Density functional modeling of long range magnetic interactions in binuclear oxomolybdenum(V) complexes

Magnetic exchange interactions have been calculated in the framework of the density functional (DF) theory for the quite rare exchange coupled binuclear compounds in which the magnetic centers belong to the 4d series: [{Mo-V(O)(Tp*)Cl}(2)(mu-X)], (where X is one of the dihydroxybenzene bridging Ligands [1,4-OC6H4O](2-) or [1,3-OC6H4O](2-) and Tp* is tris(3,5-dimethylpyrazolyl)hydroborate. The exchange coupling constant J has been nicely reproduced with the use of the broken symmetry (BS) approach to avoid the multideterminant structure of the singlet state. Several local and gradient-corrected functionals have been tested. In order to determine relevant magneto-structural correlations between structural parameters and exchange coupling constants, we also performed calculations on model systems in which the relative orientations of the two molybdenum moieties with respect to the aromatic ring were varied. These calculations showed that the actual value of the magnetic coupling constant J is influenced not only by the topology, 1,3 or 1,4, of X, but a correlation with the relative orientation of the two branches containing the two Mo atoms exists. This magneto-structural, correlation is;bound to superexchange pathways, which are, therefore, also important in transmitting magnetic interactions through dihydroxybenzene ligands.