The dinuclear (Fe-II, Gd-III) complexes studied in this report derive from hexadentate Schiff base ligands abbreviated H2L' (i = 1, 2, 3). H2L1 = N,N'-bis (3-methoxysalicylidene)-1,3-diamino-2,2'-dimethyl-propane, H2L2 = N,N'-bis(3-methoxysalicylidene) -1,2-diamino-2-methylpropane, and H2L3 = N,N'-bis(3-methoxysalicylidene)-1,2-diaminoethane. The crystal and molecular structures of three complexes have been determined at 160 K. Depending on the solvent used in the preparation, (LFe)-Fe-1(CH3OH)Gd(NO3)(3)(CH3OH)(2), 1, or (LFe)-Fe-1((CH3)(2)CO)Gd(NO3)(3), 1', is obtained from H2L1. A similar complex, (LFe)-Fe-2((CH3)(2)CO)Gd(NO3)(3), 2, is obtained from H2L2. Complex 1 crystallizes in the orthorhombic space group Pca2(1) (No. 29): a = 22.141(3) Angstrom, b = 9.4159(16) Angstrom, c = 15,2075(17) Angstrom, V = 3170.4(7) Angstrom(3), Z = 4. Complexes 1' and 2 crystallize in the monoclinic space group P2(1)/c (No. 14): 1', a = 9.6264(17) Angstrom, b = 19.662(3) Angstrom, c = 16.039(3) Angstrom, beta = 95.15(2)degrees, V = 3023.6(9) Angstrom(3), Z = 4; 2, a = 9.7821(13) Angstrom, b = 18.7725(17) Angstrom, c = 16.100(2) Angstrom, beta = 96.497(16)degrees, V = 2937.5(6) A(3), Z = 4. Complexes 1, 1', and 2 possess an Fe(O-phenoxo)(2)-Gd core. The mononuclear (LFe)-Fe-3 complex could be prepared from H2L3 but not the related dinuclear (Fe, Gd) species. Mossbauer spectroscopy evidences that the iron center is in the +2 oxidation state for the six complexes. The experimental magnetic susceptibility and magnetization data of complexes 1, 1', and 2 indicate the occurrence of weak Fe-II-Gd-III ferromagnetic interactions. Single ion zero-field splitting of the iron(II) must be taken into account for satisfactorily fitting the data by exact calculation of the energy levels associated to the spin Hamiltonian through diagonalization of the full matrix for axial symmetry (1, J = 0.50 cm(-1), D = 2.06 cm(-1); 1', J = 0.41 cm(-1), D 3.22 cm(-1); 2, J = 0.08 cm(-1), D = 4.43 cm(-1)).