A. R. Lotz, M. Fröba
Analysis and Measurements. Powder X-ray diffraction patterns were
recorded at room temperature with a Bruker AXS D8 Advance
diffractometer (Cu Kα) in θ/θ geometry with a secondary mono-
chromator.
Physisorption measurements were carried out using a Quanta-
chrome Autosorb 6 instrument with nitrogen as adsorptive at 77 K.
The BET surface areas were calculated from p/p0 ϭ 0.03 Ϫ 0.3
in the adsorption branch. The BJH pore size distributions were
calculated from the desorption branch; the DFT pore size distri-
butions were determined using the equilibrium model. Before each
sorption measurement the sample was outgassed at 40 °C for 10
days under turbomolecular pump vacuum.
The transmission electron micrographs were recorded on a Philips
CM 30 ST.
Thermogravimetry measurements were carried out on a Netzsch
STA 409 C instrument using Al2O3 crucibles under nitrogen with
a heating rate of 10 °C/min.
Figure 8 DFT pore size distributions of pristine SBA-15 silica
(dashed) and [Au55(PPh3)12Cl6]@SBA-15 after stirring in dichloro-
methane.
Conclusion
Two different pathways for the preparation of the cluster
compound Au55(PPh3)12Cl6 within mesoporous SBA-15 sil-
ica have been investigated: Incorporation of pre-formed
clusters and intra-pore synthesis. The X-ray reflections of
the silica matrix decrease considerably in intensity due to
the filling of the pores with the guest species. The preser-
vation of the host structure and the presence of Au55 clus-
ters inside the pore system is confirmed by nitrogen physi-
sorption and transmission electron microscopy. The BET
surface area of the host/guest compounds is strongly re-
duced compared to pristine silica and the DFT pore diam-
eter changes from 7.0 to 5.0 nm. TEM images show the
individual clusters arranged within the mesopores at the
walls, bulk formation on the outer surface does not occur.
The Au55 clusters can be decomposed to metallic gold
within the pores by annealing, whereas the resulting particle
size depends on the temperature. In summary we could
show that the formation of the ligand-stabilized cluster
compound Au55(PPh3)12Cl6 within the pores of mesoporous
SBA-15 silica is possible via different pathways, resulting in
very similar products.
resulting gel was transferred into a Teflon-lined steel autoclave and
heated up to 80 °C for 24 hours. The resulting white powder was
washed several times with warm deionized water, and the surfac-
tant was removed by calcination at 550 °C for 24 h (heating rate:
1 °C/min).
Synthesis of pristine Au55(PPh3)12Cl6. The synthesis of
Au55(PPh3)12Cl6 was carried out following ref. 28 under an argon
atmosphere and using dried solvents. Diborane(6) was generated
by dropping 100 mL of BF3-ether into a stirred mixture of 20 g
of Na[BH4] and 100 mL of 1,2-dimethoxyethane. The stream of
diborane(6) was passed through a Dry Ice condenser and a trap
cooled with Dry Ice and then fed into a solution of 3.94 g of
AuCl(PPh3) and 150 mL of benzene. The temperature was in-
creased to 55 °C. After the diborane(6) evolution, taking approx.
40 min, had finished, the reaction mixture was cooled down to
room temperature and the atmosphere of diborane in the apparatus
was driven out by a stream of argon. The dark precipitate was
removed by filtration and washed with benzene and pentane. Then
the raw product was treated with 100 mL of dichloromethane. The
red-brown solution was filtered through membrane filters (What-
man Anotop 25 0.2 µm) to remove any traces of colloidal gold.
The solvent was rapidly evaporated and the filtered product was
dried under vacuum.
Acknowledgements. Financial support by the Fonds der Chem-
ischen Industrie is gratefully acknowledged. We thank Dr. Jan
Hanss (University of Augsburg) for carrying out the thermal analy-
sis.
Incorporation of Au55(PPh3)12Cl6 into SBA-15 silica. 0.5 g of SBA-
15 silica was added to a solution of 0.45 g of Au55(PPh3)12Cl6 in
50 mL in dichloromethane. The suspension was stirred for 30 min
at room temperature. The solvent was evaporated and the obtained
host/guest compound was dried under vacuum.
References
Intra-pore synthesis of Au55(PPh3)12Cl6 within SBA-15 silica. The
synthesis was carried out as described above for the pristine cluster
compound, but 1.4 g of SBA-15 silica were added to the solution
of AuCl(PPh3) in benzene before starting the reaction.
[1] G. Schmid, R. Boese, R. Pfeil, F. Bandermann, S. Meyer, G.
H. M. Calis, J. W. A. van der Velden, Chem. Ber. 1981, 114,
3634.
[2] G. Schmid, B. Corain, Eur. J. Inorg. Chem. 2003, 3081.
[3] U. Simon, Adv. Mater. 1998, 10, 1487.
Annealing of [Au55(PPh3)12Cl6]@SBA-15. The host/guest com-
pound was heated up at air to 150 °C, 200 °C and 250 °C with a
heating rate of 1 °C/min.
[4] G. Schmid, R. Pugin, Th. Sawitowski, U. Simon, B. Marler,
Chem. Commun. 1999, 1303.
Leaching of the guest species. The host/guest compound was stirred
in dichloromethane at room temperature for 10 minutes. The sus-
pension was filtered and the resulting powder was dried under vac-
uum.
[5] G. Schmid, N. Beyer, Eur. J. Inorg. Chem. 2000, 835.
[6] G. Schmid, U. Simon, Chem. Commun. 2005, 697.
[7] O. Vidoni, T. Reuter, V. Torma, W. Meyer-Zaika, G. Schmid,
J. Mater. Chem. 2001, 11, 3188.
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