A high spin (S) compound has been synthesized whose properties straddle the interface between the classical and quantum mechanical spin descriptions. The cluster [Mn7O4(pdpm)(6)(N-3)(4)](ClO4)(2) (Mn-7) has an unprecedented core structure comprising an octahedral [Mn-6(III)(mu(4)-O)(mu(3)-O)(3)(mu(3)-N-3)(4)](6+) unit with one of its faces capped by a Mn ion. Magnetization and susceptibility studies indicate an S = (29)/2 ground state, the maximum possible. Variable-temperature, high-frequency electron paramagnetic resonance (HF-EPR) spectra on powder and single-crystal samples of Mn-7 exhibit sharp spectral features characteristic of a quantum spin that are well resolved in a certain temperature range but which transform to a continuum of peaks characteristic of :a classical spin m another; these features have,been well reproduced by computer simulations. A fast. transform analysis of the sharp spectral features and the low temperature EPR. spectra suggests that more than one spin state are involved.