EMSL Bimonthly Report: June 2007 through July 2007 Page: 3 of 19
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theory (DFT) calculations to observe and
characterize Au16- and Au17 doped with a Cu
atom (Cu@Au1 and Cu@Au17-).
Figure 1 shows the spectra of CuAu16- and
CuAu17- ions along with the of the parent gold
clusters. First, we focus on the CuAu16- ion
(Figure 1b), whose PE spectrum is remarkably
similar to that of its parent gold cluster Au1w-
(Figure 1a). The similarity between the spectra
of these two species suggests that Cu doping
does not alter the geometric and electronic
structures of the Au1w- cluster anion significantly,
which is only possible if the Cu is trapped inside
the Au1w- cage.a) Au,~ c c) Auf
A t
Im Ir B D u I~
b) Cu@Auc d ) CuSAu1g
' i " " C
1 "2, .3 "4 5 6 1 .2. .3 ;4 5 6
E eV- EIeV-
Figure 1. Photoelectron spectra of the cluster anions CuAu16 and
CuAu1- (Figures lb and ld), compared to the parent gold clusters
Au6 and Aun- (Figures la and ic).The spectrum of the doped cluster anion CuAu17- is also very similar to that of the parent gold cluster Au17,
except that there is one low-binding-energy peak followed by a large energy gap in the spectrum of the
Cu-doped cluster (Figures1 c and d). This spectral similarity again suggests that the Cu dopant induces very
little structural change in the Au17- cage except that it donates one electron. Au17- is a closed-shell species
with 18 valence electrons; therefore, the extra electron is expected to enter its lowest occupied molecular
orbital and give rise to the low-binding-energy peak (X) in the PE spectrum of the CuAu17- cluster anion
(Figure 1d). All these observations again imply that Cu stays in the center of the Au17 ion cage (Cu+@Au172)
and does not perturb the electronic and geometric structures of the cage significantly.
We carried out theoretical studies to confirm theseobservations. The results revealed that the
endohedral Cu@Au16 and Cu@ Au17 cluster anions
are overwhelmingly favored over any other structure
with the Cu atom on the outside of the cage. Figure 2
shows the simulated PE spectra for two endohedral
structures each for the Cu@Au16 and Cu@Au17-
cluster anions along with those of the parent clusters.
In one structure, the Cu atom is located in the center
of the cages, and in the other structure, it is displaced
slightly from the center. The energy differences
between the two isomers are very small, and their
simulated PE spectra are also very similar to each
other. The calculated vertical detachment energies for
the Cu@Au1- and Cu@Au17- cluster anions also are
in good agreement with the experimental values.
Overall, the excellent agreement between theory and
experiment unequivocally confirms the endohedral
structures of these Cu-doped gold cages.a) Aus
tiai
b) CuCAu1,
c) Cu@Auj
1 2 3Ev -V
AB
BC
C
x
4 5 6d) AU.?
Jri
tt\ ABC D
e) Cu@AuiE
f) Cj@Au17A
1 2 3 4 5 6
Elev -Figure 2. Simulated photoelectron spectra for two
endohedral structures each for Cu@Au16 and Cu@Aul;
along with those for Au16 and Au1;.Doping gold clusters could be a powerful way to tune their chemical and physical properties, and the results
reported in this highlight suggest that a new class of endohedral gold cages is indeed viable. In these
examples, the cage structures of Au16- and Au17 cluster anions are maintained simply by changing the
dopants, which is reminiscent of the behavior of endohedral fullerenes. It would be particularly interesting to
dope transition-metal atoms inside these gold cages to create magnetic gold clusters as the resulting material
may exhibit new, physical, chemical, and catalytic properties that are distinct from the pure gold clusters.2
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Showalter, Mary Ann. EMSL Bimonthly Report: June 2007 through July 2007, report, October 3, 2007; Richland, Washington. (https://digital.library.unt.edu/ark:/67531/metadc842997/m1/3/: accessed March 28, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.