We investigated the magnetic properties of a series of dinickel(II) complexes with hexaaza-dithiophenolate ligand [(L)Ni-2(mu-L')(n+) bridged by L' = N-3(-), BH4-, NO2-, acetato, benzoato and pyridazine using density functional theory calculations. We show that the experimental observed behavior can be understood with help of the Hay-Thibeault-Hoffmann model, where ferromagnetic coupling is related to the degeneracy of the magnetic orbitals. Further, we calculate the magnetic anisotropy parameters including spin-orbit coupling effects in a perturbative way. (c) 2007 Elsevier B.V. All rights reserved.