Metalloid Chalcogen–pnictogen σ-hole bonding competition in stibanyl telluranes

In this manuscript a curious behavior observed in the solid state of several X-ray structures retrieved from the Cambridge structural database (CSD) is described and analyzed. These structures have in common the presence of a metalloid–metalloid pnictogen (Pn)–chalcogen (Ch) covalent bond (i.e., Sb–Te bond) in the structure. The Sb–Te bond presents different σ-holes at both ends of the bond in terms of size and intensity. These compounds have a tendency to form short intermolecular Sb•••Te interactions in the solid state. The aim of this work is to investigate, by using dispersion-corrected density functional theory (DFT-D3) calculations, whether the Sb•••Te contacts observed in the solid state correspond to PnB (Sb is the Lewis acid) or ChB (Te is the Lewis acid). Moreover, using two model stibanyl telluranes, the interaction energies with a series of Lewis bases and anions using both ends of the Sb–Te covalent bond have been computed to investigate which side (PnB or ChB donor) is able to establish stronger interactions with common electron rich atoms. Finally, several computational tools such as the quantum theory of atoms-in-molecules (QTAIM), noncovalent interaction plot (NCIPlot) index and electron localization (ELF) function (2D and 3D maps) have been used to further characterize the physical nature of the Sb•••Te interactions. The results reported herein suggest that in the Sb•••Te contacts the Te atom acts as σ-hole donor and the Sb as electron density donor.