Rationalizing and functionalizing stannaspherene: Very stable stannaspherene "alloys".

It is illustrated here by ab initio calculations based on density functional theory and other high level methods that the high stability of the icosahedral Sn(12) (2-) dianion known as stannaspherene, reflects stability toward ionization rather than cohesion. This could be also connected with novel fluxional rearrangements and paths of Sn(12) (1-) leading eventually to Sn(12) (2-) involving charge transfer. In view of the very similar structural and electronic properties with the corresponding isovalent borane (B(12)H(12))(2-), it is demonstrated that stannaspherene can be further rationalized and functionalized on the basis of an isolobal analogy between group 14 clusters and isovalent boranes, carboranes, and bisboranes. Such analogy is of the same nature with analogous isolobal and isovalent similarities between silicon, hydrogenated silicon-carbon clusters and deltahedral boranes and carboranes, which the present author, scoptically and synoptically, has described as the "boron connection." It is predicted and verified theoretically: First, that the isovalent Bi(2)Sn(10) and Sb(2)Sn(10) clusters, considered as the microscopic analogs of tin-bismuth alloys, are very stable (more stable than stannaspherene itself) very symmetric and isolobal to Sn(12) (2-); and second, that embedded clusters of the form M@Sn(12) (2-), M@Bi(2)Sn(10), M=Pt,Pd are very stable and highly symmetrical (I(h) and D(5d) respectively) with large highest occupied-lowest unoccupied molecular orbital gaps and very large embedding energies of the order of 5-6 eV. It is furthermore predicted that Pt@Sn(12) (2-) and Pt@Bi(2)Sn(10) can be synthesized in view of their higher stability compared to Pt@Pb(12) (2-) which has already been synthesized. The marginal energy difference of 0.03 eV between the meta- and the para-isomer of Bi(2)Sn(10) indicates a fluxional behavior with respect to Bi-Sn interchange which should be related with the Sn(12) (1-) fluxionality leading eventually to Sn(12) (2-). This rearrangement is also associated with a strange aromatic behavior. The same type of Bi-Sn fluxionality is also encountered in higher energy structures. Due to the "inert pair effect" in tin, the validity of the isolobal analogy is much stronger and fully valid compared to isovalent species based on germanium or silicon, such as Ge(12) (2-), Bi(2)Ge(10), and Ge(10)C(2)H(2) and Si(12) (2-), Bi(2)Si(10), and Si(10)C(2)H(2). The present ideas are in full agreement with available experiments and suggest even further functionalization of stannaspherene, analogous to metaloboranes, metalocarboranes, and stannaboranes with several potential applications.