Oxygen Pentagonal bipyramids

Figure 4.37 Structure of Ta76W6O203 (a) projection down 001 (b) metal only positions and (c) undulating chains of pentagonal bipyramids, shaded. The metal atoms are small circles and the oxygen atoms are large circles. [Data from S. Schmid, J. G. Thompson, A. D. Rae, B. D. Butler, and R. L. Withers, Acta Crystallogr, B51, 698-708 (1995).]...

In certain complexes, even though the coordination number is the same, two molecules in the same unit cell exhibit different conformations. Thus, in Eu(thd)3 DMSO, the gross geometry around Eu(III) is a distorted pentagonal bipyramid with the oxygen of the DMSO occupying one of the apices 283, 284), but the structure of the two molecules in the unit cell differs in detail. A similar situation also exists in Eu(thd)3(DMF)2 283, 284). 

X-Ray studies have shown that oxohydroxobisoxalatoniobic acid penta-hydrate, H2[NbO(0H)(C2 04)2],4H2 0, contains seven-co-ordinate niobium(v), the atom having an approximately pentagonal-bipyramidal environment of oxygen atoms. (parH)3[Nb0(C204)3],3H20 [par = 4-(2-pyridylazo)-... 

Most of the EF-hand motifs have one water (—X). On the other hand, in Rhizopus chinensis aspartic proteinase (Suguna et al., 1987) there is one main-chain carbonyl oxygen bound to calcium and six water molecules to complete the pentagonal bipyramidal coordination. Calcium coordination has been measured in several viruses, such as Southern bean mosaic virus (Silva and Rossmann, 1985), satellite tobacco necrosis virus (Jones and Liljas, 1984), and tomato bushy stunt virus IV (Olson et al., 1983). 

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