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.