Hydrogen-bonded networks in crystals built from bis(biguanides) and their salts

Abstract

Biguanide groups and biguanidinium cations incorporate multiple sites that can donate or accept hydrogen bonds. To assess their ability to associate and to direct the formation of extended hydrogen-bonded networks, we examined the structure of crystals of four compounds in which two neutral biguanide groups or the corresponding cations are attached to the 1,4- and 1,3-positions of phenylene spacers. As expected, all four structures incorporate extensive networks of hydrogen bonds and reveal other reliable features. In particular, (1) neutral biguanide groups favor a roughly planar conformation with an intramolecular hydrogen bond, and they associate as hydrogen-bonded pairs, (2) despite coulombic repulsion, biguanidinium cations can also associate as hydrogen-bonded pairs, and (3) the 1,3-phenylenebis(biguanidinium) dication favors a pincerlike conformation that allows chelation of suitable counterions. However, the precise patterns of hydrogen bonding in the structures vary substantially, limiting the usefulness of biguanide and biguanidinium as groups for directing supramolecular assembly.Key words: bis(biguanide), bis(biguanidinium), structure, hydrogen-bonded network, noncovalent interaction, supramolecular chemistry, crystal engineering.