Synthesis, spectroscopic and redox properties of the mononuclear NiII, NiII(BPh2)2 containing (B-C) bond and trinuclear CuII-NiII-CuII type-metal complexes of N,N′-(4-amino-1-benzyl piperidine)-glyoxime

Abstract

The novel vic-dioxime ligand containing the 4-amino-1-benzyl piperidine group, N,N′-(4-amino-1-benzyl piperidine)-glyoxime, (LH2) has been prepared from 4-amino-1-benzyl piperidine with anti-dichloroglyoxime at −15°C in absolute THF. Mononuclear NiII metal complex has been obtained with 1: 2 metal/ligand ratio. The NiII complex of this ligand is proposed to be square planar geometry. IR spectra show that the ligand acts in a tetradentate manner and coordinates N4 donor groups of LH2 to NiII ion. The detection of H-bonding (O-H···O) in the [Ni(LH)2] (1) metal complex by IR spectra supported the square-planar MN4 coordination of mononuclear complex. The disappereance of H-bonding (O-H···O) in the [Ni(L)2(BPh2)2] (2) complex shows that the BPh +2 -capped groups (BPh +2 cation formed BPh4 anion) attaches to the main oxime core. MN4 coordination of the [Ni(LH)2] (1) and [Ni(L)2(BPh2)2] (2) metal complexes were also determined by 1H-NMR spectroscopy. In the trinuclear CuII-NiII-CuII metal complexes, the NiII ion centered into the main oxime core by the coordination of the imino groups while the two CuII ions coordinate dianionic oxygen donors of the oxime groups and linked to the ligands of 1,10-phenanthroline, 2,2′-bipyridine, and 4,4′-bipyridine. The ligand and their mono and trinuclear metal complexes were characterized by elemental analyses, FT-IR, UV-Vis, 1H and 13C-NMR spectra, magnetic susceptibility measurements, molar conductivity, cyclic voltammetry, mass spectra and X-ray powder techniques. The cyclic voltammetric results show that the cathodic peak potential of [Ni(L)2(BPh2)2] shifted toward more negative value compared to that of [Ni(LH)2], probably due to a decreasing effect of back donation of metal-oxime moieties as a result of the BPh +2 -bridged complex formation. Also, the formation of the trinuclear CuII-NiII-CuII metal complexes caused considerable changes on the CV behaviour of mononuclear [Ni(LH)2] (1) complex. The spectroelectrochemical study of [Ni(L)2(BPh2)2] (2) showed distinctive spectral changes that the intensity of the band (λ = at 364 nm, assigned to n → π* transitions) decreased and a new broad band in low intensity about 460 nm appeared as a result of the reduction of the nickel centered in the oxime core.