Series of Mn(II)/Mg(II)/Zn(II) Coordination Polymers with Azo/Alkene Functionalized Ligands

A series of six novel coordination polymers based on Mn­(II)/Mg­(II)/Zn­(II) metal ions with azo/alkene functionalized carboxylic acid have been synthesized and well-characterized using several state-of-art techniques. Compound 1, {[Mn2(ABDCA)2(DPE)­(DMF)2]·2DMF}n, (where ABDCA = Azobenzene-4,4′-dicarboxylic acid, DPE = 1,2-Di­(4-pyridyl)­ethylene, and DMF = N,N′-Dimethylformamide) is a three-dimensional structure with threefold interpenetration. Compound 2, {[Mn3(ABDCA)3(DMF)4]·2DMF}n contains Mn3O16 cluster unit which is connected with ABDCA ligands to form a two-dimensional layered structure. Compound 3, {[Mg3(ABDCA)3(DMF)4]·4DMF}n contains Mg3O16 clusters, associated with ABDCA ligands, forming the 3D structure. Coordination polymers 4 and 5 ({[Zn­(ABDCA)­(2,2′-BPy)]·H2O}n, (4), {[Zn­(SDCA)­(2,2′-BPy]}n, (5)), respectively, (where SDCA = stilbene-4,4′-dicarboxylic acid and 2,2′-BPy = 2,2′-Bipyridine) are identical structures with a difference in carboxylate ligand. In both cases, the one-dimensional chains are π-stacked through 2,2′-bipyridine molecules to form the supramolecular three-dimensional structure. Compound 6 ({[Zn­(4,4′-BPy)­(ABDCA)]·DMF}n (where 4,4′ BPy = 4,4′-Bipyridine) adopts three-dimensional architecture with fivefold interpenetration. Photoluminescence studies showed that all these compounds were emissive due to either intraligand or ligand to metal charge transfer. Optical band gap energy measurements showed that the values are less for ABDCA based compound compared to SDCA based compounds, and this is due to the difference in the HOMO–LUMO gap in the corresponding ligands. The magnetic measurements of compounds 1 and 2 showed that 1 behaves weakly antiferromagnetic while 2 as paramagnetic.