Partially disordered structures

This is, for instance, the case of PTFE, which at atmospheric pressure presents two reversible first-order transitions at 19 °C and 30 °C [67], In the transition at 19 °C the molecular conformation changes slightly, from a 13/6 to a 15/7 helix and the molecular packing changes from an ordered structure with a triclinic unit cell (corresponding to a positioning of the chain axes nearly hexagonal) toward a partially disordered structure (partial intermolecular rotational disorder) with a... 

The cage skeleton of most silatranes possesses an approximate threefold (C3) symmetry and in its five-membered (N—Si) chelate rings the carbon atoms in the a-position to the nitrogen deviate from the plane formed by the other atoms15,29 (Scheme 2). The partial disordered structure observed for some silatranes may be regarded as a frozen state of the dynamic flapping of the cr-C atoms in the crystals15. 

Analysis of Partially Disordered Structures 11.2.1 Solving the Structural Problem... 

In contrast to the examples described above, there are partially disordered structures which may mimic ordered ones but with false or deformed geometry of molecular moieties. As a convenient example, the semi-clathrate hydrate1 of tetra(iso-amyl)... 

From either hydrogenated binary Mg3lr alloy or by sintering powder mixtures of the elements at up to 773 K under a H2 pressure of up to 150 bar. Red colored hydride partially disordered structure (Figure 45) from npd on deuteride, P2 /c, Z = 8 contains four symmetry independent Ir hydride complexes a spy [IrHs]" " and three sad [lrFl4] complexes of which two are disordered, and five hydride anions are exclusively bonded to Mg all complexes are surrounded by Mg in distorted cubic... 

By sintering powder mixtures of alkali hydrides and Os under conditions similar to NagOsHy (XLIII). Partially disordered structure (Figure 44) by npd on deuteride of Cs compound at room temperature Pm3m, Z = 1 contains... 

Similar conclusions hold for the block copolymers of partially disordered structure and lower BC-2 and BC-3, which show moreover a tendency to form less defined microphases and a continuous soft phase at high concentrations. 

The interatomic distances for ice are presented in Table 15.3. The mean-square amplitudes of atomic vibrations are also shown. At temperatures 223-233 K (—50 to —40° C) ampUtude of proton vibration reaches up to 22-24% of interatomic O-H distance. The amplitudes of transverse vibrations is greater than those of longitudinal ones. Large values of amplitudes like these are not characteristic features for metallic and ionic crystals. This fact confirms a partially disordered structure of ice. 

Interestingly, in the case of the studied sample, the reconstructed layered structure is more ordered than the parent LDH. Asymmetric peaks of crystallographic planes (102), (105), and (108), resulting from partial disordered structure, packing the LDH layers (characteristic for the HS synthesis method) after the memory effect become symmetrical, is probably due to the sufficient time that was available for sample to reconstruct the layered structure, in contrast to the quick synthesis of parent LDH by HS coprecipitation method. 

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