Incorporation of Mn12 single molecule magnets into mesoporous silica

Abstract

The incorporation of four Mn₁₂ derivatives, namely [Mn₁₂O₁₂(O₂CR)₁₆(H₂O)₄] (R = CH₃ (1), CH₃CH₂ (2), C₆H₅ (3), C₆F₅ (4)), into the hexagonal channels of the MCM-41 mesoporous silica has been studied. Only the smallest clusters 1 and 2, i.e. those with compatible size with the pores of MCM-41, could enter into the mesoporous silica. Powder X-ray diffraction analysis, HRTEM images and N₂ adsorption–desorption isotherm experiments show that the well-ordered hexagonal structure of MCM-41 is preserved and that the Mn₁₂ clusters are inside the pores. The magnetic properties of the MCM-41/2b nanocomposite material obtained in CH₂Cl₂ indicate that the structure of the cluster is maintained after incorporation on the MCM-41 walls, but some differences appear in the case of the MCM-41/1 and MCM-41/2a nanocomposite materials obtained in CH₃CN. Calcination of the composite samples leads to materials with magnetic properties that are very different from those obtained after calcination of pristine 1 and 2. The incorporation of the Mn₁₂ clusters inside the MCM-41 pores may induce the formation of new Mn–oxide nanoparticles after the loss of the carboxylate ligands. The incorporation of Mn₁₂ derivatives into UVM-7, a mesoporous silica with a hierarchical pore system at two different length scales, gives rise to similar results.