Does the Al ₁₃- core exist in the Al ₁₃ polyhalide Al ₁₃I _n- (n=1-12) clusters?

We have studied the structures and stabilities of Al13 In- (n=1-12) clusters at the density-functional level of theory. Unlike the case of Al13 I-, the Al13 In- (n=2-12) clusters do not have an Al13- core electronically. Population analysis shows that a significant charge transfer occurs from the Al cluster to the I atoms, where the populations for Al13 vary from -0.48 (Al13 I2-) to +0.97 (Al13 I12-). Moreover, the shape of Al13 moieties in the Al13 In- (n≥6 or 7) clusters is significantly distorted from the structure of Al13-, an icosahedron, and is a "cagelike" form, which can be explained by both electronic and steric reasons. Our theoretical results are in good agreement with the experimental observations of Bergeron [Science 307, 231 (2005)].