Deltahedron alternative

The structural patterns illustrated in Figure 3.1, and the shapes shown in column 3 for arachno species, are essentially those first suggested by Williams in 1971,2 and have stood the test of time remarkably well. However, the shapes shown should be regarded as illustrative rather than definitive. As with the nido species, alternative shapes to those shown in Figure 3.1 are possible for arachno species, with different sites left vacant on the parent deltahedron. We have already noted that many nido boranes and carboranes with eight skeletal atoms show deviations in their atom connectivities from those shown in Figure Nevertheless, apart from these particular exceptions,... 

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