Halogen Bonding in the Assembly of Coordination Polymers Based on 5-Iodo-Isophthalic Acid

A series of seven divalent coordination polymers based on 5-iodo-isophthalic acid (5-iipa) and ancillary nitrogen ligands (phen = 1,10-phenanthroline, bpe = 1,2-bis(4-pyridyl)ethene, p-bix = 1,4-bis(imidazol-1-ylmethyl)-benzene, m-bix = 1,3-bis(imidazol-1-ylmethyl)-benzene), namely, [Zn2(5-iipa)2(phen)2(H2O)]n (1), [Zn(5-iipa)(bpe)1.5]n (2), [Cd2(5-iipa)2(phen)2]n (3), [Mn2(5-iipa)2(phen)2]n (4), [Mn4(5-iipa)4(bpe)4·5H2O]n (5), [Co(5-iipa)(p-bix)]n (6), and [Co(5-iipa)(m-bix)]n (7), have been synthesized. The structure of compound 1 exhibits a double zigzag metal–organic chain, and such chains are further united together to generate a three-dimensional (3D) supramolecular structure through interchain I···π interactions. Compound 2 features interesting 3-fold parallel interpenetrated two-dimensional (2D) → 3D network motifs which are stabilized by interlayer I···π, π···π, and C–H···π interactions. In isomorphous compounds 3 and 4, the 5-iipa2– ligand acts as a μ3-bridge to connect metal atoms to form a 2D metal–organic layer, and such layers are united together to yield a 3D supramolecular structure through interlayer I···π and C–H···π interactions. In the structures of 5 and 7, the rare 2-fold interpenetrating 3D supramolecular architectures based on I···I interactions or O···I halogen bonding are found, respectively. In compound 6, 3-fold interpenetrated 2D → 3D network motifs based on covalent bonding are expanded to a rare 3D supramolecular structure based on O···I halogen bonding. The above results demonstrate a useful guideline in the crystal engineering of supramolecular architectures in coordination network assembly under the influence of halogen bonding as well as related I···I and I···π interactions. Their thermal analysis, X-ray diffraction, UV–vis absorption spectra, and photoluminescent properties have been investigated as well.