Pentagonal bipyramidal clusters

The spectrum of [Au7(PPh3)7][OH] shows two doublets thought to correspond to the axial and equatorial Au atoms of a pentagonal bipyramidal cluster. However, the area ratio of the two subspectra is approximately 1.4 1 instead of the expected 0.4 1. Even when the expected relative intensities are treated to take the effective masses of the recoiling units into account, as described by Parish, Salter, and co-workers (111), the expected ratio increases to only 0.48 1. 

Exercise 4.7. How many valence electrons does [Cp 2Co2(Et2C2B3H3)] (structure in Figure 4.17) possess Can one reasonably view this compound as an example of a closo-M2E5 pentagonal-bipyramidal cluster ... 

An Au cluster with seven metals is found in [AnyCPPh,),]" (VIII). The Au core is a pentagonal bipyramid. ... 

Figure 11 Character of the arrangement of the spin magnetic moments, and average magnetic moment, in seven-atom clusters with a pentagonal bipyramid structure and interatomic distances ranging from <4ulk to 80% <4ulk- Reproduced with permission from Ref. 79.

Rivard E, Steiner J, Fettinger JC et al (2007) Convergent syntheses of Sn7 CgH3-2, 6-(C6H3-2, 6-Pr-i2)2 a cluster with a rare pentagonal bipyramidal motif. Chem Commun 46 4919 921... 

According to Wade s rules, one non-bonding electron pair is allocated to each metal atom in polyionic metal clusters of the p-block elements. Thus the planar five-membered M5 anions are 16-electron species comprised of two valence electrons contributed by each metal atom and the 6- charge. Since there are eight electron pairs for bonding five cluster atoms, Wade s rules predict an arachno structure ( + 3 electron pairs for n cluster atoms), i.e. a pentagonal bipyramid with two vacant sites. 

Both 10 and 11 react with halide ions to give [M5C(CO),5X] products. The iodopentaosmium cluster [Os5C(CO)I5I], 12, has been fully characterized by X-ray diffraction (Fig. 12) and adopts an open arachno structure based on a pentagonal bipyramid but lacking two equatorial vertices (31). 

The structures of 13 (33), 14 (34), and 15 (35) are shown in Figs. 13, 14, and 15. Each of the products is a 76-electron five-vertex cluster in 13 the phosphorus ligand donates three electrons to the cluster, 14 is the trimethyl-phosphite substitution product of 13, and in 15 the phosphorus ligand contributes five electrons to the cluster. As with the isoelectronic [Os5C(CO)l5I]-, the Os5C cores take open structures based on a pentagonal bipyramid in which only three of the equatorial vertices are present. The structures of the Os5C cores are very similar for 13,14, and 15. Mean Os-Os distances are 2.90 0.06 A for all three, and the carbido carbon atom is... 

Fig. 41. Rh15C2(CO)jg, 33, as in its H30+ salt (75). Bonds to the carbon atoms (shaded circles) and the interstitial rhodium atom are omitted. The cluster is most easily visualized as a tetracapped pentagonal bipyramid. Two octahedral cavities with a common vertex are provided by the capped square faces and the interstitial rhodium atom. The carbon atoms, which are remote from one another, occupy these octahedral cavities, with Rh-C distances ranging from 1.93 to 2.12 A (mean 2.04 A). Rh-Rh distances range from 2.738 to 3.332 A (mean 2.87 A).

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