The effect of temperature and pressure on the crystal structure of piperidine.

Background: The response of molecular crystal structures to changes in externally applied conditions such as temperature and pressure are the result of a complex balance between strong intramolecular bonding, medium strength intermolecular interactions such as hydrogen bonds, and weaker intermolecular van der Waals contacts. At high pressure the additional thermodynamic requirement to fill space efficiently becomes increasingly important.

Results: The crystal structure of piperidine-d11 has been determined at 2 K and at room temperature at pressures between 0.

A novel isomorphic phase transition in β-pyrochlore oxide KOs2O6: a study using high resolution neutron powder diffraction.

We have carried out adiabatic calorimetric and neutron powder diffraction experiments on the β-pyrochlore oxide KOs(2)O(6), which has a superconducting transition at T(c) = 9.6 K and another novel transition at T(p) = 7.6 K.

Temperature- and pressure-induced proton transfer in the 1:1 adduct formed between squaric acid and 4,4'-bipyridine.

We have applied a combination of spectroscopic and diffraction methods to study the adduct formed between squaric acid and bypridine, which has been postulated to exhibit proton transfer associated with a single-crystal to single-crystal phase transition at ca. 450 K. A combination of X-ray single-crystal and very-high flux powder neutron diffraction data confirmed that a proton does transfer from the acid to the base in the high-temperature form.

Structure and phase behavior of the expanded-metal compound 7Li(ND3)4.

Metal lite: High-resolution neutron powder diffraction data reveals that the body-centered cubic crystal structure of lithium(0)tetraamine transforms to a simple cubic structure below 22 K. The detailed structure determinations will allow new insights into the coupled structural and electronic properties of the lightest metal.

Structure and superconductivity of LiFeAs.

Lithium iron arsenide phases with compositions close to LiFeAs exhibit superconductivity at temperatures at least as high as 16 K, demonstrating that superconducting [FeAs](-) anionic layers with the anti-PbO structure type occur in at least three different structure types and with a wide range of As-Fe-As bond angles.

Polymorphism in cyclohexanol.

The crystal structures and phase behaviour of phase II and the metastable phases III' and III of cyclohexanol, C(6)H(11)OH, have been determined using high-resolution neutron powder, synchrotron X-ray powder and single-crystal X-ray diffraction techniques. Cyclohexanol-II is formed by a transition from the plastic phase I cubic structure at 265 K and crystallizes in a tetragonal structure, space group P42(1)c (Z' = 1), in which the molecules are arranged in a hydrogen-bonded tetrameric ring motif. The structures of phases III' and III are monoclinic, space groups P2(1)/c (Z' = 3) and Pc (Z' = 2), respectively, and are characterized by the formation of hydrogen-bonded molecular chains with a threefold-helical and wave-like nature, respectively.

Solid-state structures of the covalent hydrides germane and stannane.

The low-temperature crystal structures of perdeuterogermane (m.p. 108 K) and perdeuterostannane (m.

Solid phases of cyclopentane: combined experimental and simulation study.

The phase diagram of cyclopentane has been studied by powder neutron diffraction, providing diffraction patterns for phases I, II, and III, over a range of temperatures and pressures. The putative phase IV was not observed. The structure of the ordered phase III has been solved by single-crystal diffraction.

Accurate molecular structures of chlorothiazide and hydrochlorothiazide by joint refinement against powder neutron and X-ray diffraction data.

The compounds chlorothiazide and hydrochlorothiazide (crystalline form II) have been studied in their fully hydrogenous forms by powder neutron diffraction on the GEM diffractometer. The results of joint Rietveld refinement of the structures against multi-bank neutron and single-bank X-ray powder data are reported and show that accurate and precise structural information can be obtained from polycrystalline molecular organic materials by this route.

The low-temperature phase III structure and phase transition behaviour of cyclohexanone.

The crystal structure of phase III of perdeuterocyclohexanone, C(6)D(10)O, has been determined at 5 K using high-resolution neutron powder diffraction. Below its melting point of 245 K cyclohexanone forms a plastic crystal in the space group Fm3m. On cooling below 225 K the crystal transforms to the monoclinic phase III structure in the space group P2(1)/n.

Single-crystal X-ray and neutron powder diffraction investigation of the phase transition in tetrachlorobenzene.

The polymorphic phase transition of 1,2,4,5-tetrachlorobenzene (TCB) has been investigated using neutron powder diffraction and single-crystal X-ray diffraction. The diffraction experiments show a reversible phase change that occurs as a function of temperature with no apparent loss of sample quality on transition between the two phases. Neutron powder diffraction gives detailed information on the molecular structural changes and lattice parameters from 2 K to room temperature.

Structure determination and phase transition behaviour of dimethyl sulfate.

The crystal structures of phase I and phase II of dimethyl sulfate, (CH3O)2SO2, have been determined using complementary high-resolution neutron powder and single-crystal X-ray diffraction techniques. Below its melting point of 241 K dimethyl sulfate crystallizes in an orthorhombic structure (I) in the space group Fdd2. On cooling below approximately 175 K the crystal transforms to a monoclinic structure (II) in the space group I2/a.

Neutron powder diffraction studies of dimethyl sulfoxide.

The crystal structure of perdeuterodimethyl sulfoxide, (CD3)2SO, has been refined at 2 and 100 K, and characterized as a function of temperature up to 275 K against high-resolution neutron powder diffraction data. The structure determined previously by Thomas, Shoemaker & Eriks [Acta Cryst. (1966), 21, 12-20] (T=278 K) is shown to remain down to 2 K.

Formation of isomorphic Ir3+ and Ir4+ octamers and spin dimerization in the spinel CuIr2S4.

Inorganic compounds with the AB2X4 spinel structure have been studied for many years, because of their unusual physical properties. The spinel crystallographic structure, first solved by Bragg in 1915, has cations occupying both tetrahedral (A) and octahedral (B) sites. Interesting physics arises when the B-site cations become mixed in valence.