Nanoscaled Sn and Pb particles aligned in Al2O3 tubes obtained from molecular precursors

Article abstract of DOI:10.1002/ejic.200500368

Tin and lead nanoparticles and metal sponges were prepared by reducing Me₂Si(NtBu)₂Sn (7) and Me₂Si(NtBu) ₂Pb (9) with [H₂AlOtBu] (3), [HAl(OtBu)₂] (13), [H₂AlOSiMe₂tBu] (8), and [(Me₂tBuSiO) ₂AlH] (15). Together with dihydrogen and the metals in their elemental state the monomeric compounds [Me₂Si(NtBu) ₂Al(OSiMe₂tBu)(THF)] (10) and [Me₂-Si(NtBu) ₂Al(OtBu)(THF)] (11) can be obtained, to mention only two examples. Each monomer is stabilized by a THF molecule coordinated to aluminum, which on sublimation loses its donor molecule and dimerizes through Lewis acid-base interactions to the spiro compounds [Me₂Si(NtBu)₂AlO- SiMe₂tBu]₂ (12) and [Me₂Si(NtBu) ₂AlOtBu]₂ (4), respectively. The molecular structures of 10, 11, and 12 were determined by single-crystal X-ray diffraction techniques. The reduction of 7 at -115°C is gradually indicated by a color change of the reaction mixtures from red to dark brown with increasing temperature and depending on the reducing agent used. The tin powders that were obtained were identified as β-tin using X-ray powder diffraction techniques and their average crystallite size depends on the polarity of the solvent and hydride used. Under certain conditions metal sponges are formed. Pycnometric measurements were carried out on the tin and lead sponges. These showed almost the known densities for the metals when helium was used whereas significantly smaller ones were measured in water. Porous alumina membranes of different pore diameters were filled with tin and lead particles. Metal nanoparticles were prepared within the tubes of the membranes by reduction of the metal amides in the pores. The infiltration process can be repeated up to ten times increasing the amount of particles within the tubes monitored by SEM. The obtained brown or black membranes were characterized by SEM, EDX, and UV/Vis analysis. The filled membranes show sharp impervious ranges in the UV/ Vis spectrum between 270 and 525 nm and could therefore be used as wavelength filters. Wiley-VCH Verlag GmbH & Co. KGaA, 2005.

Full text of DOI:10.1002/ejic.200500368

FULL PAPER
Nanoscaled Sn and Pb Particles Aligned in Al2O3 Tubes Obtained from
Molecular Precursors
Michael Veith,*[a] Jacqueline Frères,[a] Peter König,[a] Oliver Schütt,[a] Volker Huch,[a] and
Joel Blin[a]
Keywords: Tin and lead clusters / Nanoparticles / Al2O3 tubes / Alignment of metal clusters / Alkoxy- and siloxyaluminum
amides
Tin and lead nanoparticles and metal sponges were prepared
by reducing Me2Si(NtBu)2Sn (7) and Me2Si(NtBu)2Pb (9)
with [H2AlOtBu] (3), [HAl(OtBu)2] (13), [H2AlOSiMe2tBu] (8),
and [(Me2tBuSiO)2AlH] (15). Together with dihydrogen and
the metals in their elemental state the monomeric com-
pounds [Me2Si(NtBu)2Al(OSiMe2tBu)(THF)] (10) and [Me2-
Si(NtBu)2Al(OtBu)(THF)] (11) can be obtained, to mention
only two examples. Each monomer is stabilized by a THF
molecule coordinated to aluminum, which on sublimation
loses its donor molecule and dimerizes through Lewis acid–
base interactions to the spiro compounds [Me2Si(NtBu)2AlO-
SiMe2tBu]2 (12) and [Me2Si(NtBu)2AlOtBu]2 (4), respectively.
The molecular structures of 10, 11, and 12 were determined
by single-crystal X-ray diffraction techniques. The reduction
of 7 at –115 °C is gradually indicated by a color change of
the reaction mixtures from red to dark brown with increasing
temperature and depending on the reducing agent used. The
tin powders that were obtained were identified as β-tin using
X-ray powder diffraction techniques and their average crys-
tallite size depends on the polarity of the solvent and hydride
used. Under certain conditions metal sponges are formed.
Pycnometric measurements were carried out on the tin and
lead sponges. These showed almost the known densities for
the metals when helium was used whereas significantly
smaller ones were measured in water. Porous alumina mem-
branes of different pore diameters were filled with tin and
lead particles. Metal nanoparticles were prepared within the
tubes of the membranes by reduction of the metal amides in
the pores. The infiltration process can be repeated up to ten
times increasing the amount of particles within the tubes
monitored by SEM. The obtained brown or black membranes
were characterized by SEM, EDX, and UV/Vis analysis. The
filled membranes show sharp impervious ranges in the UV/
Vis spectrum between 270 and 525 nm and could therefore
be used as wavelength filters.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2005)
siloxy- or alkoxyalanes in organic solvents leading to tin or
lead particles, together with dihydrogen and siloxy or al-
koxy compounds. A proposal for the mechanism of the for-
mation of the aluminum compounds is given in this report.
By controlling different parameters, e.g. temperature and
concentration of the starting materials, it was possible to
obtain tin and lead particles either stabilized as colloids or
as metal powders and sponges.
We have been able to insert the metal particles into po-
rous alumina membranes of different pore diameters. The
membranes were produced for our use by G. Schmid et al.,
who have already used such membranes for one-dimen-
sional ordering of gold colloids.[7]
Introduction
During the last years metal clusters and colloids have
become more and more important as building blocks in the
synthesis of organized nanostructured materials. Because of
the various applications of metal nanoparticles many arti-
cles have emerged, especially in the field of surface-en-
hanced spectroscopy or photocatalysis. In addition, studies
on the size-controlled synthesis and the self-assembly of
clusters have appeared.[1,2] Interestingly, the majority of the
publications deal with the synthesis and the properties of
transition or noble metal nanoparticles,[3] whereas compar-
atively little is known about colloidal nanoparticles of main
group metals.[4]
In this work we describe the preparation of tin and lead
colloids and clusters on the nanometer scale using chemical
control. The syntheses are based on an organometallic
route, which we have already described in former re-
ports.[5,6] In this route, tin and lead amides are reduced by
Results and Discussion
Syntheses and Reaction Mechanism
Tin and lead particles can be efficiently obtained by re-
duction of tin or lead amides with siloxy- or alkoxyalanes
in organic solvents. Besides dihydrogen, a siloxy- or an al-
koxyaluminum amide is formed through ligand exchange.
[a] Institut für anorganische Chemie, Universität des Saarlandes,
Postfach 151150, 66041 Saarbrücken, Germany
E-mail: veith@mx.uni-saarland.de
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In former publications we reported on the formation of
the alkoxy(amino)alane [(Me3Si)2N(H)AlOtBu] (1) in a re-
dox reaction between the lead amide Pb[N(SiMe3)2]2 (2)[8]
and a double equivalent of the tert-butoxyalane [H2Al-
OtBu] (3)[9] [Equation (1)].[6] The spirocyclic compounds
[Me2Si(NtBu)2AlOtBu]2 (4) and [Me2Si(NtBu)2AlOSiMe3]2
(5) have been obtained by stoichiometric reactions of
[H2AlOtBu] (3) or [H2AlOSiMe3] (6),[10] respectively, with
the cyclic diazastannylene Me2Si(NtBu)2Sn (7)[11] [Equa-
tion (2)].[5]
(1)
(2)
Figure 1. Selected bond lengths [Å] and angles [°] of 12: Si(1)–N(1)/
N(2) 1.746/1.742, Al(1)–N(1)/N(2) 1.838/1.827, Si(2)–N(3)/N(4)
1.746/1.744, Al(2)–N(3)/N(4) 1.832/1.834, Al(1)–O(1) 1.869, Al(1)–
O(2) 1.879, Al(2)–O(1) 1.822, Al(2)–O(2) 1.876, O(1)–Si(3) 1.718,
O(2)–Si(4) 1.713, N(1)–Si(1)–N(2) 90.89, N(1)–Al(1)–N(2) 85.43,
Al(1)–N(1)–Si(1) 91.65, Al(1)–N(2)–Si(1) 92.09, N(3)–Si(2)–N(4)
91.01, N(3)–Al(2)–N(4) 85.59, Al(2)–N(3)–Si(2) 91.65, Al(2)–N(4)–
Si(2) 91.65, Al(1)–O(1)–Al(2) 97.54, Al(1)–O(2)–Al(2) 97.42, O(1)–
Al(1)-(O2) 82.65, O(1)–Al(2)-(O2) 82.37.
Using a similar procedure we have recently treated the
stannylene Me2Si(NtBu)2Sn (7) with [H2Al(OSiMe2tBu)]
(8) and the plumbylene Me2Si(NtBu)2Pb (9) with [H2Al-
OtBu] (3) in equimolar ratios [Equations (3)–(5)]. We were
able to isolate the monomeric compounds [Me2Si(NtBu)2-
Al(OSiMe2tBu)(THF)] (10) and [Me2Si(NtBu)2Al(Ot-
Bu)(THF)] (11), each monomer being stabilized by a donor
solvent molecule [Equation (3)]. If the compounds 10 and
11 are sublimed, they release the solvent donors and dimer- former workup the crude products were directly sublimed
ize to the spiro compounds [Me2Si(NtBu)2Al(OSiMe2- [Equation (5)].
tBu)]2 (12) or to 4 [Equation (4)]. Both spirocyclic com-
The molecular structure of compound 12 (Figure 1) in
pounds can also be prepared in solution by heating the re- the crystal is very similar to those of compounds 4 and 5.[5]
action mixtures [Equation (4)]. The monomeric compounds Selected bond lengths and angles are given in the caption
10 and 11 have until now not been observed, and as in our of Figure 1 and are found within the expected ranges.
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Nanoscaled Sn and Pb Particles Aligned in Al2O3 Tubes from Molecular Precursors
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In Figures 2 and 3 some ball-and-stick representations of sums of the angle of 359.8° for 10 and 359.9° for 11. The
the structures of the compounds 10 and 11, which may be dimensions found in the rings and around the metal atoms
considered as molecular halves of the spirocyclic systems, are similar to those found in the corresponding spirocyclic
are shown.
molecules.
On treating the plumbylene 9 or the stannylene 7 with a
double equivalent of the monohydridoalane [(tBuSiO)2AlH]
(13) in THF, the spiro compound 4 was formed, along with
tri-tert-butoxyalane (14) [Equation (6)]. For this reaction,
we assume a mechanism as shown in Figure 4.
(6)
The corresponding reaction between the stannylene 7 and
two equivalents of the siloxyalane [(Me2tBuSiO)2AlH] (15)
did not lead to a spiro compound but to the monomeric
THF adduct 10 [Equation (7)]. A further product in this
reaction is most likely to be the alumosiloxane (Me2tBu-
SiO)3Al (16), but we have not been able to isolate or ident-
ify this compound yet.
Figure 2. Selected bond lengths [Å] and angles [°] of 10: Si(1)–N(2)
1.745, Si(1)–N(1) 1.730, Al(1)–N(1) 1.831, Al(1)–N(2) 1.824, Al(1)–
O(1) 1.727, Al(1)–O(2) 1.877, O(1)–Si(2) 1,635, N(1)–Si(1)–N(2)
90.83, N(1)–Al(1)–N(2) 85.24, Al(1)–N(1)–Si(1) 92.01, Al(1)–N(2)–
Si(1) 91.75, O(2)–Al(1)–O(1) 98.15, C(2)–Si(1)–C(1) 105.68.
Figure 3. Selected bond lengths [Å] and angles [°] of 11: Si(1)–N(2)
1.733, Si(1)–N(1) 1.720, Al(1)–N(1) 1.820, Al(1)–N(2) 1.823, Al(1)–
O(1) 1.702, Al(1)–O(2) 1.895, N(1)–Si(1)–N(2) 91.15, N(1)–Al(1)–
N(2) 85.24, Al(1)–N(1)–Si(1) 92.03, Al(1)–N(2)–Si(1) 91.50, O(2)–
Al(1)–O(1) 94.63, C(2)–Si(1)–C(1) 105.5.
Both molecular structures differ from each other only in
the oxy ligands at the aluminum atoms. The compounds
have a 1,3-diaza-2-sila-4-aluminacyclobutane unit with the
aluminum atoms in tetrahedral sites coordinated by two ni-
trogen and two oxygen atoms. The Al–N–Si–N four-mem-
bered rings are almost planar as may be deduced from the Figure 4. Mechanism for the reaction of Equation (6).
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(7)
Materials Part
By using our reduction procedure of the tin and lead
amides it is possible either to stabilize the tin and lead par-
ticles as colloids in solution or to obtain them as nano-
scaled powders or metal sponges depending on the chosen
reaction conditions (temperature or concentration of the
starting materials). With regard to the lead formation we
have already reported in detail on the different species that
may be produced.[6] Here we mainly want to discuss our
results from the reduction of the tin compounds.
The polarity of the solvents used has an important influ-
ence on the diameters of the tin crystallites that are pro-
duced. We studied the reactions of 7 with 3 or 6 [see Equa-
tion (2)] in different polar solvents or solvent mixtures,
respectively (see Table 1).
Figure 5. Colors of the reaction mixtures correlated with the tem-
perature. Reaction of Me2Si(NtBu)2Sn (7) with [H2AlOtBu] (3) (a),
or with [H2AlOSiMe3] (6) (b).
diagrams.[13] The results of this line analysis are shown in
Table 1.
The tin particles formed by the reduction of [Me2-
Si(NtBu)2Sn] (7) with the more reactive hydride 6 [R =
SiMe3, (b) in Table 1] show a larger average crystallite size
Table 1. Average crystallite sizes from analysis of peaks in X-ray
powder diffraction data. Reaction of Me2Si(NtBu)2Sn (7) with than those formed when the hydride 3 [R = tBu, (a) in
[H2AlOtBu] (3) (a), or with [H2AlOSiMe3] (6) (b).
Table 1] is used. This becomes very obvious when toluene
is used as a solvent, because then the differences in the sizes
are approximately 300 nm. The siloxy groups may have an
influence on the most apolar solvent. On the other hand,
in the more polar THF, the average crystallite sizes lie in
both cases below 30 nm and using hydride 3 the crystallite
size may even be below that of 20 nm. Obviously, the donor
molecules like THF as well as thiophene and TMEDA in
the solvent mixtures are able to stabilize the colloids in such
a way that the crystallite growth is hindered. This can also
be concluded from experimentally determined carbon/hy-
(a) Medium
Average
crystallite
size
(b) Medium
Average
crystallite
size
THF
THF/thiophene
(10%)
THF/TMEDA
(10%)
Toluene
Ͻ20 nm
60–80 nm
THF
THF/thiophene
(10%)
THF/TMEDA
(10%)
20–30 nm
60–80 nm
160–180 nm
500–520 nm
200–220 nm
800–820 nm
Toluene
When the reaction is started at –115 °C (ethanol/liquid drogen contents of the precipitates generated from toluene
N2) a clear yellow solution forms. By warming the reaction and THF. They are, for those powders formed in THF, be-
mixture to room temperature a dramatic color change from tween 7 and 11 times higher than for those generated in
red to dark brown takes place. On further heating the mix- toluene (Tables 2 and 3). So it is very likely that solvent
tures above 40 °C, black suspensions are formed. Obviously, molecules are coordinated on the surface of the particles.
the tin particles are in the first instance formed in a colloi- We have tried to perform HRTEM analyses on the powders,
dal form (clear intensively colored solutions) and with but observed high reactivities with oxygen prior to the mea-
higher temperatures they grow and agglomerate to finally surements, almost excluding a proper experiment. Although
precipitate. When the siloxyalane 6 is used instead of [H2Al- we have no data for tin, we assume similar behavior as for
OtBu] (3) in solvents like toluene or THF as reductive lead.[6]
agents, the reduction already starts at lower temperatures,
since the color change is observed earlier on the tempera- another for longer times, or toluene is used as the solvent,
ture scale (Figure 5). the agglomeration continues and metal sponges are formed.
If the metal powders are allowed to interact with one
The precipitates that were obtained were isolated at room In Figures 7 and 8 fragments of such a tin sponge and the
temperature and characterized by X-ray powder diffraction corresponding SEM images are shown. The nanoscopic po-
and revealed to be in all cases β-tin. In the X-ray powder rosity of the sponges is clearly proved by the SEM images.
diffraction diagrams of precipitates generated in polar THF,
significantly broader diffraction signals appear compared to the tin sponges. When water was used, an average density
those of the powders obtained from toluene (Figure 6).
of 1.5 g/cm3 was determined, indicating that some of the
Several pycnometric measurements were carried out on
Using a modified Scherrer method it was possible to esti- holes could not be penetrated by water. With the inert and
mate an average crystallite size from the X-ray diffraction smaller helium (which is able to fill the pores in a much
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Figure 6. Powder diffraction analysis. Product from the reaction of 7 with 3 a) in toluene and b) in THF with locations of the signals
and intensities of β-tin.[12]
Table 2. C and H contents of precipitates generated in toluene.
Reducing agent
C content
H content
[H2AlOtBu]2 (2)
[H2AlOSiMe3]n (3)
1.47%
0.83%
0.35%
0.17%
Table 3. C and H contents of precipitates generated in THF.
Reducing agent
C content
H content
[H2AlOtBu]2 (2)
[H2AlOSiMe3]n (3)
10.86%
7.70%
2.45%
1.91%
Figure 7. Fragments of a tin sponge. The diameters of the two big-
ger pieces are around 2 to 3 mm.
better way) we determined an average density of approxi- sponges obtained from the reactions between the lead
mately 7 g/cm3 for the same sponges, which is near the value amides and the hydrides (see ref.[6]). With water, a value of
of 7.3 g/cm3 for pure tin.[14] For the sake of comparison we almost 8 g/cm3 was obtained, and with helium the density
also measured the density of the corresponding lead of approximately 11 g/cm3 was again close to that of lead
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Figure 8. SEM images of a tin sponge to illustrate its high porosity. The two pictures have different scales.
(ref.[14]: 11.3 g/cm3). The mean values of the pycnometric amount of solvent in order to clean the surface. Finally, the
measurements for the metal sponges in water seem to indi- metal clusters were synthesized within the membranes by
cate a higher porosity and smaller diameters of the channels reaction with the added hydrides. The channels of the mem-
for the precipitates of tin than for those of lead.
branes were filled with the amide solutions using vacuum-
To fill porous alumina membranes as templates with lead assisted diffusion. The routes (iii) and (iv) of Table 4 proved
or tin nanoparticles we used different techniques. We have to be the most effective methods to fill the templates. Be-
recently reported on our first attempts to fill the mem- sides the different filling methods we also varied the con-
branes with lead particles.[6] We managed to fill the pores centrations of the reaction solutions, the temperature
up to a certain extent by treatment of the templates with [Ͻ–100 °C for (i) and (ii) and 20 °C for (iii) and (iv)] and
colloidal solutions of different concentrations, but because the filling time. Finally, we repeated the filling process se-
of the relatively large diameters of the particles in those veral times. We cannot completely exclude a side reaction
colloids (up to 200 nm) they covered mainly the surface of of the metal amides with remaining hydroxy groups on the
the membranes and did not fill the much smaller pores with inner surfaces of the alumina membranes; the concentra-
diameters of approximately 60 nm.
tions of the stannylene solutions were chosen in such a way
For new attempts we not only used membranes with vari- that these side reactions may be almost neglected. Further-
ous pore diameters of 25, 30, 50, 60, 80, 90, 120 and more, we could not observe spectroscopically any of the
300 nm,[7] but also varied the filling techniques. The thick- hydrolysis byproducts of the stannylene 7. Also the molecu-
ness of the membranes varied between ca. 25 µm and 90 µm lar byproducts described in the first section of this article
and the particle sizes in the membranes are linked to the have not been isolated and separated for each filling pro-
diameters of the channels as checked by XRD on selected cess. In the following, we want to describe in more detail
samples after destruction. We finally succeeded in the infil- mainly the filling of the membranes with tin. The experi-
tration of the membranes. Table 4 gives an overview of dif- ments with lead amides showed similar results, some of
ferent possibilities to fill the membranes with tin or lead which have already been documented.[6] With increasing
particles.
concentrations and filling time (or repetitions of the filling
process) a significant color change of the originally trans-
parent membranes from light brown to dark brown and fi-
nally to black is observed. The infiltration can be moni-
tored by EDX analysis. Figure 9 contains spectra of (a) a
non-treated 50 nm membrane, (b) a light brown and (c) a
dark brown membrane after filling with tin particles.
The signal at 3.5 keV found in the EDX spectra is char-
acteristic for tin and a comparison of these signals with the
ones of aluminum at 1.8 keV confirms a higher Sn content
Table 4. Possibilities for membrane filling.
For methods (i) and (ii) the membranes were put into for the dark brown membrane. The different intensities in
already prepared colloidal solutions of the metal and were color of the membranes treated with differently concen-
filled by pure or vacuum-induced diffusion. Methods (i) trated stannylene solutions (up to 210 mmol/L) are reflected
and (ii) led to dark membranes because of agglomeration in their UV spectra shown in Figure 10. In Figure 10 (a)
of the metal particles on their surfaces. These membranes and (b) the spectra are shown when the hydride 3 was used
were not further investigated with regard to their optical for reduction, whereas Figures 10 (c) and (d) contain the
properties. For methods (iii) and (iv) the membranes were spectra for when the hydride 6 was used (the self absorption
treated, after careful washing with the solvents and drying, of the membrane is subtracted in the spectra on the right-
in a first instance with the stannylene or plumbylene solu- hand side). With increasing concentrations of stannylene
tions. In a second step, they were washed with a small and longer filling times the maxima of the absorptions be-
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Nanoscaled Sn and Pb Particles Aligned in Al2O3 Tubes from Molecular Precursors
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Figure 9. EDX spectra of (a) a nontreated 50 nm membrane, (b) a light brown and (c) a dark brown membrane after filling with tin
particles. Experimental conditions: concentration of 7 137 mmol/L or 411 mmol/L in THF, hydride 3, method (iv) of Table 4, vacuum
induction time 5 min each.
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Figure 10. UV spectrum of a 50 nm membrane with respect to the concentration of stannylene 7 and the time of vacuum induction. The
reductive agent for (a) and (b) is hydride 3 (− cstannylene = 137 mmol/L, 5 min vacuum induction; –½– cstannylene = 210 mmol/L, 5 min
vacuum induction; ··· absorption of the membrane), for (c) and (d), hydride 6 (− cstannylene = 121 mmol/L, 5 min vacuum induction; –½–
cstannylene = 200 mmol/L, 10 min vacuum induction; ··· absorption of the membrane). On the right-hand side the absorption of the
membrane is subtracted.
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come more intense and the bands are widened due to the a membrane could be used as a wavelength filter, which
bigger sizes and the larger amounts of particles. In addition, absorbs the light completely within a well-defined range.
the absorption maxima are shifted towards higher wave- The transmission spectrum shown in Figure 12 (concentra-
lengths when the amount of aggregating tin clusters in- tion of stannylene 7: 411 mmol/L; reductive agent hydride
creases leading to an interaction of their plasmon reso- 6) underlines this possibility for use. Here one finds an im-
nances (see also ref.[6] for further discussion).
pervious range between 250 and 525 nm.
Already from a visual comparison it becomes evident
that the different reactivities of the reductive agents 3 and
6 has only little influence on the color of the treated mem-
branes as shown by their UV spectra. All filled membranes
show almost identical absorption curves depending on the
concentration of tin clusters.
Dark brown or black membranes result from very high
concentrations of stannylene (Ͼ350 mmol/L). The absorp-
tion spectra show broad signals with very high intensities.
Such a spectrum is presented in Figure 11 (concentration of
stannylene 7: 360 mmol/L; reductive agent hydride 3). It
shows an impervious range between 270 and 500 nm. Such
Figure 12. UV/Vis transmission spectrum of a very colored mem-
brane; concentration of stannylene 7: 411 mmol/L; reductive agent
hydride 6.
As mentioned above, we have used membranes with dif-
ferent pore diameters and the UV spectra of these mem-
branes (filled under similar conditions) show a shift of the
absorption maxima towards higher wavelengths (Fig-
ure 13). Obviously, the size of the metal clusters plays an
important role.[6] As the absorption maxima shift with the
pore diameter (with parallel increase of the metal particle
diameters) one may use the process to produce wavelength
filters of different absorption maxima.
We noticed an improvement in the infiltration of the
membranes when we repeated the filling process several
times. As expected, the filling of the channels is most effec-
Figure 11. UV/Vis absorption spectrum of a very colored mem-
brane; concentration of stannylene 7: 360 mmol/L; reductive agent
hydride 3.
Figure 13. Comparison of the position of the absorption maxima using membranes of different pore diameters filled with tin particles (a
and b stand for different probes of the same material).
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Nanoscaled Sn and Pb Particles Aligned in Al2O3 Tubes from Molecular Precursors
FULL PAPER
Figure 14. SEM images of (a) 5 and (b) 10 times filled 300 nm Al2O3 membranes to show the increase in the amount of lead particles
within the pores (ca. 10 kV sputtered with approximately 10 nm Au).
tive for membranes with large pore diameters. The SEM
Experimental Section
images of a 300 nm Al2O3 membrane filled with lead par-
Physical Measurements: The elemental analyses of the compounds
ticles after five and ten infiltrations are presented in Fig-
were carried out using a CHN analyzer from LECOTM Corpora-
ure 14. They show an increase in the amount of lead clus-
tion, St. Joseph, MI, U.S.A. The NMR spectra were measured with
ters with repetitive filling. The repetition is nevertheless lim-
ited due to a blocking of the pores after ca. 7–8 cycles. The
particles in the 300 nm pores have mean diameters of 80–
90 nm.
Bruker 200 MHz spectrometers, model AC 200 F (1H and 13C spec-
tra) and AC 200 P (29Si spectra), using [D6]benzene as solvent. The
single-crystal X-ray analyses were performed either with an Image
Plate (IPDS I), or a four-circle diffractometer (STADI 4) (Stoe,
Dramstadt). The structure calculations were carried out with
SHELXS97[15] and the graphical representation with Diamond
3.[16] The complete crystal structure data are deposited with the
Cambridge Crystallographic Data Centre (CCDC), 12 Union
Road, Cambridge CB2 1 EZ (UK) [CCDC-270194 (10), 270195
(11), and 270196 (12)]. The powder diffraction measurements of
the tin and lead precipitates were performed in a glass capillary
with a Stoe diffractometer, model STADIP, using Cu-Kα radiation
with a wavelength of 1.540598 Å and a linear PSD detector. The
measurements were analyzed with the software WinXPow. The elec-
tron microscopy (SEM) and energy-dispersive X-ray analyses
(EDX) were performed with a scanning electron microscope CAM-
SCAN S4 with Si(Li) semiconductor detectors and with thin win-
dows (Cameca and Noran). To perform the SEM analyses of the
filled membranes, the membranes were covered with gold. The UV/
Vis spectra were measured with a Perkin–Elmer spectrometer,
model Lambda 35.
Summary and Conclusion
Tin and lead nanosized particles and metal sponges have
been prepared by reduction of molecular tin() and lead()
amides with siloxy- and alkoxyalanes in non-aqueous me-
dia. The resulting molecular byproducts have been isolated
and (structurally) characterized. Colloidal solutions of tin
were obtained when the reaction mixture was slowly
warmed from –115 °C to room temperature. With agglom-
eration of the particles in this solution, tin powders formed
and precipitated, and have been identified as β-tin by EDX
analysis. Their average particle size diameter can be con-
trolled either by using different donor solvents or different
hydrides as reducing agents. The smallest particles were ob-
tained when tert-butoxyalane 3 was used as hydride and
THF as donor solvent. The metal sponges were charac-
terized by pycnometric measurements with helium and
water and show a lower density compared with their value
known from literature when water was used because of its
surface tension and the high porosity of the metal precipi-
tates. Porous aluminum oxide membranes with different
pore diameters were used as templates for ordering tin or
Synthetic Procedures: All compounds were synthesized under dry
nitrogen using standard Schlenk techniques. The solvents were
dried by refluxing with appropriate drying agents and distilled be-
fore being used.
[Me2(NtBu)2Al(OtBu)(THF)] (11): Me2Si(NtBu)2Pb (9) (2.82 g,
6.92 mmol) in THF (25.0 mL) was added dropwise to a stirred
solution of [H2AlOtBu]2 (3) (0.71 g, 3.46 mmol) in dry THF
(25.0 ml) and allowed to react at room temperature for 24 h. The
lead clusters within the pores. The metal particles were pre- reaction mixture turned grey, the lead precipitated and gas (hydro-
gen) evolved. When the reaction was complete, the solution was
separated from the lead and concentrated until crystals of
[Me2(NtBu)2Al(OtBu)(THF)] (11) formed. After recrystallization
of the crude product from THF, 11 (1.48 g, 3.97 mmol) may be
obtained, at 4 °C, as colorless crystals (yield: 57%). Molecular
mass: 372.60 g/mol. 1H NMR (200 MHz, C6D6, 25 °C): δ = 0.45
[s, 3 H, Si(CH3)2], 0.57 [s, 3 H, Si(CH3)2], 1.09 (m, 4 H, THF), 1.37
pared by reduction of the metal amides within the mem-
branes and the amount of particles could be increased by
repetition of the filling process, which was an improvement
in the infiltration compared to our former attempts. Dif-
ferently colored membranes resulted from the filling process
and were characterized by UV/Vis spectroscopy. Depending
on the concentration of the starting materials and the pore
diameters of the membranes they showed impervious ran-
ges, which enabled these membranes to be used as wave-
length filters.
(s, 18 H, NtBu), 1.51 (s, 9 H, OtBu), 3.82 (m, 4 H, THF) ppm. 13
C
NMR (200 MHz, C6D6, 25 °C): δ = 7.09 [s, 1 C, Si(CH3)2], 7.27 [s,
1 C, Si(CH3)2], 24.81 (s, 2 C, THF), 34.12 (s, 3 C, OtBu), 36.45 (s,
6 C, NtBu), 49.50 (s, 2 C, quat. C, NtBu), 71.03 (s, 2 C, THF),
Eur. J. Inorg. Chem. 2005, 3699–3710
www.eurjic.org
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3709

M. Veith, J. Frères, P. König, O. Schütt, V. Huch, J. Blin
FULL PAPER
78.16 (s, 1 C, quat. C, OtBu) ppm. 29Si NMR (200 MHz, C6D6,
25 °C): δ = –15.55 [s, 1 Si, Si(CH3)2] ppm. Compound 11 crys-
tallizes in the monoclinic space group I2/a with Z = 8 [a =
15.724(3), b = 15.529(3), c = 19.917(4) Å, β = 92.97(3)°, V =
4856.8(16) Å3], 1.84° Ͻ θ Ͻ 23.92°, 14862 reflections collected,
3738 unique (Rint = 0.1329), the structure was solved by direct
methods and refined by full-matrix least squares on F2. Final R1 =
0.0555 (I Ͼ 2σI) and wR2 = 0.1331 with an electron density left of
0.409/–0.279 e/Å3.
[2] G. Schmid (Ed.), Clusters and Colloids, VCH, Weinheim, 1994.
[3] a) G. Schmid, Nach. Chem. Tech. Lab. 1987, 35, 249; b) G.
Schmid, Chem. Unserer Zeit 1988, 22, 85; c) G. Schmid, B.
Morun, J.-O. Malm, Angew. Chem. 1989, 101, 772; d) G.
Schmid, A. Lehnert, U. Kreibig, Z. Adamczyk, P. Belouschek,
Z. Naturforsch., Teil B 1990, 45, 989–994; e) G. Schmid, R.
Küpper, H. Hess, J.-O. Malm, J.-O. Bovin, Chem. Ber. 1991,
124, 1889–1893; f) G. Schmid, M. Harms, J.-O. Malm, J.-O.
Bovin, J. Van Ruitenbeck, H. W. Zandbergen, W. T. Fu, J. Am.
Chem. Soc. 1993, 115, 2046–2048; g) U. Simon, G. Schön, G.
Schmid, Angew. Chem. 1993, 105, 264–267; h) J. G. A. Dubois,
J. W. Gerritsen, G. Schmid, H. van Kempen, Physica B 1995,
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1568–1569; j) J. G. A. Dubois, J. W. Gerritsen, G. Schmid, H.
van Kempen, Physica B 1996, 218, 262; k) A. Bezryadin, C.
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1997, 623, 719–723; m) G. Schmid, J. Chem. Soc., Dalton
Trans. 1998, 1077–1082; n) G. Schmid, N. Beyer, Eur. J. Inorg.
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[4] a) C. Nayral, T. Ould-Ely, A. Maisonnat, B. Chaudret, P. Fau,
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Maisonnat, B. Chaudret, Chem. Eur. J. 2000, 6, 4082; c) G.
Cardenas-Trivino, M. Alvial, K. J. Klabunde, O. Pantoja, H.
Soto, Colloid Polym. Sci. 1994, 272, 310–316; d) P. Cheyssac,
M. Geddo, R. Kofman, P. G. Merli, A. Migliori, A. Stella, P.
Tognini, Mater. Sci. Forum 1995, 195, 161; e) B. Ocker, R.
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[Me2Si(NtBu)2Al(OSiMe2tBu)(THF)] (10): Analogous to the syn-
thesis of compound 11 (at room temperature). Yield: 63%. Molecu-
lar mass: 430.76 g/mol, calcd. C 55.77, H 11.0, Al 6.26, N 6.5;
found C 55.18, H 10.78, Al 6.62, N 6.57. 1H NMR (200 MHz,
C6D6, 25 °C): δ = 0.28 [s, 6 H, OSi(CH3)2], 0.44 [s, 3 H, Si(CH3)2],
0.57 [s, 3 H, Si(CH3)2], 1.08 (m, 4 H, THF), 1.14 (s, 9 H, SitBu),
1.34 (s, 18 H, NtBu), 3.8 (m, 4 H, THF) ppm. 13C NMR (200 MHz,
C6D6, 25 °C): δ = –1.91 [s, 2 C, OSi(CH3)2], 6.36 [s, 1 C,
Si(CH3)2], 6.7 [s, 1 C, Si(CH3)2], 18.39 (s, 1 C, quat. C, SitBu), 24.33
(s, 2 C, THF), 26.26 (s, 3 C, SitBu), 35.89 (s, 6 C, NtBu), 48.85 (s,
2 C, quat. C, NtBu), 70.74 (s, 2 C, THF) ppm. 29Si NMR
(200 MHz, C6D6, 25 °C): δ = –14.98 [s, 1 Si, Si(CH3)2], 4.8 (s, 1 Si,
OSi) ppm. Compound 10 crystallizes in the monoclinic space group
P21/c with Z = 4 [a = 12.095(2), b = 10.637(2), c = 21,629(4) Å, β =
97.67(3)°, V = 2757.8(9) Å3], 1.90° Ͻ θ Ͻ 23.99°, 16615 reflections
collected, 4214 unique (Rint = 0.1215), the structure was solved by
direct methods and refined by full-matrix least squares on F2. Final
R1 = 0.0546 (I Ͼ 2σI) and wR2 = 0.1393 with an electron density
left of 0.358/–0.287 e/Å3.
[5] M. Veith, O. Schütt, J. Blin, J. Fréres, S. Becker, V. Huch, Z.
Anorg. Allg. Chem. 2001, 628, 138–146.
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Rammo, V. Huch, H. Shen, G. Schmid, C. R. Chim. 2004, 7,
509–519.
[Me2Si(NtBu)2Al(OSiMe2tBu)]2 (12): Compound 12 can be synthe-
sized in the same manner as compound 10, but by heating the reac-
tion mixture under reflux. Yield: 81%. Molecular mass: 789.83 g/
mol, calcd. C 48.69, H 9.96, Al 6.84, N 7.1; found C 48.16, H 9.76,
[7] a) G. Hornyak, M. Kröll, R. Pugin, T. Sawitowski, G. Schmid,
J.-O. Bovin, G. Karsson, H. Hofmeister, S. Hopfe, Chem. Eur.
J. 1997, 3, 1951–1956; b) G. Schmid, L. F. Chi, Adv. Mater.
1998, 10, 515; c) T. Hanaoka, H.-P. Kormann, M. Kröll, T.
Sawitowsky, G. Schmid, Eur. J. Inorg. Chem. 1998, 807; d) P.
Braunstein, H. P. Kormann, W. Meyer-Zaika, R. Pugin, G.
Schmid, Chem. Eur. J. 2000, 6, 4637–4646.
1
Al 6.91, N 6.83. H NMR (200 MHz, C6D6, 25 °C): δ = 0.51 [s, 18
H, OSi(CH3)2], 0.61 [s, 12 H, Si(CH3)2], 1.12 (s, 18 H, SitBu), 1.38
(s, 36 H, NtBu) ppm. 13C NMR (200 MHz, C6D6, 25 °C): δ =
–0.41 [s, 4 C, OSi(CH3)2], 7.27 [s, 4 C, Si(CH3)2], 19.49 (s, 2 C,
quat. C, SitBu), 27.06 (s, 6 C, SitBu), 36.27 (s, 12 C, NtBu), 49.62
(s, 4 C, quat. C, NtBu) ppm. 29Si NMR (200 MHz, C6D6, 25 °C):
δ = –9.39 [s, 2 Si, Si(CH3)2], 29.46 (s, 2 Si, OSi) ppm. Compound
12 crystallizes in the monoclinic space group P21/n with Z = 8 [a
= 27.779(6), b = 11.612(2), c = 28.043(6) Å, β = 97.89(3)°, V =
8960(3) Å3], 1.90° Ͻ θ Ͻ 24.05°, 55081 reflections collected, 13935
unique (Rint = 0.0897), the structure was solved by direct methods
and refined by full-matrix least-squares on F2. Final R1 = 0.0904
(I Ͼ 2σI) and wR2 = 0.2245 with electron density left: 2.689/–1.741
e/Å3.
[8] M. Veith, M. Grosser, Z. Naturforsch. B. Anorg. Chem. 1982,
37, 1375–1381.
[9] M. Veith, S. Faber, H. Wolfanger, V. Huch, Chem. Ber. 1996,
129, 381.
[10] J. Blin, Dissertation, Universität des Saarlandes 1999.
[11] M. Veith, Angew. Chem. 1975, 87, 278; Angew. Chem. Int. Ed.
Engl. 1975, 14, 263.
[12] JCPDS-Datei, [4-673], from ICDD database.
[13] Steuerungssoftware des STOE-Transmissions-Diffraktometers
STADIP: WINXPOW Version 1.03, 1998, and STOE VIS-
UALXP.
Acknowledgments
[14] A. F. Holleman, E. Wiberg, N. Wiberg, Lehrbuch der anorgan-
ischen Chemie, 2nd ed., Walter de Gruyter, Berlin, New York,
1995.
[15] G. Sheldrick, Program for Crystal Structure Solution, version
SHELX-97, Göttingen, 1997.
[16] M. Berndt, K. Brandenburg, H. Putz, Visual Crystal Structure
Information System, Diamond version 3, Bonn, 1996–2005.
Received: April 26, 2005
Authors thank the “Deutsche Forschungsgemeinschaft (DFG)” for
providing financial support in the framework of the research pro-
gram “Halbleiter und Metallcluster als Bausteine für organisierte
Strukturen” (SPP 1072) as well as Prof. Dr. G. Schmid, Essen, for
providing the membranes. Dr. M. Ehses, Saarbrücken, is acknowl-
edged for kindly reading the manuscript.
Published Online: August 30, 2005
[1] U. Kreibig, M. Vollmer, Optical Properties of Metal Clusters,
Springer, New York 1995.
3710
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Inorg. Chem. 2005, 3699–3710