Interplay between Halogen/Hydrogen Bonding and Electrostatic Interactions in 1,1′-Bis(4-iodobenzyl)-4,4′-bipyridine-1,1′-diium Salts

We present herein the crystal structures I−IV of a series of 1,1′-bis(4-iodobenzyl)-4,4′-bipyridine-1,1′-diium salts 1a−d. The inherent structural features of these viologen derivatives, i.e. the electrostatic potential distribution on the dication 12+ and the nature of the counteranions, give rise to a series of potential hydrogen/halogen bond synthons A−E that, in conjunction with electrostatic interactions, play a key role in the supramolecular organization of these salts in the crystalline state. A subtle combination of hydrogen and halogen bonding guides the solid state assembly of hydrates I−II, leading to 2D → 2D parallel 3-fold interpenetration of (6,3) noncovalent nets.