Crystal structures triclinic

Formula weight 242.75. The colorless crystals are identical with the mineral tarbutite. The water of hydration is given off above 450°C. Crystal structure triclinic. 

The minerals exist as plates, laths, blocks, tubes, and hollow hexagonal prisms. Those with the most perfectly formed crystal structures— triclinic kaolinite, dickite and nacrite— occur as plates usually with many hexagonal angles [Figure l(above)]. Those with imperfect structures—halloysite and monoclinic disordered kaolinite—occur as laths, tubes, and hollow prisms [Figure 1 (below)]. 

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. 

Hori and Ohashi [162] found three crystal forms for the compound 4 -hexyloxy-4-biphenyl p-[(S)-2-methylbutyl]benzoate. The structures of two crystal forms I-T (triclinic) and II-M (monoclinic) of this compound were determined. The crystal structure of I-T contains four crystallographically independent molecules. The dihedral angles between the phenyl rings of the... 

Ethyl a-cyano-4-[2-(2-pyridyl)ethenyl]cinnamate (7 OEt) also crystallizes with /3-centrosymmetric-type packing yielding photoreactive crystals and, upon photoirradiation (>410 nm), is converted into the /3-hetero-type dimer (7 OEt-dimer) nearly quantitatively. The 7 OEt-dimer (space group PT, triclinic) has the structure which is predicted from the crystal structure of 7 OEt (space group PT, triclinic). 

PET crystallizes in a triclinic crystal structure with unit cell dimensions as follows [44] ... 

The crystal structure of Compound 4, which was found to possess a centro-symmetric triclinic unit cell containing six tetraphenylarsonium cations, two [Nii2(CO)2iH]3 trianions, and two solvent acetone molecules, also was solved by the combined Patterson-Fourier method, based on the assumption of the dodecanickel core of the trianion being analogous to that of the dianion. Peaks corresponding to all of the nickel and arsenic atoms were first located from successive Fourier syntheses in the unit cell under noncentrosymmetric PI symmetry, after which initial atomic coordinates for the 12 independent nickel and three independent arsenic atoms were obtained by an origin shift to an approximate center of symmetry relating pairs of these peaks to one another. 

Properties of PET Molding Resins. The full crystal structure of poly (ethylene terephthalate) has been established by x-ray diffraction (134—137). It forms triclinic crystals with one polymer chain per unit cell. The original cell parameters were established in 1954 (134) and numerous groups have re-examined it over the years. Cell parameters are a = 0.444 nm, b = 0.591 nm, and c = 1.067 nm Oc = 100°, (S = 117°, and 7 = 112° and density = 1.52 g/cm2. One difficulty is determining when crystallinity is fully developed. PET has been annealed at up to 290°C for 2 years (137). 

Physical Properties of PBT. Unlike PET, the polymer PBT exists in two polymorphs called the a- and p-forms, which have distinctly different crystal structures. The two forms are interconvertible under mechanical stress (158,159). Both crystal forms are triclinic and the crystal parameters are shown in Table 7. 

The X-ray crystal structure of Co(PhN3Ph)3 was solved by two groups. Krigbaum and Rubin103 determined the structure of a monoclinic toluene-solvated form, while Corbett and Hoskins104 worked on the triclinic solvent-free form (Table 3). The bond distances and bond angles are not appreciably different and are in line with the values of the other compounds in Table 3. 

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