Heterodinuclear MIINiII (M = Co, Ni, Cu, Zn) Complexes of a Macrocyclic Compartmental Ligand. Anomalous EPR of CuIINiII Complex by Coordination of 1-Methylimidazole

Abstract

Abstract A phenol-based macrocyclic compartmental ligand, (L2;2)2-, having N(amine)2O2 and N(imine)2O2 metal binding sites sharing two phenolic oxygen atoms, has formed the following heterodinuclear MIINiII complexes: [CoNi(L2;2)(AcO)]PF6·CH3CN (1), [NiNi(L2;2)(AcO)]PF6 (2), [CuNi(L2;2)(AcO)]PF6 (3) and [ZnNi(L2;2)(AcO)]PF6·CH3CN (4). Furthermore, [CuNi(L2;2)(CH3CN)](PF6)2·CH3CN (3′) was obtained when 3 was recrystallized from acetonitrile. X-ray crystallographic studies for 1, 2, 3′ and 4 demonstrate that the MII resides in the N(amine)2O2 site and the NiII in the N(imine)2O2 site. The NiII in the N(imine)2O2 site has a planar geometry and is diamagnetic in all the complexes. The CoII of 1 and the NiII of 2 in the N(amine)2O2 site have a six-coordinate geometry together with a bidentate acetate group. The CuII in 3′ has a five-coordinate geometry together with one acetonitrile molecule, and the ZnII in 4 has a square-pyramidal geometry together with a unidentate acetate group. Complex 3′ in DMF combines 1-methylimidazole (MeIm) at the axial site of the NiII and the MeIm adduct in frozen DMF solution at 77.4 K shows EPR signals of g|| = 2.06 and g⊥ = 2.26 with a multi-line structure superimposed on the g|| component (A|| = 15.8 × 10-4 cm-1). The EPR signals are ascribed to the spin-doublet ground state (ST = 1/2) of antiferromagnetically coupled CuII(S = 1/2) - NiII(S = 1), and the multi-line structure is explained by considering hyperfine interaction with Cu nucleus (ACu = 50.0 × 10-4 cm-1) and superhyperfine interaction with N nucleus of MeIm (AN = 15.0 × 10-4 cm-1).