J. Paul Attfield

Cation-size control of structural phase transitions in tin perovskites

The structural evolution at 300 K of the series SrxBa1?xSnO3 and SrxCa1?xSnO3 at x = 0.2 intervals has been determined by powder neutron diffraction. All SrxCa1?xSnO3 samples (x = 0?1) have the Pbnm superstructure. In the series SrxBa1?xSnO3, the x = 1.0 and 0.8 samples have the Pbnm superstructure. The x = 0.6 sample has a second orthorhombic structure with space group Imma. There is a tetragonal I4/mcm phase at x = 0.4 and the undistorted cubic structure for x = 0.2 and BaSnO3. The octahedral tilt angles show a smooth variation with average A cation radius over the range of superstructures described by mean field theory close to the transition. The transitions are also analysed via the variation of spontaneous strains.

Structure solution and refinement of tetracaine hydrochloride from X-ray powder diffraction data

The previously unknown crystal structure of the local anaesthetic tetracaine hydrochloride (C15H25N2O2+Cl−) has been solved from synchrotron X-ray powder diffraction data using a direct-space global optimisation method in which the position and conformation of a structural model is adjusted. The C15H25N2O2+ moiety and the chloride counterion were treated as independent units during the structure solution process. This complex structure has been solved despite the nine torsional degrees of freedom in the cation. A restrained Rietveld refinement of the initial solution gives an excellent fit to the data, with Rwp = 0.0956 and RF2 = 0.1638, and reveals the presence of a significant degree of preferred crystallite orientation in the sample. The crystal structure shows efficient packing involving parallel sheets made up of molecules lying parallel to one another, head-to-tail, in chains. Hydrogen bonds are observed between adjacent molecules and an extensive pattern of N+–Cl− contacts is apparent.

Synthesis and optical characterisation of platinum(ii) poly-yne polymers incorporating substituted 1,4-diethynylbenzene derivatives and an investigation of the intermolecular interactions in the diethynylbenzene molecular precursorsElectronic supplementary information (ESI) available: atomic cooordinates for 6 and 7. See http://www.rsc.org/suppdata/nj/b2/b206946f/

A series of 1,4-diethynylbenzene (1) derivatives, H–CC–R–CC–H with R=C6H3NH2 (2), C6H3F (3), C6H2F2-2,5 (4), C6F4 (5), C6H2(OCH3)2-2,5 (6) and C6H2(OnC8H17)2-2,5 (7) has been synthesised and their crystal structures determined by single crystal (2–5) or powder (6, 7) X-ray diffraction. The CCH⋯πCC hydrogen bonds dominating structure 1 are gradually replaced by CC–H⋯F ones with the increase of fluorination (3→5), or completely replaced by CCH⋯N and NH⋯πCC bonds in 2, and CCH⋯O in 6 and 7. The related platinum-based polymers, trans-[–Pt(PnBu3)2–CC–R–CC–]n (R=as above and C6H4,) have been prepared and characterised by spectroscopic methods and thermogravimetry, which show that the amino- and methoxy-derivatives have lowest thermal stability while the fluorinated ones exhibit increasing thermal stability with increasing fluorination. Optical spectroscopic measurements reveal that substituents on the aromatic spacer group do not create strong donor–acceptor interactions along the rigid backbone of the organometallic polymers.

Cation distribution in the superconducting Tl, Pb-1223 phase (“Tl0.5Pb0.5Sr2Ca2Cu3O9”) from resonant synchrotron powder X-ray diffraction

Abstract The cation distribution in a polycrystalline sample of nominal composition “Tl0.5Pb0.5Sr2Ca2Cu3O9” with Tc = 118 K has been determined from resonant synchrotron X-ray diffraction data collected at the Cu K, Tl LIII, Pl LIII and Sr K edges. Cation disorder is found at all the non-copper sites according to the formula (Tl1−xPbx) (Sr2−yCay) (Ca2−zTlz)Cu3O9 where x = 0.53(2), y = 0.42(2) and z = 0.064(4) for our sample. The overall composition Tl0.53Pb0.53Sr1.58Ca2.36Cu3O9 confirms that an excess of Ca and a deficiency of Sr can stabilise the Tl, Pb-1223 structure.

Variable temperature powder neutron diffraction study of the Verwey transition in magnetite Fe3O4

Abstract Neutron powder diffraction data have been collected from a sample of polycrystalline Fe 3 O 4 . High resolution data collected at 60 K are fitted using a simple rhombohedral distortion of the cubic unit cell. This model accounts for all of the peak splittings that occur upon cooling through the Verwey transition temperature ( T V ). Lower resolution data collected between 2 and 280 K are fitted using the same model, which gives T V =110±5 K. These data show a change in the thermal expansion due to the softening of phonons above T V and a change in crystallite extinction arising from twinning at the transition.

Disorder effects on structural and electronic transitions in high tolerance factor manganite perovskites

Abstract A series of Ln0.7M0.3MnO3 perovskites (Ln=La, Pr, Nd and M=Ca, Sr, Ba) with fixed mean A-cation radius, =1.26 A and variable A cation size disorder, quantified by the variance σ3 is studied. The results on seven samples show that the electronic, magnetic and structural transitions are affected by changes in σ2. Furthermore, the Curie and metal-insulator transition temperatures are sensitive to the perovskite superstructure which changes from rhombohedral R 3 c to orthorhombic Imma as σ2 increases.

A synchrotron X-ray powder diffraction study of 4-(2,3,4-trifluorophenyl)-1,2,3,5-dithiadiazolyl. Crystal structure determination using a global optimisation method

The crystal structure of the title compound, C6H2F3CNSSN, containing two independent molecules in the asymmetric unit, was determined from synchrotron powder X-ray diffraction data using a global optimisation model building method and confirmed using rigid-body Rietveld refinement; the asymmetric unit contains two independent molecules linked through intermolecular S···S contacts at 3.25 and 3.30 A.

The use of restraints in Rietveld refinement of molecular compounds; a case study using the crystal structure determination of tryptamine free base

The previously unknown crystal structure of the biogenic compound tryptamine, in the form of a free base (C(10)H(12)N(2)), has been solved from X-ray powder diffraction data using simulated annealing followed by restrained Rietveld refinement [space group P2(1)2(1)2(1), a = 12.28593 (6), b = 8.53351 (4), c = 8.49385 (4) A, Z = 4, final reduced-chi(2) = 5.255]. A restrained Rietveld refinement was carried out in which the global weight factor, f, of the stereochemical restraints was gradually lowered. The effect of the relaxation of restraints on the crystal structure and on chi(2) was studied and a criterion for the final choice of f is reported. The crystal structure reported here shows efficient packing involving weak intermolecular hydrogen bonding and a herringbone-type packing pattern.

X-Ray and neutron powder diffraction studies of the crystal structure of vitamin K3

The previously unknown structure of vitamin K3 (menadione, 2-methyl-1,4-naphthoquinone, C11H8O2), a synthetic compound from which it is possible to derive the naturally occurring K vitamins, has been solved from X-ray powder diffraction data. Solution was achieved using simulated annealing and restrained Rietveld refinement, using restraints derived from similar known structures. Further refinement has been carried out using neutron diffraction data; this confirmed the molecular packing and allowed further insight into the structural detail with regard to methyl group orientation, thus allowing the proposal of an extensive C–H⋯O hydrogen bonding scheme by reference to comparable known structures. The crystal structure consists of chains of molecules lying head-to-tail. This study may aid the understanding of the biological activity of vitamin K.

Relation between structure and ionic conductivity in the lithium derivatives, LiMnXO4(OH) (X=P, As)

Abstract In this paper, a thermal and ionic conductivity study of the title lithium derivatives is reported. LiMnPO 4 (OH) is a good ionic conductor with σ(200°C)=3×10 −5 Ω −1 cm −1 and an activation energy of 0.61 eV. The conductivity data for LiMnAsO 4 (OH) are σ(200°C)=1×10 −9 Ω −1 cm −1 and E a =1.24 eV . The relation between the crystal structures and the conductivity p roperties is also discussed.