An important special case is the proper
bipyramid [-1, 1] [direct sum] Q over Q.
An introduction of fluorine into Te[O.sub.2]-based glass system results in reduction of Te-O-Te linkages due to a gradual transformation of trigonal
bipyramid TeO4 (tbp) through TeO3+1 to trigonal pyramid TeO3 decreasing the connectivity of the tellurite glass former network.
The [Al.sub.6] and [Al.sub.7] clusters have a distorted tetragonal
bipyramid ([D.sub.2d]) and an antitrigonal prism with a capping atom ([C.sub.3v]), respectively.
Example 3.3 Consider the equatorial
bipyramid: the two-dimensional simplicial complex B with vertices [5] and facets 123, 124, 125, 134, 135, 234, 235.
The pseudocrystals, to 3.5 cm, are dull milky white but textbook-sharp, composed about equally of a tetragonal prism and a tetragonal
bipyramid, with small basal pinacoid faces topping (and bottoming) off the shape.
Sb(III) ion is five-coordinated by two amido N atoms and three carboxyl O atoms from a single [Hedta.sup.3-] ligand, forming a distorted trigonal
bipyramid geometry.
Forms include a first-order and second-order prism, two first-order
bipyramids, one second order
bipyramid and the basal pinacoid.