Bismuth, cationic cluster

There are no well-characterized polymeric bismuth catenates, although a black ether-insoluble substance, described as (PhBi)x, results from the reduction of phenylbismuth halides with LiAlH4.200 A polymeric bismuthine is thought to result from the decomposition of l,T-bibismolane.201 To date, bismuth catenation is limited to Bi2 in the case of free molecules and to some complex anionic and cationic clusters. 

Since these homopolyatomic ZiniD anions and cations are devoid of ligands, they are sometimes referred to as naked" clusters. In general there is a good correlation between electronic structure and geometry as predicted by Wade s rules for the.se clusters, though some exceptions are known. Thus whereas Sn " and Bi are isoelectronic. they have different structures, the latter violating the rules. Only a small distortion of the bismuth cation, however, would convert it to the geometry ob.served for the tin cluster. 

Polyhedral clusters in which the electron count is less than Sn are electron-poor in the sense that the number of skeleton electrons is insufficient to form localized, 2c,2e bonds. Instead, models involving 3c,2e bonds or full global electron delocalization ( three-dimensional aromaticity) must be invoked to describe the bonding conditions. Electron-poor naked clusters are, as would be expected, formed by the early post-transition elements in groups 13 and 14. In addition, the cationic clusters of group 15 are electron-poor. Examples, derived from the compilation in Table 5, include the iso-electronic Pbg and Big " clusters and the 22-electron M5 species of thallium, tin, lead, antimony, and bismuth. 

In all the cluster compounds discussed above there are sufficient electrons to form 2-centre 2-electron bonds between each pair of adjacent atoms. Such is not the case, however, for the cationic bismuth species now to be discussed and these must be considered as electron deficient . The unparalleled ability of Bi/BiCb to form numerous low oxidation-state compounds in the presence of suitable complex anions has already been mentioned (p. 564) and the cationic species shown in Table 13.12 have been unequivocally identified. 

Wade expanded the 1971 hypothesis to incorporate metal hydrocarbon 7T complexes, electron-rich aromatic ring systems, and aspects of transition metal cluster compounds [a parallel that had previously been noted by Corbett 19) for cationic bismuth clusters]. Rudolph and Pretzer chose to emphasize the redox nature of the closo, nido, and arachno interconversions within a given size framework, and based the attendant opening of the deltahedron after reduction (diagonally downward from left to right in Fig. 1) on first- and second-order Jahn-Teller distortions 115, 123). Rudolph and Pretzer have also successfully utilized the author s approach to predict the most stable configuration of SB9H9 (1-25) 115) and other thiaboranes. 

Mixed group 15 group 16 polycations are rare and tend to form clusters. For example, the arsenic-chalcogen cations [As3E4]" (E = S, Se) have polycyclic structures similar to those of the well-known isovalent species P4S3 and the bismuth-tellurium cation [Bi4Te4]" " adopts a slightly distorted cubic... 

Cationic Naked Clusters of Bismuth Reduced Bismuth Halide Phases... 

Na(crypt-222)]3[In4Bi5], all of which are prepared (mostly as solvates with 1,2-ethanediamine) in a similar way to reaction 14.52. The [PbySby], [GaBi3] and [InBi3] ions are tetrahedral in shape. The [In4Bi5] ion adopts a monocapped square-antiprism in which the Bi atoms occupy the unique capping site and the four open-face sites. These structures are consistent with Wade s rules (see Section 12.11) The syntheses of cationic bismuth clusters were described in Section 8.12. 

The syntheses of cationic bismuth clusters were described in Section 9.12. The [Bis] ion may also be obtained by oxidation of Bi using GaCls in benzene, or using AsFs. Although [Bis], [Big] and [Bi9] have been known for many years, no well-characterized example of a homopolyatomic antimony cation was reported until 2004. 

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