The creation of modulated monoclinic aperiodic composites in -alkane/urea compounds.

-Dodecane/urea is a member of the prototype series of -alkane/urea inclusion compounds. At room temperature, it presents a quasi-one dimensional liquid-like state for the confined guest molecules within the rigid, hexagonal framework of the urea host. At lower temperatures, we report the existence of two other phases.

Long-range modulation of a composite crystal in a five-dimensional superspace.

The intergrowth crystal of -tetracosane/urea presents a misfit parameter, defined by the ratio = / (/), that is very close to a commensurate value ( ≅ 1/3). High-resolution diffraction studies presented here reveal an aperiodic misfit parameter of = 0.3369, which is found to be constant at all temperatures studied.

On the sensitivity of f electrons to their chemical environment.

Density functional calculations have been carried out on three families of lanthanide complexes of D3 or C4 symmetry, namely [Ln(H2O)9]3+, [Ln(DPA)3]3-, and [Ln(DOTAM)]3+ (Ln = Y, La, Lu; DPA = pyridine-2,6-dicarboxylate; DOTAM = 1,4,7,10-tetracarbamoylmethyl-1,4,7,10-tetraazacyclododecane), to get some insights concerning the sensitivity of 4f electrons to the surrounding ligands. We show that the electron density accumulations found within 0.7 A of the metal center, that precisely give the opposite image of the coordination sphere as they are located trans with respect to the Ln-ligand bonds, are almost exclusively due the f electrons.

Hidden degrees of freedom in aperiodic materials.

Numerous crystalline materials, including those of bioorganic origin, comprise incommensurate sublattices whose mutual arrangement is described in a superspace framework exceeding three dimensions. We report direct observation by neutron diffraction of superspace symmetry breaking in a solid-solid phase transition of an incommensurate host-guest system: the channel inclusion compound of nonadecane/urea. Strikingly, this phase transition generates a unit cell doubling that concerns only the modulation of one substructure by the other-an internal variable available only in superspace.

Tricaesium tris-(pyridine-2,6-dicarboxyl-ato-κO,N,O)lutetium(III) octa-hydrate.

Colourless block crystals of the title compound, Cs(3)[Lu(dipic)(3)]·8H(2)O [dipic is dipicolinate or pyridine-2,6-dicarboxyl-ate, C(7)H(3)NO(4)] were synthesized by slow evaporation of the solvent. The crystal structure of this Lu(III)-complex, isostructural with the Dy(III) and Eu(III) complexes, was determined from a crystal twinned by inversion and consists of discrete [Lu(dipic)(3)](3-) anions, Cs(+) cations and water mol-ecules involving hydrogen bonding. The Lu atom lies on a twofold rotation axis and is coordinated by six O atoms and three N atoms of three dipicolinate ligands.

Interstitial Zn atoms do the trick in thermoelectric zinc antimonide, Zn4Sb3: a combined maximum entropy method X-ray electron density and ab initio electronic structure study.

The experimental electron density of the high-performance thermoelectric material Zn4Sb3 has been determined by maximum entropy (MEM) analysis of short-wavelength synchrotron powder diffraction data. These data are found to be more accurate than conventional single-crystal data due to the reduction of common systematic errors, such as absorption, extinction and anomalous scattering. Analysis of the MEM electron density directly reveals interstitial Zn atoms and a partially occupied main Zn site.

Laser-induced ferroelectric structural order in an organic charge-transfer crystal.

We report the direct observation by x-ray diffraction of a photoinduced paraelectric-to-ferroelectric structural phase transition using monochromatic 100-picosecond synchrotron pulses. It occurs in tetrathiafulvalene-p-chloranil, a charge-transfer molecular material in which electronic and structural changes are strongly coupled. An optical 300-femtosecond laser pulse switches the material from a neutral to an ionic state on a 500-picosecond time scale and, by virtue of intrinsic cooperativity, generates self-organized long-range structural order.