For a theoretical description of the ZFS in cisfac-[3] 3+ , we performed complete active space self-consistent field calculations with spin-orbit coupling and N-electron valence state perturbation theory to correct for the missing dynamic electron correlation (SOC-CASSCF(7,12)-NEVPT2, see SI for details). The calculations yielded D = -6.6 cm -1 and E = 1.65 cm -1 which reasonably agrees with the magnitude of the experimental ZFS, but gives the wrong sign for D. The same behavior has been observed for the V II analog of cisfac- [3] 3+ , where the calculated ZFS parameters showed good agreement with experimental data for selected active spaces, while for others, the sign of D was inverted. In summary, SQUID magnetometry and EPR spectroscopy yield a consistent picture of the electronic ground state of cisfac- [3] 3+ with a total electron spin S of 3 /2, ZFS parameters of D = 6.7(1) cm -1 and E = 0.8(5) cm -1 , gxx,yy,zz = [1.61(3), 2.12(5), 1.90 (3)] and an exchange coupling constant of J = -0.7 cm -1 (Table ). Literature reports on spin Hamiltonian parameters of monomeric molybdenum(III) complexes are scarce with many studies focusing on polynuclear compounds or clusters. Apparent g-values were reported for Mo(acac)3 (acac -= acetylacetonate), but the ZFS parameters were not explicitly considered in the analysis. Cisfac- [3] 3+ shows a significantly higher ZFS than cyanide-bridged Mo-Ni complexes with |D| values of 0.44 to 2.7 cm -1 .