Assembly of 3D Metal-Organic Frameworks Based on Different Helical Units: Chiral and Achiral Structures Constructed by Length-Modulated N-Donor Ligands

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Two coordination polymers constructed from two structurally related ligands, 4,4′-bis(imidazol-1-ylmethyl)benzene (L1) and 4,4′-bis(imidazol-1-ylmethyl)bibenzene (L2) have been synthesized, [Zn2(ODPT)(L1)]·3H2O (1) and [Zn2(ODPT)(L2)2] (2), where H4ODPT is 4,4′-oxidiphthalic acid. Their structures have been determined by single crystal X-ray diffraction analyses. In 1, two kinds of L1 ligands coordinate to chiral centers Zn(II) cations to form two types of zigzag chains, which entwine each other to generate the snakelike chains. The phthalic groups from ODPT4− ligands link Zn(II) cations to form a right-handed 21 helical chain. This helical chain and the entwined snakelike chains entangle together to form a chiral subunit by co-ZnII cations. Then, intramolecular oxygen atoms from ODPT4− ligands bridge these subunits to extend a chiral three-dimensional framework with (52·84)(53·62·7)2 topology. In 2, Zn(II) cations are connected by ODPT4− anions and one kind of L2 ligand to form a double helical chain, which is linked by other helical chain constructed by other kind of L2 ligand and Zn(II) cation to generate a 3D framework. Two kinds of networks showing opposite helical units interpenetrate each other giving rise to a 2-fold interpenetrating network with a (3·6·74)(32·72·82)(64·72) topology. By careful inspections of two structures, we find that Zn(II) cations, the ODPT4− anions, and N-donor ligands show the same coordination modes or analogous configurations. Compound 1 is a chiral structure, and 2 is an achiral framework. The compounds are also characterized by elemental analyses, IR spectra, and thermogravimetric analyses. In addition, the luminescent properties of these compounds are discussed.