Trigonal prismatic structure

The trigonal prismatic structure shown in the illustration was once proposed for the [CoC12(NH,)4] complex. Use the fact that only two isomers of the complex are known to rule out the prismatic structure. 

The versatile binding modes of the Cu2+ ion with coordination number from four to six due to Jahn-Teller distortion is one of the important reasons for the diverse structures of the Cu-Ln amino acid complexes. In contrast, other transition metal ions prefer the octahedral mode. For the divalent ions Co2+, Ni2+, and Zn2+, only two distinct structures were observed one is a heptanuclear octahedral [LnM6] cluster compound, and the other is also heptanuclear but with a trigonal-prismatic structure. 

The fact that the trigonal prismatic structure does not afford the correct number of isomers is a clear indication that the ion actually adopts some other structural form (i.e., the theoretical model is contradicted by the experimental result). We know now of course, that this ion has an octahedral structure and as a result, it can exist only in cis and trans configurations. 

All attempts to produce optical isomers of [Co(en)3]3+ based upon a trigonal prismatic structure are shown below. The ethylenediamine ligand appears as an arc in each diagram below ... 

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

The sulfur atoms are also clustered in all-cis positions in the txtxp2p2 bicapped trigonal prismatic structure of tetrakis(A-methyl-p-thiotolylhydroxamato)hafnium(IV) [HffMeQJlr C(S)N Oj Me 4]. Averaged metal-ligand bond distances are Iff—0 = 2.150 and Hf—S =... 

Examples of monomeric Mo11 complexes are much less common. It has been demonstrated that the [Mo(CN)7]5 ion has a pentagonal bipyramidal structure. Other examples are nitrile (i.e. isocyanide) complexes [Mo(CNR)7]2+, which has a capped trigonal prismatic structure, and the diarsine complex [Mo(diars)2X2]. 

Mo(CNR)7]2+ [Mo(CNR)s(chel)]2+ (chel = dppm, dppe, bipy, etc.)-, [MoCl(CNBut)4(bipy)]+ Mo(CNC6H11)s(bipy)]2+ [Mo(CNR)3(bipy)2]2+. They are generally prepared by displacement of CO, bipy, OAc, NO or other ligands from a suitable precursor by RNC and have capped octahedral or capped trigonal prismatic structures.10,70... 

Polymetallic anions, prepared by dissolution of alloys of the alkali and post-transition metals in amine solvents (often with a complexand for the alkali metal cation), have been characterized in crystalline and solution phases. Clusters TlSng3, Ge92 (with 20 skeletal bonding electrons), Sn93- (21 skeletal e) and Bi95+ (22 skeletal e) possess a tricapped trigonal prismatic structure, symmetry D3A, with variations of dimensional detail which correlate with the electron population.291 292 This structure is a ctoso-deltahedron, and with 20 (2h + 2) skeletal electrons can be construed to be three-dimensionally aromatic.292 The 22e clusters M94 (M = Ge, Sn, Pb) occur as the C4v monocapped square antiprism, a nido polyhedron. 

A rare ytterbium(III) complex [Yb(HB(pz)3)3] has an eight-coordinate bicapped trigonal prismatic structure (48) with two tridentate ligands and one bidentate ligand. The complex is stereochemi-cally rigid in solution. 1 A number of thorium and uranium complexes have been reported. These include [U(HB(pz)3)4], [U(H2B(pz)2)4], [U(HB(pz)3)2Cl2], and mono- and di-Cp metal-halogen complexes.49... 

Figure 9-8. Two views of the complex [Re(PhCSCSPh)3 emphasising the trigonal prismatic structure. The phenyl groups have been represented by the black spheres to simplify the structure. It is thought that interactions between the sulfur atoms are responsible for the adoption of the trigonal prismatic geometry.

---