Tricapped trigonal prismatic coordination

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. 

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

Fig. 5.25. Tricapped trigonal prismatic coordination in Nd2(C204>3 IO.5H2O. FromHansson [139].

The tricapped trigonally prismatic coordination of europium in Eu(terpy)3(C104)3 is probably the first example of 9-coordination involving nitrogen donors [150], Tricapped trigonal prismatic geometry is present in some simple hydrated compounds [165,166] such as Nd(H20)9(Br03>3 and M OMC H SC Xq, where M = Pr, Er, Ho, V. The structure of [Yb(DPC)3]3 is shown in Fig. 5.26. 

Structures of [La(MeCN)9] (AsF6)3-MeCN [Sm(MeCN)9] (AsF6)3-3MeCN [Ln(MeCN)9] (AlCl4)3-MeCN (Ln=Pr, Sm) and [Yb(MeCN)8] (AlCl4)3 are all known, the [Ln(MeCN)9] + ions having the familiar tricapped trigonal prismatic coordination of the lanthanide. ... 

Dipicolinates (pyridine-2,6-dicarboxylates) have been investigated in some detail with structures determined for several tris complexes such as Na3[Nd(dipic)3]-15H20 and Na3[Yb(dipic)3]13H20, typical of the early and later lanthanides, respectively. The lanthanides have essentially tricapped trigonal prismatic coordination geometries, isostruc-tural along the lanthanide series they have been the subject of important solution NMR studies. Mono and bis complexes can also be synthesized the mono complex [Nd(dipic)(H20)4] CIO4 has a polymeric structure in which each picolinate is bound to three different (nine-coordinate) neodymium ions. 

It was only in 1995 that the first structure of a hydrated salt of scandium containing only water molecules in its coordination sphere was reported. Refluxing scandium oxide with triflic acid leads to the isolation of hydrated scandium triflate Sc(03SCF3)3 9H20. It is isomorphous with the hydrated lanthanide triflates, containing tricapped trigonally prismatic coordinate scandium in the [Sc(H20)g] ions, with Sc—O (vertices) = 2.171(9) A and Sc—O (face capped) 2.47(2) A. 

The CaTa206 structure has been illustrated with other octahedral structures in Chapters. As in the CaFe204 structure Ca is 8-coordinated the ninth, more distant, 0 would complete a tricapped trigonal prismatic coordination group. 

Nonadentate ligands are scarce, and the most common ones present the topologies shown in Scheme 24, which favor tricapped trigonal prismatic coordination spheres in nine-coordinate complexes. 

Fig. 30. Schematic representation of the structure of the R(ppp)2 -alkali metal ion adduct. A tricapped trigonal prismatic coordination of the R ion is assumed (Ramasamy et al. 1991).

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