Mono- and dinuclear cadmium(II) complexes based on polybenzimidazole-containing tetradentate and heptadentate ligands: Synthesis, structures and fluorescent properties

Two novel cadmium(II) complexes, [Cd(ntb)(O2CC6H4-p-Cl)]ClO4·3CH3OH (1) and [Cd2(bbap)(O2CC6H4-p-Cl)2]NO3·3C2H5OH·H2O (2) have been synthesized and structurally characterized by elemental analysis, IR, 1H NMR and single crystal X-ray diffraction, where ntb is tris(2-benzimidazolymethyl)amine, bbap− is anion of 2,6-bis[bis(2-benzimidazolylmethyl)aminomethyl]-4-methylphenol. In complex 1, the cadmium ion is coordinated with four nitrogen atoms of ntb and two oxygen atoms of 4-chlorobenzoate anion in bidentate O,O′-chelating mode. In complex 2, the two cadmium ions are held together by the μ-phenoxo bridge of bbap- with Cd1⋯Cd2 separation of 3.934 Å. Each of the two cadmium ions is further coordinated with the carboxylate group of 4-chlorobenzoate in bidentate O,O′-chelating mode. Complexes 1 and 2 are interlinked through hydrogen bonds to form 1D chain structures, the chains are further extended to 2D supramolecular network through hydrogen bonding and π–π stacking interactions. Both complexes present strong fluorescent emission in the solid state at room temperature. Experiment shows that there is a higher coordination ability of the carboxylate group of 4-chlorobenzoate as coligand with the dinuclear [Cd2(bbap)]3+ core than with the mononuclear [Cd(ntb)]2+ core.