Unit cells monoclinic

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°... 

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. 

Polyethylene terephthalate crystallizes very slowly into only one stable crystalline form, containing monoclinic unit cells. To maximize its physical strength, high crystallinities must... 

A monoclinic unit-cell with a = 8.2 A (820 pm), b(fiber axis) = 10.30 A (1.030 nm), c — 7.90 A (790 pm), and /3 = 83.3° is used. The distance between the terminal oxygen atoms in the cellobiose unit is taken to be 10.3912 A (1.03912 nm). A left-handed, helical structure, with seven cellobiose residues in a pitch of 72.1 A (7.21 nm) was proposed. The packing arrangement involves the central reversed and comer chains, and a relative shift between them of 0.25 repeat length along the b axis. 

Figure 2.23 Models of packing of chains in form IV of sPP according to space groups (a) P1148 and (b) C2149. Arrows indicate crystallographic twofold axes, present in (b) and lost in (a). In (a) chains are rotated by 6.5° according to direction indicated by arrows and continuous and dashed lines show triclinic and monoclinic unit cells, respectively.

Figure 2.39 Models of packing of threefold helical chains in (a) y-form and (b) a-form of iPP. Dashed lines delimit bilayers of chains. Subscripts y and a identify unit-cell parameters of orthorhombic and monoclinic unit cells of y-141 and a-forms,174 respectively. R and L identify rows of all right- and all left-handed helices, respectively.185 (Reprinted with permission from Ref. 185. Copyright 2001 by the American Chemical Society.)...

The unique axis in the monoclinic unit cell is mosdy taken as the b axis. Rhombohedral unit cells are often specified in terms of a bigger hexagonal unit cell. 

Akaganeite (named after the Akagane mine in Japan) is isostructural with hollan-dite. Compounds with this structure have a tetragonal or monoclinic unit cell. Bernal et al. (1959) and Keller (1970) both concluded that the unit cell of akaganeite was tetragonal with a = 1.000 nm and c = 0.3023 nm. The structural refinement of a natural sample using XRD and Rietveld analysis indicated, however, that the unit cell is monoclinic with a = 1.060 nm, b = 0.3039 nm, c = 1.0513 nm and p = 90.24° (Post Buchwald, 1991). There are eight formula units per unit cell. 

Fig. 7 Diffraction profile collected from Te-III at 8.5 GPa. The data were collected on beamline 9.1 at the SRS synchrotron, with an exposure time of 23 min. The tick marks beneath the profile identify those reflections that are explained by the body-centred monoclinic unit cell...

The structure of tetraphenylhexaazanthracene was confirmed as 3 by X-ray crystallography and revealed a monoclinic unit cell, with the zwitterionic molecules arranged in stacks along the shortest crystallographic c axis. The charges are delocalized as depicted in 3 <1998JA2989>. 

In (b) and (c), the cross section of a monoclinic unit cell is indicated. 

It was possible to index all of the observed reflections by using a reduced, one-chain, monoclinic unit-cell, with a = 0.446 nm, b (fiber axis) = 1.034 nm, c = 0.725 nm, and )8 = 98.6°. The space group is P21 with one chain per unit cell. Thus, the chains have parallel polarity. There are two intrachain hydrogen-bonds of the type OH-3— 0-5 and OH-2—0-6, and an OH-6—0-3, interchain hvdrogen-bond. 

Cellulose II, derived by mercerization of cotton, crystallizes in a monoclinic unit-cell, with a = 0.802 nm, b = 0.899 nm, c = 1.036 nm, and y = 116.6°. The space group is P2,. Two chains, each with a 2(0.518) confonnation, are packed in the unit-cell, with antiparallel polarity. In addition to the OH-3—0-5 (0.269 nm), intrachain hydrogen-bond, an OH-2 —0-6 (0.272 nm), intrachain hydrogen-bond is possible only for the center down chain. This is due to the g+ orientation of the C-6-0-6 bonds in the corner chains and t orientation in... 

Isotropic solutions (12-15% by weight) of XVI in m-cresol were dry-jet wet spun into a coagulation bath of water/methanol. The as-spun fibers were drawn at temperatures above 380 °C to give fibers having a tensile strength of about 3.2 GPa and a modulus of 130 GPa. The annealed fibers displayed distinct wide-angle X-ray patterns from which a monoclinic unit cell was determined. 

Figure 9. Stereographic drawing of the molecular packing of four [Ct2(CO)io(m2- )]-anions and four [(P/igP)2N]+ cations in the monoclinic unit cell of symmetry Cz/c. The anions lie on a crystallographic center of symmetry whereas the [(PhsP N] cations contain a crystallographic twofold rotation axis which bisects the P-N-P bond angle...

Both bis-oxalato, [TiO(ox)2],7S and tris-oxalato, [Ti(ox)3]2-,76 complexes are known. It is also observed that 1,2-dimethoxyethane (DME) forms chelates TiX DME) (X = F, Cl).77 The nitrate group is also bidentate in anhydrous Ti(N03)4. This complex crystallizes with four Ti(N03)4 in each monoclinic unit cell of dimensions a =7.80, b = 13.57, c = 10.34 A, P = 125.0°, and space group Pljc. The structure, (16), consists of individual molecules in each of which four symmetrically bidentate nitrato groups are arranged according to symmetry... 

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