2n 2n 2n 2n 2n 2n n n Group I metals Donate 1 electron to cage M 2n − Distribution similar to empty cages (ie, C 60 and C 70 dominate) Group II metals Donate 2 electron to cage M 2n 2− exhibit much greater abundance, although 60 just a bit more dominate. 70 forms in lower abundance Group III metals Donate 3 electron to cage M 2n 3− Now, 44 dominates over other endo cages. 50 is also highly abundant. 60 no longer dominates Comparison of Group I, II, III metallofullerene growth distributions

Metallofullerenes “grow slower” than empty cages in carbon vapor? La 80 + carbon vapor m/z 1,8001,7001,6001,5001,4001,3001,2001,1001,000 La 82 La 80 C 84 + carbon vapor C 84 Compare growth of La 80 to C 84 from our Nature Communications paper

C 84 + carbon vapor C 84 Metallofullerenes “grow slower” than empty cages in carbon vapor? + carbon vapor C 84 Compare 80 to C 84 from our Nature Communications paper

Does more charge transfer from metal to cage render metallofullerenes less reactive? That could explain striking difference in growth of metallofullerenes vs empty cages Thus, as one moves from Group I to Group III metals, 2n should become less reactive due to more transfer to cage. Thus, Group III would exhibit a greater distribution of smaller fullerenres than Group II, and Group I A good test of this is to look at the Lanthanides It is known there are two groups of lanthanides, those that transfer 3 electrons to cage  M 2n 3-  La, Ce, Pr, Nd, Pm, Gd, Tb, Dy, Ho, Er, Lu And those that only transfer 2 electrons to cage  M 2n 2-  Sm, Eu, Tm, Yb

2n 2n 2n 2n 2n 2n 2n 2n 2n 2n 2n 2n 2n Comparison of Lanthanides M 3+ 2n 3− Lanthanides M 2+ 2n 2− Lanthanides

Striking difference for Sm, Eu, Tm, Yb  These are M 2+ 2n 2−  60 >  44 is weak  Matches Group II metal 2n distributions (for example, 2n below), which can, of course, only donate 2 electrons 2n 2n Comparison of Lanthanides M 3+ 2n 3− Lanthanides M 2+ 2n 2− Lanthanides La, Ce, Nd, Gd, Tb, Dy, Ho, Er, Lu all exhibit the same distributions  44 >  60 relatively weak for these M 3+ 2n 3− Lanthanides  Matches the growth distributions of the Group III metals….for example, 2n below 2n n

Clear correlation to charge transfer and growth More charge transferred, the distribution of fullerenes shifts to very small metallofullerenes Thus, when more charge is transferred they “grow slower”. As the number of transferred electrons are increased, the growth distribution is shifts to smaller fullerenes. This can explain why the larger metallofullerenes appear to only form as a small fraction of, for example, empty cage C 60. Under conditions where empty cage C 60 dominates of C 2n distribution, the 2n distributions exhibits mostly small fullerenes…….which will likely “react away” in the solid state, in solution, or air. Charge transfer appears to be extremely important in determining metallofullerenes formation. It is likely the most important growth factor