Reinvestigation of the structure of BaCuSi₂O₆ – evidence for a phase transition at high temperature

Superstructure reflections have been observed in the room-temperature X-ray diffraction pattern of BaCuSi₂O₆. At 610 K the compound undergoes a structural phase transition upon which these superstructure reflections disappear.

Geikielite–ecandrewsite solid solutions: synthesis and crystal structures of the Mg_1−xZn_xTiO₃ (0 ≤ x ≤ 0.8) series

Crystal structure determination by Rietveld analysis of powder X-ray diffraction data shows that members of the geikielite–ecandrewsite solid-solution series Mg_1−xZn_xTiO₃ (0 ≤ x ≤ 0.8) adopt the R ilmenite structure. Data are presented for cell dimensions, atomic coordinates and bond lengths together with volumes and distortion indices for all coordination polyhedra.

Structures of three salts of phthalic acid; variation in crystal packing and geometry of the hydrogen phthalate ion

The crystal structures of salts of phthalic acid with MgO, diethylamine and 2,2′-dipyridylamine have been determined. An analysis is made of the two different hydrogen-bond patterns observed in the crystal structures of the hydrogen phthalate salts found in the Cambridge Structural Database.

Water molecules insert into N—H⋯Cl—M hydrogen bonds while M—Cl⋯X—C halogen bonds remain intact in dihydrates of halopyridinium hexa­chloroplatinates

Crystals of the dihydrates of three halopyridinium hexachloroplatinate salts form networks that are propagated via N—H⋯O and O—H⋯Cl—Pt hydrogen bonds and Pt—Cl⋯X—C halogen bonds. The water molecules can be considered to have been inserted into N—H⋯Cl—Pt hydrogen bonds anticipated in the anyhdrous form of such salts.

Strategies for the structure determination of endohedral fullerenes applied to the example of Ba@C₇₄·Co(octa­ethylporphyrin)·2C₆H₆

Strategies for the structure determination of endohedral fullerenes were applied to the example of Ba@C₇₄·Co(OEP)·2C₆H₆.

Structures of Fe^II spin-crossover complexes from synchrotron powder-diffraction data

Using synchrotron powder-diffraction data and direct-space search techniques, crystal structures have been obtained at room temperature and 90 K for the compounds [Fe(teeX)₆](BF₄)₂ (teeX is haloethyltetrazole, and X = I and Br), which both show a gradual, complete high-spin-to-low-spin transition according to molar magnetic susceptibility and ⁵⁷Fe Mössbauer spectroscopy.

Distribution of molecular centres in unit cells with respect to packing patterns

The position of the molecular centre in the unit cell in relation to the symmetry operators of a space group has been found to correlate with the packing pattern used to describe the crystal structure.

Isostructurality in one and two dimensions: isostructurality of polymorphs

An analysis of polymorphs retrieved from the Cambridge Structural Database shows that common one-, two- or three-dimensional molecular arrangements in the different forms can be identified for approximately half of the polymorphic systems investigated.

Experimental electron density study of the supramolecular aggregation between 4,4′-di­pyridyl-N,N′-dioxide and 1,4-di­iodo­tetra­fluoro­benzene at 90 K

The electron density of the complex of 4,4′-dipyridyl-N,N′-dioxide with 1,4-diiodotetrafluorobenzene has been determined by X-ray diffraction at 90 K and by accurate theoretical calculations. The topological properties of the I⋯O halogen bond are reported and compared with those of the I⋯N halogen bond obtained in a previous study.

A crystallographic titration of the dipeptide L-isoleucyl-L-isoleucine

Crystal structure determinations are presented for L-isoleucyl-L-isoleucine in four different protonation states: as a zwitterion, a cation, an anion and a dimeric cation.

Torsional vibration and central bond length of N-benzylideneanilines

Variable-temperature X-ray crystal structure analyses of N-benzylideneanilines revealed that the torsional vibration of the C—Ph and N—Ph bonds causes an apparent shortening of the C=N bond at room temperature.

Conformational change of N-benzylideneanilines in crystals

Variable-temperature X-ray crystal structure analyses of several N-benzylideneanilines revealed that a conformational change through a pedal motion takes place in the crystals.

Conformational analysis: crystallographic, molecular mechanics and quantum chemical studies of C—H⋯O hydrogen bonding in the flexible bis­(nosylate) derivative of catechol

The bis(nosylate) derivative of catechol, 2-{[(4-nitrophenoxy)sulfonyl]oxy}phenyl 4-nitrophenyl sulfate, exhibits an unusual extended solid-state structure (a one-dimensional hydrogen-bonded polymer) that is based on the formation of complementary intermolecular (aryl)C—H⋯O(nitro) hydrogen-bond pairs. The molecular and `supramolecular' structure of this system has been further delineated using quantum chemical calculations (AM1 method) and molecular mechanics (MM+) simulations.

X-ray diffraction and packing analysis on vintage crystals: Wilhelm Koerner's nitro­benzene derivatives from the School of Agricultural Sciences in Milano

The crystal structures of six nitrotoluene derivatives, synthesized by Wilhelm Koerner about a century ago and retrieved from a depository at the University of Milano, were determined. The crystal packings have been analyzed and lattice energies have been calculated by atom–atom potential methods and by the newly proposed Pixel method.

Temperature dependence of the crystal structure of 3,5-di-tert-butylpyrazole from 10 K

The disordered crystal structure of 3,5-di-tert-butylpyrazole in its high-temperature phase has been described in terms of the superposition of two tautomeric forms. A phase transition at ∼ 110 K leads to the reorganization of the lattice to an ordered array of different conformers.