Novel alkali earth borohydride Sr(BH4)2 and borohydride-chloride Sr(BH4)Cl.

Two novel alkali earth borohydrides, Sr(BH4)2 and Sr(BH4)Cl, have been synthesized and investigated by in-situ synchrotron radiation powder X-ray diffraction (SR-PXD) and Raman spectroscopy. Strontium borohydride, Sr(BH4)2, was synthesized via a metathesis reaction between LiBH4 and SrCl2 by two complementary methods, i.e., solvent-mediated and mechanochemical synthesis, while Sr(BH4)Cl was obtained from mechanochemical synthesis, i.e., ball milling. Sr(BH4)2 crystallizes in the orthorhombic crystal system, a = 6.97833(9) Å, b = 8.39651(11) Å, and c = 7.55931(10) Å (V = 442.927(10) Å(3)) at RT with space group symmetry Pbcn. The compound crystallizes in α-PbO2 structure type and is built from half-occupied brucite-like layers of slightly distorted [Sr(BH4)6] octahedra stacked in the a-axis direction. Strontium borohydride chloride, Sr(BH4)Cl, is a stoichiometric, ordered compound, which also crystallizes in the orthorhombic crystal system, a = 10.8873(8) Å, b = 4.6035(3) Å, and c = 7.4398(6) Å (V = 372.91(3) Å(3)) at RT, with space group symmetry Pnma and structure type Sr(OH)2. Sr(BH4)Cl dissociates into Sr(BH4)2 and SrCl2 at ~170 °C, while Sr(BH4)2 is found to decompose in multiple steps between 270 and 465 °C with formation of several decomposition products, e.g., SrB6. Furthermore, partly characterized new compounds are also reported here, e.g., a solvate of Sr(BH4)2 and two Li-Sr-BH4 compounds.

The structure, thermal properties and phase transformations of the cubic polymorph of magnesium tetrahydroborate.

The structure of the cubic polymorph of magnesium tetrahydroborate (γ-Mg(BH(4))(2)) has been determined in space group Ia3d from a structural database of the isoelectronic compound SiO(2); this has been corroborated by DFT calculations. The structure is found to concur with that recently determined by Filinchuk et al. (Y. Filinchuk, B. Richter, T. R. Jensen, V. Dmitriev, D. Chernyshov and H. Hagemann, Angew. Chem. Int. Ed., 2011, DOI: 10.1002/anie.201100675). The phase transformations and subsequent decomposition of γ-Mg(BH(4))(2) on heating have been ascertained from variable-temperature synchrotron X-ray diffraction data combined with thermogravimetric and mass spectrometry measurements. At ~160 °C, conversion to a disordered variant of the ß-Mg(BH(4))(2) phase (denoted as ß') is observed along with a further unidentified polymorph. There is evidence of amorphous phases during decomposition but there is no direct crystallographic indication of the existence of Mg(B(12)H(12)) or other intermediate Mg-B-H compounds. MgH(2) and finally Mg are observed in the X-ray diffraction data after decomposition.

A multidisciplinary combinatorial approach for tuning promising hydrogen storage materials towards automotive applications.

HyStorM is a multidisciplinary hydrogen-storage project aiming to synthesise and tune materials hydrogen storage properties for automotive applications. Firstly, unique high-throughput combinatorial thin-film technologies are used to screen materials' hydrogen storage properties. Then promising thin-film candidate compositions are synthesised and examined in the bulk. In this paper, we report on our results within the ternary compositions Mg-Ti-B and Ca-Ti-B. Primary screening of the Mg-Ti-B ternary identified a high capacity hotspot corresponding to Mg0.36Ti0.06B0.58, with 10.6 wt% H2 capacity. Partial reversibility has been observed for this material in the thin-film. Bulk Ti-doped Mg(BH4)2 composites show rehydrogenation to MgH2 under the conditions used. The synthesised thin-film Ca-Ti-B ternary showed only low hydrogen storage capacities. In the bulk, Ti-doping experiments on Ca(BH4)2 demonstrated reversible storage capacities up to 5.9 wt% H2. Further characterisation experiments are required to decipher the role of the Ti-dopant in these systems in both films and in the bulk.

Structure determination from powder diffraction data.

Advances made over the past decade in structure determination from powder diffraction data are reviewed with particular emphasis on algorithmic developments and the successes and limitations of the technique. While global optimization methods have been successful in the solution of molecular crystal structures, new methods are required to make the solution of inorganic crystal structures more routine. The use of complementary techniques such as NMR to assist structure solution is discussed and the potential for the combined use of X-ray and neutron diffraction data for structure verification is explored. Structures that have proved difficult to solve from powder diffraction data are reviewed and the limitations of structure determination from powder diffraction data are discussed. Furthermore, the prospects of solving small protein crystal structures over the next decade are assessed.

Hydrogen energy.

The problem of anthropogenically driven climate change and its inextricable link to our global society's present and future energy needs are arguably the greatest challenge facing our planet. Hydrogen is now widely regarded as one key element of a potential energy solution for the twenty-first century, capable of assisting in issues of environmental emissions, sustainability and energy security. Hydrogen has the potential to provide for energy in transportation, distributed heat and power generation and energy storage systems with little or no impact on the environment, both locally and globally. However, any transition from a carbon-based (fossil fuel) energy system to a hydrogen-based economy involves significant scientific, technological and socio-economic barriers. This brief report aims to outline the basis of the growing worldwide interest in hydrogen energy and examines some of the important issues relating to the future development of hydrogen as an energy vector.

Order-disorder transition in monoclinic sulfur: a precise structural study by high-resolution neutron powder diffraction.

High-resolution neutron powder diffraction has been used in order to characterize the order-disorder transition in monoclinic cyclo-octasulphur. Rapid data collection and the novel use of geometrically constrained refinements has enabled a direct and precise determination of the order parameter, based on molecular site occupancies, to be made. The transition is critical and continuous; with a transition temperature, Tc=198.4 (3) K, and a critical exponent, beta=0.28 (3), which is indicative of three-dimensional ordering. Difficulties encountered as a consequence of the low thermal conductivity of the sample are discussed.

Powder Diffraction: Least-Squares and Beyond.

This paper addresses some of the underlying statistical assumptions and issues in the collection and refinement of powder diffraction data. While standard data collection and Rietveld analysis have been extremely successful in providing structural information on a vast range of materials, there is often uncertainty about the true accuracy of the derived structural parameters. In this paper, we discuss a number of topics concerning data collection and the statistics of data analysis. We present a simple new function, the cumulative chi-squared distribution, for assessing regions of misfit in a diffraction pattern and introduce a matrix which relates the impact of individual points in a powder diffraction pattern with improvements in the estimated standard deviation of refined parameters. From an experimental viewpoint, we emphasise the importance of not over-counting at low-angles and the routine use of a variable counting scheme for data collection. Data analysis issues are discussed within the framework of maximum likelihood, which incorporates the current least-squares strategies but also enables the impact of systematic uncertainties in both observed and calculated data to be reduced.

Placental histopathology of congenital syphilis.

OBJECTIVE: To evaluate the contribution of placental histopathology to the diagnosis of congenital syphilis. METHODS: From January 1, 1986, through December 31, 1998, all pregnant women presenting to a large, urban Dallas County labor and delivery unit with untreated syphilis at delivery and who had placental evaluation performed were identified. Women were clinically staged, and the infants were evaluated for congenital syphilis using a standard protocol. Each placenta was evaluated by two independent pathologists. Histologic characteristics of the placenta related to congenital syphilis in live-born and stillborn infants were then analyzed. RESULTS: Sixty-seven women met the study criteria: 33 (49%) stillborn and 18 (27%) live-born infants with congenital syphilis, 15 (22%) uninfected live-born infants, and one uninfected stillborn fetus diagnosed by current criteria. There were no differences between the groups with regard to demographic characteristics, prenatal care, or stage of syphilis. Stillborn infants were more likely to deliver preterm (P <.001). Controlling for gestational age, histopathology revealed necrotizing funisitis, villous enlargement, and acute villitis associated with congenital syphilis. Erythroblastosis was more common in stillborn infants with congenital syphilis than all live-born infants (odds ratio 16, 95% confidence interval 1, 370). The addition of histologic evaluation to conventional diagnostic evaluations improved the detection rate for congenital syphilis from 67% to 89% in live-born infants, and 91% to 97% in stillborn infants. CONCLUSION: Our results show that histopathologic examination of the placenta is a valuable adjunct to the contemporary diagnostic criteria used to diagnose congenital syphilis.

Chiral metal-dithiolene/viologen ion pairs: synthesis and electrical conductivity.

Enantiomerically pure dithiolene complexes NBu4[Ni[(R,R)-diotte)2] and NBu4[Ni((S,S)-diotte]2] (diotte2- = a 1,3-dioxolane-tetrathiaethylene), were prepared from the corresponding enantiomers of a diotte2- precursor. The structure of the precursor was solved by single-crystal X-ray analysis; desulfurization afforded a novel tetrathiafulvalene derivative. Combination of the complex monoanion with the enantiomers of the viologen derivative bis(2-methyl-3-hydroxypropyl)-4,4'-dipyridinium (HiBV2+) afforded enantiomeric and diastereomeric ion-pair complexes of the type HiBV[Ni(diotte)2]2. For comparison, the analogous compounds A[Ni(diotte)2]2, (A2+ = methyl (MV2+), octyl (OV2-), stearyl (StV2+) viologen or two 2,2'-bipyridinium acceptors), HiBV-[Ni(diotte)L] [L = mnt2- (maleonitrile-1,2-dithiolate), dmit2- (2-thioxo-1,3-dithiol-4,5-dithiolate)], MV[Ni(dmit)2)]2, [Ni(diotte)2], and [Ni(diotte)(dmit)] were synthesized. An X-ray powder diffraction structural analysis of MV-[Ni(dmit)2)]2 revealed the presence of mixed stacks that contain the sequence anion-anion-cation. While no short contacts are observable within a stack, these are observed between the stacks for the dication-anion interaction by short S...H distances in the range of 2.77 to 2.86 A, and for the anion-anion interaction short S...S distances of 3.55 to 3.65 A. In agreement with the absence of intrastack interactions, no ion-pair charge-transfer band can be detected in this and the other complexes. ESR and UV/Vis data suggest that in [Ni(diotte)2]- electron delocalization is less pronounced than in the corresponding mnt2- and dmit2- complexes. The specific electrical conductivity (sigma) of pressed powder pellets ranges from 10(-2) to 10(-12) ohm(-1) cm(-1) and in all cases increases with increasing temperature (293 - 393 K) according to an Arrhenius law. Corresponding activation energies vary from 0.14 to 0.93 eV and increase linearly with log a for structurally similar ion pairs. Charge generation is postulated to occur by disproportionation of the monoanion as suggested by the almost linear increase of log(sigma) with decreasing disproportionation energy. The conductivity of diastereomers of ions with two unlike configurations like [(S,S)-HiBV]-[Ni[(R,R)-diotte]2]2 (1.1 x 10(-1) ohm(-1) cm(-1)) is one to two orders of magnitude higher as compared to the diastereomers with two like-configured ions.

A probabilistic approach to space-group determination from powder diffraction data.

An algorithm for the determination of the space-group symmetry of a crystal from powder diffraction data, based upon probability theory, is described. Specifically, the relative probabilities of different extinction symbols are assessed within a particular crystal system. In general, only a small number of extinction symbols are relatively highly probable and a single extinction symbol is often significantly more probable than any other. Several examples are presented to illustrate this approach.

Diffuse X-ray scattering from benzil, C(14)H(10)O(2): analysis via automatic refinement of a Monte Carlo model.

A recently developed method for fitting a Monte Carlo computer-simulation model to observed single-crystal diffuse X-ray scattering has been used to study the diffuse scattering in benzil, diphenylethanedione, C(6)H(5)-CO-CO-C(6)H(5). A model involving 13 parameters consisting of 11 intermolecular force constants, a single intramolecular torsional force constant and a local Debye-Waller factor was refined to give an agreement factor, R = [summation operator omega(Delta I)(2)/summation operator omega I(obs)(2)](1/2), of 14.5% for 101,324 data points. The model was purely thermal in nature. The analysis has shown that the diffuse lines, which feature so prominently in the observed diffraction patterns, are due to strong longitudinal displacement correlations. These are transmitted from molecule to molecule via a network of contacts involving hydrogen bonding of an O atom on one molecule and the para H atom of the phenyl ring of a neighbouring molecule. The analysis also allowed the determination of a torsional force constant for rotations about the single bonds in the molecule. This is the first diffuse scattering study in which measurement of such internal molecular torsion forces has been attempted.

Structural transformations in zopiclone.

A monoclinic centrosymmetric form of zopiclone dihydrate undergoes a sequential, two-step transformation in the solid-state upon heating which results in separation of the enantiomers into a racemic conglomerate or racemic twins.

Structural characterization of three crystalline modifications of telmisartan by single crystal and high-resolution X-ray powder diffraction.

Three crystalline modifications (A, B, and C) of 4'-[[2-n-propyl-4-methyl-6-(1-methyl-benzimidazol-2-yl)benzi midazol-1-yl]methyl]biphenyl-2-carboxylic acid (INN name, telmisartan) have been detected and their crystal structures have been determined by single-crystal X-ray diffraction (pseudopolymorph C) and the method of simulated annealing from high-resolution X-ray powder diffraction data (polymorphs A and B). The compound is of interest because of its use as an angiotensin II receptor antagonist. Polymorph A crystallizes in space group P2(I)/c, Z = 4, with unit cell parameters a = 18.7798(3), b = 18.1043(2), and c = 8.00578(7) A, beta = 97.066(1) degrees, and V = 2701.31 A(3). Polymorph B crystallizes in space group P2(I)/a, Z = 4, with unit cell parameters a = 16.0646(5), b = 13.0909(3), and c = 13.3231(3) A, beta = 99.402(1) degrees, and V = 2764.2(1) A(3). The solvated form C crystallizes in space group C2/c, Z = 8, with unit cell parameters a = 30.990(5), b = 13.130(3), and c = 16.381(3) A, beta = 95.02(2) degrees, and V = 6639(2) A(3). For the structure solutions of polymorphs A and B, 13 degrees of freedom (3 translational, 3 orientational, 7 torsion angles) were determined in approximately 2 h of computer time, demonstrating that the crystal packing and the molecular conformation of medium-sized (MW approximately 500) pharmaceutical compounds can now be solved quickly and routinely from high-resolution X-ray powder diffraction data.