Linked Trigonal Prisms

Layer of edge-sharing trigonal prisms in MoS2 

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In metal borides the metal atoms are not stacked as in the corresponding metal lattices (hcc, fee, or bcc) but form stacks to accommodate the boron nets or chains. In MB2 the metal atoms form face-linked trigonal prisms. The perovskite structure is rare in borides but it does occur in some ternary subborides, e.g., in LnRh3Bi in which Ln is a lanthanide. 

The radius of the 24-coordinate metal site in MBs is too large (215-225 pm) to be comfortably occupied by the later (smaller) lanthanide elements Ho, Er, Tm and Lu, and these form MB4 instead, where the metal site has a radius of 185-200 pm. The structure of MB4 (also formed by Ca, Y, Mo and W) consists of a tetragonal lattice formed by chains of Bs octahedra linked along the c-axis and joined laterally by pairs of B2 atoms in the xy plane so as to form a 3D skeleton with tunnels along the c-axis that are filled by metal atoms (Fig. 6.11). The pairs of boron atoms are thus surrounded by trigonal prisms of... 

Boron chains linked to form open nets trigonal prism Zigzag chains with side chains trigonal prism... 

The Yb(III) ion in [Yb(acac)3 H2O 0.5CeH6] is seven coordinated and the coordination polyhedron for this complex is identical with the polyhedron found for Yb(l) in the unsolvated complex, i.e. a capped trigonal prism. Like the unsolvated complex, the hemibenzene solvated ones are also linked in pairs by hydrogen bonds. The benzene molecule occupies a centre of S3unmetry in the complex. All intermolecular contacts involving benzene carbon atoms and acac carbons or oxygens are above 3.5 A (84). 

Nine-metal arrays in conventional coordination clusters are the confacial bioctahedron and two M4 cubanes linked through a non-cluster metal atom among naked metal clusters the M9 polyhedron is the tricapped trigonal prism or the monocapped square antiprism, and in gold clusters the metal array is the centred cube, the centred crown, or a fragment of the centred icosahedron. 

Fig. 4a. Structure of Caj jLij jSij (skew [001] view) with planar silicon polyanions of para-linked flat six-membered rings the trigonal prismatic cation array is indicated by the polyhedral representation trigonal prisms and extended trigonal prismatic coordination of the Zintl anion (CN6 (Ca) light blue, CN6 (Li, Ca) green, CN7 (Li, Ca) purple) trigonal prisms coordinating the central part of the anion are exclusively composed of Ca atoms...

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