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}_<i>n</i> (<b>1</b>), {[Cd­(L)­(MDA)]·DMF·CH₃OH}_<i>n</i> (<b>2</b>), {[Zn­(L)­(MDA)]·3H₂O}_<i>n</i> (<b>3</b>), {[Cd­(L)­(DPA)]}_<i>n</i> (<b>4</b>), {[Cd₂(L)₂(BIPH)₂(H₂O)₂]·H₂O}_<i>n</i> (<b>5</b>), {[Cd₂(L)₂(BIOXY)₂]·H₂O·CH₃OH}_<i>n</i> (<b>6</b>), {[Zn₃(L)₅(LMA)₂]·2.5H₂O}_<i>n</i> (<b>7</b>) and {[Co­(L)­(DBDPA)]·H₂O}_<i>n</i> (<b>8</b>). 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 <b>7</b>, which is (4,6). Moreover, the degree of interpenetration varies in <b>1</b>–<b>8</b>. Complexes <b>1</b>, <b>4</b> and <b>6</b> exhibit commonly occurring <i>sql</i> topology, while complexes <b>2</b> and <b>3</b> are 8-fold interpenetrated <i>dia</i> net. Contrary to this, complexes <b>5</b> and <b>8</b> show rare <i>cdl</i> and <i>dmp</i> nets with three and five mutual interpenetrative nets, respectively. However, <b>7</b> forms a novel <i>pkb</i>6 topological net with 2-fold interpenetration. Upon excitation at 322 nm, complexes <b>1</b>–<b>8</b> exhibit solid-state luminescence at room temperature