Exchange interaction in linear trimeric copper(II) complexes with ferromagnetic and antiferromagnetic ground states

Abstract

The different magnetic properties of two linear trimeric copper(II) complexes, a complex with a ferromagnetic spin ground state, [Cu₃(C₆H₅CO₂)₄{(C₂H₅)₂NC₂H₄O}₂(CH₃OH)₂], 1 and a complex with an antiferromagnetic ground state, [Cu₃{(C₂H₅)₂NC₂H₄N(H)C₃H₆O}₂(OH)₂]Δ(ClO₄)₂, 2, are described using MO methods and are discussed. 1 presents a folded geometry, whereas in 2 the coordination planes around the copper atoms are nearly coplanar. SCF calculations have been performed on models of both compounds. The coefficients of the AOs of the metal centres and ligands involved in the three singly occupied MOs are reported and their different contributions are discussed. The orthogonality of the magnetic orbitals in 1 is due to the non-coplanarity of the Cu1 and Cu2 coordination planes, which leads to the predominant ferromagnetic exchange interaction. In 2 the nature of the magnetic orbitals favours an antiferromagnetic interaction as consequence of the nearly planar geometry.