Magnetocaloric effect in a high-spin ferromagnetic molecular cluster

The reaction of MnCl₂·4H₂O with HL ((1-methyl-1H-imidazol-2-yl)methanol) and pdH₂ (1, 3 propanediol) in a basic MeCN solution results in the formation of a mixed-valence [Mn₂₀] cationic cluster and two [Mn^IICl₄] counter anions. The metallic skeleton of the cluster describes two geometrically equivalent mixed-valent, linked [Mn^III ₆Mn^II ₄] supertetrahedra in which nearest-neighbor metal ions have a different oxidation state. Magnetic susceptibility, magnetization data and heat capacity measurements support evidence of predominant ferromagnetic correlations, leading to a <i>s</i> = 22 spin ground state for the [Mn^III ₆Mn^II ₄] supertetrahedra, which are pair-linked by a weak antiferromagnetic coupling. The properties are discussed in the context of the magnetocaloric effect and the potential application of this compound in cryogenic refrigeration.