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

Two coordination polymers constructed from two structurally related ligands, 4,4'-bis(imidazol-1-ylmethyl)benzene (L-1) and 4,4'-bis(imidazol-1-ylmethyl)bibenzene (L-2) have been synthesized, [Zn-2(ODPT)(L-1)]center dot 3H(2)O (1) and [Zn-2(ODPT)(L-2)(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 L-1 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 2(1) helical chain. This helical chain and the entwined snakelike chains entangle together to form a chiral subunit by co-Zn-II cations. Then, intramolecular oxygen atoms from ODPT4- ligands bridge these subunits to extend a chiral three-dimensional framework with (5(2)center dot 8(4))(5(3)center dot 6(2)center dot 7)(2) topology. In 2, Zn(II) cations are connected by ODPT4- anions and one kind of L-2 ligand to form a double helical chain, which is linked by other helical chain constructed by other kind of L-2 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 center dot 6 center dot 7(4))(3(2)center dot 7(2)center dot 8(2))(6(4)center dot 7(2)) topology. By careful inspections of two structures, we Find that Zn(II) cations, the ODPT 4- 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.