Distorted tricapped trigonal prism

A by-product of the preparation of U(Et2NC02)4 from the tetrachloride and the amine is a product of composition U402(Et2NC02)i2 this is a tetramer in which there are two non-equivalent uranium(lV) sites. In one of them the coordination geometry is a distorted tricapped trigonal prism, and the geometry of the other does not fit any type of regular polyhedron.1 5... 

Trifluorides are known for all the rare-earth elements. The structure of SCF3 is close to the cubic ReCb structure [Fig. 10.4.4(a)], in which Sc3+ has octahedral coordination. The YF3 structure has a nine-coordinate Y3+ in a distorted tricapped trigonal prism, eight F at approximately 230 pm, and the ninth at 260 pm. The YF3 structure type is adopted by the 4f trifluorides from SmF3 to LuF3. ... 

The malonate complex of Eu(III), Eu2(malonate)3 8H2O is interesting since there are two different coordination geometries, and only five of the water molecules are coordinated [167], One of the Eu ions is eight-coordinate in the form of a distorted square antiprism and the other Eu ion is nine-coordinate, distorted tricapped trigonal prism. In the analogous neodymium complex, six water molecules are coordinated because of the difference in ionic radius. The neodymium complex is nine-coordinate with monocapped antiprismatic geometry [168]. 

A second form of Nd2(malonate)3 6H2O complex has been reported [169]. In this complex neodymium is nine-coordinate surrounded by six carboxylate, and three water oxygen atoms and the geometry is intermediate between the distorted capped square antiprism and the distorted tricapped trigonal prism. 

In the compound CSU2F9, whose structure has recently been carefully determined, the TJ4+ coordination involves a very distorted tricapped trigonal prism (775). In this case, however, eight of the neighboring fluorines are shared with adjacent polyhedra to form a layered polyion. The ninth corner of the coordination polyhedron is effectively occupied by only one half a fluorine in a statistically occupied set. Thus the coordination number might be said to be 8.5. 

FIGURE 9 Complexes with Larger Coordination Numbers, (a) A 9-coordinate Eu(lll) complex, (b) The Eu core of the complex in (a) is described as a distorted tricapped trigonal prism, (c) Nonahydridorhenate,... 

Gd Cl N. The structure of the colorless compound (Gd " )3(Cl )gN contains GdgN2 bitetrahedra as a characteristic unit (fig. 17) (Simon and Koehler 1986). This unit is surrounded by Cl atoms in a way to yield rather distorted tricapped trigonal prisms as typical coordination polyhedra for Gd. The close relation between the atomic arrangements in a-Gd2Cl3N and Gd3ClgN becomes evident from fig. 18. In fact, the bitetrahedron is the characteristic building unit in both the structures of cx- and p-Gd2Cl3N. 

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