Quantum chemical calculations have been performed to determine the magnetic coupling between transition metals in the anionic layers of bifunctional materials. These layers are characterized by a hexagonal grid of oxalato-bridged transition metal ions, [M-2(ox)(3)](2-), with M = Cu2+, Ni2+, Co2+, Fe2+. No experimental information is available for the coupling constants in these lattices. The magnetic coupling parameters are calculated through an embedded cluster containing two metal ions and the oxalato ligands coordinated to these. The calculated parameters are used to construct a larger model for which the temperature dependence of the magnetic susceptibility is calculated. The curves obtained compare reasonably well with experimental curves, validating the theoretical estimates of the magnetic coupling between the transition metals in the hexagonal lattices.