Spectral and electro-chemical characterization of transition metal complexes of a modified [N6] macrocycle.: A mimic to cyclic hexapeptide

The 16-membered modified [N-6] macrocylic ligand (L), a mimic to cyclic, hexapeptide is reacted with MCl2 and MCl3 resulting in complexes with stoichiometrices [MLCl2] (M = Cr, Mn, Co, Ni, Cu), [MLCl3] (M = Pt, Pd) and [MLCl2]Cl (M = Fe, Ru). Its reactions with the precursors [M(Ph3P)(2)Cl-2] (M = Co, Ni, Pt, Pd) follow a ligand displacement path affording the final products which do not contain coordinated Ph3P. Complexes have been characterized from results of elemental analyses, conductometric, magnetic susceptibility, i.r. and u.v.-vis (ligand field) spectral studies. Magnetic susceptibility and ligand field spectral data are consistent with a hexacoordinate geometry for Cr2+, Mn2+, Fe3+, Co2+, Ni2+ and Cu2+ and four coordinate square-planar geometry for Pt2+ and Pd2+. Molecular orbital computations using CSChem ultra MOPAC software for an optimized minimum energy plot of the structure shows that the ligand binds metal ions as a tetradentate (N,N,N,N) chelating agent. Cyclic voltammetric studies indicate formation of stable reversible or quasi-reversible redox couples in solutions, which corroborates a kinetic stability of these complexes in their variable oxidation states.