Solvent-free thallium(I) tetrakis[3,5-bis(trifluoromethyl)phenyl]borate: crystal structure, supramolecular interactions and anisotropic thermal expansion.

Abstract

Thallium salts of weakly coordinating anions are common reagents in organometallic chemistry for generating reactive cationic species via salt metathesis. Despite their frequent use, their composition is often ambiguous due to cocrystallized solvents, rendering well-characterized solvent-free structures rare. Herein, we report the synthesis, crystal structure and thermal properties of truly solvent-free thallium(I) tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, Tl[BC32H12F24], as determined by single-crystal X-ray diffraction (SC-XRD), powder X-ray diffraction (PXRD) and thermogravimetric analysis (TGA). The structure features short Tl...F contacts and a complex supramolecular architecture that is closely related to disorder and tilting of the anion arene rings, which generate distinct intermolecular interaction motifs. Key features include a herringbone arrangement of nonclassical C-H...F hydrogen bonds and a `fluorous' interlayer defined by F...F and C-F...π contacts. This leads to hinge-like networks in the structure, depending on the tilt of the arene rings. These features are associated with anisotropic thermal expansion, with significantly greater expansion along the crystallographic a and b axes, as inferred from PXRD measurements. In agreement with the solvent-free structure determined by SC-XRD, TGA confirms that the bulk material is solvent-free.