Twinning by Merohedry and Thermal Expansion of Zeolitic Clathrasil Deca-dodecasil 3R.

Rhombohedral crystal particles of zeolitic clathrasil deca-dodecasil 3R (DDR), hydrothermally synthesized from a mixture consisting of fumed silica, water, and 1-adamantanamine, were characterized by single-crystal and powder X-ray diffractometry as a function of temperature and pole figure analysis. The crystallite was bounded by six equivalent {101̅1} faces and exhibited twin-free appearance, whereas the structure was resolved with the binary twin by merohedry, defined by the twin point group 3̅2'/m'1, consisting of two twin domains with nearly equal volume fractions. This twinning modifies the positions of O atoms in the Si-O-Si framework while preserving the positions of Si atoms that define the topology of polyhedral cages. This type of twinning therefore does not disrupt the microporous channels via the 8-membered rings of the 19-hedral cages and little disturbs the adsorption and permeation of gas molecules in DDR. The cell volume of DDR increased monotonically with an increase in temperature up to ∼673 K accompanied by an elongation perpendicular to the [0001] axis and a shrinkage along the [0001] axis. Above ∼673 K, the cell volume decreased with temperature. These positive and negative volume expansion coefficients observed in this study were roughly one-half and one-third of the values currently available.

Spectroscopic tracking of Schiff base compounds' hydrogen bonding reorganization associated with solid-to-solid phase transition.

A series of 2,6-dihydroxynaphthalene-1-methylidene alkylamines whose alkyl chain lengths ranged from 9 to 12 was spectroscopically examined. Transmission ultraviolet-visible absorption microspectroscopy revealed that the spectra of solid thin-films of the crystalline samples showed two distinct profiles depending on polymorphs as well as on alkyl chain length. We concluded that these spectral changes occurred not because of conventional intramolecular proton transfer but because of the molecules' interactions with an external proton source, that is, the intermolecular proton transfer. The spectral changes were accompanied by changes in the intermolecular hydrogen bonding network. When a crystal of a sample compound was heated, its spectrum changed dramatically before the crystal underwent a solid-to-solid phase transition to another polymorph. We concluded that these spectral changes indicated strengthening of intermolecular hydrogen bonding or intermolecular proton transfer, which would have triggered a drastic change in the hydrogen bonding network structure.

Liquid-Crystalline Biomacromolecular Templates for the Formation of Oriented Thin-Film Hybrids Composed of Ordered Chitin and Alkaline-Earth Carbonate.

Macroscopically ordered inorganic thin films have been formed on unidirectionally oriented, liquid-crystalline chitin matrices. In the presence of poly(acrylic acid) (PAA), unidirectionally oriented chitin films act as templates for the formation of oriented thin-film crystals of alkaline-earth carbonates such as SrCO3 and BaCO3. The morphology and orientation of crystals are dependent on the metal ion concentration. For SrCO3 crystallization, unidirectional thin films and hexagonal-shaped thin films have been deposited from 200 and 25 mm concentration strontium solutions, respectively.