where B is the magnetic field, Ŝi = ( Ŝx,i , Ŝy,1 , Ŝz,i ) T the spin operator of the respective spin center (1 and 2 for the two Cobalt ions, b for the radical bridge) and µ B the Bohr magneton. In line with the inversion symmetry of the compound, the same Zeeman tensors g and axial ZFS parameters D are used for both metal centers, as well as the same isotropic exchange coupling parameter J for the interaction of each Co(II) ion with the radical bridge. The g-tensor of the radical bridge is denoted g b and will be assumed to be isotropic with a fixed value of 2.0. The best agreement between experiment and simulation is obtained by using an axial ZFS value of D = -145(29) cm -1 , as well as principal values of the g-tensor of g x = 2.13 (14), g y = 2.13( ) and g z = 3.1(1) for the two Co(II) centers, and an antiferromagnetic exchange coupling parameter of J = 322(88) cm -1 . However, the least-squares fit reveals a large covariance of the parameters D and J and a sizeable error bar for both parameter values. Hence, the susceptibility curve alone does not give sufficient physical insight into the system, which prompted us to tackle this system by a combined spectroscopic and theoretical approach.