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

Complexes of phenol-based dinucleating macrocycles, (L2;2)2− and (L2;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(L2;2)] and [Cu(L2;4)], and dinuclear [PbCu(L2;2)][ClO4]2 and [PbCu(L2;4)][ClO4]2. The reaction of [Cu(L2;2)] and [Cu(L2;4)] with MCl2 salts formed dinuclear [MCu(L2;2)Cl2] and [MCu(L2;4)Cl2] (M = Mn, Co, Ni, Cu or Zn), respectively. A crystallographic study of [NiCu(L2;2)Cl2] indicates the NiII to reside in the aminic site and the CuII in the iminic site. The complexes, except for that of M = ZnII, show a significant antiferromagnetic interaction within each dinuclear unit. The reaction of [PbCu(L2;2)][ClO4]2 with MSO4 salts formed dinuclear CuIIMII perchlorate complexes [CuM(L2;2)][ClO4]2 (M = Co, Ni, Cu or Zn). A similar transmetallation for [PbCu(L2;4)][ClO4]2 caused a scrambling of the metal ions. A crystallographic study of [CuNi(L2;2)(dmf)][ClO4]2·MeOH indicates that the CuII migrates from the iminic to the aminic site to accommodate the NiII in the iminic site. Kinetic and thermodynamic effects of the macrocycles upon the site selectivity for the metal ions are discussed.