Face-shared octahedra

Lithium. salts show a great propensity to crystallize as hydrates, the trihydrates being particularly common, e.g. LiX.3HiO, X = Cl, Br, I, CIOi, CIOj, MnO.1, NO3, BF4, etc. In most of these Li is coordinated by 6H2O to form chains of face-sharing octahedra ... 

When m-RuCl2(DMSO)4 is stirred in methanol containing traces of water (to catalyse the formation of intermediate aqua species) Ru2C14(DMSO)5 isformed this has the unsymmetrical structure (DMSO)2C1RuQl(-C1)3Ru(DMSO)3 based on face-sharing octahedra [110]. 

Two face-sharing octahedra in ions [M2X9]3 and a string of face-sharing octahedra in Zrl3... 

Alternate layers can be occupied by two different kinds of metal atom, then every pair of the face-sharing octahedra contains two different metal atoms this is the ilmenite type (FeTi03). Ilmenite is, along with perovskite, another structure type for the composition AiiMiv03. The space for the A2+ ion is larger in perovskite. Which structure type is preferred can be estimated with the aid of the ionic radius ratio r(A2+)/r(02-) < 0.7 ilmenite... 

The nickel arsenide type (NiAs) is the result of linking layers of the kind as in cadmium iodide. Continuous strands of face-sharing octahedra perpendicular to the layers... 

Which of the following compounds could possibly form columns of face-sharing octahedra as in Zrl3 ... 

In cubic closest-packing, consideration of the face-centered unit cell is a convenient way to get an impression of the arrangement of the interstices. The octahedral interstices are situated in the center of the unit cell and in the middle of each of its edges [Fig. 17.3(a)], The octahedra share vertices in the three directions parallel to the unit cell edges. They share edges in the directions diagonal to the unit cell faces. There are no face-sharing octahedra. 

In the RuBr3 type a succession of face-sharing octahedra form a strand in the c direction. The metal atoms in adjacent octahedra are shifted in pairs from the octahedron centers, forming metal-metal bonds (Fig. 16.10, p. 175). This seems to be the condition for the existence of this structure type, i.e. it only occurs with transition metals that have an odd-numbered d electron configuration. 

Face-sharing octahedra occur only in hexagonal closest-packing. 

Figure 4.38 Idealized structure of SrxTiS3 modulated phases (a) an idealized TiS6 octahedron (the shaded faces are shared to form columns) (b) idealized hexagonal unit cell formed by columns of face-shared TiS6 octahedra (c) idealized unit cell formed by columns of face-sharing octahedra and Sr atoms (shaded) and (d) idealized structure of Sr8(TiS3)7.

K2Hg7 has a unique structure [7] characterized by chains of alternating empty and filled face sharing octahedra of Hg atoms [d(Hg-Hg) > 300 pm, Figure 2.4-8(b)]. 

FIGURE 1.34 The conversion of (a) corner-shared MXe octahedra to (h) edge-shared octahedra, and (c) edge-shared octahedra to (d) face-shared octahedra. 

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