The numerical simulations of the magnetic properties of extended three-dimensional networks containing M(II) ions with an S = 5/2 ground-state spin have been carried out within the framework of the isotropic Heisenberg model. Analytical expressions fitting the numerical simulations for the primitive cubic, diamond, together with (10-3) cubic networks have all been derived. With these empirical formulas in hands, we can now extract the interaction between the magnetic ions from the experimental data for these networks. In the case of the primitive cubic network, these expressions are directly compared with those from the high-temperature expansions of the partition function. A fit of the experimental data for three complexes, namely [(N(CH3)(4)][Mn(N-3)] 1, [Mn(CN4)](n) 2, and [Fe-II(bipy)(3)][Mn-2(II)(ox)(3)] 3, has been carried out. The best fits were those obtained using the following parameters, J = -3.5 cm(-1), g = 2.01 (1); J = -8.3 cm(-1), g = 1.95 (2); and J = -2.0 cm(-1), g = 1.95 (3).