Extended metal atom chains (EMACs) are molecular linear arrangements of metal atoms featuring magnetic properties. By means of the density functional theory (DFT), we have studied the magnetic coupling constants for [Cu3(dpa)4Cl2]+, Ni3(dpa)4Cl2 and Ni5(tp- da)4Cl2 to understand which is the origin of the previously reported theoretical underestimation of J for nickel complexes. We have decomposed J = Js + Jd, finding that the former contribution is underestimated and the latter part is overestimated at the DFT/ B3LYP level of computation. Varying the amount of Hartree-Fock exchange, we show that the B3LYP functional fails to describe the s interaction properly, whereas the d coupling is exaggerated.