The Structure of m-Xylylenediguanidinium Sulfate:  A Putative Molecular Tweezer Ligand for Anion Chelation

While solution 1H and 13C NMR spectra of the sulfate salt of m-xylylenediguanidinium dication 2 indicate a symmetrical conformation for the cation, a single-crystal X-ray structural determination of 2 reveals that this dication does not offer symmetrical tweezer-like coordination toward sulfate in the solid state (consistent with solid phase 13C NMR spectra) but rather assembles into a complex three-dimensional H-bonded network in which the two guanidinium arms adopt different conformations, and all guanidinium N−H units plus one C−H unit of each CH2 group are involved in H-bonds to sulfate.