Effect of carboxylate coligands on the crystal structures of two nickel(II) coordination polymers constructed from a flexible bis(5,6-dimethylbenzimidazole) ligand

Two Ni(II) coordination polymers, Ni(dmbbbi)(pic)₂·3H₂O] _n (1) and Ni(dmbbbi)_1.5(pdc)·2H₂O] _n (2) (dmbbbi = 1,1′-(1,4-butanediyl)bis(5,6-dimethylbenzimidazole), Hpic = 2-picolinic acid, H₂pdc = pyridine-2,6-dicarboxylic acid), have been hydrothermally synthesized by self-assembly of nickel chloride with a flexible bis(5,6-dimethylbenzimidazole) ligand and two different pyridine carboxylic acids. The compounds were characterized by physico-chemical and spectroscopic methods and by single-crystal diffraction. Compound 1 possesses 1D ribbon-like chains connected by dmbbbi ligands in bis-bridging mode, which are further extended into a 2D supramolecular network through O–H···O hydrogen bonding interactions between pic anions and lattice water molecules, giving a novel trinodal (3,3,4)-connected topology with the point symbol of (4.6.8)₂(6.8⁴.10). Compound 2 shows a 2D undulant {6³} hexagonal (hcb) network. The structures of the two complexes are further stabilized by intramolecular π···π stacking interactions between the imidazole and N-containing nickel chelate rings. In addition, the fluorescence properties of 1 and 2 have been investigated in the solid state.