50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90

48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90

Cs@Cn

48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90

K@Cn

Rb@Cn

Group I Group I MetallofullerenesDonate 1 electron to cage M+@C2n

− Distribution similar to empty cages C60 and C70 dominant

n = 60

n = 70

42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80

44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80

Ca@Cn

Ba@Cn

44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80 82 84

Sr@Cn

Group II metals• Donate 2 electron to cage M2+@C2n

2−

• M@C50 exhibits dominance as well as M@C60 M@C70 no longer dominant

n = 50 60

36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70

36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80

Sc@Cn

Y@Cn

Group III metals• Donate 3 electron to cage• M3+@C2n

3−

• Now, M@C44 dominates • M@C50 is also abundant.• M@C60 no longer dominates

n = 44

n = 50

n = 60

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 C60. Under conditions where empty cage C60 dominates of C2n distribution, the M@C2n 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

C84

+ carbon vapor

C84

1,1751,1701,165

m/z1,6001,5001,4001,3001,2001,1001,000900

1165 1170 1175

Gd@C82 Gd@C82 calculated

Gd@C84

Metallofullerenes “grow slower” than empty cages in carbon vapor?

+ carbon vapor

C84

m/z20001900180017001600150014001300120011001000900800700600

Compare Gd@C80 to C84

from our Nature Communications paper

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90

Cs@C2n

48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90

Rb@C2n

42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80

Ca@C2n

44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80

Ba@C2n

36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70

Sc@C2n

36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80

Y@C2n

Cs@C60

Cs@C70

Ca@C50

48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90

K@C2n

K@C60

K@C70

Rb@C70

Rb@C60

Ba@C50

Ca@C60

Sc@C44Ca@C70

Ba@C70

Ba@C60

44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80 82 84

Sr@C2n

Sr@C60

Sr@C50

Sr@C70

Sc@C50

Sc@C60

Y@C50Y@C44

Y@C50

Group I metals• Donate 1 electron to cage• M+@C2n

−

• Distribution similar to empty cages (ie, C60 and C70 dominate)

Group II metals• Donate 2 electron to cage• M2+@C2n

2−

• M@C50 exhibit much greater abundance, although M@C60 just a bit more dominate. M@C70 forms in lower abundance

Group III metals• Donate 3 electron to cage• M3+@C2n

3−

• Now, M@C44 dominates over other endo cages. M@C50 is also highly abundant.

• M@C60 no longer dominates

Comparison of Group I, II, III metallofullerene growth distributions

m/z20001900180017001600150014001300120011001000900800700600

Metallofullerenes “grow slower” than empty cages in carbon vapor?

La2@C80

+ carbon vapor

m/z

1,8001,7001,6001,5001,4001,3001,2001,1001,000

La2@C82

La2@C80

C84

+ carbon vapor

C84

Compare growth of La2@C80 to C84

from our Nature Communications paper

C84

+ carbon vapor

C84

1,1751,1701,165

m/z1,6001,5001,4001,3001,2001,1001,000900

1165 1170 1175

Gd@C82 Gd@C82 calculated

Gd@C84

Metallofullerenes “grow slower” than empty cages in carbon vapor?

+ carbon vapor

C84

m/z20001900180017001600150014001300120011001000900800700600

Compare Gd@C80 to C84

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, M@C2n 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 M3+@C2n

3-

La, Ce, Pr, Nd, Pm, Gd, Tb, Dy, Ho, Er, Lu

• And those that only transfer 2 electrons to cage M2+@C2n

2-

Sm, Eu, Tm, Yb

36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80

La@C2n

36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80

Ce@C2n

36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80

Pr@C2n

42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80

Sm@C2n

42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80

Eu@C2n

36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80

Tb@C2n

36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80

Dy@C2n

36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80

Ho@C2n

36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80

Er@C2n

36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80

Nd@C2n

44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80 82

Yb@C2n

36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80

Lu@C2n

36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80

Gd@C2n

Comparison of Lanthanides

La@C44

La@C50

La@C60

Tb@C44 Tb@C50

Tb@C60

Sm@C44

Sm@C50

Sm@C70

Sm@C60

M3+@M@C2n3− Lanthanides

M2+@M@C2n2− Lanthanides

• Striking difference for Sm, Eu, Tm, Yb

These are M2+@M@C2n2−

M@C60 > M@C50 >M@C70

M@C44 is weak

Matches Group II metal M@C2n distributions (for example, Sr@C2n below), which can, of course, only donate 2 electrons

36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80

La@C2n

42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80

Sm@C2n

Comparison of Lanthanides

La@C44La@C50

La@C60

Sm@C44

Sm@C50

Sm@C70

Sm@C60

M3+@M@C2n3− Lanthanides

M2+@M@C2n2− Lanthanides

• La, Ce, Nd, Gd, Tb, Dy, Ho, Er, Lu all exhibit the same distributions

M@C44 > M@C50 >M@C60

M@C60 relatively weak for these M3+@M@C2n

3− Lanthanides

Matches the growth distributions of the Group III metals….for example, Y@C2n below

44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80 82 84

Sr@C2n

Sr@C60

Sr@C50

Sr@C70

36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80

Y@C2nY@C50Y@C44

Y@C50

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 C60. Under conditions where empty cage C60 dominates of C2n distribution, the M@C2n 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