Synthesis and Characterization of Nickel(II) Schiff Base Complexes with Methoxy or Methyl Groups at 2,6-Positions of the Pendant Phenyl Ring: the Control of cis and trans Geometries

Two nickel(II) complexes with N,S chelates were prepared by the reaction of nickel(II) acetate tetrahydrate with 2-substituted benzothiazolines. Bis[2-(2,6dimethoxyphenylmethyleneamino)benzenethiolato]nickel(II) 1, in which the 2,6-positions of the pendant phenyl ring are occupied by methoxy groups, has an approximately square-planar geometry around a nickel atom with a cis-N2S2 donor atom arrangement. X-ray and variable-temperature 1H NMR studies indicated the existence of an apical Ni···OMe interaction in 1. On the other hand, bis[2-(mesitmethyleneamino)benzenethiolato]nickel(II) 2 with methyl groups at the 2,4,6positions of the pendant phenyl ring exhibits a perfect planar trans-N2S2 coordination around the nickel atom. An X-ray study revealed the existence of an intraligand CH/(pi) interaction in 2. A difference in the geometry around -CH=N- (E and Z) was also observed between 1 and 2 (Z for 1 and E for 2).