Incorporation of Mn12 single molecule magnets into mesoporous silica

The incorporation of four Mn-12 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 N-2 adsorption-desorption isotherm experiments show that the well-ordered hexagonal structure of MCM-41 is preserved and that the Mn-12 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 Mn-12 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 Mn-12 derivatives into UVM-7, a mesoporous silica with a hierarchical pore system at two different length scales, gives rise to similar results.