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

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), [Zn-3(L)(6)(bpp)](n) (2), [Cd-1.5(L)(3)(bpp)](n) (3), [Ni(L)(2)(bpe)center dot H2O](n) (4), [Co(L)(2)(p-bix)](n) (5), [Co-1.5(L)(3)(bpy)(0.5)](n) (6), [Mn-3(L)(6)(bpe)](n) (7), and [Mn-3(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 center dot center dot center dot I halogen bond interactions, or hydrogen bonding and type I I center dot center dot center dot I contacts, respectively. Moreover, pi center dot center dot center dot pi 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 center dot center dot center dot I halogen bond interactions or type I I center dot center dot center dot I contacts, respectively. Our structural analyses promise to help demonstrate that organic iodine prefers type II I center dot center dot center dot I halogen bond interactions. In addition, it is of importance to evaluate the contributing role of I center dot center dot center dot I halogen bonds or I center dot center dot center dot 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.