Unit monoclinic

Q -SeBr4 crystallizes in the trigonal system and contains cubane-like [SeBr4]4 units. Monoclinic /3-SeBr4 also consists of tetrameric cubane-Uke [SeBr4]4 molecules. /3-SeBr4 is isotypic withTeCU and with jS-SeCU its chemical behavior and reactions are similar to SeCU-... 

Properties Units Monoclinic zirconia Zr02 (m)" Partially stabilized ZrOj (c) + 2.65 mol% MgO zirconia (PSZ) ZrOj (c) + 5.1 mol% Y2O3 Transformation Toughened ... 

The equimolar copolymer of ethylene and tetrafluoroethylene is isomeric with poly(vinyhdene fluoride) but has a higher melting point (16,17) and a lower dielectric loss (18,19) (see Fluorine compounds, organic-poly(VINYLIDENE fluoride)). A copolymer with the degree of alternation of about 0.88 was used to study the stmcture (20). Its unit cell was determined by x-ray diffraction. Despite irregularities in the chain stmcture and low crystallinity, a unit cell and stmcture was derived that gave a calculated crystalline density of 1.9 g/cm. The unit cell is befleved to be orthorhombic or monoclinic (a = 0.96 nm, b = 0.925 nm, c = 0.50 nm 7 = 96%. 

The crystal stmcture of PPT is pseudo-orthorhombic (essentially monoclinic) with a = 0.785/nm b = 0.515/nm c (fiber axis) = 1.28/nm and d = 90°. The molecules are arranged in parallel hydrogen-bonded sheets. There are two chains in a unit cell and the theoretical crystal density is 1.48 g/cm. The observed fiber density is 1.45 g/cm. An interesting property of the dry jet-wet spun fibers is the lateral crystalline order. Based on electron microscopy studies of peeled sections of Kevlar-49, the supramolecular stmcture consists of radially oriented crystaUites. The fiber contains a pleated stmcture along the fiber axis, with a periodicity of 500—600 nm. 

Sulfur crystallizes in at least two distinct systems the rhombic and the monoclinic forms. Rhombic sulfur, Sa, is stable at atmospheric pressures up to 95.5°C, at which transition to monoclinic sulfur, SP, takes place. Monoclinic sulfur is then stable up to its natural melting point of 114.5°C. The basic molecular unit of both of these crystalline forms of sulfur is the octatomic sulfur ring Other forms of sohd sulfur include hexatomic sulfur as well as... 

Copolymers of vinyUdene chloride and methyl acrylate have been studied by x-ray techniques (75). For example, the long period (lamellar thickness) for an 8.5 wt % methyl acrylate copolymer was found to be 9.2 nm by smaH-angle x-ray scattering. The unit cell is monoclinic, with a = 0.686 and c = 1.247 nm by wide-angle x-ray scattering. 

Orthorhombic HBO2 consists of trimeric units B303(0H)3 which are linked into layers by H bonding (Fig. 6.26) all the B atoms are 3-coordinate. Monoclinic HBO2 is built of chains of composition [B304(0H)(H20)] in which some of the B atoms are now 4-coordinate, whereas cubic HBO2 has a framework structure of tetrahedral BO4 groups some of which are H bonded. The increase in CN of B is paralleled by an increase in density and mp. 

The structural relationships in Bi203 are more complex. At room temperature the stable fonn is monoclinic o -Bi203 which has a polymeric layer structure featuring distorted, 5-coordinate Bi in pseudo-octahedral iBiOs units. Above 717°C this transforms to the cubic -form which has a defect fluorite structure (Cap2, p. 118) with randomly distributed oxygen vacancies, i.e. [Bi203D]. The )3-form and several oxygen-rich forms (in which some of the vacant sites are filled... 

Figure 6-3. Top Structure of the T6 single crystal unit cell. The a, b, and c crystallographic axes are indicated. Molecule 1 is arbitrarily chosen, whilst the numbering of the other molecules follows the application of the factor group symmetry operations as discussed in the text. Bottom direction cosines between the molecular axes L, M, N and the orthogonal crystal coordinate system a, b, c. The a axis is orthogonal to the b monoclinic axis.

Physical Properties. According to Lagowski (Ref 32), X-ray analysis of a single crystal of nitric acid shows a monoclinic unit cell (symmetry P21/a-Cfh) the following dimensions a=16.23, b=8.57, and c=6.3lA, and 0=90°. The unit cell contains 16 molecules, and the calc d is 1.895g/cc at —41.6°... 

For instance, in the three crystalline forms (a, 3, y) of i-PP the chains are always in the conformation of threefold helix (s(3/l)l symmetry) but are packed in different ways in monoclinic [24], hexagonal [25], and orthorhombic [26] unit cells, respectively. The X-ray diffraction spectra of unoriented samples in the crystalline forms a, P, y are reported in Fig. 6. 

The dimensions of the unit in the basal plane closely approximate those for the similarly pseudohexagonal crystal hydrargillite, Al(OH)3, as well as of the hexagonal layers in two forms of silica, /3-tridymite and 0-cristo-balite. The monoclinic (pseudohexagonal) unit of structure of hydrargillite8 has a = 8.70 A, b = 5.09 A, c = 9.76 A, and 0 = 85°29, and contains 8A1(0H)3. The crystal is composed of layers of octahedra,... 

The second choice is a simpler solution. According to Sarko and Muggli,66 all 39 observed reflections in the Valonia X-ray pattern are indexable by a two-chain triclinic unit cell with a = 9.41, b =8.15 and c = 10.34 A, a = 90°, 3 = 57.5°, and y = 96.2°. Ramie cellulose, on the other hand, is completely consistent with the two-chain monoclinic unit cell. Also, there are significant differences between their high-resolution solid-state l3C NMR spectra, indicating that Valonia and ramie celluloses, the two most crystalline forms, reflect two distinct families of biosynthesis. On this basis, the Valonia triclinic and the ramie monoclinic forms are classified69 as Ia and Ip, respectively. It has been shown from a systematic analysis of the NMR spectra by these authors, and from electron-dif-... 

A putative packing arrangement in the monoclinic unit cell (Fig. 40b) reveals that there are no direct interactions among the main chains of adjacent helices. However, the peripheral side chains form hydrogen bonds with both main and side chains. As in the case of 46, the ordered structure of 47 supports the hypothesis that side chains often promote the formation of stable, branched polysaccharide helices. 

Fig. 40. (continued)—(b) A putative packing arrangement of helices in the monoclinic unit cell viewed down the c-axis. The helices are connected by hydrogen bonds involving the side chains. 

Monoorganotin(IV) complexes of the above ligands with the compositions MeSn(SPy)3 and PhSn(Spy)3 I.5CHCI3 are monoclinic. In the discrete monomeric RSn(Spy)3 units, three bidentate SPy ligands together with R form a distorted PBP structure around the (Sn). One (Sj and one (Cj atom are in the ax positions. Two (S) atoms and three (N) atoms form the pentagonal plane. 

M0S2CI3, monoclinic (P2i/c). Figure 23 shows the translational unit, with atom designations. The sulfur atoms form pairs having a distance of 1.98 A. The molybdenum atoms also occur in pairs enclosed by two bridging S2 groups. With two chlorine atoms in terminal and... 

M03S7X4 (X = Cl, Br), monoclinic (P2i/c). Figure 24 shows the asymmetrical unit of the crystal structure. The three, independent molybdenum atoms form an almost equilateral triangle. Six of the seven sulfur atoms occur in three S2 groups, each one bridging one Mo-Mo... 

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