Single-crystal parallel-mode EPR spectroscopy of an S=6 ground-state transition-metal cluster -: art. no. 134424

We present a parallel-mode EPR study of a very high-spin ground-state cluster complex [Cr12O9(OH)(3)(O2CCMe3)(15)], where Me indicates the methyl group. This high-symmetry (D-3) molecule has a well-isolated S=6 ground state characterized by D=+0.088 cm(-1), E=0, g(zz)=1.965, g(xx)=g(yy)=1.960. Low-temperature (5 K) single-crystal and powder parallel- and perpendicular-mode EPR spectra are presented. The forms of the spectra are discussed with respect to the composition of the wave functions as a function of the angle of the static magnetic field to the molecular Z axis, the selection rules of the two excitation modes, and the resultant transition probabilities. This is the largest spin state studied by parallel mode EPR spectroscopy to date, and the results demonstrate the applicability of parallel-mode EPR to high-spin ground-state molecular clusters such as single-molecule magnets.