It is computationally impossible to quantitatively analyse the magnetic data of a molecule containing 30 x S = 5/2 spins via conventional matrix diagonalisation techniques. Even the finite-temperature Lanczos method which can approximately solve problems in Hilbert spaces with dimensions up to 10 11 cannot be applied here. We thus resort to a classical spin model and classical Monte Carlo (CMC). This allows approximations of the magnetisation and the magnitude of the exchange interactions to be obtained. Note however that classical spin models constitute a high-temperature approximation and thus can be inaccurate at (low) temperatures smaller than the typical interaction strength. Although there are nine different exchange interactions present in 1, DFT calculations (vide infra) suggest they can be grouped into two categories: strongly antiferromagnetic and weakly ferroor antiferromagnetic based on the larger Fe(tet)-O-Fe(tet/oct) angles and the smaller Fe(oct)-O-Fe(oct) angles, respectively. We therefore simplified the numerical simulations by employing a model with just two different J values representing these two different Fe-O-Fe exchange pathways. Simulations with one strong AF coupling of -20.85 ≤ 𝐽 𝑠 ≤ -27.80 cm -1 and one weak AF coupling of -6.95 ≤ 𝐽 𝑤 ≤ -11.82 cm -1 (𝐻 ̂= -∑ 𝐽 𝑖𝑗 𝑖<𝑗 𝑠 ⃗ ̂𝑖 • 𝑠 ⃗ ̂𝑗) come closest to replicating the magnetic observables (Figure ), being superior to a model containing just one exchange interaction, 𝐽 = -6.95 cm -1 . To further support the relative sign and magnitude of the coupling constants obtained above, we have performed DFT calculations (see the SI for the computational details) on model complexes derived from complex 1 (Figure ). These suggest that the nine independent exchange interactions (Scheme S1; Figures show the spin density plots) are in the range |J| ≈ 6-71 cm -1 (Table ). All the computed exchange interactions are antiferromagnetic, with the exception of 𝐽 3  where a weak ferromagnetic exchange of +14.3 cm -1 has been estimated. The large antiferromagnetic interactions originate from multiple strong overlap integrals between the SOMOs of Fe III centres bridged by 3/4-O 2-ions (Tables ). The overlap integral is much smaller for the 𝐽 3  exchange pathway where only one dominant dz 2 |pz|dz 2 overlap integral is found (Table ). This results in a very small contribution to the antiferromagnetic part of the interaction (JAF, where J = JAF + JF) resulting in a small ferromagnetic interaction overall (Table ). The results are in agreement with previous magneto-structural developed for oxo-bridged Fe III complexes in which the magnitude of J is dictated by the Fe-O-Fe angle and Fe-O/Fe distances, and with the results observed for [Fe17] and [Fe34] in which J(tet-oct) >> J(octoct).