Bimetallic, oxalate-bridged compounds with bi- and trivalent transition metals comprise a class of layered materials which express a large variety in their molecular-based magnetic behavior. Because of this, the availability of the corresponding single-crystal structural data is essential to the successful interpretation of the experimental magnetic results. We report in this paper the crystal structure and magnetic properties of the ferromagnetic compound {[N(n-C3H7)(4)][(MnCrIII)-Cr-II(C2O4)(3)]}(n) (1), the crystal structure of the antiferromagnetic compound {[N(n-C4H9)(4)][Mn-II-Fe-III(C2O4)(3)]}(n) (2), and the results of a neutron diffraction study of a polycrystalline sample of the ferromagnetic compound {[P(C6D5)(4)][(MnCrIII)-Cr-II(C2O4)(3)]}(n) (3). Crystal data : 1, rhombohedral, R3c, a = 9.363(3) Angstrom, c = 49.207(27) Angstrom, Z = 6; 2, hexagonal, P6(3), a = 9.482(2) Angstrom, c = 17.827(8) Angstrom, Z = 2. The structures consist of anionic, two-dimensional, honeycomb networks formed by the oxalate-brid,oed metal ions, interleaved by the templating cations. Single-crystal field dependent magnetization measurements as well as elastic neutron scattering experiments on the manganese(II)-chromium(III) samples show the existence of long-range ferromagnetic ordering behavior below T-c = 6 K. The magnetic structure corresponds to an alignment of the spins perpendicular to the network layers. In contrast, the manganese(II)-iron(III) compound expresses a two-dimensional antiferromagnetic ordering.