Disphenoid

XeOF square pyramid XeOF+3 disphenoid (C ) 67 XeOF-3 pentagonal 69,70... 

Xe02F2 disphenoid (C2 ) Xe02F+ trigonal pyramid 71-73 Xe02F 2 square pyramid 27,55... 

Thus all AX4E molecules have the shape of a trigonal bipyramid with one missing vertex, which can be formally called a disphenoid. It is sometimes described as the SF4 geometry... 

Figure 4.23 Lone pairs always occupy the less crowded equatorial sites of a trigonal bipyramid, (a) The disphenoidal geometry of the AX4E molecule SF4. (b) and (c) T-shaped AX3E2 molecules, (d) A linear AX2E3.

Known M4 polyhedra intermediate between the planar array and the regular tetrahedron are the Clv butterfly in which one M—M distance is longer than the other five, the D2j disphenoid with M—M distances in sets of four and two, and the trigonal pyramid with M—M distances in sets of three and three. 

This reduction in symmetry of the metal array occurs in Pdi0( i3-CO)4(p-CO)g(PBu3)6,304 where there is also a lower symmetry set of ligand connections. There is still a (Pd )6 octahedron, capped by (p3-CO) on four tetrahedrally arrayed faces, but the Pd° are located unsymmetrically over the remaining faces, being connected by doubly-bridging carbonyls to the equatorial Pd only. The Pd° thereby constitute a disphenoid rather than a tetrahedron. Phosphine ligands terminate the Pd° and the two axial Pd . 

E, 254, C2 Tetragonal disphenoid, tetragonal prism, pinacoid Ca2B(0H)4As04... 

E, C2, C2, C2 Orthorhombic Disphenoid, prism, pinacoid ZnS04 7H2O... 

A2m E, C2, 2C 2, 2o-d, 254 Tetragonal scalenohedron, tetragonal disphenoid, tetragonal bipyramid, ditetragonal prism, tetragonal prism, pinacoid Cu2peSnS4... 

The stmcture of UP04C1(H20)2 is also adopted by its Br analog [33]. From the Wyckoff positions of the atoms, the actinide site in the stmcture appears to contain UO6X2 (X = Cl, Br) polyhedra that approximate a Johnson snub disphenoid, also known as a Siamese dodecahedron, but as the halogen site is half-occupied, the actual coordination number is seven [35]. These polyhedra share vertices with phosphate tetrahedra to form an open framework with voids that extend parallel to the [100] direction. The halogen atoms that coordinate uranium line these voids (Fig. 5). 

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