Ross O. Piltz

A combined single crystal neutron/X-ray diffraction and solid-state nuclear magnetic resonance study of the hybrid perovskites CH3NH3PbX3 (X = I, Br and Cl)

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.

Chinese Puzzle Molecule: A 15 Hydride, 28 Copper Atom Nanoball

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.

The giant piezoelectric effect: electric field induced monoclinic phase or piezoelectric distortion of the rhombohedral parent?

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.

X–N Charge density analysis of the hydrogen bonding motif in 1-(2-hydroxy-5-nitrophenyl)ethanoneElectronic supplementary information (ESI) available: multipole population coefficients and pseudoatom parameterization. See http://www.rsc.org/suppdata/ob/b2/b211683a/

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 > 2 sigma(I). Topological analysis of the total experimental charge density rho(r) and its Laplacian, -[symbol: see text]2 rho(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 pi-delocalisation throughout the molecule.

Scrutinizing negative thermal expansion in MOF-5 by scattering techniques and ab initio calculations

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.

Hydrogen bonding in cis-bis(l-alaninato)copper(II): a single crystal neutron diffraction study

Abstract 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.

Combined X-ray and neutron diffraction study of vacancies and disorder in the dimorphic clathrate Ba8Ga16Sn30 of type i and VIII

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.

Nitrile groups as hydrogen-bond acceptors in a donor-rich hydrogen-bonding network

A complex hydrogen-bonding network involving the guanidinium cation and the dinitrile anion C(CN)2(CONH2)− has been studied using Laue neutron diffraction. The role of nitrile groups as hydrogen bond acceptors is highlighted in this donor-rich system combined with a survey of the CSD exploring R12(6) synthons containing nitrile groups.

Crystal structures of fluorinated aryl biscarbonates and a biscarbamate: a counterpoise between weak intermolecular interactions and molecular symmetry

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.

Interstitial Oxide Ion Distribution and Transport Mechanism in Aluminum-Doped Neodymium Silicate Apatite Electrolytes

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 Nd(28+x)/3AlxSi6-xO26 (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(2-) transport mechanism along the channels to date, clarifies the mode of interchannel motion, and presents a complete picture of O(2-) percolation through apatite. Previously reported crystallographic and conductivity measurements are re-examined in the light of these new findings.