Structure and bonding in Al3On and Al3On- aluminum oxide clusters where n = 1-3 are studied with electronic structure calculations and are compared with some experimental results. Geometry optimizations with the B3LYP/6-311+G(2d,p) density functional method produced minima which were verified with frequency calculations. Several initial geometries and distinct spin multiplicities were considered for each case. The most stable anionic structures from density functional calculations were confirmed with additional. geometry optimizations at the QCISD level. Equilibrium geometries, harmonic frequencies, and atomic charges. are presented. These results, in combination with previous assignments of anion photoelectron spectra, provide a consistent explanation for changes in isomerization energies between anionic and neutral species.