“Selective Precipitation of Gadolinium Metallofullerenes with Lewis Acids”
Kristine Arvola, Khristina Rottinger, and Steven Stevenson (Advisor)
Stevenson Research Group, Chemistry, IPFW, Fort Wayne, IN 46805
[email protected] (260-481-6290)
Abstract
Experimental Details and Scheme
Goal: Recently, we crudely separated metallofullerenes from
empty-cage fullerenes using Lewis Acid chemistry. However,
there was poor selectivity among individual metallofullerenes
with this approach. Precipitation of the entire metallofullerene
family of compounds was due to not optimizing the precipitation
threshold for these species. The use of AlCl3 as the Lewis Acid
precipitated all metallofullerenes with a 1st oxidation potential
less than 0.7 V. In contrast, CuCl2 successfully decreases the
precipitation threshold to less than 0.2 V. In this manner, most
Gd metallofullerenes remain unreacted and in solution.
However, the most reactive species precipitate and can be
separated from the more inert Gd metallofullerenes. We have
further decreased this precipitation threshold by exploring the
use of “weaker” Lewis acids (CaCl2, ZnCl2, MgCl2) to achieve even
better selectivity. Results indicate an improved selectivity toward
individual metallofullerenes with these weaker Lewis acids. In
this presentation, we report a variety of alternative Lewis acids
and their feasibility of replacing CuCl2 and AlCl3.
Precipitation of Metallofullerenes by Lewis Acids:
Metallofullerene samples are
placed in a round bottom flask
and dissolved in CS2. While
stirring, a Lewis acid (e.g., CaCl2,
CuCl2 or AlCl3) is added to the
mixture to initiate selective
complexation and precipitation.
Decomplexation of Metallofullerenes from Precipitates:
Upon filtration, the solid material is placed in a beaker for
decomplexation with ice and water for subsequent workup
in a separatory funnel. Metallofullerenes dissolve in the CS2
organic layer. HPLC and MALDI mass spectral data evaluate
the effectiveness of our new Lewis acid, separation method.
MALDI Analysis: Mass spectral analysis is performed on a
Bruker Microflex LT mass spectrometer. Samples are
deposited on a stainless steel plate without using a matrix.
The analysis is performed in the positive-ion mode.
Conclusions
Results (Too Reactive Lewis Acids)
All Metallofullerenes React
AlCl3
Gd3N@C80
Gd@C81N
C70 C76
C78
C60
FeCl3
C60
Gd3N@C88
Gd2@C79N
C84
Gd@C81N
• Basis of Selective Precipitation: The
reactivity order of metallofullerenes with
Lewis acids follows the metallofullerene’s 1st
oxidation potentials.
Gd3N@C112
• Order of Metallofullerene Precipitation:
[1st to precipitate] most Gd2@C2n species,
Gd3N@C88 (0.06V), Gd3N@C84 (0.32V),
Gd3N@C86 (0.35V), Gd3N@C112, Gd2@C79N,
and Gd3N@C80 (0.58 V) [last to precipitate].
Rd 1 PPT
(4 h)
Gd3N@C80
C70
C76 C
• Lewis Acid Reactivity: Analysis of unreacted
material reveals a reactivity trend as follows:
(least reactive) CaCl2 < ZnCl2 < MgCl2 < CuCl2
< AlCl3 < FeCl3 (most reactive)
Rd 1 PPT
(4 h)
Gd3N@C88
Gd2@C79N
78
Gd3N@C112
C84
Funding
• NSF RUI CHE #1151668
Results (Separation of Gadolinium Metallofullerenes Using Reactivity Differences of Various Lewis Acids)
Least
Reactive
CaCl2
Mix of Gd2@C2n and Gd3N@C2n
Gd3N@C88
ZnCl2
Gd3N@C88
Gd2N@C114
C70
C76 C
78
C84
Gd2@C79N
No
Reaction
Gd3N@C86
Gd3N@C80
Rd 2 PPT
(7 d)
C60
Gd3N@C80
C70
C76 C
Gd3N@C80
78 C
Gd2@C79N
84
Gd3N@C112
C60
Gd3N@C86
Gd3N@C112
No
Reaction
Gd3N@C88
C70
Gd3N@C80
C76 C
78
C84
Gd2@C79N
Gd@C81N
Rd 2 PPT
(7 d)
C60
No
Reaction
C70
C76 C
Gd3N@C80
Gd3N@C86
Gd2@C79N
Gd2@C106
Gd3N@C80
78
C84
Gd2O@C110 or
Gd2N@C110
Gd2N@C114
Rd 1 PPT
(4 h)
Gd2O@C110 or
Gd2N@C110
Gd3N@C84
CuCl2
Gd2N@C114
Rd 1 PPT
(4 h)
Rd 2 PPT
(7 d)
C60
MgCl2
Gd2N@C114
Rd 1 PPT
(4 h)
Gd3N@C88
Most
Reactive