We completed the spectroscopic investigation of cisfac- [3] 3+ by solid state X-band EPR spectroscopy (9.6 GHz) at 10 K to cover transitions in the low energy region. We obtained a rich spectrum that can only be reasonably simulated by including an exchange interaction term 92 JS1 T S2 with a coupling constant of J = -0.7 cm -1 in Eq. 1 (Figure ). This hints to a small antiferromagnetic interaction between complex cations in the solid state or an impurity that forms over time when the air-sensitive complex decomposes. However, the simulated spectrum was not able to reproduce all signals that were found experimentally, indicating a more complex interaction scheme in cisfac- [3] 3+ . We did not observe this coupling in the HFEPR spectra (Figure ) because of the large line width of the signals and the high value of D compared to the magnitude of the interaction J (Table ). Hence, the HFEPR spectra are dominated by signals arising from ZFS.