Oxygen Sublattices in Solid Oxide Fuel Cell Apatite Electrolytes” for funding the work and the Ministry of Education (MOE) Tier 2 grant T208B1212 for enabling the purchase of a single crystal X-ray diffractometer.

A new S = 1 kagome compound based on vanadium(III) is reported. The structure was refined simultaneously against single-crystal neutron and X-ray diffraction data, as a gaudefroyite-type with a new supercell (a′ = 2a + b, b′ = −a − 2b, c′ = c) driven by the ordering of columns of isolated triangular BO33− ions. Low-temperature neutron powder diffraction and magnetic (dc and ac susceptibility) data rule out the presence of long-range magnetic order above at least 1.5 K, but specific heat data suggest that the ground state involves short-range magnetic order, which is frustrated by the coexistence/competition of FM and AFM correlations, together with the characteristic geometric frustration of the kagome lattice. Magnetic susceptibility data rule out a spin-glass state, pointing to an exotic ground state comparable to the spin-ice or spin-liquid states. This makes YCa3(VO)3(BO3)4 one of the most highly frustrated experimental realizations of the kagome lattice yet discovered.

Conformational features and supramolecular structural organization in three aryl biscarbonates and an aryl biscarbamate with rigid acetylenic unit providing variable spacer lengths have been probed to gain insights into the packing features associated with molecular symmetry and the intermolecular interactions involving ‘organic’ fluorine. Four structures but-2-yne-1,4-diyl bis(2,3,4,5,6-pentafluorophenylcarbonate), 1; but-2-yne-1,4-diyl bis(4-fluorophenylcarbonate), 2; but-2-yne-1,4-diyl bis(2,3,4,5,6-pentafluorophenylcarbamate), 3 and hexa-2,4-diyne-1,6-diyl bis(2,3,4,5,6-pentafluorophenylcarbonate), 4 have been analyzed in this context. Compound 1 adopts a non-centrosymmetric “twisted” (syn) conformation, whereas 2, 3 and 4 acquire a centrosymmetric “extended” (anti) conformation. Weak intermolecular interactions and in particular those involving fluorine are found to dictate this conformational variation in the crystal structure of 1. A single-crystal neutron diffraction study at 90 K was performed on 1 to obtain further insights into these interactions involving ‘organic’ fluorine.

The tin atom in Me2Sn(phen)Cl2 is located on a crystallographic site of symmetry m2m and exists within a distorted octahedral geometry defined by a C2Cl2N2 donor set with the tin-bound methyl groups occupying trans-positions. A two-dimensional array stabilised by C–H · · · Cl interactions is established in the crystal structure. Crystal data for Me2Sn(phen)Cl2: C14H14Cl2N2Sn, M = 399.90, orthorhombic space group Cmcm, a = 11.359(2), b = 18.910(5), c = 7.536(2) Å, V = 1618.7(11) Å3, Z = 8, R = 0.073.

Magnetic properties of the $S=\frac{1}{2}$ antiferromagnet $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Cu}}_{2}{\mathrm{V}}_{2}{\mathrm{O}}_{7}$ have been studied using magnetization, quantum Monte Carlo (QMC) simulations, and neutron diffraction. Magnetic susceptibility shows a broad peak at $\ensuremath{\sim}50\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ followed by an abrupt increase indicative of a phase transition to a magnetically ordered state at ${T}_{N}=33.4(1)$ K. Above ${T}_{N}$, a fit to the Curie-Weiss law gives a Curie-Weiss temperature of $\mathrm{\ensuremath{\Theta}}=\ensuremath{-}73(1)$ K suggesting the dominant antiferromagnetic coupling. The result of the QMC calculations on the helical-honeycomb spin network with two antiferromagnetic exchange interactions ${J}_{1}$ and ${J}_{2}$ provides a better fit to the susceptibility than the previously proposed spin-chain model. Two sets of the coupling parameters ${J}_{1}:{J}_{2}=1:0.45$ with ${J}_{1}=5.79(1)$ meV and $0.65:1$ with ${J}_{2}=6.31(1)$ meV yield equally good fits down to $\ensuremath{\sim}{T}_{N}$. Below ${T}_{N}$, weak ferromagnetism due to spin canting is observed. The canting is caused by the Dzyaloshinskii-Moriya interaction with an estimated $bc$-plane component $\left|{D}_{p}\right|\phantom{\rule{4.pt}{0ex}}\ensuremath{\simeq}0.14{J}_{1}$. Neutron diffraction reveals that the $S=\frac{1}{2}\phantom{\rule{4.pt}{0ex}}{\mathrm{Cu}}^{2+}$ spins antiferromagnetically align in the $F{d}^{\ensuremath{'}}{d}^{\ensuremath{'}}2$ magnetic space group. The ordered moment of 0.93(9) ${\ensuremath{\mu}}_{B}$ is predominantly along the crystallographic $a$ axis.

The Type II phase in the Bi1 − xWxO1.5 + 1.5xsystem is shown to have a (3 + 3)-dimensional modulated δ-Bi2O3-related structure, in which the modulation vector ∊ `locks in' to a commensurate value of 1/3. The structure was refined in a 3 × 3 × 3 supercell against single-crystal Laue neutron diffraction data.Ab initiocalculations were used to test and optimize the local structure of the oxygen sublattice around a single mixed Bi/W site. The underlying crystal chemistry was shown to be essentially the same as for the recently refined (3 + 3)-dimensional modulated structure of Type II Bi1 − xNbxO1.5 + x(Linget al., 2013), based on a transition from fluorite-type to pyrochlore-typeviathe appearance of W4O18`tetrahedra of octahedra' and chains of corner-sharing WO6octahedra along 〈110〉Fdirections. The full range of occupancies on this mixed Bi/W site give a hypothetical solid-solution range bounded by Bi23W4O46.5(x= 0.148) and Bi22W5O48(x= 0.185), consistent with previous reports and with our own synthetic and analytical results.

DAST (4-dimethylamino-N-methyl-4-stilbazolium tosylate) is the most commercially successful organic nonlinear optical (NLO) material for frequency-doubling, integrated optics, and THz wave applications. Its success is predicated on its high optical nonlinearity with concurrent sufficient thermal stability. Many chemical derivatives of DAST have therefore been developed to optimize their properties; yet, to date, none have surpassed the overall superiority of DAST for NLO photonic applications. This is perhaps because DAST is an ionic salt wherein its NLO-active cation is influenced by multiple types of subtle intermolecular forces that are hard to quantify, thus, making difficult the molecular engineering of better functioning DAST derivatives. Here, we establish a model parameter, ηinter, that isolates the influence of intermolecular interactions on second-order optical nonlinearity in DAST and its derivatives, using second-harmonic generation (SHG) as a qualifier; by systematically mapping intercorrelations of all possible pairs of intermolecular interactions to ηinter, we uncover a relationship between concerted intermolecular interactions and SHG output. This correlation reveals that a sixfold gain in the intrinsic second-order NLO performance of DAST is possible, by eliminating the identified interactions. This prediction offers the first opportunity to systematically design next-generation DAST-based photonic device nanotechnology to realize such a prospect.

Neutron diffraction was used to investigate the evolution of the domain structure in PZN–4.5%PT during cooling in zero field and in a 〈0 0 1〉 poling field. The use of neutron diffraction allows penetration below the thick skin layer that has presented significant problems for earlier X-ray studies. We have confirmed the existence of a tetragonal phase existing between the cubic and rhombohedral phases, and that a poling field of 500 V/cm along 〈0 0 1〉 is sufficient for a cubic to tetragonal phase transition to occur. In the absence of a poling field we find that a “Phase X” behaviour occurs on cooling from the cubic phase. However, once the cubic to tetragonal phase transition has occurred the poling field can be removed and the phase transition to the rhombohedral phase will occur on further cooling. As expected, the domain structure of the tetragonal phase contains 90° twins and the dominant domain orientation is with the spontaneous polarization along the 〈0 0 1〉 poling field.

The domain structure of PZN-4.5%PT was studied as a function of temperature in an electric field of 500 V/cm applied along ⟨001⟩. The measurements provides direct information on the orientational relationships between the cubic, tetragonal and rhombohedral domains during the field cooling process, and on the volume fraction of domains in each set of orientations. The domains in the tetragonal phase are all related by 90° twins mainly on the (101) and (011) twin planes. The domain structure of the rhombohedral phase agrees with an earlier room temperature and zero field study.

The molecular dipole moment of MNA in the crystal has been critically reexamined, to test the conclusion from an earlier experimental charge density analysis that it was substantially enhanced due to a combination of strong intermolecular interactions and crystal field effects. X-ray and neutron diffraction data have been carefully measured at 100 K and supplemented with ab initio crystal Hartree-Fock calculations. Considerable care taken in the measurement and reduction of the experimental data excluded most systematic errors, and sources of error and their effects on the experimental electron density have been carefully investigated. The electron density derived from a fit to theoretical structure factors assisted in the determination of the scale and thermal motion model. The dipole moment enhancement for MNA in the crystal is much less than that reported previously and only on the order of 30-40% (approximately 2.5 D). In addition to the dipole moment, experimental deformation electron density maps, bond critical point data, electric field gradients at hydrogen nuclei, and atomic and group charges all agree well with theoretical results and trends. Anisotropic modeling of the motion of hydrogen atoms, integral use of periodic ab initio calculations, and improved data quality are all aspects of this study that represent a considerable advance over previous work.

An accurate structure refinement of the deuterated analog of the cesium lithium acid sulfate, formerly identified as ‘Cs₁.₅Li₁.₅D(SO₄)₂’, has been carried out using neutron diffraction methods. Like the protonated material reported earlier (Merinov et al., Solid State Ionics 69 (1994) 53), the compound is cubic, I¯43d; however, the correct stoichiometry is Cs₃Li(DSO₄)₄. There are four formula units per unit cell and six atoms in the asymmetric unit. The lattice constant measured in this work is a=11.743(2)A, comparable to the earlier results. The structure contains one disordered hydrogen bond, formed between O(2) atoms and located on two of the edges of the single LiO₄ tetrahedron. The Li site occupancy is 1/3; as is that of the deuterium site. This level of site occupancies is consistent with a structure in which hydrogen bonds are formed only when the lithium site is unoccupied, and explains the otherwise close proximity of the Li and D atoms, 1.394(10)A. This unusual structural feature furthermore leads to a fixed stoichiometry, as confirmed here by chemical analysis of both the deuterated and protonated materials, despite the partial occupancy of the lithium and deuterium (hydrogen) atom sites.

Lead zinc niobate–lead titanate (PZN–PT) single crystals show very large piezoelectric strains for electric fields applied along the unit cell edges e.g. [001]R. It has been widely reported that this effect is caused by an electric field induced phase transition from rhombohedral (R3m) to monoclinic (Cm or Pm) symmetry in an essentially continuous manner. Group theoretical analysis using the computer program ISOTROPY indicates phase transitions between R3m and Cm (or Pm) must be discontinuous under Landau theory. An analysis of the symmetry of a strained unit cell in R3m and a simple expansion of the piezoelectric strain equation indicate that the piezoelectric distortion due to an electric field along a cell edge in rhombohedral perovskite-based ferroelectrics is intrinsically monoclinic (Cm), even for infinitesimal electric fields. PZN–PT crystals have up to nine times the elastic compliance of other piezoelectric perovskites and it might be expected that the piezoelectric strains are also very large. A field induced phase transition is therefore indistinguishable from the piezoelectric distortion and is neither sufficient nor necessary to understand the large piezoelectric response of PZN–PT.

The total experimental charge density in 1-(2-hydroxy-5-nitrophenyl)ethanone (1) has been determined using high-resolution X-ray diffraction data in combination with neutron diffraction data measured at 100 K. Multipole refinement was carried out in terms of the rigid pseudoatom model. Multipole refinement converged at R = 0.026 for 5415 reflections with I > 2σ(I). Topological analysis of the total experimental charge density ρ(r) and its Laplacian, −∇2ρ(r) together with a comparison against high level theoretical gas-phase calculations reveals fine details of intra- and intermolecular bonding features, in particular the extent of the π-delocalisation throughout the molecule.

The electron densities in two analogous dimetallic transition metal compounds, namely, [M2(μ-OH2)((t)BuCOO)4((t)BuCOOH)2(C5H5N)2] (M = Co(1), Ni(2)), were determined from combined X-ray and neutron single-crystal diffraction at 100 K. Excellent correspondence between the thermal parameters from X- and N-derived atomic displacement parameters is found, indicating high-quality X-ray data and a successful separation of thermal and electronic effects. Topological analysis of electron densities derived from high-resolution X-ray diffraction, as well as density functional theory calculations, shows no direct metal-metal bonding in either compound, while the total energy density at the bond critical points suggests stronger metal-oxygen interactions for the Ni system, in correspondence with its shorter bond distances. The analysis also allows for estimation of the relative strength of binding of terminal and bridging ligands to the metals, showing that the bridging water molecule is more strongly bound than terminal carboxylic acid, but less so than bridging carboxylates. Recently, modeling of magnetic and spectroscopic data in both of these systems has shown weak ferromagnetic interactions between the metal atoms. Factors related to large zero-field splitting effects complicate the magnetic analysis in both compounds, albeit to a much greater degree in 1. The current results support the conclusion drawn from previous magnetic and spectroscopic measurements that there is no appreciable direct communication between metal centers.

A single-crystal structure determination of Nd8Sr2Si6O26 apatite, a prototype intermediate-temperature electrolyte for solid oxide fuel cells grown by the floating-zone method, was completed using the combination of Laue neutron diffraction and Raman spectroscopy. While neutron diffraction was in good agreement with P6₃/m symmetry, the possibility of P6₃ could not be convincingly excluded. This ambiguity was removed by the collection of orientation-dependent Raman spectra that could only be consistent with P6₃/m. The composition of Nd8Sr2Si6O26 was independently verified by powder X-ray diffraction in combination with electron probe microanalysis, with the latter confirming a homogeneous distribution of Sr and the absence of chemical zonation commonly observed in apatites. This comprehensive crystallochemical description of Nd8Sr2Si6O26 provides a baseline to quantify the efficacy of cation vacancies, oxygen superstoichiometry, and symmetry modification for promoting oxygen-ion mobility.

The syntheses of the first rhombicuboctahedral copper polyhydride complexes [Cu28 (H)15 (S2 CNR)12 ]PF6 (NR=N(n) Pr2 or aza-15-crown-5) are reported. These complexes were analyzed by single-crystal X-ray and one by neutron diffraction. The core of each copper hydride nanoparticle comprises one central interstitial hydride and eight outer-triangular-face-capping hydrides. A further six face-truncating hydrides form an unprecedented bridge between the inner and outer copper atom arrays. The irregular inner Cu4 tetrahedron is encapsulated within the Cu24 rhombicuboctahedral cage, which is further enclosed by an array of twelve dithiocarbamate ligands that subtends the truncated octahedron of 24 sulfur atoms, which is concentric with the Cu24 rhombicuboctahedron and Cu4 tetrahedron about the innermost hydride. For these compounds, an intriguing, albeit limited, H2 evolution was observed at room temperature, which is accompanied by formation of the known ion [Cu8 (H)(S2 CNR)6 ](+) upon exposure of solutions to sunlight, under mild thermolytic conditions, and on reaction with weak (or strong) acids.

et al., A single-crystal structure determination of Nd8Sr 2Si6O26 apatite, a prototype intermediate-temperature electrolyte for solid oxide fuel cells grown by the floating-zone method, was completed using the combination of Laue neutron diffraction and Raman spectroscopy. While neutron diffraction was in good agreement with P63/m symmetry, the possibility of P63 could not be convincingly excluded. This ambiguity was removed by the collection of orientation-dependent Raman spectra that could only be consistent with P63/m. The composition of Nd8Sr2Si 6O26 was independently verified by powder X-ray diffraction in combination with electron probe microanalysis, with the latter confirming a homogeneous distribution of Sr and the absence of chemical zonation commonly observed in apatites. This comprehensive crystallochemical description of Nd8Sr2Si6O26 provides a baseline to quantify the efficacy of cation vacancies, oxygen superstoichiometry, and symmetry modification for promoting oxygen-ion mobility. © 2014 American Chemical Society., This work was supported by A*STAR (Agency for Science, Technology and Research) SERC Grant 082 101 0021 (“Optimization of Apatite Anion Sublattices in Solid Oxide Fuel Cell Electrolytes”) and by Spanish Government Grant MAT2010-19837-C06-06. A.O. acknowledges financial support provided by the Spanish Ministerio de Ciencia e Innovación through a Juan de la Cierva contract.

A supramolecular assembly formed between phthalimide and 2-guanidinobenzimidazole, containing a short 2.692(4)AR N-H…N hydrogen bond, is reported. The crystal structure of this species was determined by both X-ray and neutron diffraction. The diffraction data reveal that the proton involved in the short hydrogen bond has been transferred from the phthalimide to the guanidinobenzimidazole to form an ion pair. There is also an interesting stacking interaction between the atoms involved in the short hydrogen bond and the π system of a phthalimide molecule that is approximately 3.3 A away. The structure is compared with the structure of a similar assembly formed between 4-nitrophthalimide and 2-guanidinobenzimidazole.

Lead zinc niobate-lead titanate (PZN-PT) single crystals are able to sustain very large piezoelectric strains, a phenomenon for which the term `giant piezoelectric effect' was recently coined. PZN-4.5%PT crystals were studied by means of single-crystal neutron diffraction at temperatures between 293 K and 438 K. Two phase transitions were observed. The first, from the room temperature rhombohedral perovskite structure (R3m) to the tetragonal lead titanate phase (P4mm) occurs at 391±2 K. The second, to the cubic perovskite aristotype, occurs at 421±2 K. These temperatures are at slight variance with the current phase diagram. The transitions are relatively abrupt, occurring over a range of only 2-3 K. A monoclinic phase recently reported to occur between the rhombohedral and tetragonal phases in the lead zirconate titanate system (PZT) does not occur here. Group theoretical analysis using the computer program ISOTROPY indicates that the intermediate monoclinic phase cannot facilitate a truly continuous transition from rhombohedral to tetragonal symmetry.

The structure of cis-bis( l -alaninato)copper(II) {cis-[Cu( l -ala)2]} was determined using single crystal neutron diffraction techniques at both low (7 K) and ambient temperature. At both temperatures the cell is orthorhombic, space group P212121. The unit cell parameters obtained show essentially an isotropic contraction upon cooling. At both temperatures the coordination sphere around the copper atom is best described as square pyramidal, where the fifth position is occupied by a weakly bonded carbonyl oxygen from an adjacent alanine unit. The alanine ligands coordinate to the divalent copper atom in an approximately square planar cis-arrangement. The significant difference between the two structure determinations is the contraction of the apical carbonyl oxygen–copper bond distance from 2.372(4) to 2.326(2) A upon cooling.

The low field magnetic susceptibility of samples cut from two single crystals of has been measured. Both samples show re-entrant spin glass behaviour in the antiferromagnetic state with significant differences between the samples which are related to their metallurgy. Both samples show spin freezing parallel to as well as perpendicular to the magnetic ordering direction, although the amount of spin freezing apparent with an applied field parallel to the ordering direction is less marked.

We report detailed structural investigations of the dimorphic clathrate Ba8Ga16Sn30 that crystallizes in both type I and VIII clathrate structures. Single crystals of type I and VIII have been examined using single crystal X-ray and Laue neutron diffraction in the temperature range T = 10 K-500 K. The utilization of both X-ray and neutron diffraction gives a unique ability to reveal the occurrence of minute vacancy occupancies in the host structure. The vacancies are shown to be located on the 6c (type I) and 24g (type VIII) framework sites. Largest vacancy densities are observed for type I p-Ba8Ga16Sn30, 1.3(4)%, and type VIII n-Ba8Ga16Sn30, 0.7(2)%. The relation between guest atom disorder and occurrence of glasslike thermal conductivity in intermetallic clathrates was also investigated. In type VIII Ba8Ga16Sn30 neither n-type (crystalline thermal conductivity) nor p-type (glasslike thermal conductivity) showed any significant disorder of the guest atoms; they do however show anharmonic motion. The glasslike thermal conductivity of p-type Ba8Ga16Sn30 is interpretable as a result of higher effective mass of p-type charge-carriers affecting phonon scattering. In type I Ba8Ga16Sn30 guest atoms are highly disordered for both carrier types and samples of both charge carrier types have glasslike thermal conductivity.

A new Si phase was obsd. using high-resoln. angle-dispersive x-ray powder diffractometry and the structure was solved and refined (no data). Si XII was reversible formed above 2 GPa via a 1st-order transition from Si III. It has a larger rhombohedral angle (110.07� at 8.2 GPa) than cubic Si III, which reduces the cell vol. by ?2% at the transition. The space group is R?3 with 8 atoms per cell. There is a wide spread of bond angles within the structure making Si XII the most complex, tetrahedrally-bonded cryst. phase of Si. Simulated transition mechanisms showed that the phase transition involves 1 bond breakage and 1 new bond formation per unit cell. [on SciFinder(R)]

Dense tetrahedral forms of the elemental semiconductors silicon and germanium can be synthesised as metastable phases by depressurisation from metallic modifications. These structures are denoted as BC8 (body-centred: 8 atoms per cell) and ST12 (simple-tetragonal: 12 atoms per cell). Despite having similar metallic phases, the III–V compounds have never been formed in the diatomic equivalent of the BC8 or ST12 structures. We report the results of our ab initio total energy calculations which suggest that the diatomic analogue of the BC8 structure, (the SC16 structure: simple cubic: 16 atoms per cell) is a stable high-pressure polymorph of several III–V compounds. We suggest that kinetic factors rather than energetics inhibit its formation. In light of the recent discovery of the pressure-induced formation of the SC16 structure in I–VII compounds, it now seems that the energetics of high-pressure phase transitions in tetrahedral semiconductors are much more similar than they once appeared to be and that the transition mechanisms are much more involved.

Complementary experimental techniques and ab initio calculations were used to determine the origin and nature of negative thermal expansion (NTE) in the archetype metal-organic framework MOF-5 (Zn(4)O(1,4-benzenedicarboxylate)(3)). The organic linker was probed by inelastic neutron scattering under vacuum and at a gas pressure of 175 bar to distinguish between the pressure and temperature responses of the framework motions, and the local structure of the metal centers was studied by X-ray absorption spectroscopy. Multi-temperature powder- and single-crystal X-ray and neutron diffraction was used to characterize the polymeric nature of the sample and to quantify NTE over the large temperature range 4-400 K. Ab initio calculations complement the experimental data with detailed information on vibrational motions in the framework and their correlations. A uniform and comprehensive picture of NTE in MOF-5 has been drawn, and we provide direct evidence that the main contributor to NTE is translational transverse motion of the aromatic ring, which can be dampened by applying a gas pressure to the sample. The linker motion is highly correlated rather than local in nature. The relative energies of different framework vibrations populated in MOF-5 are suggested by analysis of neutron diffraction data. We note that the lowest-energy motion is a librational motion of the aromatic ring which does not contribute to NTE. The libration is followed by transverse motion of the linker and the carboxylate group. These motions result in unit-cell contraction with increasing temperature.

Neutron diffuse scattering is used to explore the short-range order (SRO) in deuterated para-terphenyl, C(18)D(14). The crystal shows SRO because the central of the three phenyl groups of each molecule can twist positively or negatively and these twists are correlated over the local scale. The presence of incipient Bragg peaks at [Formula: see text] at 200 K shows that these flips are negatively correlated along the a direction (nearest neighbour correlation coefficient of ∼-0.3) and b direction (nearest neighbour correlation coefficient of ∼-0.87) and appear essentially uncorrelated along c. Diffuse peak anisotropy indicates that the range of the correlations along b is found to be ∼3 times that along a. These correlations persist, although weaker, at room temperature. A Monte Carlo simulation was used to impose a correlation structure on the population of central ring twists that was deduced from Bragg scattering. By then allowing displacive relaxation of the structure, the observed diffuse scattering was well reproduced. Modelling the displacive motions of molecules showed that the positions of nearest ab-plane neighbour molecules are strongly positively correlated, particularly for motions approximately parallel to a, while the displacive correlations are weaker between molecules stacked along c. The apparent contradiction that the displacements are most strongly correlated along a while the occupancies are most strongly correlated along b is explained in terms of the connectivity of molecular interactions.

The new title compound is synthesized by reaction of Y2O3, CaCO3, V2O5, and B2O3 (flowing 3.5% H2/Ar, 1000 °C, 7 d).

We present experimental and theoretical evidence for the creation of inversion domain boundaries (IDB's) at structural phase transitions in III-V semiconductors. A novel use of anomalous high-pressure powder x-ray diffraction with an image plate area detector allows for the study of weak difference scattering, the absence of which is attributed to IDB's. As a test of this, ab initio total energy pseudopotential calculations, including both ionic relaxation and boundary layer expansion, have been performed on a particular type of possible defect---a (110) IDB in InSb.