The magnetization curves for ammonia complex 10 show a pronounced field dependence with saturation occurring around 2.7 µB. They were fit to g = [2.01, 2.01, 2.07] (giso = 2.03) and D = -3.5(1) cm -1 (Figure , bottom). Fitting with D = +3.5 cm -1 also gave acceptable agreement with experimental data. At 10 K, the EPR spectrum of 10 shows features at geff = 6.15, 4.75, and 3.40, while signals at 2.36, 2.07, 2.05, and 1.99 are assigned to impurities (Figure , bottom). The spectrum was simulated as S = 3/2 with E/D = 0.106 using the g and negative D from the magnetization fit. An S = 1/2 impurity with g = [2.07, 2.05, 1.99] was included in the simulation in 1% relative abundance to the major S = 3/2 signal. D strain of 2.4 cm -1 (57% of D) was applied to account for the broad line shapes, though like 9, broadening could be compounded by unresolved hyperfine coupling to the ammine 14 N nucleus. A spectrum similar to that of 10 was reported for a square pyramidal ferric intermediate spin complex with E/D = 0.107. Simulations of the EPR spectrum with D = +3.5 cm -1 had a much smaller g = 6.15 component, which is inconsistent with the relatively intense signal seen experimentally. The g = 6.15 signal is most likely associated with transitions within the |±3/2⟩ doublet, and its high intensity at 10 K suggests that the ground state is |±3/2⟩, i.e. D < 0.