Bicapped square antiprisms

Pr )2(PPh3)7](PFg)2-3249 and [Au, i(PPlioIV1 e)i(l]3, 3250 The structure of the mixed-ligands clusters corresponds to a C3v metal skeletal framework and the homoleptic to a centered bicapped square antiprism (Figure 32). Other stoichiometries are known as, for example, [AunCl2(PPh3)8]Cl.3251... 

Bicapped Square Antiprism. TlSn93 has the (1)(1) + (9)(2) + 3 = 22 = 2n + 2 skeletal electrons required for an n = 10 vertex globally delocalized D4( deltahedron (cf. the bicapped square antiprism in Figure 1-7) analogous to that found in the BioHio2- anion [84]. 

A polyhedron based on bicapped dodecahedron possibly exists in decacoordi-nated [Ce(NOs)5]2- anion, which has been isolated (275) as triphenylethylphos-phonium salt (C2/c). The bicapped dodecahedron is a more appropriate description for the polyhedron than the bicapped square antiprism. However, Al-Karaghouli and Wood 215) from aesthetic point of view preferred to call the geometry of the coordination polyhedron as being trigonal bipyramid. 

The modified crown ligand (15), which is sterically unsuitable for coordination of all six ether oxygen atoms, forms a complex [Sm(N03)3(H20)(L)] where L is the 2-methoxy-l,3-xylyl crown (15).456 This is an irregular bicapped square antiprism in which three consecutive oxygen atoms of the crown ligand (the third being the OMe) are coordinated. 

Figure 101 The bicapped square antiprism, sphenocorona and trirhombohedron...

There are three important minima on the potential energy surfaces calculated for [M(bidentate)5]. At b x 1.1, isomers I and II correspond to two of the possible ways of arranging bidentate ligands around a bicapped square antiprism, whereas isomer III is a sphenocorona (Figure 102). 

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