Cobalt (II) coordination polymers based on 3,5-dinitrobenzoate and flexible bis(benzimidazole) derivatives bearing different spacer lengths and substituents

Three new CoII coordination polymers, namely [Co(DNBA)2(pbdmbm)] (1), [Co2(H2O)2(DNBA)2(ebdmbm)2] (2) and [Co2(DNBA)2(pbbm)2] (3) have been obtained by hydrothermal reactions of CoII with flexible bis(benzimidazole) ligands [1,1′-(1,3-propanediyl)bis(5,6-dimethylbenzimidazole) (pbdmbm), 1,1′-(1,2-ethanediyl)bis(5,6-dimethylbenzimidazole) (ebdmbm), 1,1′-(1,3-propanediyl)bis(benzimidazole) (pbbm)] plus 3,5-dinitrobenzoic acid (HDNBA). The complexes have been characterized by single crystal X-ray diffraction, elemental analyses, IR and TG. Complexes 1 and 3 exhibit one-dimensional chains composed of CoII centers bridged by flexible bis(benzimidazole) ligands. Complex 2 is a three-dimensional NaCl-type supramolecular framework constructed from binuclear units, which are formed by two CoII centers and two ebdmbm ligands. The spacer length and substituents on the bis(benzimidazole) ligands are crucial for the construction of these structures. The photoluminescence properties of the complexes and the cyclic voltammetry behavior of complex 1 are described.