Bicapped trigonal antiprism structure

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. 

Mo(CN)7] . In particular, octacyanometallates, [M(CN)g]" (M = Mo and W), as one of these potential connectors, may show various geometrical structures, e.g., square-antiprism, dodecahedron, or bicapped trigonal-prism.This diversity in structure makes cyanometal-lates as modules both useful and practical. 

The eight-coordination polyhedra include a bicapped octahedron (f), a cube (g), a Djd (or d)-dodecahedron (h), a square antiprism (i) or a bicapped trigonal prism (j). The bicapped octahedron (f) is found in the structures of vitusite-(Ce) and lucasite-(Ce). Fergusonite- -(Y), euxenite-(Y), fersmite and the zirconolite-group minerals have distorted cubic coordinations of the rare earth sites in their structures. The cube (g) can be derived from a distorted bicapped octahedron (f) by flattening the six pairs of triangles to squares. The D2d (or J)-dodecahedron (h) is one of the most... 

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