Al-27 NMR longitudinal relaxation times, T-1,T-obs(Al-27), of [Al(acac)(3)] and [Al(hfa)(3)] (Hacac = acetylacetone, Hhfa = hexafluoroacetylacetone) in CH3CN and CO2 were measured over a wide range of temperature and pressure. The rotational correlation times, tau(r), of the tris(beta-diketonato)aluminum(III) complexes were determined from T-1,T-obs(Al-27) using Al-27 quadrupole coupling constants, eQq/h(Al-27), which were also obtained to be 3.11 and 3.22 MHz for [Al(acac)(3)] and [Al(hfa)(3)], respectively, in CD3CN by the dual spin probe technique in the present study. At each temperature, tau(r) increased almost linearly with increasing viscosity, eta, in both CH3CN and CO2; however, tau(r) in CO2 at near critical densities deviated appreciably upward, as shown in a similar analogue of bis(acetylacetonato)beryllium(II), [Be(acac)(2)] (Umecky; et al. J. Phys. Chem. B 2002, 106, 11114). The eta/T dependence of tau(r) was examined to discuss intermolecular interactions between the complexes and solvent molecules in terms of the fluorination and geometrical effects. The degree of solute-solvent interactions increases in the order [Be(acac)(2)] < [Al(hfa)(3)] < [Al(acac)(3)] in CH3CN and [Al(acac)(3)] < [Be(acac)(2)] < [Al(hfa)(3)] in CO2. The results suggest that dipolar CH3CN molecules interact with negatively charged oxygen atoms in the complexes, whereas nonpolar CO2 prefers fluorinated substituents as well as quasi-aromatic rings in the ligands. Moreover, the relationship between the rotational and translational motions of tris(acetylacetonato)metal(III), [M-III(acac)(3)], in CO2 was investigated.