We have recently developed a computational methodology to separate the effects of size, composition, symmetry and fluxionality in explaining the experimental photoelectron spectra of mixed-metal clusters. This methodology was successfully applied first in explaining the observed differences between the spectra of Al₁₃^- and Al₁₂Ni^- and more recently to explain the measured spectra of Al_nMo^-, n=3-5,7 clusters. The combination of our approach and new synthesis techniques can be used to prepare cluster based materials with tunable properties. In this work we use the methodology to predict the spectrum of Al₆Mo^-. This system was chosen because its neutral counterpart is a perfect octahedron and it is distorted to a D_3d symmetry and was not observed in the recent experiments. This high symmetry cluster bridges the less symmetric Al₅Mo^- and Al₇Mo^-structures. The measured spectra of Al₅Mo^- has well defined peaks, while that of Al₇Mo^-does not. This can be explained by the fluxionality of Al₇Mo^-, as at least 6 different structures lie within the range that can be reached by thermal effects. We predict that Al₆Mo^- has well defined peaks, but some broadening is expected as there are two low-lying isomers, one of D_3d and the second of D_3h symmetry that are only 0.052 eV apart.