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

• Published in: Transition metal chemistry (Weinheim) Vol. 32; no. 7; pp. 913 - 921
• Main Authors: Siddiqi, Zafar Ahmad, Khalid, Mohd, Kumar, S.
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Nature B.V 01.10.2007
• ISSN: 0340-4285; 1572-901X
• DOI: 10.1007/s11243-007-0252-0

The 16-membered modified [N^sub 6^] macrocylic ligand (L), a mimic to cyclic, hexapeptide is reacted with MCl^sub 2^ and MCl^sub 3^ resulting in complexes with stoichiometrices [MLCl^sub 2^] (M = Cr, Mn, Co, Ni, Cu), [MLCl^sub 3^] (M = Pt, Pd) and [MLCl^sub 2^]Cl (M = Fe, Ru). Its reactions with the precursors [M(Ph^sub 3^P)^sub 2^Cl^sub 2^] (M = Co, Ni, Pt, Pd) follow a ligand displacement path affording the final products which do not contain coordinated Ph^sub 3^P. 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 Cr^sup 2+^, Mn^sup 2+^, Fe^sup 3+^, Co^sup 2+^, Ni^sup 2+^ and Cu^sup 2+^ and four coordinate square-planar geometry for Pt^sup 2+^ and Pd^sup 2+^. 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.[PUBLICATION ABSTRACT]