Antiprisms capped

Cages with nine vertices are rare. Representative ones are Bi + (in Bi24Cl26), B9Hi , and B7QH9, all of which have the tricapped trigonal prism structure (Fig. 1-5), and Sn9, which is a square antiprism capped on one square face. 

Ten Vertices. Species with ten vertices are well-known. In B10Hjq and B8C2Hl0 the polyhedron (1-XLIX) is a square antiprism capped on the square faces (symmetry D4[Pg.35]

Possible stereochemistries for eight-coordinate [Ln(H20)8]3+ are the dodecahedron, the square antiprism, and the cube, although the last seems less likely (295). The proposed nine-coordinate [Ln(H20)9]3+ tri-capped trigonal prism transition state is similar to the [Ln(H20)9]3+ structures observed in the solid state. Thus, the possible water exchange... 

The intensely yellow compounds 10 and 11 crystallize in the tetragonal space group PA/nnc. The oval Ei0Lii6 cluster skeleton (E = P, As) is topologically best described as a twofold capped Archimedean antiprism formed by the 10 E atoms, of which each of the 16 triangular faces are occupied by a lithium center (Fig. 12) (21). 

Bi-0 2.54(l)-2.68(2) A], In contrast, the nine-coordinate capped square antiprism geometry for bismuth in [Bi(N03)3(H20)3] (18-crown-6) does not involve the expected multidentate ether coordination to bismuth, but rather a hydrogen-bonded interaction of the crown ether with the hydrated bismuth center chelated by bidentate nitrate groups [Bi-0 2.38(2)—2.56(2) A] 32, implying that the hexado-... 

Capped Square Antiprism. Ge94, Sn94-, and Pb94- have the (9)(2) + 4 = 22 =... 

As is common with the higher coordination geometries, the interconversion of Dzh Cav niay be easily achieved. The monocapped square antiprism (C4 ) can be generated from the s-tricapped trigonal prism by raising the points a and b (Fig. 27) and lowering the two caps c and d so that the four form the basal plane of the square antiprism. 

The erbium ion is coordinated to eight carboxyhc oxygens [2.362—2.415 A)] from four oxalate (acid oxalate) moieties which forms a square antiprism around Er(III). A water molecule forms the cap (Er—OH2 =2.441 A) above the large square face of the antiprism. The acid oxalates (HOOCCOO) and oxalate ions occupy the crystallographic sites at random. The statistically averaged oxalate groups are centrosymmetric and planar. A very short H-bond (2.43 A) has been observed between two water molecules in two equivalent molecules, but the physical significance is difficult to assess because these waters are disordered in the molecule. 

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