Monoclinic cell

Since the first structure determination by Wadsley [56] in 1952 there has been confusion about the correct cell dimensions and symmetry of natural as well of synthetic lithiophorite. Wadsley determined a monoclinic cell (for details see Table 3) with a disordered distribution of the lithium and aluminium atoms at their respective sites. Giovanoli et al. [75] found, in a sample of synthetic lithiophorite, that the unique monoclinic b-axis of Wadsley s cell setting has to tripled for correct indexing of the electron diffraction patterns. Additionally, they concluded that the lithium and aluminum atoms occupy different sites and show an ordered arrangement within the layers. Thus, the resulting formula given by Giovanelli et al. 

Hexatic smectic mesophase the structure of which may be regarded as a C-centered monoclinic cell with a hexagonal packing of the molecules with the director tilted, with respect to the layer normals, towards the sides of the hexagons. 

Use Figure 5.28 to confirm that TiO is a one-sixth defective NaCl structure, by counting up the atoms in the monoclinic cell. 

It may also be used for monoclinic crystals rotated about a or c, since the projection of a monoclinic cell along either of these axes is rectangular. 

Note that there would be nothing to gain in defining a C-centered monoclinic cell since the resulting lattice would still be a primitive monoclinic lattice with shorter a and b translation vectors, a smaller volume, and the same symmetry. 

Fig. 2. Diagrammatic representation of the unit cell of cellulose, The monoclinic cell, dimensions 10.3 A x 8.35 A = S4. is delineated hy solid lines with one cellulose chain at each vertical edge and one lamiparallell in the center. Open circles = carbon atoms, solid circles - oxygen atoms. For clearness of the diagram, the hydroxyl groups on carbons 2, 3, and 6 are omitted and hydrogen atoms are omitted. TWo spacing at 6.1 A and 5.4 A are included, inasmuch as these are strongly represented in the x-ray diffraction diagram...

Faint, smeared (hkl) reflections are also observed, but are not resolved enough to be used for unit cell determination. Equatorial and meridional spacings indicate the following monoclinic cells ... 

Figure 4.28. A projection along b0 for the monoclinic cell of N2H4. On the right the packing draw is for the same view.

Figure 5.12. The 2 2PO 2PO 2 structures of CuWC>4 and ZnW04. (a) The triclinic of CUWO4. Oxygen atoms are in AB P layers. Cu and W are in 1/2 of O sites of alternate layers, (b) The monoclinic cell of ZnW04.

Figure 11.15. A projection along the ba axis of the monoclinic cell of naphthalene. The naphthalene molecules are centered at the corners and centers of two faces.

Figure 11.18. A projection along the c0 axis of the monoclinic cell of the addition compound CgHg-Ch- The cell is face centered, with CgHg molecules in the side faces.

Figure 11.19. A projection along the b0 axis of the body-centered monoclinic cell of p-di nitrobenzene.

The minerals dickite and nacrite have a theoretical composition identical to kaolinite, but have their layers stacked in alternating regular sequences. Dickite has a 2-Iayered monoclinic cell (Newnham and Brindley, 1956) and nacrite a 6-layered monoclinic cell (Hendricks, 1939a). 

In conventional Rietveld refinements, a structural model based on the arrangement of atoms in the unit cell is generally used. However, the imaging ability of MEM in the MEM/Rietveld method enables one to visualise more detailed features like the bonding electron distribution associated with hybridised orbitals [86]. was found to adopt a pseudo-monoclinic cell with... 

We note that the linear and volumetric CTEs in Refs.60 and 61 are not self-consistent in that the latter do not follow from the former according to the formal expression (for a monoclinic cell) Xv=Xa+Xb+Xc+(cosp/sinp)Pxp.. The reason for this is that xv was determined from a direct fit to the temperature dependent unit cell volume rather than from the linear CTEs (M. Herrmann, private communication). Although the same approach was used here, we obtained self-consistency to the percent level. 

A, c = 6.524(4)A, and P = 104.73(6)°. Several samples showed additional, broader lines with variable intensities relative to the phase A pattern that were not indexable on the basis of the monoclinic cell (Figure 2). These lines were ascribed to a second phase, an interpretation confirmed by experiments with acid washing. 

---