Macrocyclic effect upon site-selective CuIIMII or MIICuII core formation with unsymmetric phenol-based macrocyclic ligands

Abstract

Complexes of phenol-based dinucleating macrocycles, (L^2;2)²⁻ and (L^2;4)²⁻, comprised of two 4-bromo-2-iminomethyl-6-methylaminomethylphenolate moieties combined by an ethylene chain at the amino nitrogens and by an ethylene or a 1,4-tetramethylene chain at the imino nitrogens, have been prepared: mononuclear [Cu(L^2;2)] and [Cu(L^2;4)], and dinuclear [PbCu(L^2;2)][ClO₄]₂ and [PbCu(L^2;4)][ClO₄]₂. The reaction of [Cu(L^2;2)] and [Cu(L^2;4)] with MCl₂ salts formed dinuclear [MCu(L^2;2)Cl₂] and [MCu(L^2;4)Cl₂] (M = Mn, Co, Ni, Cu or Zn), respectively. A crystallographic study of [NiCu(L^2;2)Cl₂] indicates the Ni^II to reside in the aminic site and the Cu^II in the iminic site. The complexes, except for that of M = Zn^II, show a significant antiferromagnetic interaction within each dinuclear unit. The reaction of [PbCu(L^2;2)][ClO₄]₂ with MSO₄ salts formed dinuclear Cu^IIM^II perchlorate complexes [CuM(L^2;2)][ClO₄]₂ (M = Co, Ni, Cu or Zn). A similar transmetallation for [PbCu(L^2;4)][ClO₄]₂ caused a scrambling of the metal ions. A crystallographic study of [CuNi(L^2;2)(dmf)][ClO₄]₂·MeOH indicates that the Cu^II migrates from the iminic to the aminic site to accommodate the Ni^II in the iminic site. Kinetic and thermodynamic effects of the macrocycles upon the site selectivity for the metal ions are discussed.