An advanced approach combining solid-state NMR with powder diffraction applied to newly synthesized iso-thio-uronium salts.

Abstract

The focus here is on the structural study of iso-thio-uronium salts and the application of intermolecular distances obtained by solid-state NMR (ssNMR) in determining crystal structures from powder diffraction data. The synthesis of three new tetra-fluoro-borate salts and two bromide salts of iso-thio-uronium compounds is presented first, followed by structural and spectroscopic studies. The tetra-fluoro-borates were further analysed using advanced ssNMR techniques to obtain a set of intermolecular ¹⁹F⋯¹³C, ¹¹B⋯¹¹B, ¹H⋯¹H and ¹³C⋯¹H distances with an estimation of their precision. These distances were subsequently used as restraints in the crystal structure determination process from simulated powder diffraction data. The results show that using intermolecular distances obtained by ssNMR can increase the probability of finding the correct solution, creating new opportunities for the structural analysis of poorly diffracting compounds. This approach paves the way for solving more complex substances, such as solvates, cocrystals or complex polymorphs with many independent molecules, where traditional powder X-ray diffraction methods often reach their limits.