Tetragonal antiprism

G. Racah, J. Chem. Phya. 11, 214 (1943). Racah finds that the best eight equivalent dap orbitals have strength 2.9886 they are direoted toward the corners of a tetragonal antiprism, with angle 60°54 with the tetragonal axis. 

The configuration of the eight oxygen atoms bonded to the thorium atom in thorium(IV) acetylacetonate, Th(C H70 )4, has been found76 to be that of the tetragonal antiprism (Fig. 5-16). Each bidentate ligand connects adjacent corners of one of the squares of the polyhedron. 

Fig. 33. Co,C(CO)J , as in its (PhCH2N(CH3)4)+ salt (66). The eight cobalt atoms describe a tetragonal antiprism with Co-Co distances ranging from 2.464(4) to 2.598(4) A (mean 2.52 A). The central carbon atom forms four shorter (1.99 A) and four longer (2.15 A) bonds to the cobalt atoms.

In the HfCuSi2 structure, a portion of the tetragonal antiprisms is unfilled. The outer deformation of this structure leads to the formation of two new structure types - NdAgAs2 and LaInSb2. 

Fig. 2. Variations of the computed magnetic anisotropies Ax with respect to the distortion of a cube toward (a) elongated and compressed tetragonal prisms, (b) a tetragonal antiprism and (c) a dodecahedron (adapted from Mironov...

On the contrary, a trigonal-prismatic polyhedron arrangement is presented by the cluster [Rh6C(CO)15]2. The skeleton structure of the cluster [Co8C(CO)18]2 is a tetragonal antiprism. The structures of more complex carbide clusters are also discussed, for instance [Re8C(CO)24]2, [Os10C(CO)24]2-, and [OsuC(CO)27]2 [25]. 

Dianion [Co8(CO)i8C)] is isoelcctronic with Rh8(CO)i9C but presents a very different stereochemistry as shown in structure XX (Fig. 8) (13). Its geometry can be described as a deformed square antiprism with a carbide atom in the center of the polyhedron. This structure can be derived from that of the bicapped trigonal prism by stretching the common edge of the two capped square faces, as indicated in Fig. 8 by the dotted line. In such a process the loss of an M—M bond formally generates a square face. The idealized symmetry of a tetragonal antiprism is Did. However,... 

FIG. 10.12. Complex fluorides of Zr (a) chain of bicapped trigonal prisms in OljHeKZrFe), (b) 8-coordination group in Li6BeZrFi2, (c) relation between bicapped trigonal prism and tetragonal antiprism, (d) 7-coordination of Zr in Na5Zr2pj3. 

The structure of the decaclosoborane(-2) BioH q maybe described in terms of a tetragonal antiprism, i.e. a cube where the top face has been rotated through 45° relative to the bottom face. The two square faces of the antiprism are capped by BH fragments number... 

The coordination numbers for the Sm atoms are 22 (fig. 11a). The coordination polyhedra for the Ni atoms are tetragonal antiprisms with one additional atom and distorted cuho-octahedra with one additional apex (fig. Hb,c) those for Ge atoms are tetragonal antiprisms with two additional atoms and distorted cubo-octahedra with two additional apexes (fig. lld-g). 

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