Theoretical Study on the Stable Structures and Aromaticities for Pnictogen Dianionic Sb42, Bi42, and (SbBi)22 Clusters

Abstract

Through the theoretical calculation of structural optimization, vibrational frequencies and atomization energies with one method of density functional theory (B3LYP) and two post-Hartree-Fock approaches (MP2, CCSD(T)), several stable isomers for new three pnictogen dianionic Sb42, Bi42, and (SbBi)22 species were determined. For two homoatomic Sb42 and Bi42 species, there are three stable isomers: square (D4h), roof-shaped (C2v-1), and C2v-2 structure with the square isomer being the ground state. For the heteroatomic dianionic (SbBi)22 species, there are also three stable isomers: rhombus (D2h), roof-shaped (C1), and C2v structures with the rhombic isomer being the ground state. The calculated NICS values show that nucleus-independent chemical shifts (NICS) values of roof-shaped isomers for Sb42, Bi42, and (SbBi)22 species are all negative, consequently indicating that these roof-shaped isomers possess aromaticities. NICS values for the planar ring isomers are all positive, suggesting that these three planar ring isomers have antiaromatic characters. The aromaticity for the two stable roof-shaped and square isomers are preliminarily explained and discussed with MO analysis.