Syntheses, structures and properties of dinickel(II) macrocyclic complexes with two 2-thiophenoethyl pendant arms

Three dinickel(II) macrocyclic complexes [Ni2L(μ-OAc)]ClO4•X (L = L1, L2 and L3) with two 2-thiophenoethyl pendant arms, have been synthesized by cyclocondensation between N,N-bis(3-aminopropyl)-2-thiophenoethylamine and 2,6-diformyl-4-R-phenol (where R = Me, Cl and F and X = MeOH, 2MeCN and H2O, respectively), in the presence of nickel(II) ions. The complexes were characterized by elemental analysis, spectroscopic methods and X-ray diffraction techniques. The geometry around both of the Ni(II) ions in each molecule is a slightly distorted octahedral and the thiopheno groups do not coordinate to the Ni(II) ions, resulting that the complexes display contorted saddle-form configurations. The distances between the Ni⋯Ni centers for the complexes are 3.145, 3.171 and 3.155 Å, respectively. The influences of the substituted groups R in the benzene rings of the macrocyclic units on the structure, electrochemistry, magnetism, cleavage and antibacterial property to DNA have been investigated. The ES-MS results of the complexes confirm that [Ni2L]2+ species in methanol solution are very stable because all the peaks in ES-MS spectra contain this kind of units. The reduction potentials of the complexes shift towards anode upon increasing the drawing electronic ability of substituted groups. Magnetic measurements in the 2–300 K range indicate weak antiferromagnetism for the dinuclear Ni(II) complexes and the magnetic exchange interactions enhance with the decrease of the Ni–Ni distances. These complexes exhibit cleavage activities towards plasmid pBR322 DNA and antibacterial activities.

Graphical abstractThree new dinickel(II) macrocyclic complexes with two 2-thiophenoethyl pendant arms have been synthesized by cyclocondensation. The complexes were characterized by elemental analysis, spectroscopic methods and X-ray diffraction techniques. The influences of the substituted groups R in the benzene rings of the macrocyclic units on the structure, electrochemistry, magnetism, cleavage and antibacterial property to DNA have been investigated. These complexes exhibit cleavage activities towards plasmid pBR322 DNA and antibacterial activities.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Three Ni(II) macrocyclic complexes with two 2-thiophenoethyl pendant arms. ► The fluro-substituted complex has stronger DNA cleavage and antibacterial activities. ► The redox of the complexes changes with the substituted groups. ► The magnetic exchange interactions enhance with the decrease of the Ni–Ni distances.