  We present a joint experimental and theoretical characterization of the
magnetic properties of coordination clusters with an antiferromagnetic core of
four magnetic ions. Two different compounds are analyzed, with Co and Mn ions
in the core. While both molecules are antiferromagnetic, they display different
sensitivities to external magnetic field, according to the different strength
of the intra-molecular magnetic coupling. In particular, the dependence of the
magnetization versus field of the two molecules switches with temperatures: at
low temperature the magnetization is smaller in \{Mn$_4$\}, while the opposite
happens at high temperature. Through a detailed analysis of the electronic and
magnetic properties of the two compounds we identify a stronger magnetic
interaction between the magnetic ions in \{Mn$_4$\} with respect to \{Co$_4$\}.
Moreover \{Co$_4$\} displays not negligible spin-orbit related effects that
could affect the spin lifetime in future antiferromagnetic spintronic
applications. We highlight the necessity to account for these spin-orbit
effects for a reliable description of these compounds.
