Tricapped coordinates

Chlorides. The oHve-green trichloride [10025-93-1], UCl, has been synthesized by chlorination of UH [13598-56-6] with HCl. This reaction is driven by the formation of gaseous H2 as a reaction by-product. The stmcture of the trichloride has been deterrnined and the central uranium atom possesses a riine-coordinate tricapped trigonal prismatic coordination geometry. The solubiUty properties of UCl are as follows soluble in H2O, methanol, glacial acetic acid insoluble in ethers. 

Figure 6.24 Molecular structures of (a) tetrahedral BjCU, (b) dodecahedral BgClg, and (c) tricapped trigonal pyramidal B9CI9 and B9Br9. In BgClg note that the shortest B-B distances are between two 5-coordinate B atoms, e.g. B(l)-B(2) 168 pm the longest are between two 6-coordinate B atoms, e.g. B(4)-B(6) 201 pm and intermediate distances are between one 5- and one 6-coordinate B atom. A similar trend occurs in 69019.

Key Colour % indicates preparation but no report of colour) mp/°C (na indicates value not reported) coordination 9 ttp = tricapped trigonal prismatic 8 d = dodecahedral 8 sa = square antiprismatic 8 btp = bicapped trigonal prismatic 8,7 = mixed 8- and 7-coordination (SrBr2 structure) 7 cc = capped octahedral 7 pbp = pentagonal bipyramidal 6 o = octahedral 6 och = octahedral chain, 6 ol = octahedral layered. 

More illustrative is the structure of the fluorosilane which exhibits the same tricapped tetrahedron geometry. The three N-Si interactions take place in the frontal position towards the Si-F bond instead of the rear coordination observed in penta- and hexacoordinated structures. Furthermore, the benzylamino groups have the possibility not to be coordinated at silicon since these groups have the capability of free rotation around the carbon-nitrogen bond. 

Nine-coordinate (each NOj group is bidentate) tricapped trigonal prismatic structure... 

Nine-coordinate (each NOa group is bidentate) structure tricapped trigonal prism... 

The triphenylmethyl-substituted germanium halide 31 can be prepared in modest yield using GeCl4 and contains a formally seven-coordinate germanium metal center (Scheme 9). The structure of 31 (Figure 2, Table 11) is a tricapped tetrahedral structure where all the three Ge-O distances are shorter than the sum of the van der Waals radii (3.62 A). A series of hypervalent germanium halides 32-34 can be prepared, as shown in Scheme 10.95 The fluoride 32 is hexacoordinate, whereas the chloride 33 and bromide 34 are pentacoordinate. 

As is common with the higher coordination geometries, the interconversion of Dzh Cav niay be easily achieved. The monocapped square antiprism (C4 ) can be generated from the s-tricapped trigonal prism by raising the points a and b (Fig. 27) and lowering the two caps c and d so that the four form the basal plane of the square antiprism. 

In contrast to the monoclinic tris-malonato complexes, M2(OOCCH2COO)s 8 H2O (M=Nd) which contain nonacoordinated lanthanide ions in a monocapped square antiprismatic polyhedron, the orthorhombic tris-malonates Pnma) have a tricapped trigonal prismatic geometry for the coordination polyhedron. A rep-... 

Fig. 33. The tricapped trigonal prismatic coordination polyhedron around Eu(III) in Eu(OHCH2COO)s complex...

Polyhedra of nine-coordination trigonal prism, square face tricapped... 

As a result of the C23 - B8b transformation, the coordination number of S by K increases from 6 + 3to 6 + 5 tricapped trigonal prisms to pentacapped trigonal prisms. Some aspects of this transformation in (unstuffed) alloys (such as MnCoGe) have been discussed elsewhere. And a similar analysis of the same transformation in an oxide, LiMgP04, has recently appeared (Cf. also the next section.)... 

---