Optical Detection of Spin Polarization in Single-Molecule Magnets [Mn12O12(O2CR)16(H2O)4]

A magneto-optical study has been undertaken of the mixed-valence single-molecule magnet [MnIV4MnIII8O12L16] in which the ligands, L, are acetate (Mn12Ac) or the long-chain carboxylic acid, C14H29COOH (Mn12C15), that confers better solubility in organic solvents. Thin polymer films of these compounds in poly(methyl methacrylate) (PMM) have been cast by solvent evaporation to provide samples suitable for variable-temperature and field magnetic circular dichroism (MCD) studies. The absorption spectra in isotropic light are featureless, whereas the low-temperature MCD spectra contain resolved peaks, both positive and negative. MCD magnetization curves measured at temperatures above 4.2 K have established a ground-state spin of S = 10 and an axial zero-field parameter, D, of −0.61 K, similar to that determined for single crystals of Mn12Ac. By studying at a variety of optical wavelengths, the polarization ratios of the optical transitions relative to the unique axis of the zero-field distortion have been deter...