The difficulty of reaching the Haldane phase for S ≥ 2 is largely because the size of the Haldane gap relative to the intrachain exchange, ∆/J 1 , decreases significantly from ∆/J 1 = 0.41 for S = 1 to ∆/J 1 = 0.087 for S = 2, making the gap both more sensitive to the presence of single-ion anisotropy and non-Heisenberg exchange interactions, and harder to detect when present. These challenges have meant that although AFM S = 2 spin chains which could be candidates to host the Haldane phase have been identified, the S = 2 gap has not yet been observed. The combination of modularity and low-dimensionality of MOMs means they are an ideal platform to search for the S = 2 Haldane phases. However, the most synthetically accessible S = 2 transition metal ion is Fe 2+ , which typically possesses large single ion anisotropy due to its partially quenched 5 T 2g ground state, and other S = 2 ions, Mn 3+ and Cr 2+ , are usually sensitive to reduction or oxidation in ambient conditions. As a result, the chemistry of MOMs which could host S = 2 Haldane phases is comparatively underexplored, and their quantum states thus unrealised.