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Mutual Catalysis of Neutral and Anionic Cobalt Carbonyls in Their CO Scrambling Reactions.

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CAS Registry numbers:
KCeSe,. 144586-78-7; K,Se. 1312-74-9; Se, 7440-45-1; Ce, 7782-49-2.
El
e
8
El
El
E 200
-
h
4
100
v
0
100
0
200
T [Kl
-
300
Fig. 4. Plot of l/x, vs. T ; data taken at 500 G for KCeSe, The inset graph
shows an expanded plot of the region between 2-50 K.
The magnetic susceptibility of KCeSe, was measured from
2 to 300 K at 500 G ; a plot of l/x vs. Tis shown in Figure 4.
KCeSe, appears to be paramagnetic, although several
anomalies in the data are present. At temperatures below
100 K, the curve deviates negatively from a straight line extrapolated from the higher temperature data. Similar deviations have been reported for several Ce3+ compounds and
have been attributed to crystal-field splitting of the cation's
'FSiz ground state.[g1 At temperatures above 100 K, the
Curie-Weiss law is not strictly adhered to, and a slight curvature remains in the data. In this temperature range an average peffvalue of 2.29 pB has been calculated. This value is in
accordance with the usual range for Ce"' compounds (2.32.5 pB) and is close to that of the free ion (2.54 pB) due to the
shielding effect the outer electron cloud has on the embedded
f orbitals.["] We found that the measurements must be done
on freshly prepared samples of KCeSe,; older samples tend
to give artificially high values for peff, implying a phase
change. This phase change probably occurs to a small extent
on the sample surface because the bulk of the sample remains
intact as shown by X-ray powder diffraction.
With the synthesis of KCeSe,, we have demonstrated that
alkali metal polychalcogenide fluxes can be employed to synthesize new lanthanide polychalcogenide materials. This,
along with the recently discovered molecular complex
[U(Se,)4]4-,[111 also synthesized from a molten salt flux,
opens the entire f block to further investigation. Given the
potential these metals have for eightfold coordination and
the known structural diversity of polychalcogenido ligands,
the possibilities for synthesizing new and novel structure
types become intriguingly vast.[*]
KCeSe, was synthesized from a reaction of K,Se (0.078 g. 0.5 mmol). Ce
(0.035 g, 0.25 mmol). and Se (0.158 g, 2 mmol). These starting materials were
thoroughly mixed in a glove box under a nitrogen atmosphere and loaded into
pyrex tubes, which were subsequently evacuated to approximately
2x
mbar and flame-sealed. The mixture was heated at 300 'C for 6 days
and cooled at a rate of 2"Ch-I to 1OO'C then cooled to S O T in 1 h. The
product was isolated by dissolving away the residual polyselenide flux with
several portions of degassed dimethylformamide ( D M F ) under a nitrogen atmosphere until the solvent remained dear, indicating complete removal of the
polyselenide. The remaining material consisted of deep blue to black chunks of
KCeSe,. The oroduct was insoluble in D M F and was inert in both air and water
for extended periods, although some surface degradation was evidence in the
magnetic susceptibility studies. Homogeneity was confirmed by a comparison
of the product's powder X-ray diffraction against one calculated with X-ray
single-crystal data. A yield of 61 %, based on Ce. was typical.
Carbonyl substitution is thought to be an important step
in many syntheses and catalytic processes involving metal
carbonyls, and there is a considerable interest in methods of
assisting thermal substitution of CO ligands."] It was
thought that [Co(CO)J. like a number of mononuclear
18-electron carbonylmetalates, for example p(CO),] -,
[Mn(CO),]-, [Re(CO)J, does not react with either labeled
CO or phosphanes.['I However, it was recently shown that
alkali metal counterions accelerate the substitution reactions
.
Received: June 9, 1992 [Z 5396 IE]
German version: Angew. Cheni. 1992, 104, 1674
1596
Mutual Catalysis of Neutral and Anionic Cobalt
Carbonyls in Their CO Scrambling Reactions**
By Gitiseppe Fachinelti* and Tiziana Funaioli
Experimental Procedure
I
[l] J. Flahaut in Hundhuok on the Physics and Chemisrry of Rare Earths:
Vol. 4 . Nun-Metallic Compuunds (Eds.: K. A. Gschneidner, Jr., L Eyring),
North-Holland, Amsterdam, 1979. p. 1. and references therein.
[2] a) M. G. Kanatzidis, Chem. Muter. 1990, 2, 353-363; b) M. G.
Kanatzidis, Y. Park, J Am. Chem. Soc. 1989. 111, 3767-3769; c) M. G.
Kanatzidis, Y Park, Chem. Muter. 1990, 2, 99-101; d) Y Park, M. G.
Kanatzidis, Angew. C h ~ m .1990, 102, 945-947: Angen.. C h m . h i . Ed.
Engl. 1990. 29, 914-915.
[3] a)S. A Sunshine, D. Kang, J. A. Ibers, J Am. Chem. Sue. 1987, 109,
6202-6204; b) D. Kang. J. A. Ibers, Inurg. Chem. 1988, 27. 549-551.
[4] Crystals of KCeSe, are tetragonal. space group P4/nhm (no. 125)
with u = 6.376(2), c = 8.329(1) A, V = 338.6(2) A', 2 = 2, QGn,' =
4.855 g ~ m - Measured
~ ;
reflections: 949; independent reflections: 916:
reflections with F: > 3 0 ( F , ) : 302. Complete anisotropic refinement
(11 variables), resulted in a final R = 0.039. R, = 0.049. Measurement
temperature 23 "2. Rigaku AFC6 diffractometer (Mo,, radiation,
[ f = 572.140 cm-', 20,,,
= 60.00"); structure was solved with TEXSAN.
empirical absorbtion correction (DIFABS). Further details of the crystal
structure investigation may be obtained from the Fachinformationszentrum Karlsruhe, Gesellschaft fur wissenschaftlich-technischeInformation
mbH. D-W-7514 Eggenstetn-Leopoldshafen 2 (FRG), on quoting the depository number CSD-56489. the names of the authors. and the journal
citation.
[5] F. Hulliger, Struct. Bonding (Berlin) 1968, 4. 83-229.
[6] K. Selte. A. Kjekshus, Actu Chem. Scundu. 1964. 1R, 690-696.
[7] a) Compounds of the type ALnQ, (A = Na; Ln = La, Ce, Pr, Nd; Q = S)
were first synthesized by Ballestracci and Bertaut (R. Ballestracci, E. F.
Bertaut. Bull. Sue. Fr. Mineral. Cry~rkdlogr.1964, 87, 512). They and
others expanded the range of compounds to include A = Li, K, Rb, Cs:
Q = Se; and several other lanthanides L, [7 b-h]. In general the compounds with large values for the radius ratio, rLn,+:rAIfavor the disordered NaCl structure. whereas smaller values (0.6-1.2) tend toward the
1-NaFeO, structure type [7i,j]; b) R. Ballestracci, E. F. Bertaut, ;bid. 1965.
88. 136: c) R. Ballestracci. [hid. 1965, 88, 207, d) M. Tromme. C. R.
S e a n m Acud.Sci. Ser. C. 1971,273,849; e) W. Bronger, R. Elter, E. Mans,
T. Schmidt, Rev. Chim. M f n e r . 1974, 10, 147; f) S. Kabre. M. Juhen-Pou201. M. Guittard. Bull. SUC.Chim. Fr. 1974, 10, 1881 ; g) C. M. Plug, G. C.
Verschoor, A m Cry.rtullogr. Sect. B 1976,32, 1856; h) T. Ohtani. H. Honjo, H. Wada, Muter. Res. Bull. 1987,22, 829-840: i) W. Bronger, Crysrullogrupliy und C r j s t u l Chemistry of Muleriuls n,ith Layered Structures (Ed. :
F. Levy). Reidel Dordrecht. 1976, p. 93; j) M. Brunei, F, DeBergevin, M.
Gondrand, J Phrs. Chem. S o l i h 1972, 33%1927.
[8] Recently we have succeeded in synthesizing and structurally characterizing
by X-ray diffraction a new phase isostructural to KCeSe,: RbCeTe,. The
space group of RbCeTe, is P4/nhm with u = 6.952(3) and F = 9.084(4) A.
The Ce-Te, Te-Te. and R b T e bonds are 3.285(1), 2.776(2) and 3.765(1) A.
respectively. R = 0.031, R , = 0.024.
[9] a) H. Lueken. W. Bruggemann. W. Bronger, J. Fleischhauer, J Les.T-Cunmun Met. 1979. 65, 79-88; b) M. Duczmal. L. Pawlak, J Mugn. Mug".
Muter. 1988, 76-77, 195-196.
[lo] N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, Pergamon
Press, 1984, p. 1443.
[ l l ] A. C. Sutorik, M. G. Kanatzidis, J. Am. Chem. Sue. 1991, 113,7754-7755.
8
VCH Verlugsgesellschaft mbH, W-6940 Weinheim, 1992
[*I
Prof. Dr. G. Fachinetti, Dr. T. Funaioli
Dipartimento di Chimica e Chimica Industriale Universita di Pisa
Via Risorgimento, 35, 1-56106 Pisa (Italy)
[**I This work was supported by Minister0 dell' Universita e della Ricerca
Scientifica e Tecnologica (MURST). We thank Dr. G. Fochi for helpful
discussions.
057U-UX33/92/12i2-i596$3.50+.25/0
Angew. Chem. Inr. Ed. Engl. 1992, 31. Nu. 12
of CO groups in [Co(CO),]- in tetrahydrofuran (THF) solution: [31 the important role of ion-pairing phenomena was
recognized, and the involvement of the 16-electron species
[Co(CO)J suggested.
when we found the anionic cluster [Co,(CO),,]- as a
product of the reaction between the ion-pair activated [Co(CO),]- and traces of oxygen. After the short exposure of a
0.015 M diethyl ether solution of Na[Co(CO),] to air, the
formation of [Co,(CO),,]- was revealed by the appearance
of an intense red color (,?,,ax = 530 nm); moreover analysis
of the solution by IR spectroscopy revealed an absorption at
2006 cm- characteristic for [Co,(CO),,]- .[71On the other
hand, it has been stated that [Co,(CO),,]- participates in the
fast equilibrium reaction (a),''. and it has also been observed that CO groups of this anionic cluster interchange
rapidly with each other through a fast equilibrium between
terminal and edge-bridging CO groups [see Eq. (a)].[91
r
I
I
-
2000
2200
1900
1800
0
1-
I
1700
~~crn-'~
oc'&co
Fig. 1. IR spectrum ofa solution of [NaCo(CO),] (0.02 M) In THF equilibrated
under a I3CO atmosphere (ratio CO/13C0= l / l ) .
Our own investigations of the factors affecting lability of
CO ligands in [Co(CO),]-, however, show that ion pairing
with alkali metal counterions does not promote thermal CO
dissociation from the carbonylmetalate at room temperature. Such a dissociation would require ' 3 C 0 exchange with
Na[Co(CO),] to occur in THF, in which ion pairs are evident.[,] However, this is not the case if the solution is pretreated with a reducing agent in order to destroy adventitious oxidants. The addition of the homogeneous reducing
agent [CoCp,] (Cp = $-cyclopentadienyl) to a 0.02 M sohtion of Na[Co(CO),] (1 : 10 molar ratio) completely inhibits
the scrambling reaction between [Co(CO),]- and gaseous
I3CO. On the other hand, CO exchange is initiated by oxidizing the solution with sufficient oxygen to destroy the added
[CoCp,]: the IR spectrum shown in Figure 1 is obtained
within 30 to 90 min at room temperature, when the CO ligands of Na[Co(CO),] are equilibrated with an equimolar
amount of 13C0 in T H E It seems possible, therefore, that
the previously reported facile substitution reactions of [Co(CO),]- with acidic counterions in THF""] had arisen from
a mechanism induced by traces of oxygen. Thus, the ionpairing phenomena may merely increase the air sensitivity of
[Co(CO),]- due to perturbation by the polarizing
Accordingly, the symmetrical [Co(CO),]- with a PPN+
(PPN = bis(triphenylphosphoranylidene)ammonium)
counterion reacts only slowly with air, and was found to be
inert towards substitution reactions.
These findings indicate that CO scrambling reactions of
[Co(CO),]- follow a chemical oxidation and are therefore an
example of electron-transfer catalysis (ETC).['] A radicalchain mechanism would account for this ETC: trace
amounts of oxygen react with [Co(CO),]-, when the latter
is activated by ion pairing; the intermediate [Co(CO),]'
could thus be generated. Like other 17-electron metal carbony1 radicals [Co(CO),].is expected to be prone to substitution : electronic stabilization of the 19-electron hypervalent transition state, resulting from the association between
the 17-electron radical and the incoming ligand, supplies the
low-energy pathway for the substitution process.
An alternative mechanism for the CO scrambling of
[Co(CO),] catalyzed by electron transfer suggested itself
+
A n g c ~ .Clxw. Inr. Ed.
En$ 1992. 31, N o . 12
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Therefore, we propose that [Co,(Co),J is the intermediate which causes the observed lability of the CO ligands of
both neutral and anionic cobalt carbonyls in a solution
where [Co(CO),]- and [Co,(CO),] or [Co,(CO),,] exist
simultaneously. This hypothesis requires that even the CO
ligands of the reportedly inert PPN[CO(CO),][~"]are activated by catalytic amounts of either [Co,(CO),] or [Co,(CO), z]
and that, reciprocally, catalytic amounts of [Co(CO),]- salts
make the CO ligands of neutral cobalt carbonyls labile. We
found that under a CO atmosphere, catalytic amounts of
[Co,(CO),] promote CO scrambling in PPN[Co(CO),]
(case a), under an inert atmosphere, catalytic amounts of
[Co,(CO),,] promote the CO scrambling between PPN[Co(CO),] and PPN[CO('~CO),](case b). and that reciprocally,
catalytic amounts of Na[Co(CO),] accelerate the CO scrambling between [Co,(CO),] and gaseous I3CO (case c) and promote the scrambling between [Co,(CO),,] and [Co,(' 3CO),,]
under an inert atmosphere (case d).
Case a: While PPN[Co(CO),] is known not to incorporate 13C0 at room temperature,[3a1upon addition of [Co,(CO),] to a 0.016111 THF solution of the PPN' salt
([Co,(CO),]/PPN[Co(CO),], 0.05 molar ratio), a fast CO
scrambling occurs. The IR spectrum shown in Figure 2 is
obtained within 15 min when CO ligands bonded to cobalt
are allowed to equilibrate with equimolar amounts of
gaseous "CO.
Case b: Under an argon atmosphere, no CO scrambling is
observed in a solution of PPN[Co(CO),] and PPN[Co('3CO),] (each 0.08 M)in THF: the CO stretching region of
the IR spectrum (Fig. 2 dashed line) remains unchanged for
hours and shows two strong bands at 1887 and 1842 cm-'
due to unperturbed [Co(CO),]- and [CO('~CO),]-, respectively. A weak absorption at 1808 cm-' accompanies the
c, VCH ~ , r l [ i ~ s ~ ~ s e l l s c .mbH,
h u / t W-6940 Wrinhrim, 1992
U57O-o833/92/12r2-1597$3.50+ ,2510
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2000
1900
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1800
1700
Fig. 2. IR spectrum of a solution of PPN[Co(CO),] and PPN[Co(I3CO),] in
THF (both 0.08 M) (dashed line) and after the addition of a catalytic amount of
[Co,(CO),,] (solid line).
2iOO
band at 1842 cm-' and is probably due to traces of 13C1s0.
However, if [Co,(CO),,] is added to the solution of PPN[Co(CO),] and PPN[Co(' 3CO),] ([Co,(CO),,/tetracarbonylcobaltates, 0-01 molar ratio), the IR spectrum in Figure 2 (solid line) shows that complete CO scrambling occurs
immediately after mixing.
Case c: In agreement with Brown et al.,['OJwe found that
the [CO,(CO),]/'~COscrambling reaction proceeds even in
the absence of [Co(CO),]- ; however, the addition of Na[Co(CO),] accelerates this reaction in Et,O at 0 "C. As monitored by IR spectroscopy (Fig. 3), equilibration of a 0.013 M
solution of [Co,(CO),] in Et,O with I3CO at atmospheric
pressure requires 50 min, whereas following the addition of
Na[Co(CO),] to this solution (0.1 molar ratio) complete
scrambling is attained within 10 min.
2200
-a
2000
1900
Icrn-']
1800
1700
Fig. 3. IR spectrum of solution of [Co,(CO),] (0.013 M) in Et,O equilibrated
under a "CO atmosphere (ratio CO/13C0 = l / l ) .
Case d : Under an argon atmosphere, no CO scrambling is
observed in a solution of [Co,(CO),,] and [CO,('~CO),,]
(each 0.008 M) in Et,O on the timescale of the subsequent
experiment for the catalysis with Na[Co(CO),]. After one
hour at room temperature, the CO stretching region of the
IR spectrum of this solution is still the sum of the spectra of
isotopically pure [Co,(CO),,] and [CO,('~CO),,] (Fig. 4a).
However, the IR spectrum recorded immediately after the
addition of Na[Co(CO),] (molar ratio 1 :20) (Fig. 4b) shows
that the [Co(CO)J catalyzed CO scrambling occurs extremely rapidly.
I598
0 VCH
Verlugsgesrilsthufi mhH, W-6940 Weinhrrm,I992
-
2000
1900
1800
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Fig. 4. IR spectra of a solution of [Co,(CO),,]and [CO,('~CO),,]
in Et,O
(both 0.008 M) a) before, and h) after the addition of a catalytic amount of
Na[Co(CO),].
Our findings indicate that CO scrambling reactions of
[Co(CO),]- are electron transfer catalyzed processes that
can be initiated by traces of oxygen. While a radical-chain
mechanism was documented for other oxidatively induced
CO substitutions in metal carbonyls,isl in the present case a
redox condensation mechanism is proposed. In fact a redox
condensation between [Co(CO),]- and the neutral cobalt
carbonyls formed by the oxidation of [Co(CO),]- has been
observed"] [Eq. (a)]; this accounts for the mutual catalysis
of their respective CO scrambling. Furthermore, a radicalchain mechanism based on [Co(CO),]' cannot justify the
extremely rapid CO scrambling observed under an inert atmosphere (cases b and d), when compared to the relatively
moderate catalytic effect under a CO atmosphere (cases a
and c). On the contrary, the fact that the free, incoming CO
ligand slows the mutually catalyzed CO scrambling of both
neutral and anionic cobalt carbonyls can be rationalized by
assuming [CO,(CO),~]-as an intermediate. Its steady-state
concentration in a [Co,(CO),]/[Co(CO),]- solution is indeed controlled by CO partial pre~sure.~']Apart from the
mechanism which needs further support, this work demonstrates that the fundamental property of both neutral and
anionic cobalt carbonyls, that is, CO ligand lability, is influenced dramatically by the presence of complexes belonging
to the other class.
These observations are of general interest, first because the
[Co(CO),] ions formed in disproportionation reactions always accompany neutral cobalt carbonyls, unless in hydrocarbon solvents and under strictly controlled conditions, and
second neutral cobalt carbonyls can be formed by oxidation
of [CO(CO),] -.
~
Experimental Procedure
Solid Na[Co(CO),] (78 mg, 0.40 mmol) was added under argon to a pale red
solution of [CoCp,] (0.002 M) in T H F (20 mL) in a 150 niL closed vessel.
Through a rubber septum. I3CO (99% isotopical purity, MSD Isotopes)
(38 mL, 1.6 nimol) was added to the atmosphere above the solution with a
syringe. After the solution had been stirred for 24 h, a sample was withdrawn
for IR analysis. 3 mL of air were then added, and additional samples were
withdrawn after 15, 30,60, and 90 min. The CO scrambling in PPN[Co(CO),],
+
0570-0R33/92iI2/2-I5Y8 $ .?.50 .25:0
A ~ z f i r w .Chenz.
Int. Ed. EngI. 1992, 31. No. 12
[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
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