Phase triclinic

Fig. 6.4.2. chemical shift powder pattern spectra of Boc-Gly-Gly-[ N]Gly-OBz obtained by cross-polarization and H decoupling. (A) Crystalline phase (monoclinic). (B) Microcrystalline phase (triclinic). Dotted lines represent spectral simulations. Asymmetry, n, for the mono-clinic sample is 0.064 while 17 = 0.44 for the triclinic sample. Chemical shift reference is arbitrary. (Reprinted with permission from Hiyama et al. [10].)... 

PET is a semi-crystalline polymer but amorphous PET can be obtained by rapid cooling. In fact PET crystallization is slow and 30 % of crystalline phase (triclinic crystal structure) can be obtained to the best. In this amorphous state, PET is transparent and can be... 

As mentioned above, uranium trioxide exists in six weU-defined modifications with colors ranging from yeUow to brick-red. Of these phases, the y-phase has been found to be the most stable, however, other phases, especially a and 3, are also frequently used and studied. The stmcture of the a-modification is based on sheets of hexagons, whereas the 3-, y-, and 8-modifications contain an infinite framework. AH of these topologies have been fliUy described (105,106). They are a-brown, hexagonal 3-orange, monoclinic y-yeUow, rhombic 5-red, cubic S-brick red, triclinic and Tj-rhombic. 

Hartung and Rapthel [64] described the crystal structure of the mesogenic 2-methylthio-5-(4 -n-butyloxyphenyl)-pyrimidine which forms a monotropic smectic A phase. The chemical structure of this compound is presented in Fig. 5. The compound crystallises in the triclinic space group PI with two molecules per unit cell. The molecules adopt a fully stretched and nearly planar form. The pyrimidine ring is nearly planar. The dihedral angle between the phenyl and the pyrimidine rings is 22.7°. The molecules are arranged parallel to each other. 

Two macromolecular computational problems are considered (i) the atomistic modeling of bulk condensed polymer phases and their inherent non-vectorizability, and (ii) the determination of the partition coefficient of polymer chains between bulk solution and cylindrical pores. In connection with the atomistic modeling problem, an algorithm is introduced and discussed (Modified Superbox Algorithm) for the efficient determination of significantly interacting atom pairs in systems with spatially periodic boundaries of the shape of a general parallelepiped (triclinic systems). 

Fig. 5.19 View of the triclinic structure of the mixed-halide A [(Zr6Z)(CI,l)i8] phase (here with Z = Fe), which consists of molecular cluster units (thermal ellipsoids with 50% probability).

Many aliphatic poly(amides), more commonly known as nylons, exhibit an unusual phase transition below their melting point. First noted by Brill [122], the phenomenon has been studied extensively [128-131]. It is observed for instance in nylon (6,6) at a temperature of about 210°C, when the stable low-temperature triclinic oc phase of the crystalline polymer changes to a pseudo-hexagonal phase. 

In the paramagnetic regime, the evolution of the EPR line width and g value show the presence of two transitions, observed at 142 and 61 K in the Mo salt, and at 222 and 46 K in the W salt. Based on detailed X-ray diffraction experiments performed on the Mo salt, the high temperature transition has been attributed to a structural second-order phase transition to a triclinic unit cell with apparition of a superstructure with a modulation vector q = (0,1/2, 1/2). Because of a twinning of the crystals at this transition, it has not been possible to determine the microscopic features of the transition, which is probably associated to an ordering of the anions, which are disordered at room temperature, an original feature for such centrosymmetric anions. This superstructure remains present down to the Neel... 

Cu4Mo6Seg. The triclinic structure of these compounds has been described by McGuire et al. (2006). It contains nearly regular Mo6 clusters the Cu atoms fully occupy four sites between faces of two adjacent Mo6Se8 clusters. This compound is a member of a series of MexMogX8 Chevrel phases. Preparation and properties have been discussed. A Cu intercalation apparatus was built for... 

Note that the ordering parameter adopted by Hovis (1974) differs from the form adopted for the triclinic phase of the NaAlSi30g end-member (eq. 5.168). 

Merkel G. A. and Blencoe J. G. (1982). Thermodynamic procedures for treating the mono-clinic/triclinic inversions as a high-order phase transition in equations of state for binary analbite-sanidine feldspars. In Advances in Physical Geochemistry, vol. 2, S. K. Saxena (series ed.). New York Springer-Verlag. 

We saw previously the example of TMTSF thin films where the lattice parameters could be obtained, and proof that the triclinic phase coincides with that found for... 

It is worth noting that when trying to obtain other polymorphs of Bechgaard salts incorporating octahedral, fluorine-containing anions as in (TMTSF)2PF6 or (TMTSF)2ShF6 only the triclinic phase is obtained. 

---