Crystal structures and electrochemical properties of nickel(II) complexes with N,N′,N′′,S-tetra­dentate Schiff base ligands

The thiol­ate nickel complexes {2-[({2-[(2-amino­ethyl-κN)(meth­yl)amino-κN]eth­yl}imino-κN)meth­yl]benzene­thiol­ato-κS}nickel(II) chloride, [Ni(C(12)H(18)N(3)S)]Cl (1), and [2-({[2-(piperazin-1-yl-κ(2) N (1),N (4))eth­yl]imino-κN}meth­yl)benzene­thiol­ato-κS]nickel(II) hexa­fluoro­phosphate di­chloro­methane monosolvate, [Ni(C(13)H(18)N(3)S)]PF(6)·CH(2)Cl(2) (2), were synthesized by the reactions of 2-(tert-butyl­thio)­benzaldehyde, tri­amines, and nickel(II) salts. Both complexes have a nickel ion surrounded by an N,N′,N′′,S-tetra­dentate ligand, forming a square-planar geometry. The terminal N,N-chelating moiety is N,N-di­alkyl­ethane-1,2-di­amine for 1 and 1-alkyl­piperazine for 2. The N—Ni—N bite angle in the terminal N,N-chelate ring in 2 [76.05 (10)°] is much smaller than that in 1 [86.16 (6)°]. Cyclic voltammograms of 1 and 2 in aqueous media indicated that the reduction and oxidation potentials of 2 are more positive than those of 1. The smaller bite angle of the terminal piperazine chelate in 2 reduces the electron-donating ability of the tetra­dentate ligand, resulting in a positive shift of the redox potentials. Both complexes exhibit catalytic activity for proton reduction, and the piperazine moiety in 2 is effective in reducing the overpotential.