It is a challenge to synthesize clusters having a certain shape associated with a desirable property. In this study, we perform density functional calculations on ligand-protected Al-7 and Al-77 clusters. It is found that small ligands such as NH2 Still prefer the compact structure of bare Al clusters. However, large ligands such as N(SiMe3)(2) stabilize the experimentally observed shell-like structures due to the steric effect. This is different from the Ga-84 cluster case where small ligands can stabilize the experimental shell-like Ga-84 cluster. Our study suggests that the shape, and thus the properties, of clusters (for instance, C-3v Al-7 cluster has a finite dipole moment in contrast to the centrosymmetric D-3d cluster) can be controlled by using ligands with different sizes.