An 18-member dinucleating unsymmetrical [N10] macrocycle and its bimetallic complexes M2LCl2(ClO4) (M=Co, Ni, Cu, Zn, Cd or Hg)

Abstract

The 18-member unsymmetrical dinucleating Shiff-base decaaza [N10] macrocyclic ligand, 2,8,11,17-tetramethyl-3,5,7,12,14,16-hexaphenyl-[1,3,5,7,9,10,12,14,16,18] decaazaoctadeca-2,8,11,17-tetraene dihydroperchlorate (L · 2HClO4) was obtained as a cream colored solid from reaction of N-acetylaniline and hydrazine in the presence of HClO4 followed by cyclization (capping) using aniline and excess HCHO in methanol at RT. Reactions of L · 2HClO4 with MCl2 and [M(Ph3P)2Cl2] afforded air stable complexes, M2LCl4(ClO4)2 (M = Co, Ni, Cu, Zn or Cd). The compounds have been characterized by physico-chemical and spectroscopic studies. FAB–Mass spectral data support bimetallic coordination by the macrocycle. IR studies confirm coordination/encapsulation of metal ions involving unsymmetrical aza sites. Magnetic susceptibility and UV–Visible data indicate a low-spin, five-coordinate geometry for Co(II) and Ni(II) complexes. The anisotropic EPR signals (g ∥ > g ⊥) for Cu2+ complex suggest an axial type tetragonality. Molecular model computations have been employed for a theoretical perspective of the ligand and complexes. The important bond lengths and bond angles have been estimated using CS Chem-3D software. The ionic association constant (K 1) and thermodynamic free energy change (ΔG) were evaluated from the conductometric data of the complexes, which indicate presence of a strong ion-pair even in solution. Cyclic voltametric studies on solutions of M2LCl4(ClO4)2 (M = Co, Ni or Cu) in DMSO indicate reversible and quasi-reversible redox couples.