Eleven-coordination

Earlandite structure, 6,849 Edge-coalesced icosahedra eleven-coordinate compounds, 1, 99 repulsion energy coefficients, 1,33,34 Edta — see Acetic acid, ethylenediaminetetra-Effective atomic number concept, 1,16 Effective bond length ratios non-bonding electron pairs, 1,37 Effective d-orbital set, 1,222 Egta — see Acetic acid,... 

X-Ray structure determinations of complexes of smaller crown ligands are much fewer than those of the six-oxygen crowns, but Biinzli and co-workers have reported ten-coordinated [Eu(N03)3(12-crown-4)]452 and eleven-coordinated [Eu(N03)3(15-crown-5)],453 both of which show pyramidal coordination of the small crowns (Figure 5). 

There are no known compounds [M(unidentate)u] and it does not appear likely that any could be prepared. However, the geometry of these hypothetical compounds is a useful starting point to the stereochemistries of eleven-coordinate complexes containing chelate groups, such as [Th(N03)4(H20)3]-2H20417 418 and [La(N03)3(H20)5]H20.419... 

As for ten- and eleven-coordination, there are no twelve-coordinate complexes containing only unidentate ligands. The most common twelve-coordinate molecules are those of the type [M(bi-dentate)6]. The relevant stereochemistries are shown in Figure 104, and the repulsion energy coefficients listed below ... 

The two independent macrocycles which are coordinated to the barium have different conformations. While one of the macrocycles is coordinated via all six donor atoms (the four nitrogen atoms and both of the furan oxygen atoms), the other ligand is bound by only three of the donor atoms (one of the furan oxygen atoms and two of the nitrogen atoms). There is also a water molecule occupying one of the coordination sites on the barium. The result is an eleven coordinate Ba(II) cation. 

Idealized structures up to nine-coordination are summarized in Figure 4.21. These do not represent all of the shapes met, since, apart from all these idealized structures, it is necessary to remember that bond angle and bond length distortions of these structures can occur some of the shapes resulting from these effects are themselves common enough to be represented as named shapes, and we have discussed some examples of these earlier. Further, beyond nine-coordination, an array of additional shapes can be found, of which perhaps the best known are the bicapped square antiprism (for ten-coordination), the octadecahedron (for eleven-coordination) and the icosahedron (for twelve-coordination). Clearly, the options are extensive, so it may be time to find out what directs a complex to take a particular shape. 

Fig. 3.23 Eleven-coordination is very rare. One possible mode of coordination is the all-face capped trigonal prism (Dg ). This differs from Fig. 3.21 by the addition of ligands at the top and bottom of the figure.

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