Face-shared

Fig. 11. Clathrate hydrates (a) basic structural component (H4QO2Q pentagonal dodecahedron) (b) type I host stmcture (two face-sharing 14-hedra are...

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 ... 

A fascinating variety of discrete (or occasionally polymeric) polynuclear halogeno complexes of As, Sb and Bi have recently been characterized. A detailed discussion would be inappropriate here, but structural motifs include face-shared and edge-shared distorted (MXe) octahedral units fused into cubane-like and other related clusters or cluster fragments. Examples (see also preceding paragraph) are ... 

Figure 13.11 Structure of the binuclear anion [Sbj OCle] " showing the bridging oxygen and chlorine atoms and the pseudooctahedral coordination about Sb the O atom is at the common apex of the face-shared square pyramids and the lone-pairs are trans- to this below the SbCU bases. The bridging distances Sb-Cl are substantially longer than the terminal distances Sb-Cl,.

Face-sharing mtso-periodate anioa in K HaOvI... 

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]. 

Figure 1. Representation of the crystal structure of CsMgBr3 (a) and a selective cut along the z axis showing five units of face-sharing (MgBr6)4- where the Eu2+ dopant is placed into the position of the central Mg2 ion (h).

Larger structural units can be described by connected polyhedra. Two polyhedra can be joined by a common vertex, a common edge, or a common face (Fig. 2.3). The common atoms of two connected polyhedra are called bridging atoms. In face-sharing polyhedra the central atoms are closest to one another and in vertex-sharing polyhedra they are furthest apart. Further details concerning the connection of polyhedra are discussed in chapter 16. 

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... 

The linking of tetrahedra takes place predominantly by sharing vertices. Edge-sharing and especially face-sharing is considerably less frequent than among octahedra. 

Take pairs of face-sharing coordination octahedra and join them by common vertices to form a chain, with every octahedron taking part in one common vertex not belonging to the shared face. What is the composition of the resulting chain ... 

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

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