Abstract

Relativistic scalar and spin-orbit density functional calculations of the electronic structure, Nucleus-Independent Chemical Shift (NICS) index and ELF function of the [Re2(CO)8(?-BiPh)2] and [Re2(CO)8(?-BiPh2)2] clusters are reported. We show here that the [Re2(CO)8(?-BiPh) 2] cluster has large negative NICS values in the region defined by the Re-Bi-Re-Bi four-membered ring and the ELF function shows significant electron delocalization density in the center of the metallic ring, thus indicating an aromatic cluster. In contrast the Re-Bi-Re-Bi four-membered ring in the [Re2(CO)8(?-BiPh2)2] cluster has negligible paratropic ring currents and the ELF function shows a low-density region within the metallic ring indicating that aromaticity is switched off. However, the phenyl ligands in both clusters show the expected aromatic character. © 2010 Elsevier Ltd. All rights reserved.