Significant Positional Isomeric Effect on Structural Assemblies of Zn(II) and Cd(II) Coordination Polymers Based on Bromoisophthalic Acids and Various Dipyridyl-Type Coligands

Abstract

Seven Zn(II) and Cd(II) coordination polymers, formulated as {[Zn2(5-Br-ip)2(bpy)(H2O)]·2H2O}n (1), {[Zn(5-Br-ip)(bpa)(H2O)]}n (2), {[Cd(5-Br-ip)(bpp)(H2O)]}n (3), {[Zn(5-Br-ip)(bpe)]}n (4), {[Zn2(4-Br-ip)2(bpy)]·H2O}n (5), {[Zn(4-Br-ip)(bpa)(H2O)]}n (6), and {[Cd(4-Br-ip)(bpp)]}n (7), were prepared by hydrothermal reactions based on 4-bromo- or 5-bromoisophthalic acid (4-Br-H2ip or 5-Br-H2ip) and different dipyridyl-type coligands 4,4′-bipyridyl (bpy), 1,2-bi(4-pyridyl)ethane (bpa), 1,3-di(4-pyridyl)propane (bpp), and 1,2-di(4-pyridyl)ethene (bpe). All complexes 1−7 were characterized by elemental analysis, IR spectra, and X-ray single-crystal diffraction. Complex 1 is a 2D (6,3) coordination network and further assembled into a 3D framework via π−π stacking interactions. Complex 2 shows a 1D coordination array and further forms a 2D supramolecular network via H-bonding interactions. Complex 3 has a 2-fold interpenetrating 3D diamond framework. Complex 4 is a 3-fold interpenetrating 3D network with CdSO4 topology, constructed from alternately left- and right-handed helical arrays. Complex 5 has a 3D (3,4)-connected network with (4·82)(4·82·103) topology. Complex 6 features a 1D coordination chain and further forms a 2D helical supramolecular pattern by H-bonding. Complex 7 exhibits a (3,5)-connected 2D layer with the Schläfli symbol of (42·6) (42·67·8). The results reveal that the diverse coordination networks of 1−7 can be adjusted by the different dispositions of the -Br substituent of isophthalate building blocks, as well as the metal ions and the dipyridyl coligands. Moreover, the luminescent properties of the complexes have been investigated.