Interplay of Spin-Orbit Coupling and Exchange Coupling in Compound 2. The computed energy levels for compound 2 (Fig. ) indicate that its electronic structure is substantially more complex than that of 1. From these states and their corresponding magnetic moments, we can also compute the temperature-dependent magnetic susceptibility and find a very good agreement with the experimental data (Fig. ), demonstrating the accuracy of the computed energy levels. In addition to the salient feature of the electronic structure of 1, which is the presence of a low-lying excited quartet that strongly mixes with the ground state by spin-orbit coupling, for 2 also strong exchange couplings between the radical bridge and the cobalt ions must be considered. As a first step, we have analyzed the exchange coupling by fitting the electronic states, computed without including spin-orbit coupling, to a simple Heisenberg Hamiltonian of the type Ĥ = J Ŝi • Ŝj . As shown in the supporting information Section S3.4, the computed electronic levels can be well understood as four intertwined spin ladders, of which the central two are degenerate, resulting from two quartet states on each cobalt ion coupled to a doublet state on the central bridge. Due to the inversion symmetry of the complex, the exchange coupling strength (J = 316 cm -1 ) of both cobalt ions to the radical must be the same, while direct exchange coupling between the cobalt sites can be neglected. The computations confirm antiferromagnetic exchange coupling leading to a ferrimagnetic sextet (S = 5 2 ) ground state, and S = 3 2 , 1 2 , 1 2 , 3 2 , 5 2 , 7 2 excited states for each spin ladder.