Trigonal-prismatic geometry examples

Table IV lists specific examples of compounds related through this form of dimensional reduction, By far, the majority of these are zirconium chloride and iodide phases, in which case lower main group and even transition metals have been found to incorporate as interstitial atoms. A few analogues are known with hafnium (135), and very recently it has been shown that nitrogen can be substituted for carbon in tungsten chloride clusters adopting the centered trigonal-prismatic geometry (see Fig. 2) (32). It is hoped that a variability similar to that exposed for the octahedral zirconium clusters will be attainable for such trigonal-prismatic cluster phases.

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. 

Transition metal dithiolene complexes have received considerable attention since their discovery in 1962 because of their unusual optical, magnetic, electronic, and electrochemical properties (170, 294, 370). Dithiolene ligands, 26 (R = H, Me, Ph, CN, CF3 R = H, Me, etc.) have been shown to stabilize unusual formal oxidation states (294) and geometries (133), for example, Rh, and the trigonal prismatic geometry in Re(S2C2H2)s. 

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