Capped trigonal prism geometry

The anions [Mo(S2CNR2)X(CO)2j (R = Me or Et X = F or N3) are obtained by treatment of [Mo(S2CNR2)(CO)2] with X" the crystal structure of [NEt4][Mo(S2CNR2)F(CO)2] shows the geometry at molybdenum to be a fluoride-capped trigonal prism, very similar to that seen... 

Fig. 8.4. Coordination geometries for seven- and eight-coordination (a) pentagonal bipyramid, (b) capped trigonal prism, (c) capped octahedron, (d) cube, (e) square antiprism and (/) triangulated dodecahedron. Central atom-ligand bonds are shown by full lines dashed lines indicate the edges of the polyhedral figure.

Of special interest is the recently described red zero-valent titanium complex [Ti(CO)2(PF3)(dmpe)2] (dmpe = Me2PCH2CH2PMe2) which is a PF3 derivative of the nonexistent titanium carbonyl complex [Ti(CO)7] (365). A single-crystal X-ray crystallographic study has established the structure shown in Fig. 21 in which the geometry around the metal is approximately a capped trigonal prism. 

Routes to homoleptic isocyanide complexes have been defined in thf (Scheme 46).616 [M L7]+ (L = xylyl isocyanide) are fluxional in solution but do not exchange ligand with free L. The cation in [ML7][BF4] is very crowded with the shortest Me- -Me contact being 4.59 A. The TaC7 core has a geometry intermediate between the capped octahedron (Cjv) and capped trigonal prism (C2v). 

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