Magneto-optical Response of 3d‑Decorated Polyoxomolybdates with ε‑Keggin Structure

A family of virtually isostructural tetra-capped ε-Keggin-type polyoxomolybdate­(V) cluster compounds, [Mo12VO28(μ2–OH)10(μ3–OH)2­{MII(H2O)3}4]·nH2O ({M4IIMo12V}, M = Ni, Co), exhibits magnetic-field-dependent optical response in their electronic absorption spectra in the 0–33 T range. On the basis of Effective Hamiltonian Crystal Field calculations, we find that the observed field-induced decrease in reflectance of these compounds can be related to the formally spin-forbidden on-site d–d excitations. We tentatively position the observed effect among other known magneto-optical effects and predict that similar features may be found for other {M4IIMo12V} analogues.