Multinuclear metal complexes have been designed with ferromagnetic interactions between the metal centers by considering the topological network of d pi spin to the bridging ligand. The four complexes [Cu-3(tpa)(3)-(ta)](ClO4)(3).4H(2)O (1), [Fe-2(bpepm)(NCS)(4)] (2), [Fe-2(bpmar)(H2O)(4)](NO3)(4).3H(2)O (3), and [Cu-2(bpmar)(NCS)(2)] (4), with tpa = tris(2-pyridylmethyl)amine, H(3)ta = trimesic acid, bpepm = 4,6-bis[(bis(2’-pyridyrethyl)-amino)methyl]pyrimidine, and H(2)bpmar = 4,6-bis [(N,N-bis(2’-pyridylmethyl)amino)methyl]-2-methylresorcinol, have been synthesized, and crystal structures of 1 and 2 have been determined. Magnetic properties have been investigated in the 2-270 K temperature range. Central metal ions in each complex are cupric for 1 and 4, high spin ferrous for 2, and high-spin ferric species for 3, respectively. Magnetic susceptibility measurements for 1, 2, and 4 showed antiferromagnetic behavior, and the Weiss constants for the data above 100 K are -3.26, -3.86, and -2.09 K, respectively. Magnetic data for 3 have been quantitatively studied above 10 K and have revealed that 3 exhibits ferromagnetic coupling with a magnetic exchange coupling constant of J = +0.65(3) cm(-1) (where H = -2S(1)S(2)). The measurement of magnetization (M) versus the field (H) for 3 has shown that the quantum number of the total angular momentum (J) at 4.0 and 8.5 K is larger than J = 4, where the expected value (J) in absence of ferromagnetic interaction is 5/2. The ferromagnetic interaction in 3 was interpreted by the spin polarization of d pi spin to the ligand p pi orbital. Crystal data : [Cu-3(tpa)(3)(ta)](ClO4)(3).4H(2)O (1), monoclinic, space group C2/c, a = 36.228(8) Angstrom, b = 19.565-(3) Angstrom, c = 26.341(6) Angstrom, beta 122.07(1)degrees, V = 15821(6) Angstrom(3), Z = 8, R = 0.090 (R(w) = 0.096) for 4992 data points with F-o > 3 sigma(F-o); [Fe-2(bpepm)(NCS)(4)] (2), monoclinic, space group C2/c, a = 42.28(1) Angstrom, b = 13.467(4) Angstrom, c = 15.527(3) Angstrom, beta = 94.83(2)degrees, V = 8810(4) Angstrom(3), Z = 8, R = 0.050 (R(w) = 0.048) for 2676 data points with F-o > 3 sigma(F-o).