Synthesis and characterization of two novel bimetallic macrocyclic complexes generated from 1,2,4-triazole-containing semi-rigid ligands andM(NO3)2units (M= Ni and Zn)

Abstract

Bimetallic macrocyclic complexes have attracted the attention of chemists and various organic ligands have been used as molecular building blocks, but supramolecular complexes based on semi-rigid organic ligands containing 1,2,4-triazole have remained rare until recently. It is easier to obtain novel topologies by making use of asymmetric semi-rigid ligands in the self-assembly process than by making use of rigid ligands. A new semi-rigid ligand, 3-[(pyridin-4-ylmethyl)sulfanyl]-5-(quinolin-2-yl)-4H-1,2,4-triazol-4-amine (L), has been synthesized and used to generate two novel bimetallic macrocycle complexes, namely bis{μ-3-[(pyridin-4-ylmethyl)sulfanyl]-5-(quinolin-2-yl)-4H-1,2,4-triazol-4-amine}bis[(methanol-κO)(nitrato-κ2O,O′)nickel(II)] dinitrate, [Ni2(NO3)2(C17H14N6S)2(CH3OH)2](NO3)2, (I), and bis{μ-3-[(pyridin-4-ylmethyl)sulfanyl]-5-(quinolin-2-yl)-4H-1,2,4-triazol-4-amine}bis[(methanol-κO)(nitrato-κ2O,O′)zinc(II)] dinitrate, [Zn2(NO3)2(C17H14N6S)2(CH3OH)2](NO3)2, (II), by solution reactions with the inorganic saltsM(NO3)2(M= Ni and Zn, respectively) in mixed solvents. In (I), two NiIIcations with the same coordination environment are linked byLligands through Ni—N bonds to form a bimetallic ring. Compound (I) is extended into a two-dimensional network in the crystallographicacplaneviaN—H...O, O—H...N and O—H...O hydrogen bonds, and neighbouring two-dimensional planes are parallel and form a three-dimensional structureviaπ–π stacking. Compound (II) contains two bimetallic rings with the same coordination environment of the ZnIIcations. The ZnIIcations are bridged byLligands through Zn—N bonds to form the bimetallic rings. One type of bimetallic ring constructs a one-dimensional nanotubeviaO—H...O and N—H...O hydrogen bonds along the crystallographicadirection, and the other constructs zero-dimensional molecular cagesviaO—H...O and N—H...O hydrogen bonds. They are interlinked into a two-dimensional network in theacplane through extensive N—H...O hydrogen bonds, and a three-dimensional supramolecular architecture is formedviaπ–π interactions between the centroids of the benzene rings of the quinoline ring systems.