Coordination Polymers Built with a Linear Bis-Imidazole and Different Dicarboxylates: Unusual Entanglement and Emission Properties

The linear linker bis(4-imidazol-1-ylphenyl)diazene (L) has been used to construct eight new coordination polymers with Zn(II), Cd(II) and Co(II) metal ions and different carboxylate donor ligands, viz., 1,1′-ferrocenedicarboxylic acid (H2Fc), 2′,5′-dimethylterphenyl-4,4″-dicarboxylic acid (H2MDA), diphenic acid (H2DPA), biphenyl-4,4′-dicarboxylic acid (H2BIPH), 4,4′-oxybis (benzoic acid) (H2BIOXY), l-(−)-malic acid (H3LMA) and 2,2′-dibromo-6,6′-dinitrobiphenyl-4,4′-dicarboxylic acid (H2DBDPA). Compounds formed solvothermally are {[Cd(L)(Fc)(H2O)]·(H2O)2}n (1), {[Cd(L)(MDA)]·DMF·CH3OH}n (2), {[Zn(L)(MDA)]·3H2O}n (3), {[Cd(L)(DPA)]}n (4), {[Cd2(L)2(BIPH)2(H2O)2]·H2O}n (5), {[Cd2(L)2(BIOXY)2]·H2O·CH3OH}n (6), {[Zn3(L)5(LMA)2]·2.5H2O}n (7) and {[Co(L)(DBDPA)]·H2O}n (8). All the complexes have been characterized by single crystal X-ray diffraction, IR spectroscopy, thermogravimetry, elemental analysis and powder X-ray diffraction (PXRD). Interestingly, all complexes topologically exhibit 4-connected net except complex 7, which is (4,6). Moreover, the degree of interpenetration varies in 1–8. Complexes 1, 4 and 6 exhibit commonly occurring sql topology, while complexes 2 and 3 are 8-fold interpenetrated dia net. Contrary to this, complexes 5 and 8 show rare cdl and dmp nets with three and five mutual interpenetrative nets, respectively. However, 7 forms a novel pkb6 topological net with 2-fold interpenetration. Upon excitation at 322 nm, complexes 1–8 exhibit solid-state luminescence at room temperature.