Mössbauer spectrum of 2 in acetonitrile, recorded at 4.2 K in parallel field as indicated. Solid lines are spectral simulations based on an S = 1 spin Hamiltonian[23] using the zero-field splitting parameters D = +27 cm−1, E/D = 0, 57Fe magnetic hyperfine tensor Ax,y,z/gnβ = (−23.7,−20.5, −4.5) T, quadrupole parameters ΔEQ = 0.73 mm·s−1, η = 1, and isomer shift δ = 0.05 mm·s−1.