Vertex-sharing

In the families of heptanuclear clusters, two geometries are found the capped octahedron that is typical for 98-valence electrons, and the vertex-sharing open tetrahedral (butterfly) stmctures typical for 106-valence electrons. An example of the former is Osy(CO)22 (51) an example of the latter is [H2AuOsg(CO)2Q] (52). In the AuOs cluster anion, the gold atom is at the vertex-sharing position. 

The primary Cr—O bonded species is cbromium (VT) oxide, CrO, which is better known as chromic acid [1115-74-5], the commercial and common name. This compound also has the aliases chromic trioxide and chromic acid anhydride and shows some similarity to SO. The crystals consist of infinite chains of vertex-shared CrO tetrahedra and are obtained as an orange-red precipitate from the addition of sulfuric acid to the potassium or sodium dichromate(VI). Completely dry CrO is very dark red to red purple, but the compound is deflquescent and even traces of water give the normal mby red color. Cbromium (VT) oxide is a very powerful oxidi2er and contact with oxidi2able organic compounds may cause fires or explosions. 

The late transition metals, either Co or Ni, bond to four apical oxygen atoms of two vertex-shared 5 units (Fig. 17.9a), two each to layers both above and below, and also bond to two bridging pyrazine ligands in a trans fashion. The al-... 

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. 

Limits of the mutual rotation of vertex-sharing tetrahedra and of vertex-sharing octahedra and the resulting bond angles at the bridging atoms. The minimum distance between vertices of different polyhedra (dotted) was taken to be equal to the polyhedron edge... 

MX4 layer of vertex-sharing octahedra, and the packing of such layers in the K2NiF4 type. The packing in SnF4 is obtained by leaving out the K+ ions and shifting the layers towards each other in such a way that every octahedron apex of one layer comes to be between four apexes of the next layer... 

Some forms of rings and chains of vertex-sharing tetrahedra in silicates. How the chain conformations adapt to the size of the cation octahedra is shown for two chains (the octahedron chain is a section of a layer)... 

Take the network of vertex-sharing tetrahedra of the Cu atoms in MgCu2 (Fig. 15.4) and assume that there is an additional atom inside of every tetrahedron. What structure type would this be ... 

A novel series of Au—Ag supraclusters whose metal frameworks are based on vertex-sharing polyicosahedron have been reported. In the structure of these compounds the basic building block... 

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