Bicapped square prism

Pentagonal antiprism Pentagonal prism Bicapped square prism... 

Other coordination polyhedra with D41, symmetry are the tetragonal bipyramid (CN = 6), which can be seen as a distortion of the octahedron, and the bicapped square prism (CN=10). The tetragonal bipyramid is not discussed here, because an angular distortion cannot lower the symmetry to D4. The distortion scheme of a bicapped square prism (BSP, D4h) to a bicapped square antiprism (BSAP, D4d) is analogue to the one described above. The PCEM expressions for the B and 5 parameters will be exactly the same as for the SP-SAP distortion scheme, since axial ligands do not have an influence on... 

Octacoordination is often encountered in lanthanide complexes. The preferred poly-hedra for eight coordination expected on the basis of interligand repulsivities are square antiprism (D ), dodecahedron with triangular faces (Z)2d), bicapped octahedron (D3(i), truncated octahedron (Z)2ft), 4,4-bicapped trigonal prism (C2v), distorted cube (C2v), and cube (0/,). The most commonly observed polyhedra for this coordination number are, however, the square antiprism and the dodecahedron. 

FBP = pentagonal bipyramid CTP = C , monocapped trigonal prism CO = monocapped octahedron DD = dodecahedron SAP = square antiprism BTP = bicapped trigonal prism. 

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,... 

The species is fluxional in solution119 . The energy separation between the three related structures, dodecahedron D2d, bicapped trigonal prism C2V and square antiprism D4d has been shown to be very small by UB NMR spectroscopy. 

D, dodecahedron A, square antiprism BCTP, bicapped trigonal prism BCO, bicapped octahedron DTC, N,N-diethyldithiocarbamate HFA, hexafluoroacetylacetonato FOD, l,l>l>2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octane dionato NTA, nitrilotriacetato acac, acetylacetonato PCN, phthalocyaninato DMP, 2,6-dimethyl-4-pyrone BA, benzoyacetonato pip, piperidine DPM, 2,2,6,6-tetramethylheptane-3,5-dionato py, pyridine phen, 1,10-phenanthroline trop, troplonato. 

Bicapped trigonal prism Square antiprism Dodecahedral [Nb(trop)4]+ Na3TaF8 Ta(S2CNMe2)4... 

Figure 12 Closo polyhodra with n vortices tetrahedron (4), trigonal bipyramid (5), octahedron (6), pentagonal bipyramid (7), dodecahedron (8), tricapped trigonal prism (9), bicapped square antiprism (10), and icosahedron (12)...

Fig. 1. Perspective views of a (a) dodecahedron, (b) square antiprism, and (c) 4,4-bicapped trigonal prism.

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