A series of coordination polymers constructed by a flexible tetracarboxylic acid: synthesis, structural diversity and luminescent properties

Abstract

By using a flexible tetracarboxylic acid ligand, 5,5′-(p-xylylenediamino)-1,1′,3,3′-(benzene-tetra-carboxylic acid) (H₄L), and three N-donor rigid co-ligands, ten coordination polymers, [Cu(4bipy)₂](H₂L) (1), [Cd₂(L)(2bipy)₂]·5H₂O (2), [Cd₂(L)(H₂O)₆]·2H₂O (3), [Mn₂(L)(H₂O)₆]·4H₂O (4), [Co₂(L)(H₂O)₆]·4H₂O (5), [Zn₂(L)(2bipy)₂]·3H₂O (6), [Zn₂(L)(phen)₂]·2H₂O (7), [Ni₂(L)(2bipy)₂(H₂O)₂]·2H₂O (8), and [Cu₂(L)(phen)₂(H₂O)₂] (9), and [Zn₂(L)(phen)₂(H₂O)₂] (10) (4bipy = 4,4′-bipyridine, 2bipy = 2,2′-bipyridine, and phen = 1,10-phenanthroline) have been synthesized and structurally characterized by elemental analysis, IR, single-crystal X-ray diffraction and thermogravimetric analysis. The single crystal of ligand H₄L reveals that there are two pairs of hydrogen bonds between two H₄L molecules, which lead to a 1-D linear supramolecular chain. Complex 1 shows a three-dimensional (3D) two-fold interpenetrated Cu²⁺-4bipy cationic host framework, [Cu(4bipy)₂]²⁺ with the 4-connected dia net, in which there are 1-D guest supramolecular chains formed by the intermolecular hydrogen bonds between adjacent (H₂L)²⁻ anions. 2 has a two-dimensional (2D) 4-connected {4⁴·6²} uninodal sql/Shubnikov tetragonal plane network. 3–10 display a new 2D 2-nodal (2,4)-connected network with a {8⁴·12²}{8}₂ topology. Complexes 3–5, 9 and 10 generate a 3D supramolecular structure by the hydrogen bonds between adjacent layers. 6–8 form a 3D network through strong π⋯π stacking interactions between adjacent layers. The co-ligand effects on the complex structures are studied. Also, we investigate the solid-state luminescence of compounds H₄L, 2–10 at room temperature.