Halogen···Halogen Interactions in the Assembly of High-Dimensional Supramolecular Coordination Polymers Based on 3,5-Diiodobenzoic Acid

Abstract

The synthesis and determination of the crystal structures of eight mixed-ligand divalent coordination polymers based on 3,5-diiodobenzoic acid (HL) and ancillary nitrogen ligands (bpy = 4,4′-bipyridine, bpe = 1,2-bis(4-pyridyl)ethene, p-bix = 1,4-bis(imidazol-1-ylmethyl)-benzene, bpp = 1,3-bi(4-pyridyl)propane, bbi = 1,1′-(1,4-butanediyl)bis(imidazole), namely, [Zn(L)2(p-bix)]n (1), [Zn3(L)6(bpp)]n (2), [Cd1.5(L)3(bpp)]n (3), [Ni(L)2(bpe)·H2O]n (4), [Co(L)2(p-bix)]n (5), [Co1.5(L)3(bpy)0.5]n (6), [Mn3(L)6(bpe)]n (7), and [Mn3(L)6(bbi)]n (8), have been reported. They were well characterized by elemental analysis, IR spectra, and single crystal X-ray diffraction. Compounds 1–5 all exhibit three-dimensional (3D) supramolecular structures based on interchain type II I···I halogen bond interactions, or hydrogen bonding and type I I···I contacts, respectively. Moreover, π···π interactions are found in the structure of 3. In compounds 6–8, similar two-dimensional (2D) metal–organic layers are expanded to 3D supramolecular structures based on type II I···I halogen bond interactions or type I I···I contacts, respectively. Our structural analyses promise to help demonstrate that organic iodine prefers type II I···I halogen bond interactions. In addition, it is of importance to evaluate the contributing role of I···I halogen bonds or I···I contacts in crystal structure packing. In addition, their thermal analysis, X-ray powder diffraction, and UV–vis absorption spectra have been investigated as well.