Capped trigonal prism coordination

Possible stereochemistries for eight-coordinate [Ln(H20)8]3+ are the dodecahedron, the square antiprism, and the cube, although the last seems less likely (295). The proposed nine-coordinate [Ln(H20)9]3+ tri-capped trigonal prism transition state is similar to the [Ln(H20)9]3+ structures observed in the solid state. Thus, the possible water exchange... 

The Yb(III) ion in [Yb(acac)3 H2O 0.5CeH6] is seven coordinated and the coordination polyhedron for this complex is identical with the polyhedron found for Yb(l) in the unsolvated complex, i.e. a capped trigonal prism. Like the unsolvated complex, the hemibenzene solvated ones are also linked in pairs by hydrogen bonds. The benzene molecule occupies a centre of S3unmetry in the complex. All intermolecular contacts involving benzene carbon atoms and acac carbons or oxygens are above 3.5 A (84). 

Figure 51 Transformation of the capped trigonal prism (left) to the pentagonal bipyramid (right) with retention of a twofold axis. The angular coordinates are defined as the angles between the metal—ligand bonds and the twofold axis along the M—A bond. The 6 angular coordinates are defined relative to 0p = 0 and 6q = 180°...

The transformation of a pentagonal bipyramid to a capped trigonal prism with retention of a twofold axis is shown in Figure 51. The twofold axis passes through atom A, while the 0B and c coordinates are defined relative to 0F = 0 and 0G = 180°. The potential energy surface for this transformation is shown projected on to the 8B—8C plane in Figure 52. Movement along the flat valley corresponds to free rotation of the four BCDE atoms relative to the two FG atoms. 

Fig. 8.4. Coordination geometries for seven- and eight-coordination (a) pentagonal bipyramid, (b) capped trigonal prism, (c) capped octahedron, (d) cube, (e) square antiprism and (/) triangulated dodecahedron. Central atom-ligand bonds are shown by full lines dashed lines indicate the edges of the polyhedral figure.

Treatment of [Mo(CO)3Tp] with X2 (X = Br, I) affords the seven-coordinate complexes [MoX(CO)3Tp], which has been characterized crystallographically for X = Br. The structure can either be viewed as a distorted capped trigonal prism with Br capping a quadrilateral face or as a 3 4 piano stool.73... 

There are many complexes of lanthanides of coordination number seven [11]. There are many polyhedra for this coordination number, namely pentagonal bipyramid (Dsh) capped octahedron (C3V), tetragonal base trigonal base (Cs), capped trigonal prism (C2V) and capped trigonal prism (C3V). Inter ligand repulsivities have been studied as the function of the form of power law used for energy comparisons between different polyhedra for several coordination numbers [45,46], The order of preference for the different idealized... 

The structures are known for a number of these compounds thus, of the eight-coordinate compounds, Eu(acac)3(phen) is square antiprismatic, Eu(dpm)3(py)2 and Nd(tta)3(Ph3PO)2 are dodecahedral seven-coordinate Lu(dpm)3(3-picoline) is a face-capped trigonal prism and Eu(dpm)3(quinuclidine) a capped octahedron. Nine-coordination is found in Eu(dpm)3(terpy) and also in Pr(facam)3(DME)3(facam = 3-trifluoroacetyl-D-camphorate). 

The coordination of the metal atoms varies between a bi-capped trigonal prism (C.N. = 8) at the mirror planes normal to b (in the central portion of the strips) -lamellae of YF3 type - and a baddeleyite-like polyhedron (C.N. = 7) at the apb [a. Sect. 4.4.]. 

---