(IUCr) Contents for Acta Crystallographica Section B Vol. 62 Part 4 (August 2006)

Acta Cryst. (2006). B62, 521-529 [ doi:10.1107/S0108768106015527 ]

Neutron and electron diffraction studies of La(Zn_1/2Ti_1/2)O₃ perovskite

R. Ubic, Y. Hu and I. Abrahams

Synopsis: The structure of the perovskite compound La(Zn_1/2Ti_1/2)O₃ is monoclinic, space group P2₁/n. The B site is ordered on {110}, but the presence of the pseudocubic $1\over2$ (111) reflection is insufficient by itself to indicate the existence of such order.

Online 12 July 2006

Acta Cryst. (2006). B62, 530-536 [ doi:10.1107/S0108768106013188 ]

Classification of stacking faults and their stepwise elimination during the disorder order transformation of nickel hydroxide

T. N. Ramesh, P. V. Kamath and C. Shivakumara

Synopsis: Stacking faults in nickel hydroxide are classified by comparing their local structures with the structures of different theoretically possible polytypic modifications. The stacking faults are eliminated by a two-step process on hydrothermal treatment to yield ordered [beta] -nickel hydroxide.

Online 12 July 2006

Acta Cryst. (2006). B62, 537-546 [ doi:10.1107/S0108768106018842 ]

Structures and phase transitions in the ordered double perovskites Ba₂Bi^IIIBi^VO₆ and Ba₂Bi^IIISb^VO₆

B. J. Kennedy, C. J. Howard, K. S. Knight, Z. Zhang and Q. Zhou

Synopsis: High-resolution neutron powder diffraction has been used to investigate structures and phase transitions in the title compounds over a range of temperatures. The charge-ordered BaBiO₃ and chemically ordered Ba₂BiSbO₆ compounds show closely similar behaviour, except that the former shows a transition to a low-temperature phase that does not occur in the latter. The structure of this low-temperature phase has been determined for the first time.

Online 12 July 2006

Acta Cryst. (2006). B62, 547-555 [ doi:10.1107/S0108768106016612 ]

Structure and phase transitions in Ca₂CoSi₂O₇-Ca₂ZnSi₂O₇ solid-solution crystals

Z. H. Jia, A. K. Schaper, W. Massa, W. Treutmann and H. Rager

Synopsis: Experimental studies are reported of the structure and phase transitional behavior of synthetic Co/Zn melilite single crystals using X-ray and electron diffraction as well as calorimetry. The commensurate lock-in phase was refined as a pseudomerohedral twin in the space group P2₁2₁2.

Online 12 July 2006

Acta Cryst. (2006). B62, 556-566 [ doi:10.1107/S0108768106010238 ]

The incommensurately and commensurately modulated crystal structures of chromium(II) diphosphate

L. Palatinus, M. Dusek, R. Glaum and B. El Bali

Synopsis: The structure of chromium(II) diphosphate is incommensurately modulated at room temperature and locks into a commensurately modulated structure at 285 K. The superspace structure model is found to also apply to other members of the thortveitite structure family.

Online 12 July 2006

Acta Cryst. (2006). B62, 567-579 [ doi:10.1107/S0108768106019677 ]

Searching the Cambridge Structural Database for the `best' representative of each unique polymorph

J. van de Streek

Synopsis: A computer program is described that eliminates problem entries from the Cambridge Structural Database, clusters the remaining entries per unique polymorph and selects the best representative based on four criteria.

Online 12 July 2006

Acta Cryst. (2006). B62, 580-591 [ doi:10.1107/S0108768106011426 ]

Structural characterization of selenium and selenium-diiodine analogues of the antithyroid drug 6-n-propyl-2-thiouracil and its alkyl derivatives

C. D. Antoniadis, A. J. Blake, S. K. Hadjikakou, N. Hadjiliadis, P. Hubberstey, M. Schröder and C. Wilson

Synopsis: The structures of selenium analogues of the antithyroid drug 6-n-propyl-2-thiouracil, the charge-transfer complex 6-n-propyl-2-selenouracil·I₂, two diselenides and the deselenation product 6-n-propyl-2-uracil all show extended architectures. These are based on hydrogen-bonding and, in the case of 6-n-propyl-2-selenouracil·I₂, on SeI interactions.

Online 12 July 2006

Acta Cryst. (2006). B62, 592-598 [ doi:10.1107/S0108768106015485 ]

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

R. M. Ibberson

Synopsis: The crystal structure of phase III of perdeuterocyclohexanone, C₆D₁₀O, has been determined at 5 K using high-resolution neutron powder diffraction. The structure is monoclinic in the space group P2₁/n and crystallizes from the face-centred cubic plastic phase I structure below 225 K. Details of the orthorhombic phase II structure, thought previously to exist only at high pressure, are also reported, and isotope effects on the phase behaviour are discussed.

Online 12 July 2006

Acta Cryst. (2006). B62, 599-605 [ doi:10.1107/S0108768106015424 ]

Hexamer formation in tertiary butyl alcohol (2-methyl-2-propanol, C₄H₁₀O)

P. A. McGregor, D. R. Allan, S. Parsons and S. J. Clark

Synopsis: The crystal structure of phase II of tertiary butyl alcohol (2-methyl-2-propanol) has been solved using a combination of single-crystal X-ray diffraction techniques and ab initio density functional calculations. The calculations indicate that the trigonal P $\bar 3$ phase II structure is slightly more stable at elevated pressure than that of the triclinic $P\bar 1$ phase IV.

Online 12 July 2006

Acta Cryst. (2006). B62, 606-611 [ doi:10.1107/S0108768106013887 ]

Structures of (S)-(-)-4-oxo-2-azetidinecarboxylic acid and 3-azetidinecarboxylic acid from powder synchrotron diffraction data

A. J. Mora, M. Brunelli, A. N. Fitch, J. Wright, M. E. Báez and F. López-Carrasquero

Synopsis: The crystal structures of the four-membered heterocycles (S)-(-)-4-oxo-2-azetidinecarboxylic acid and 3-azetidinecarboxylic acid were solved by direct methods using powder synchrotron X-ray diffraction data.

Online 12 July 2006

Acta Cryst. (2006). B62, 612-626 [ doi:10.1107/S0108768106017393 ]

Intra- and intermolecular interactions in small bioactive molecules: cooperative features from experimental and theoretical charge-density analysis

P. Munshi and T. N. Guru Row

Synopsis: The intra- and intermolecular interactions based on the experimental and theoretical topological features of the charge densities of three bioactive molecules, 2-thiouracil, cytosine monohydrate and salicylic acid, have been analyzed on a quantum basis.

Online 12 July 2006

Acta Cryst. (2006). B62, 627-633 [ doi:10.1107/S0108768106011608 ]

Synchrotron and neutron diffraction study of 4-methylpyridine-N-oxide at low temperature

F. Damay, A. Carretero-Genevrier, A. Cousson, W. Van Beek, J. Rodriguez-Carvajal and F. Fillaux

Synopsis: A structural investigation of 4-methylpyridine-N-oxide between 300 K and 10 K by synchrotron and neutron powder diffraction is reported.

Online 12 July 2006

Acta Cryst. (2006). B62, 634-641 [ doi:10.1107/S0108768106013966 ]

Role of strong intramolecular N-HN hydrogen bonds in determining the conformation of adenosine-receptor antagonists

V. Ferretti, L. Pretto, M. A. Tabrizi and P. Gilli

Synopsis: The crystal structures of four adenosine antagonists containing the -N=C-NH-C(=X)-NH- fragment and forming a strong intramolecular N-HN hydrogen bond have been determined. A CSD search and DFT calculations have been performed in order to review the occurrence of this strong interaction in similar molecules and to evaluate the energy associated with its formation.

Online 12 July 2006

Acta Cryst. (2006). B62, 642-650 [ doi:10.1107/S0108768106012584 ]

Blind crystal structure prediction of a novel second polymorph of 1-hydroxy-7-azabenzotriazole

H. Nowell, C. S. Frampton, J. Waite and S. L. Price

Synopsis: The crystal structure of a novel conformational polymorph of 1-hydroxy-7-azabenzotriazole has been independently predicted in an informal blind test.

Online 12 July 2006

Acta Cryst. (2006). B62, 651-665 [ doi:10.1107/S0108768106015497 ]

Nine N-aryl-2-chloronicotinamides: supramolecular structures in one, two and three dimensions

S. Cuffini, C. Glidewell, J. N. Low, A. G. de Oliveira, M. V. N. de Souza, T. R. A. Vasconcelos, S. M. S. V. Wardell and J. L. Wardell

Synopsis: Substituted N-aryl-2-chloronicotinamides, 2-ClC₅H₃NCONHC₆H₄X-4', can have supramolecular structures which are one-, two- or three-dimensional, and are all built from different combinations of direction-specific intermolecular interactions.

Online 12 July 2006

Acta Cryst. (2006). B62, 666-675 [ doi:10.1107/S010876810601439X ]

Isomers and polymorphs of (E,E)-1,4-bis(nitrophenyl)-2,3-diaza-1,3-butadienes

C. Glidewell, J. N. Low, J. M. S. Skakle and J. L. Wardell

Synopsis: Five isomeric (E,E)-1,4-bis(nitrophenyl)-2,3-diaza-1,3-butadienes all display different direction-specific intermolecular interactions and all give different supramolecular structures.

Online 12 July 2006

Acta Cryst. (2006). B62, 676-688 [ doi:10.1107/S0108768106016326 ]

Molecular and crystal properties of ethyl 4,6-dimethyl-2-thioxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate from experimental and theoretical electron densities

V. G. Tsirelson, A. I. Stash, V. A. Potemkin, A. A. Rykounov, A. D. Shutalev, E. A. Zhurova, V. V. Zhurov, A. A. Pinkerton, G. V. Gurskaya and V. E. Zavodnik

Synopsis: The electron-density and electronic energy-density features in ethyl 4,6-dimethyl-2-thioxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate derived from accurate X-ray diffraction measurements at 110 K and theoretical calculations have been analyzed to estimate their reproducibility in molecules and crystals.

Online 12 July 2006

short communications

Acta Cryst. (2006). B62, 689-691 [ doi:10.1107/S0108768106016211 ]

Further errors in polymorph identification: furosemide and finasteride

S. Karami, Y. Li, D. S. Hughes, M. B. Hursthouse, A. E. Russell, T. L. Threlfall, M. Claybourn and R. Roberts

Synopsis: Reassessment of the reported single-crystal X-ray diffraction characterization of polymorphs of furosemide and finasteride shows that, in each case, incomplete data collections have resulted in the mistaken identification of two forms that are, in fact, identical.

Online 12 July 2006

Acta Cryst. (2006). B62, 692-694 [ doi:10.1107/S010876810601322X ]

On measuring the size of distortions in coordination polyhedra

I. D. Brown

Synopsis: The increase in average bond length is a useful measure of the distortion in a coordination polyhedron.

Online 12 July 2006

Acta Crystallographica Section B

Structural Science

Volume 62, Part 4 (August 2006)

research papers

Neutron and electron diffraction studies of La(Zn1/2Ti1/2)O3 perovskite

R. Ubic, Y. Hu and I. Abrahams

Classification of stacking faults and their stepwise elimination during the disorder order transformation of nickel hydroxide

T. N. Ramesh, P. V. Kamath and C. Shivakumara

Structures and phase transitions in the ordered double perovskites Ba2BiIIIBiVO6 and Ba2BiIIISbVO6

B. J. Kennedy, C. J. Howard, K. S. Knight, Z. Zhang and Q. Zhou

Structure and phase transitions in Ca2CoSi2O7-Ca2ZnSi2O7 solid-solution crystals

Z. H. Jia, A. K. Schaper, W. Massa, W. Treutmann and H. Rager

The incommensurately and commensurately modulated crystal structures of chromium(II) diphosphate

L. Palatinus, M. Dusek, R. Glaum and B. El Bali

Searching the Cambridge Structural Database for the `best' representative of each unique polymorph

J. van de Streek

Structural characterization of selenium and selenium-diiodine analogues of the antithyroid drug 6-n-propyl-2-thiouracil and its alkyl derivatives

C. D. Antoniadis, A. J. Blake, S. K. Hadjikakou, N. Hadjiliadis, P. Hubberstey, M. Schröder and C. Wilson

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

R. M. Ibberson

Hexamer formation in tertiary butyl alcohol (2-methyl-2-propanol, C4H10O)

P. A. McGregor, D. R. Allan, S. Parsons and S. J. Clark

Structures of (S)-(-)-4-oxo-2-azetidinecarboxylic acid and 3-azetidinecarboxylic acid from powder synchrotron diffraction data

A. J. Mora, M. Brunelli, A. N. Fitch, J. Wright, M. E. Báez and F. López-Carrasquero

Intra- and intermolecular interactions in small bioactive molecules: cooperative features from experimental and theoretical charge-density analysis

P. Munshi and T. N. Guru Row

Synchrotron and neutron diffraction study of 4-methylpyridine-N-oxide at low temperature

F. Damay, A. Carretero-Genevrier, A. Cousson, W. Van Beek, J. Rodriguez-Carvajal and F. Fillaux

Role of strong intramolecular N-HN hydrogen bonds in determining the conformation of adenosine-receptor antagonists

V. Ferretti, L. Pretto, M. A. Tabrizi and P. Gilli

Blind crystal structure prediction of a novel second polymorph of 1-hydroxy-7-azabenzotriazole

H. Nowell, C. S. Frampton, J. Waite and S. L. Price

Nine N-aryl-2-chloronicotinamides: supramolecular structures in one, two and three dimensions

S. Cuffini, C. Glidewell, J. N. Low, A. G. de Oliveira, M. V. N. de Souza, T. R. A. Vasconcelos, S. M. S. V. Wardell and J. L. Wardell

Isomers and polymorphs of (E,E)-1,4-bis(nitrophenyl)-2,3-diaza-1,3-butadienes

C. Glidewell, J. N. Low, J. M. S. Skakle and J. L. Wardell

Molecular and crystal properties of ethyl 4,6-dimethyl-2-thioxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate from experimental and theoretical electron densities

V. G. Tsirelson, A. I. Stash, V. A. Potemkin, A. A. Rykounov, A. D. Shutalev, E. A. Zhurova, V. V. Zhurov, A. A. Pinkerton, G. V. Gurskaya and V. E. Zavodnik

short communications

Further errors in polymorph identification: furosemide and finasteride

S. Karami, Y. Li, D. S. Hughes, M. B. Hursthouse, A. E. Russell, T. L. Threlfall, M. Claybourn and R. Roberts

On measuring the size of distortions in coordination polyhedra

I. D. Brown

Neutron and electron diffraction studies of La(Zn_1/2Ti_1/2)O₃ perovskite

Structures and phase transitions in the ordered double perovskites Ba₂Bi^IIIBi^VO₆ and Ba₂Bi^IIISb^VO₆

Structure and phase transitions in Ca₂CoSi₂O₇-Ca₂ZnSi₂O₇ solid-solution crystals

Hexamer formation in tertiary butyl alcohol (2-methyl-2-propanol, C₄H₁₀O)