Theoretical investigation of magnetic properties of a dinuclear copper complex [Cu2(μ-OAc)4(MeNHph)2]

We have investigated the magnetic properties of a recently synthesized dinuclear complex, [Cu-2(mu-OAc)(4)(MeNHpy)(2)], by broken-symmetry (BS) density functional (DFT) methodology. The complex has several pairs of magnetic orbitals. Therefore, we have explicitly calculated the overlap integral S-ab between the two natural magnetic orbitals, and found a value of 0.8589. Deviating from the common practice of approximating S-ab by 1 for the strongly delocalized systems, the computed value has been used in calculating the magnetic exchange coupling constant (J) from the two electron-two orbital BS model. The calculated J is -290 cm(-1), in excellent agreement with the observed value of -285 cm(-1). The contribution of the overlap between the orbitals of the two copper atoms to S-ab is negligibly small. Also, the calculated J value is a weakly varying function of the Cu-Cu distance. The last two observations confirm that the through-ligand superexchange phenomenon is responsible for the high magnetic exchange interaction in the Cu-2(mu-OAc)(4) complex(es). Furthermore, we have shown that the onset of intramolecular hydrogen bonding reduces the spin density on the bridging atoms and consequently the magnitude of J. This explains why the complex under investigation has a J value smaller than that of [Cu-2(mu-OAc)(4)(H2O)(2)] (-299 cm(-1)). While establishing this trend, we predict that the complex [Cu-2(mu-OAc)(4)(py)(2)] would have a higher J value, about -300 cm(-1) (c) 2006 Elsevier B.V. All rights reserved.