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, [Mo12(V)O28(μ(2)–OH)10(μ(3)–OH)2{M(II)(H2O)3}4]·nH2O ({M4(II)Mo12(V)}, 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 {M49(II)Mo12(V)} analogues.