Molecular Networks Created by Charge-Assisted Hydrogen Bonding in Carboxylate Salts of a Bis(amidine)

Amidines can be protonated by carboxylic
acids to give amidinium
carboxylates, and the ions can associate by forming multiple charge-assisted
hydrogen bonds according to reliable motifs. Extended hydrogen-bonded
networks can be constructed by treating suitable bis­(amidines) with
acids containing multiple carboxyl groups. To further explore the
potential of this strategy, we have determined the structures of salts
produced by treating 2,2′-bi-2-imidazoline, a cyclic bis­(amidine),
with oxalic, fumaric, terephthalic, and trimesic acids. The structures
of the salts proved to incorporate features resulting predictably
from the geometry of the ions and their ability to engage in charge-assisted
hydrogen bonds.