Cationic and anionic 1D chains based on NH+⋯N charge-assisted hydrogen bonds in bipyridyl derivatives and polyiodides

Abstract

The possibility of constructing extended networks based on NH⁺⋯N charge-assisted hydrogen bonding and N⋯I interactions was explored. The organic modules 3,5-di-(3-pyridyl)-1,2,4-thiadiazole (L1) and 3,5-di-(4-pyridyl)-1,2,4-thiadiazole (L2) possess two pyridyl groups, allowing them to act both as hydrogen-bond acceptors and hydrogen-bond donors with H⁺ acting as the main linker between the molecular units. The crystal structure of the ionic compounds (HL1)I₃, (HL1)I₅, (HL1)IBr₂, (HL2)I₃, and (HL2)IBr₂ are described; the position of the nitrogen atoms in the outwards pyridyl rings in L1 and L2 leads to the formation of 1D helices of interacting cations (HL1)⁺ and zig-zag chains of interacting cations (HL2)⁺. In the case of (HL1)I₅, cationic helices of (HL1)⁺ and helices of I₅⁻ take place in a highly shape-complementary arrangement. The crystal structure of the bis-adduct L1·2I₂ features the presence of intermolecular iodine–iodine long contacts to form infinite I₂ chains. A comparative structural analysis carried out using the XPac procedure identifies three common molecular arrangements and confirms the importance of directional interactions and molecular shape of the target molecules in directing the packing preferences of this family of structures.