Magnetic properties of diphosphonate-bridged binuclear copper(II) complex: a density functional theory study

The magnetic exchange interaction in the quasi one-dimensional chain complex [Cu-2(hedp)(2)](n)(4n-) is investigated on the basis of the density functional theory combined with the broken symmetry approach. The title complex is modeled by binuclear models 1a and 1b. In the O-P-O bridged unit (model 1a), the magnetic exchange interaction exhibits antiferromagnetic characteristic, with the calculated magnetic coupling constant of -248 cm(-1); while in the O atom bridged unit (model 1b), magnetic exchange interaction is ferromagnetic with the calculated magnetic coupling constant of +3.6 cm(-1). In comparison with the analogue Cu-2(CH3COO)(4)(H2O)(2) it is found that in both the complexes the magnetic exchange interactions between the magnetic centers Cu(II) mainly are a super-exchange through the bridge groups, but not through a direct exchange between the Cu(II) ions. The analyses of molecular magnetic orbitals show that the magnetic exchange pathways in the two complexes are involved in sigma-orbital on the bridging group, but not pi-orbital. From Mulliken overlap spin population, the super-exchange interactions in both the acetate-bridged and diphosphonate-bridged Cu(II) complexes reveal a spin delocalization mechanism. (C) 2004 Elsevier B.V. All rights reserved.