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C60 and C70 in a Basket Ц Investigations of Mono- and Multilayers from Azacrown Compounds and Fullerenes.

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[Co,(CO),], and [Co,(CO),,] was studied by similar techniques. Na[Co(”CO),] was synthesized by Hieber’s cyanide method [I I]. The product was
isolated as an analytically pure solid on saturation of the water solution with
NaCi followed by continuous extraction with Et,O. The extract was dried with
Na,SO, and finally evaporated to dryness. Typical yields were 6 0 % based on
the ‘CCO introduced. PPN[CO(’~CO),] was prepared by a metathesis reaction
between PPNCI and Na[Co(”CO),] in CH,OH/H,O.
[CO,(’~CO),,I: To a suspension of N ~ [ C O ( ’ ~ C O ) (480
, ] mg, 2.42mmol) in
ri-hexane (100 mL) was added HCI (60 mL, 2.50 mmol) through a rubber septum. The suspension was stirred for 24 h at 50°C and then refluxed for 3 h.
Solid impurities were removed by filtration. and black crystals of [Co,(’3CO),,]
were obtained (210 mg; 6 0 % yield) by cooling the mother liquor to -20 C.
firmed these
We report here on mono- and multilayers of 1: 1 mixtures of the C,, and C,, fullerenes (represented by 1) and amphiphilic molecules 2 containing a
lipophilic cavity (the “basket”) (Scheme 1 ) .
f)
10 A
Received: June 19, 1992 [Z 5419 IE]
German version: An,Tew Chrm. 1992, 104, 1692
+uc
.
)
14-18 A
2
1
Scheme 1
CAS Registry numbers:
[Co(CO)J. 14971-27-8; [Co,(CO),]. 10210-68-1
[I] J. P. Collmann, L. S. Hegedus, J. R. Norton, R. G. Finke, Princip1i.r und
Applicurrons o / Orgunotrunsilion Metal Chemistr?, University Science
Book. Mill Valley, CA, USA, 1987. Chapter 4, and references therein.
[2] a ) R . D. W. Kemmitt, D. R. Russel in Comprehensive Orgunomelullic
Clicmisrry, Vol. 5 (Eds.: G. Wilkinson, F, G. A. Stone, E. W. Abels), Pergamon Press, Oxford, 1982; b) A. Davison, J. R. Ellis, J: Organumel. Chem.
1971. 31. 239; c) W. Hieber. K. Wollmann, Chem. Ber. 1962, 95. 1552;
d ) P. A. Bellus. T. L. Brown, J. Am. Chem. Soc. 1980, 102, 6020.
[3] a) F. Ungvary, A. Wojcicki, J. A m . Chem. Soc. 1987, 109, 6848; b) F.
Ungvary. J. Gallucci. A. Wojcicki, OrgunometnNics 1991, 10, 3053.
[4] a ) D. P. Schussler, W. R. Robinson, W. F. Edgell. Inorg. Chem. 1974, 13,
153. b) M. Y. Darensbourg. Prog. Inorg. Chem. 1985, 33, 221
[ 5 ] T. Graat: R. M. J. Hofstra, P. G. M. Schilder, M. Rijkhoff. D. J. Stufkens,
J. G M . Linden. Organornerullics 1991, 10. 3668. and references therein.
[6] M. J. Therien. W. C. Trogler. J: Am. Chem. Soc. 1988, 1111, 4942.
[7] G. Fachinetti, J. Cliem. Soc. Chem. Commun. 1979, 396.
I
Orgunomet. Chem. 1988. 353,
[S] G. Fachinetti, T. Funaioli, M. Marcucci, .
393.
[9] H.-N. Adams, G. Fachinetti, J. Strihle. Angew. Chem. 1980. 92, 411;
Aiz,qf,ii, c‘h~m.In[. Ed. Engi. 1980, 19, 404.
[lo] M . Abri-Halabi. J. D. Atwood, N. P. Forbus, T. L. Brown, J. Am. Chem.
so(..1980, 102, 6248.
[ I l l W. Hieber, C. Bartenstein, Z . Anorg. A&. Chem. 1954, 276, 1.
c6, and C,, in a Basket? - Investigations
of Mono- and Multilayers from Azacrown
Compounds and Fullerenes
By Francois Diederich, Jochem Effing,
Ulrich Jonas, Ludovic Jullien, Thomas Plesnivy,
Helmut Ringsdor$* Carlo Thilgen, and David Weinstein
The spreading behavior of fullerenes at the air-water interface and the formation of Langmuir-Blodgett (LB) films
on solid substrates has already been described in several
publications. - 4 1 The results are in part contradictory. The
behavior of pure fullerenes C,, and C,, at the air-water
interface indicates a collapsed film rather than a homogeneous monolayer. Even mixed films of C,, and fatty acids or
long-chain alcohols in a 1 :1
do not give the expected areas. but also point to C,,-aggregates; we have con[*] Prof. Dr. H. Ringsdorf, Dipl.-Chem. J. Effing, U. Jonas, Dr. L. Jullien,
Dipl.-Chem. T. Plesnivy
Institut fur Organische Chemie der Universitit
J. J. Becher-Weg 18- 20, D-W-6500 Mainz (FRG)
Prof. Dr. F. Diederich, Dr. C. Thilgen
Labordtorium fur Organische Chemie, ETH-Zentrum
CH-8092 Zurich (Switzerland)
D . Weinstein
Department of Chemistry and Biochemistry
University of California
Los Angeles. CA 90024-1596 (USA)
Angrw. (‘hcm. Inr. Ed. Engl. 1992, 31, N o . 12
(C>
Although hydrophobic cyclodextrins,[6.’I ~alixarenes,~’~
and alkylated and acylated azacrown derivatives of different
ring sizes were used as component 2 of Scheme 1, only the
results with the alkylated hexaazacrown compound 3 and
the acylated octaazacrown compound 4 will be reported
here.
R
I_\
=R
A
3
Figure 1 shows the surface pressure-area behavior of pure
hexaazacrown 3 and that of 1 :1 mixtures of 3 with C,, or
C,,. The surface density, that is, the number of spread molecules 3 per air-water surface area, was the same in all experiments.[*]All curves are reproducible, and repeated compression-expansion experiments (hysteresis curves) give identical
plots.
The fact that for all three systems similar collapse areas
were found is a first indication that the fullerenes may at
least partially be situated inside the cavities of the crown
molecules. This is supported by the comparison of the width
of the “transition regions” of the different mixing ratios
(C6,/3). The less C,, is incorporated into the crowns, the
narrower is the width of the plateau. Further indications
pointing to such a complexation are the slight shifts in the
UVjVIS spectra of the multilayers (see below).
The incorporation of the fullerenes into the monolayers of
the azacrown compounds has a stabilizing effect on the film
as clearly shown in Figure 2 for the octaazacrown 4 with C,,
and C,,.
Although 4 has a larger diameter than 3, the collapse area
of 4 increases slightly in the presence of the fullerenes (average of three experiments); this is not the case for 3. The
VCH Verlugsgesellschufi mbH. W-6940 Weinheim,1992
0570-0833192/12/2-1599$3.50+ . Y O
1599
70 n
n
In addition, apparently well-defined multilayers can be
built from all monolayers of azacrown/fullerene mixtures by
the LB technique. However, all attempts to transfer pure
hexaazacrown 3 to a hydrophilic substrate (quartz, glass,
mica) or to hydrophobic supports (teflon, hydrophobized
quartz) were unsuccessful. Likewise, it was not possible to
transfer a defined monolayer of pure C,, , as already shown
by other r e ~ e a r c h e r s . l ~Multilayers
-~~
from mixtures of C,,
with classical amphiphiles like icosanoic acidL3]or octade~ a n o l , ' which
~]
themselves can form stable multilayers, were
described. Both 3 and the fullerene are unable to form LB
films alone. In contrast, the 1 :1 mixtures of 3 with C,, and
C,, form homogeneous LB multilayers (Y-type, both on
hydrophilic and on hydrophobic substrate) with an average
bilayer thickness of approximately 47 A (SAXS19]).The incorporation of 3 and of the fullerenes into the multilayers
was confirmed by UVjVIS spectroscopy. Figure 3 shows the
absorption spectrum of the C,,/3 LB film and a calculated
spectrum (addition of the spectra of the components). Simi-
-'
IrnN rn 1
0
3m
200
100
1.00
200
100
0
300
-
A [A2 rno~ecu~e-']
Fig. 1. Top: Surface pressure area diagram (IZ,'A isotherms) of pure hexaazaIS]. Bottom: 11:4 isotherms
crown 3 and the 1 : 1 mixtures o f 3 with C,, and C7<]
of pure hexaazacrowu 3 and the 1 : l . ?:I.
and 3 : l mixtures of 3 with C,,
t
O-'j
Ad.
0.50
0.25
7(J
60
R
1
--
/
0.00
4
100
200
300
'
Table I.Data for inonolayers of the hexa- and octaaracrown compounds 3 and
4. respectively. with and wjithout C,, or Ci, [a].
4
4!C,,
4:c,,
47 & 3
52 3
54 t 3
40 t l
48 i l
46 i 3
*
170 k 6
5
205-15
275 2
325 * I S
325 9
22s
*
*
*
[a] A,: collapse area. p : collapse pressure. A,,: area ar O m N m - ' pressure. A
mol-'1 = area per croun molecule o r fullerene,'crown molecule pair. The
numbers are average values of three or four experiments.
[A'
I
200
300
400
500
-- - - - - _ _ _
I
600
I
I
I
700
800
900
-
400
A [A2 rnolecu!e"l-
collapse area, the collapse pressure, and the area at pressure
0 m N m - of the azacrown/fullerene monolayers are given
in Table 1.
148 _+ 3
141 f 6
137 k 6
229 5 3
263 ? I 2
269 _+ 8
I
Fig. 3 . Experimental and theoretical UV'VlS spectra of an LB multilayer consisting of LB films of a 1 .Imixture of C,, and 3 (2 x 17.5 bilayers). Solid line:
recorded spectrum. Broken line: the spectrum obtained by addition of the
spectra of films of pure 3 and C6". The absorption values are relative (A,>,,);the
highest peak is arbitrarily set to 1. The inset shows the UV:VIS spectra of the
iilrns of pure 3 and C,,
Fig. 2. f i ; A isotherm of pure oxtaazacrown 4 and the 1 : I mixtures o f 4 with
C,,, and C,,,[8].
3
3,'C,"
3:c-,
I
d[m]
4
0
I
lar results were obtained for the multilayers of C,,/3. The
microscopic environment of the fullerene molecules in the
azacrown films (layer composition) seems to remain unchanged if more layers are added, as shown by the linear
relationship between the number of layers and the absorption maxima of the peaks in the UV/VIS spectra.
The UVjVIS spectrum of the C,,/4 film (Fig. 4) shows, in
addition to the typical absorptions of the two pure compounds, a new peak at 256 nm, possibly arising from interactions between the C,, z-electron system and the cinnamic
amide n electrons. Another interesting feature of the multilayer spectra is the fact that the broad band of the absorption
of pure C,, (at 400-480 nm). arising from the interaction
between different fullerene molecules (microcrystallites),"
is diminished. This could indicate that the C,,-aggregation
existing in the solid is in this case somewhat reduced.
As observed with the films of 3, the regularity of the formation of the multilayers of4 with and without the fullerenes
was also confirmed by SAXS measurements (see Fig. 5). For
all three multilayers Kiesig fringes were found. The bilayer
thickness of the pure azacrown derivative 4 is about 40 A.
and thus only slightly greater than that for the 1 :1 mixtures:
which each fullerene molecule is located inside a crown molecule: C,, in the basket.
We obtained some support for the structure A from atomic
force microscopy (AFM) measurements. Monolayers of
pure 4 have homogeneous, flat surfaces. However, when the
4/C,, mixture is tran$ferred at 25 m N m - ’ , irregular aggregates (ca. 1000 x 200 A) appear, indicating C,, microcrystallites. These aggregates are also observed in the system 3/C,,
(Fig. 6b); here they are transferred at the Same pressure
(above the “transition region” in Fig. 1). If the mixed monolayer is transferred below the “transition region” at
5 m N m - I , the surface is flat, and no aggregates are visible
in the A F M image (Fig. 6a). This can indicate a well-mixed
1.00
t
A re).
0.75
0.50
h.[nm]
-.t
0.25
0.00
I
I
I
I
I
200
300
400
500
600
I
a[nm]
700
.
__
800
!NO
Fig. 4. Experimental and theoretical UV:VIS spectra of a LB multilayer consisting of LB lilms o f a 1 : 1 mixture of C,,, and 4 ( 2 x 1 2 3 bilayers). Solid line:
recoi-dcd spectrum. Broken line: the spectrum obtained by addition of the
spectra of films of pure 4 and C 6 ” .The absorption values are relative (A,,, ), the
highesr peak is ;irbitrarily set to 1. The absorption at 256 nm is not present in
thc spectra of the pure compounds shown in the inset.
lo?
1
105
Fig. 6. Atomic force micrographs of monolayers of C,,;3 (1 : 1 mixture)
a ) transferred at 5 m N m - ’ and showing 3 flat film on mica (film edge visible
on the right): b) transferred a t 25 m N m - and revealing crystallites on the film.
X
’
1000
10
E
0
I
I
1
2
1
3
2 8P 1
I
4
I
1
5
6
Fig. 5. Small-angle X-ray scattering plots of a) the LB film of pure 4
(15Sbilayers). b) the C,,/4
film (12.5 bilayers). and c) the C,,i4
film
(15.5 bilayers), all o n quartz. The upper two curves are shifted in intensity by
a factor of 12 for b) and by a factor of 120 for c) . s = counts per 5s.
approximately 37 8, for the C,,/4 LB film and approximately 38 8, for the C,,/4 film.
O n the basis of the present data one can only speculate on
the real packing of the multilayers. Since the measured bilayer thicknesses of the pure 4 film and the 1 : 1 mixture films
differ by just 2-3 A, the possibility of finding the fullerenes
in ordered layers on top of the films of 4 (C in Scheme 2)
seems unlikely. Two hypothetical structures for regular films
are depicted in Scheme 2 as A and B. In B the fullerenes
would sit between the deformed crown compounds. However, this structure cannot explain the slight increase in area
of the fullerene/crown complexes at the air-water interface
(see Table 1 ) . We prefer the hypothetical structure A, in
monolayer at low pressure in which C,, molecules are possibly situated inside the crown molecules. At pressures of 1520 m N m - ’ a demixing might occur, resulting in crystallization of the fullerenes.[”s ‘’I
In addition, A F M measurements on monolayers of calixarenes and hydrophobized cyclodextrins acting as “baskets”
are under way [7]. Their mono- and multilayer behavior
agree very well with the results described here for the azacrown/fullerene mixtures.
Received: June 5, 1992
Revised: September 5, 1992 [Z 53911EI
German version: Angew. Chem. 1992, 104, 1683
[I] F u k r e n e fever (T. Braun,
Angekr. Chem. 1992, /04. 6 0 2 ~ - 6 0 3(see also
p. 1697);Angew.Chem. I n [ . Ed. EngI. 1992.31. 5x8 -5R9(seealso p. 1350))
could not be cooled by water-as shown by this and other publications
(2-41 about C,, at the air-water interface!
[2] Y S. Obeng, A. J. Bard. J. Am. Chem. Soc. 1991, /f3.6279-6280.
[3] T. Nakamura, H. Tachibana, M. Yumura, M. Matsumoto, R. Azumi. M.
Tanaka, Y Kawabata. Lrmnpnir 1992, 8. 4-6.
[4] J. Milliken, D. D. Dominguez, H. H. Nelson, W. R. Barger. Cl7rm. M u m .
1992.4, 252-254.
[5] Area-pressure measurements were performed on a self-built, computercontrolled teflon trough with a surface of approximately I80 cm’ and a
Langmuir pressure pickup system. The measured area for the fullerei~esis
dependent on the spreaded amount and varied from ca. 70 A’ molecule(spreading volume: 0.14 ~ L c m of
- ~a 0.1 mM concentrated solution) to
ca. 2 5 A 2 molecule-’ (1.7 FL c m d 2 ; 0.1 mM) in the GISK of C 6 ” . Areas
from ca. 5 0 A 2 moiecu~e-’ ( o . I ~ ~ L c ~ 0.1
- ’ :mM) to ca. 25 A’ molecu1c-I (1.7pLcm-’;O.l mM)wereobtainedforC,,.This behaviorvaries
with the trough dimensions. and is most probably due to crystallization
and collapse of the film at the water-teflon rim.
[6] A y-cyclodextrin/C,, complex was previously described by T. Anderson,
K. Nilsson. M. Sundahl, G. Westman, 0. Wennerstrom ( J . C / i m . Soc.
Chem. Commun. 1992. 604-606).
171 V. Bohmer, F. Diederich, J. Effing, U . Jonas, L. Jullien, T. Plesnivy. H.
Ringsdorf. W. Vogt, unpublished.
’
Scheme 2.
[8] The alkyldted hexaazacrown 3 and the acylated octaazacrown 4 were
spread from a 0.1 mM solution of the pure crown compound in benzene at
20;C on a water suhphase (distilled, millipore filtered, 18 MQcm). The
same trough as in [S] was used, on which 50 or 1OOpL were spread in
different runs. The 1 :1 mixtures were prepared by combining equal volumes of the fullerene and the crown solution (hoth 0.1 mM in benzene). To
obtain the same surface density of the crown compounds, 100 and 200 pL
of these 1 : l mixtures were spread. As a result of the hypothesis that
fullerenes are accommodated inside the crown molecule. all area calculations are based on the concentration of the crown molecules.
[9] Small-angle X-ray scattering (SAXS) measurements were performed on
LB films consisting of about 17 hilayers on quartz slices with a 8-28 goniometer from Siemens.
[lo] The long wavelength absorption between 400 and 480 nm due to C,,
aggregation is relatively intense and must not be mistaken for the very
weak hands between 500 and 650 nin for homogeneous solutions of C,,
(violet!). Arguments that this relatively strong absorption at 400-480 nm
is caused by C,, aggregation result from the comparison of the spectriim
of a hexane solution (H. Ajie, M. M. Alvarez, S . J. Anz, R. D. Beck, F.
Diederich, K. Fostiropoulos, D. R. Huffman, W. Kratschmer, Y. Rubin.
K. E. Schriver, D. Senshanna, R. L. Whetten, J. Phys. Chem. 1990, 94,
8630) with a solid C,, film (W. Kratschmer, L. D. Lamb, K. Fostiropoulos,
D. R. Huffman, Nature 1990,347, 354-358). Furthermore, the spectrum
of a C,,,/CHCI, solution with C,, precipitate, which shows the normal
absorptions of the dissolved fullerene, changes upon sonication to the
spectrum of solid C,, (suspension of C,, aggregates, brown color).
[ll] In cooperation with Dr. Lifeng Chi and Dr. Harald Fuchs (BASF Aktiengesellschaft); measured in air with commercially available force microscope (Park Scientific Instruments).
[I21 I n cooperation with Dr. Christoph Gerher and Dr. Bruno Michel (IBM
Research Laboratories Riischlikon, Switzerland), measured in air with a
commercially available force niicroscope (Nanoscope 111, Scientific Instruments).
4 (4) D,,
5 (4)
c3>
Scheme 1. Schematic structures of isomers 1 - 5 . The numbers in parentheses
indicate the number of imaginary frequencies at the HF/3-21G level. None of
these isomers corresponds to a minimum on the potential energy surface and all
are much higher in energy than 6 - 13.
have now proven to be high in energy and to have several
imaginary frequencies; we will not refine them further at
higher levels here. Note in particular that at the HF/3-21G
level the ethylene-like D,, structure 1 has five imaginary
frequencies and is 41.0 kcalmol-' higher in energy than
structure 6. Structures 6-13 (Scheme 2) are energetically
much more favorable. All geometries were optimized1'] at
the electron-correlated MP2/6-31G* level, and single-point
calculations were carried out at the MP4(SDTQ)(FC)/631 + G* level [MP4(SDTQ)(FC)/6-31+ G*//MP2(FU)/631G*].['ol Structures 6- 13 all have short carbon-carbon
bonds (1.265-1.281 A), and while the average length ex-
The Isomers of the Acetylene Derivatives C,Li,:
Transferable Structural Units in Hyperlithiated
Compounds**
-
By Andrea E. Dorigo, Nicolaas J. R. van Eikema Hommes,
Karsten Krogh-Jespersen, and Paul von Ragut Schleyer*
Hyperlithiated molecules['"I such as CLi, ,[I3 OLi4,[31
PLi, ,I4] and OLi,,1'"*41which formally violate the octet rule,
cannot be defined in terms of classical Lewis structures. Instead they involve bonding between the metal ligdnd~[~'
and
between the metal ligands and the central atom. We now
describe C,Li, isomers which are not ethylene-like but which
also exhibit hypermetallic bonding. Several stable Li, structural units common to hyperlithiated molecules are discernable in the optimized structures.
The experimental evidence for C,Li, is modest: Lagow
etal. observed C,D, among the deuterolysis products of
lithiated substrates.[61Although we have computed various
structures of C,Li, for over more than a decade, no thorough comprehensive study has been undertaken before. Only a few calculations of several possible C,Li, structural
candidates, performed at the SINDOl, HF/STO-3G, and
HF/3-21G levels, have been mentioned in the l i t e r a t ~ r e . ~ ~ .
However, the highly symmetrical structures 1-5 (Scheme 1)
Q
\
W
[*] Prof. Dr. P. von R. Schleyer, Dr. A. E. Dorigo,
Dr. N. 1. R. van Eikema Hommes
Institut fur Organische Chemie der UniversitXt Erldngen-Nurnberg
D-W-8520 Erlangen (FRG)
[**I
Prof. Dr. K. Krogh-Jespersen
Department of Chemistry, Rutgers
The State University of New Jersey
New Brunswick, NJ 08903 (USA)
This work was supported in Erlangen by the Fonds der Chemischen Industne, the Deutsche Forschungsgemeinschaft, and the Convex Computer
Corporation. A. E. D. was supported through a postdoctoral fellowship
from the Alexander von Humboldt Stiftung. We thank J. A. Pople, E. D.
Jenimis. and A. J. Kos for early computations on this project.
1602
'0VCH
V~rlag.~~esellschafi
mhH, W-6940 Weinherm. 1992
4.3
12 (0). c,
Scheme 2. MP2/6-31G* optimized structures and relative energies of the C,Li,
isomers 6-13. The number of imaginary frequencies (0 = minimum, 1 =
transition state) at the MP2/6-31G* level is given in parenthesis after the compound number. Relative energies (bold, in kcalmol-') were calculated at the
MP4(SDTQ)/6-31+G*,'/MP2!6-31G* level.
0570-0833/92:1212-16(J2$3.50+ .2Si0
Angew. Chem. Int. Ed. Engl. 1992, 31, No. 12
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