Structural reciprocity effect in binary silicon–bismuth clusters

It is shown by density functional theory using doubly polarized basis sets that the lower energy structures of silicon–bismuth clusters Bi4Si2 and Bi2Si4 have the same overall geometry and symmetry and can be formally obtained from each other by mutual substitution and optimization or by direct Bi-substitution to the corresponding neutral Si6 cluster. Such ‘structural reciprocity’, which is attributed to the fluxionality of Si6 cluster and the similarity of Bi and Si electronegativities, can be generally true for other pairs of Bi–Si clusters to a lesser degree, and could be remotely related with the metal–semiconductor transition in Bi–Si alloys.