From discrete dinuclear to 1-D and 2-D structures: nickel dipicolinate complexes with flexible bis(imidazole) ligands

Three new complexes, [Ni2(dpc)2(L1)2(H2O)2] · 4H2O (1), [Ni(dpc)(L2)1.5] n (2), and {[Ni(dpc)(L3)1.5] · 2H2O} n (3), where H2dpc = dipicolinic acid, L1 = 1,4-bis(2-methylimidazol-1-yl)butane, L2 = 4,4′-bis(2-methylimidazol-1-ylmethyl)biphenyl, and L3 = 1,4-bis(benzimidazol-1-yl)-2-butylene, have been synthesized by hydrothermal methods and characterized by elemental analyses, infrared spectra, thermogravimetric analysis, and X-ray crystallography. The common structural characteristic of the three complexes is that the Ni2+ is coordinated by tridentate dipicolinate through nitrogen of pyridine and oxygen of carboxylate, serving as a terminal ligand. In 1, two L1 link two [Ni(dpc)(H2O)] units to a discrete binuclear metallomacrocycle with a 22-membered ring, which is assembled through multiple O–H ··· O hydrogen bonds to form a 3-D supramolecular framework. Complex 2 exhibits a 1-D ladder-like chain structure constructed by cis/trans-conformation L2 linking metal centers; 3 displays a 2-D (6,3) topology, be...