Short Sb···Sb Contacts in Polymorphic Tris(p-Tolyl)Antimony: A Hallmark of Organoantimony(III) Solid-State Chemistry?

Discovery of a polymorph of tris(p-tolyl)antimony(III) reveals solid-state supramolecular dimers connected through short, attractive Sb∙∙∙Sb contacts that, based on theoretical calculations and a systematic screen of the Cambridge Structural Database (CSD), could be an overlooked hallmark of the solid-state and supramolecular chemistry of trivalent organoantimony(III) compounds. While the previously reported crystal structure of tris(p-tolyl)antimony(III) is known to exhibit phenyl embrace motifs, resembling the arsenic or phosphorus analogs, the new polymorph exhibits supramolecular dimers characterized by direct Sb∙∙∙Sb contacts shorter than the sum of the van der Waals radii, and stabilized by a significant dimer dissociation energy of ca. -26 kJ mol-1 established by periodic density-functional calculations. Theoretical analysis indicates that the contacts are attractive and dispersion-dominated, with an overview of the CSD showing that such direct Sb···Sb contacts are not unique to this polymorphic form of tris(p-tolyl)antimony(III) but appear to be a more general feature of trivalent organoantimony in the solid state. Specifically, the CSD shows that dimers based on short Sb···Sb contacts are found across a number of organoantimony structures, including some of the simplest representatives of the series, such as triphenyl- and trimethylantimony, for which the dimer interaction energy is herein calculated to be ca. -13 kJ mol-1.