Structures of homoatomic nine-atom clusters

The deviations of the structures of nine-atom clusters relative to the ideal poly-hedra A and B can be expressed by various distances and angles (see Fig. 3, and Tables 5 and 6)  

The deviation from ideal trigonal prismatic structures tends toward C2V symmetry for all 21-electron clusters with the exception of Sn9 which retains almost ideal Dsh synunetry. For Ge9, formulated as a 20-electron species, distortion is similar to that of other 21-electron clusters. The two clusters in in 2a and 2a might be assigned as Ge9 they show, however, gradual distortion from C4V symmetry as a function of the co-crystallized solvent molecules (Table 6). 

For compound numbers see the legend of Table 5 charge allocation (3- or 4-) unclear cluster III corresponds to the average picture of the two superimposed disordered clusters Ilia and Illb. 

The nine-atom clusters that have been investigated have structures intermediate between the boundary structures A and B the paramagnetic Sng cluster in lb forms an almost perfect tricapped trigonal prism and one of the Gc9 clusters in 2a forms an almost ideal monocapped quadratic antiprism. When the charge allocation is ambiguous, one cluster always has the structural characteristics of 21-electron clusters. Likewise, 22-electron clusters can deviate from C4V symmetry. As a result we find that the relatively large deviations of the clusters from the expected ideal point symmetry makes it difficult to correlate their structures directly with their numbers of skeletal electrons. 

5 Crystal packing in compounds with nine-atom clusters 

---