Heterodinuclear MIICuII complexes of a constrained macrocyclic compartmental ligand. EPR studies of spin-coupled MnIICuII (ST=2) and NiIICuII (ST=1/2)

Abstract

A phenol-based macrocyclic compartmental ligand (L)2−, having an N(amine)2O2 metal-binding site with 1,3-trimethylene chain between the two aminic nitrogen atoms and an N(imine)2O2 site with 1,8-naphthalene chain between the two iminic nitrogen atoms, has afforded the following heterodinuclear MIICuII complexes, [MCu(L)(dmf)2](ClO4)2 (M=Mn (1), Co (2), Ni (3), Zn (4)). X-ray crystallographic studies for 1–4 demonstrate that the MII resides in the N(amine)2O2 site and the CuII in the N(imine)2O2 site of the constrained macrocyclic ligand. The MII has a six-coordinate geometry together with two dmf molecules at the axial site and the CuII has a square-pyramidal geometry with a perchlorate oxygen atom at the apical site. Magnetic, visible spectral and electrochemical properties of the complexes are examined. A frozen dmf solution of 1 at liquid nitrogen temperature shows an EPR signal with a Mn hyperfine structure (AMn=103×10−4 cm−1) at ∼2400 Ga, which is attributed to the ST=2 ground state of the spin-coupled MnII (S=5/2)–CuII (S=1/2). A qualitative analysis is made for the EPR of 1 in comparison with the EPR of the ST=1/2 state of spin-coupled NiII (S=1)–CuII (S=1/2) of 3.