Spectral and electrochemical characterization of bimetallic complexes of a novel 32-membered unsymmetrical [N12] macrocycle

Abstract

Reactions of a 32-membered [N12] macrocyclic ligand, L.2HClO4 with metal salts MCl3 (M=Cr or Fe) and MCl2 (M=Co, Ni or Cu) have produced complexes of stoichiometries M2LCl4(ClO4)2 and M2LCl2(ClO4)2, respectively. However, reactions with [M(Ph3P)2Cl2] (M=Co or Ni) and [(η5-C5H5)Ni(Ph3P)I] follow a ligand substitution path resulting in products with stoichiometries M2LCl2(ClO4)2 and [(η5-C5H5)2Ni2L(ClO4)2], respectively. The mode of bonding and geometry of the complexes have been derived on the basis of i.r., ligand field spectral and magnetic susceptibility measurements. EPR of CuII complex shows anisotropy with \(\hbox{g}_{||} > \hbox{g}_{\bot}> 2.0\), G \hbox{K}_{||}(0.853)\). Thermodynamic first ionic association constants (K1) and the corresponding free energy change (ΔG) of complexes in DMSO have been determined and discussed. Cyclic voltammetric studies indicate the presence of a quasi-reversible redox couples CrIII/II, CoII/I, NiII/I, NiII/III and CuII/I in solutions suggesting flexible nature of the macrocyclic cavity.