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Application of the LangmuirЦBlodgett Technique to Polyoxometalates Towards New Magnetic Films.

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'i9Sn{iH} NMR (111.92 MHz, CDCI,): 6 =118.0 [4J(1'9Sn,ii7Sn)=I59 Hz],
131.1 [4J ('i9Sn,ii7Sn)=169 Hz]; ' HNMR (400.13 MHz, CDCI,): 6 = 0.18 (s,
18H, SiMe,), 0.37 (s, 6H, SiMe,), 0.89 [s, 2J(iH,1i9Sn)= 91 Hz, 4H, SnCH,Si],
1.04 [s, 2J('H,i'9Sn) =79 Hz, 4H, SnCH,Si], 1.82 (t. 4H, CH,Sn), 1.93 (t, 4H,
CH,Sn), 2.33 (quint, 4H, CH,); i3C{'H} NMR (100.63 MHz, CDCI,): 6 =1.00
(SiMe,), 1.19 (SiMe,), 12.04,12 44(SnCH,Si), 20.80 (CH,), 29.27,30.42 (CH,Sn);
29Si{'H} NMR (59.63 MHz, CDCI,): 6 = 2.66 [zJ(29Si,ii9Sn)= 35 Hz, SiMe,],
5.55 [zJ(29Si,1i9Sn)= 49 Hz, SiMe,]. M.p. 79-81 'C. Analysis calcd. for
C 19.60, H 3.99; found: C 19.20, H 3.92%.
3 . (tBu,SnO), (225 mg, 0.30 mmol) was added in small portions to a solution of 1
(500 mg, 0.60 mmol) in CH,CI, (20 mL). After heating at reflux for 15 min, the
solvent was distilled off. The residue was washed several times with n-hexane and
recrystallized from chloroform to give 3 as colorless crystals (430mg, 96%).
'i9Sn{iH}NMR (111.92 MHz, CH,CI,/D,O,.,): 6 = - 94.0 [2J("9Sn,i'7Sn) =
65 Hzl, -114 4 [2J(ii9Sn,ii'Sn) = 62 Hz], -134.0 [2J(i'9Sn,"7Sn) = 65 Hz],
-142.8 [2J("9Sn,''7Sn) = 61 Hz]; ' H N M R (400.13 MHz, CDCI,): 6 = 0.17 (s,
36H, Me,Si), 0.23 (s, 36H, Me,Si), 0.85 [s, 2J('H,ii9Sn)= 120 Hz, 8H, SnCH,Si],
= 122 Hz, 8H, SnCH,Si], 1.73 (m, 16H, CH,), 2.02 (t. 8H,
0.96 [s, zJ(iH,liYSn)
CH,), 2.11 (t, 8H, CH,), 2.47 (m. 8H, CH,), 2.58 (m, 8H, CH,); l3C{'H} NMR
(100.63 MHz, CDCI,): 6 =1.21, 1.74 (Me,Si), 17.48, 20.34, 20.48, 20.92
(SnCH,Si), 34.96, 35.56 (CH,Sn), 35.93, 39.56 (CH,). M.p. 297-299'C. Analysis
calcd. for C,,H,,,CI,,O,Si,Sn,,:
C 22.58, H 4.56; found: C 23.12, H 4.76%.
4: (tBu,SnO), (273 mg, 0.37 mmol) and 2 (607 mg, 0.55 mmol) were allowed to
react analogously to the procedure described for the synthesis of 3 to give 180 mg
(37%) 4 as colorless crystals after recrystallization from toluene. '"Sn{'H) NMR
(111.92MHz. CDCI,): 6 = -91.2, -106.7, -129.4, -141.7; ' H N M R
(400.13 MHz, CDC1,): 6 = 0.12 (s, 36H, Me,Si). 0.19 (s, 36H, Me,Si), 0.26, 0.35
(s, 24H, SiMe,), 0.86,0.95,0.97, 0.98 (s, 32H, SiCH,), 2.05,2.15 (t, 16H, SnCH,),
2.64 (m, 8H, CH,); IsC{'H} NMR (100.63 MHz, CDCI,): 6 = 1.18, 1.67 (Me,Si),
4.06, 5.96 (SiMe,), 14.71, 16.96, 17.00,20.37 (SnCH,Si), 20.64,20.98 (CH,), 30.90,
34.27, 37.90, 38.01 (CH,Sn). M.p. 259-261 "C Analysis calcd. for
C 21.77, H 4.43; found: C 21.21, H 4.25%.
Received : November 18, 1996
Revised version: January 31, 1997 [29793 IE]
German version: Angew,. Chem. 1997, i09, 1150- 1152
Keywords: ladder structures
0 VCH Verlagsgesellschaft mbH, 0.69451
Weinhelm, 1997
Application of the Langmuir-Blodgett
Technique to Polyoxometalates:
Towards New Magnetic Films""
Miguel Clemente-Leon, Christophe Mingotaud,*
Beatrice Agricole, Carlos J. G6mez-Garcia,
Eugenio Coronado,* and Pierre Delhaes
- structure elucidation - tin
[l] D. C. Gross, Inorg. Chem. 1989, 28, 2355.
[2] P. G. Harrison, M. J. Begley, K. C. Molloy, J Organomet. Chem. 1980, i86,
[3] S:G. Teoh, E:S. Looi, S:B. Teo, S.-W. Ng, J Organomet. Chem. 1996,509,57.
[4] S . P. Narula, S . Kaur, R. Shankar, S. K. Bharadwaj, R. K. Chadha,
J. Organornet. Chem. 1996, 506, 181.
[5] a) C. Vatsa, V. K. Jain, T. Kesavedas, E. R. T. Tiekink, J Organornet. Chem.
1991, 408, 157, and references therein; b) J. J. Daly, F. Sanz, Helv. Chim. Acta
1970, 53, 1879; c) A. J. Banister, W. Clegg, W. R. Gill, J Chem. Soc. Chem.
Commun. 1987,850; d) D. R. Armstrong, D. Barr, W. Clegg, S . M. Hodgson,
R. E. Mulvey, D. Reed, R. Snaith, D. S. Wright, J Am. Chem. Soc. 1989,111,
4719; e) E. Hey-Hawkins, E. Sattler, J Chem. SOC.Chem. Commun. 1992,775;
f ) B. Neumiiller, F.Gahlmann, M. Schafer, S. Magull J Orgummet. Chem.
1992, 440, 263; g) P. Losier, J. Zaworotko Angew. Chem. 1996, 108, 2957;
Angew. Chem. Int. Ed. Engl. 1996, 35, 2779.
[6] a) J. Otera, T. Yano, A. Kawabata, H. Nozaki, Tezrahedron Leu. 1986, 27,
2383; b) J. Otera, T. Yano, Y Himeno, H. Nozaki, ibid. 1986, 27, 4501; c) J.
Otera, H. Nozaki, ibid. 1986, 27, 5743.
[7] a) J. Otera, N. Dan-Oh, H. Nozaki, J Org. Chem. 1991, 56, 5307; b) J. Otera,
S . Ioka, H. Nozaki, ibid. 1989, 54, 4013.
[8] J. Otera, N. Dan-Oh, H. Nozaki, Tetrahedron 1992, 48, 1449.
[9] J. Otera, N. Dan-Oh, H. Nozaki, J Chem. Soc. Chem. Commun. 1991,
[lo] J. Otera, K. Kawada, T. Yano, Chem. Lett. 1996, 225.
[ll] R. P. Houghton, A. W. Mulvaney, J Organornet.Chem. 1996, 517, 107.
[12] D. Dakternieks, K. Jurkschat, D. Schollmeyer, H. Wu, Organometallics1994,
M , = 2980.05, monoclin[13] Crystal structure data for 3: C,,H,,,CI,,O,Si,Sn,,,
ic, space group C2jc. a = 31.4100(17), b = 24.100(13), c = 21.602(12)A,
fl =125.34(4)", V=13339(15)A3,Z=4,pca,cd=1.484g~m-~,20,,, = 20.5",
= 0.71073 A, 0126' measurement, T = 200 K, 7428 reflecMo,, radiation, i.
tions measured with a Siemens-P4 diffractometer, 5858 independent reflections
(R,",.= 0.0464), refinement based on 5858 reflections, no u limits, no absorption corrections, Lp corrections, structure solution with direct methods
(SHELXTL), all non-hydrogen atoms were refined anisotropically, 426
parameters, H atoms were refined in idealized positions, R1 = 0.0889,
wR2 = 0.1942, R1 = 0.0673, wR2 = 0.01772 (I>2uI corresponding to 4535
reflections), full-matrix least-squares refinement against F 2 with SHELXL-93,
largest positive and negative difference peaks 1.300 and - 1.029 e k 3 .
[14] T. Yano, K. Nakashima, J. Otera, R. Okawara, Organomerallics 1985,4, 1501
[15] Crystal structure data for 4: C,,H,,CI,0,Si,Sn8.2C,H,, M , = 2170.99, triclinic, space group P1, a =12.724(3), h =13.002(13), c =14.334(11)&
a = 107.30(7), fl = 106.64(4), y = 103.36(4)", V = 2036(3) A', Z = 1, pCllcd=
= 0.71073 A, 0120 measure1.771 gem-,, 20,,, = 25.0", Mo,, radiation, i.
ment, T = 291 K, 7480 reflections measured with an Enraf Nonius CAD4
diffractometer, 7128 independent reflections (R,,, = 0.0334), refinement based
on 7128 reflections, no G limits, no absorption corrections, Lp corrections,
structure solution with direct methods (SHELXTL), all non -hydrogen atoms
except toluene were refined anisotropically, 31 1 parameters, H atoms were
refined in idealized positions, Rl = 0.1260, n'R2 = 0.0960, R1 = 0.0473,
nR2 = 0.0802 ( I > 2oI corresponding to 3483 reflections), full-matrix leastsquares refinement against F2 with SHELXL-93, largest positive and negative
difference peaks 0.747 and -0.558 e k ' . Crystallographic data (excluding
structure factors) for the structure reported in this paper have been deposited
with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC-179-171. Copies of the data can be obtained free of charge on
application to The Director, CCDC, 12 Union Road, Cambridge CB2 lEZ,
UK (Fax: Int. code +(1223)336-033; e-mail:
[16] M. Gielen, J. Topart, Bull. Soc. Chrm. Belges 1971, 80, 655; the compounds
were prepared according to a procedure described for Ph,Sn(CH,),X (X = CI,
Br) .
[17] (Ph,SnCH,),SiMe, (m.p. 91-92"C, 'i9Sn{'H} NMR (111.92 MHz, CDCI,):
6 = - 89.7) is prepared by the reaction of Me,Si(CH,MgCI), with Ph,SnCI. It
isconverted into almost insoluble (Ph,FSnCH,),SiMe, by subsequent reaction
with two equivalents of iodine and aqueous K F solution.
Soluble metal-oxide clusters (polyoxometalates) are receiving
increasing interest in materials science owing to their chemical,
structural, and electronic versatility."] Thus, because of the ability of these polyoxoanions to act as electron acceptors and to
accommodate magnetic transition metal centers in their structures, they are being used as the inorganic component of conducting radical salts based on tetrathiafulvalene-type organic
donors. Of particular interest is the preparation of organic-inorganic composites in which the localized magnetic moments of
the polyoxometalate cluster coexist with the mobile conducting
electrons of the organic network.[* 51 Other properties of these
materials, such as electrochromism r61 and electrocatalysis, have
been recently exploited in the preparation of conducting catalytic electrodes based on conducting polymers such as polypyrrole,['I polyaniline,[8.91 polythiophene['O1and poly(3-methylthiophene) .I1
More recently, the use of poly(N-methylpyrrole) with Fe3+-containing polyoxometalates has provided a
sensitive electrode for detection of nitrite." 31
[*] Dr. C. Mingotaud, Dr. B. Agricole, Dr. P. Delhaes
Centre de Recherche Paul Pascal - CNRS
Avenue A. Schweitzer, F-33600 Pessac (France)
Fax: Int. code +556845600
e-mail :
Prof. Dr. E. Coronado, M. Clemente-Leon, Dr. C. J. Gomez-Garcia
Dept. Quimica Inorginica Universitat de Valencia.
Dr. Moliner 50, E-46100 Burjasot (Spain)
Fax: Int. code +(6)386-4322
e-mail :
This work was supported by the European Union (Network on New Molecular
Conductors), the Ministerto de Educacion y Ciencia (CICYT) and the Generalitat de Cataluiia (CIRIT) (Grant QFN93-4510), and the Caja de Ahorros del
Mediterraneo. MCL thanks the Generalitat Valenciana for a predoctoral fellowship.
0570-0833/97/36i0-iii4 $17.50+ .SO10
Angew. Chem. I n / Ed. Engl. 1997,36, No 10
Here we show that organic-inorganic films containing well
organized layers of polyoxoanions can be built by using the
Langmuir- Blodgett (LB) technique. Such new hybrid materials
could be an important step towards the creation of new
supramolecular assemblies with a high degree of order and,
therefore, with improved physical properties.
To prepare the LB films we used the chemically stable Keggin
polyoxometalates [X"+W12040](s-n)-[X"' = 2(H+), Pv, SiIV,
B"', Co"]. All these anions have the same structure (Figure I),
v [cm-I]
Figure 2. Infrared spectra of the H,SiW,,O,, polyanion (KBr pellet) and of a
DODA/SiW,,O,, LB film (20 layers) on zinc selenide. The absorbance is given in
arbitrary units. The asterisk indicates the band associated with the CH, rocking
mode of DODA.
Br >N>
Figure 1. Polyhedral representation of the Keggin polyanions (a) and the formula
of the DODA molecule (b).
but depending on the nature of X, their charge varies between
-3 and -6. A monolayer of a cationic surfactant [dimethyldioctadecylammonium (DODA), see Figure I] was used as template for adsorption of the polyoxometalates. DODA monolayers on water or sodium chloride solution exhibit a poor lipid
density at the gas-water interface. Consequently it is not possible to produce ordered LB films having more than one layer
from these mono layer^['^^ because of the strong repulsion between polar heads in the monolayer and the strong interaction
of these polar heads with the water surface. In contrast, DODA
monolayers on solutions containing Keggin anions lead to ordered multilayers for anion concentrations in the range
1 0 - 7 ~Thus,
from a 1 0 - 6 solution
of H,PW,,O,,, DODA
monolayers could be efficiently deposited onto hydrophilic
solid substrate with a maximum transfer ratio between 0.9 and
1 at a surface pressure of 30 mNm-' and a dipping speed of
0.5 cmmin- Lowering the surface pressure or increasing the
dipping speed above 3 cmmin-' led to a drop in the transfer
ratio. These are general features for all the investigated polyanions that lead to Y-type deposits and optically defect-free LB
films designated as DODA/XW,,O,, .["I
Infrared linear dichroism and X-ray diffraction experiments
prove the well-defined lamellar structure of these built-up films
and the existence within the LB films of heteropolyoxometalates
organized in monolayers. The IR spectrum of DODA/SiWl,O,o
LB films is shown in Figure 2. Besides the peaks at 2920, 2851,
and 1467 cm- ' associated with the CH bonds of DODA alkyl
chains, very strong peaks are observed below 1200 cm-' for the
polyanion vibrations. These peaks are much narrower and generally slightly shifted relative to those in the spectrum of the
pure polyanions in a KBr pellet. This could be the result of a
lower degree of hydration of the Keggin anions in the multilayers and/or the organization of the polyanions within the LB
films. Indeed, the strong bands around 3300-3500 and 16001650 cm- ' assigned to stretching and bending modes of water
are absent in the LB films. This demonstrates that the anions are
largely dehydrated within the multilayers. Moreover, the observed peak shifts are surely related to the ordering and, in
particular, to the presence of positively charged DODA in the
film. Shifts in the Keggin IR peaks similar to those observed in
the LB films have been reported by Rocchioli-Deltcheff et a1.['61
for a series of Keggin salts with tetralkylammonium counterAngeu
Chrtn I n t
Ld Engl 1997, 36,No f0
ions. If we follow the interpretation of the frequency shift given
by these authors, our results indicate that the anion-anion distance within the LB films is so large that anion-anion interactions are negligible. Another remarkable feature of the IR spectra of the DODA/XW,,O,, LB films is the strong out-of-plane
dichroism (Figure 3). Thus, when the IR electrical field is not
9 0
v [cm-I]
Figure 3. Infrared spectra of a DODA/SiW,,O,, LB film (20 layers) on zinc selenide. The angle between the plane of the substrate and the electric field is either 0"
(solid line) or 60" (dashed line). The absorbance is given in arbitrary units. The
asterisk indicates the band associated with the CH, rocking mode of DODA.
parallel to the plane of the substrate, new peaks can clearly be
seen. This result shows that the Keggin polyanions have one
particular orientation (and distortion) in the multilayers, and
that they can be oriented by the Langmuir-Blodgett technique.
Finally, the dichroism of bands associated with the alkyl chains
allows a tilt angle of the DODA chains close to 30" to be estimated for all the prepared LB films.
X-ray diffractograms of DODA/XW12040LB films exhibit
three or four Bragg peaks. Such a number of peaks indicates
that the lamellar structure of those LB films is well defined. The
periodicity calculated from these data is close to 49 8, and is
independent of the nature of the polyanion. From these results,
one can estimate a thickness of about 10 8, for the inorganic
layer. In comparison with the radius of a Keggin polyanion
(ca. 5.2 A), such a value clearly demonstrates that each inorgan-
0 VCH Verlagsgesellschaft mbH, 0-694j1 Wernheim, 1997
$17 SO$
ic layer consists of one polyanion monolayer (and not a bilayer,
as would be conceivable for the Y-type transfer).
The magnetic susceptibility of a LB film was measured after
deposition onto a diamagnetic substrate (see Experimental Section). As can be seen in the insert of Figure4, the magnetic
4 1.Ox1O'1
0.61 .
Figure 4 Plot of %T(normahzcdvalue) versus temperature for the K jHCoW,,O,,
polyanion in the powder (open circles) and for the DODA/CoW,,O,, LB film (full
[cmu] of the DODA;CoW,,O,, LB
circles). insert reciprocal magnetization M
film vei-sus temperature. All data for the LB film are corrected for thc substrate
diamagnetism. and points around 40 K associatcd with adsorbed oxygen wcre
susceptibility of the DODA/CoW,,O,,
LB film follows the
Curie law down to about 20 K, as expected from the behavior
of K,HICoWi,O,,]. From such measurements and by comparison with the potassium salt, one can calculate how many paramagnetic polyanions are trapped within the LB film. The number of DODA molecules in the LB film is easily evaluated from
the size of the substrate, the transfer ratio, and the molecular
area at the deposition surface pressure. A comparison of these
two numbers gives a ratio of DODA molecules and polyanions
in the LB film close to 5 1. Such a value is close to the maximum charge of the polyanion in K,H[COW,,O,~](- 6).
At low temperature, the susceptibility of this polyanion decreases (see Figure 4) because of the zero-field splitting of Co"
in a tetrahedral e n ~ i r o n m e n t . "From
~ ~ such experiments, it appears that the magnetic site of such polyanions encapsulated in
the LB film is weakly (or not) sensitive to the surrounding
charge of the DODA molecules.
We have used the adsorption of Keggin heteropolyanions on
a positively charged monolayer of DODA and the LangmuirBlodgett technique to construct new organic-inorganic superlattices. Independent of the charge and the heteroatom in the
Keggin structure, these polyanions can be organized in monolayers in well-defined LB films. F o r the first time, we have performed susceptibility measurements on LB films and have
shown that the magnetic behavior of such an ultrathin material
can be characterized by using a magnetometer. Currently we are
investigating the effect of the size and shape of polyoxometalates on the formation of multilayers by using planar (Anderson
type) and elongated (Dawson- Wells type) anions. The preliminary results clearly indicate that the method described in this
paper can be extended to all types of polyanions or charged
clusters, to give rise to new lamellar organized materials. Appropriate choice of polyoxometalate and lipid molecule should
allow LB films having particular magnetic, optical, electrochromic, or electrochemical properties to be constructed.
mide was obtained from Kodak. All commercial compounds were used without
furthcr purification. Chloroform (HPLC grade, Prolabo) was used as spreading
solvent, and the lipid solutions (concentration ca. 1 0 - 3 ~wcrc
kept at -18'C
during cxperiments to limit solvcnt evaporation Built-up films wcrc obtained by the
vertical lifting mcthod at room tetnpcrature under a continuous stream of dry
nitrogen with a home-made LB Teflon trough A barricr moved by a d.c. motor
allows stepwisc compression of the monolayer. After cach increase of the surface
pressure, the system is allowed to reach equilibrium Steps of 2 m N m - ' wcre usually chosen. The subphase was Millipore Q-grade water with a resistivity higher than
18 MQcm. Dipping speed wasgenerally set to 0 5 cmtnin-I. Films werc transferrcd
onto optically polished calcium fluoride (precoatcd with three layers of bchenic acid
if necessary) or zinc aelenide for infrared linear measurements, and onto optically
polished glass substrate (treated with dichlorodiiiiethylsilane if needed) for low-angle X-ray experiments.
IR spectra were recorded on a FTIR 750 Nicolct spcctromcter. The IR linear
dichroism was measured to calculate the usual dichroic ratio R = A ( ; = 60-)i
A(i = 0'). wherc A(;) is the absorption coefficient, and I is the angle between the
plane of the LB film and the IR clectric vector. This ratio R is related to the degree
ofanisotropy outside the substrate plane and allows the angle between thc normal
to the substrate and thc dipole moment of a particular vibration [21]to be calculated
with a precision of few degrees. X-ray diffraction experiments (0-20 scans) wcre
performed with an INEL curve detcctor and an IBM computer for peak assignments [22]. The magnetic susceptibility was measured with a Quantum Design
MPMS-5 SQUID magnetometer between 2 and 300 K . For such experiments.
about 300 layers were deposited on a diamagnetic mylar shcet (0.075 x 5 x 15 mm).
Two experiments (substrate alone and then substrate with the LB film) wcre carried
out successively undcr the same experimcntal conditions (applied magnetic field
1 T). The difference gives the intrinsic magnetic susceptibility of the LB film. Experimental error on the calculated multilayer susceptibility was evaluated to be ca. 5 %
below 10 K , ca. 15% at 100 K, and over 30% at 300 K.
Received November 4, 1996 [Z9720IE]
German version: A n ~ e i i Cl7m7.
1997, 109, 1143--1145
Keywords: magnetic properties monolayers * organic-inorganic composite hybrids polyoxometalates * thin films
[l] (a) M. T Pope, Hrreropolj nnd 1 . ~ 0 p d jU.~ome/n/u/rs,
Springer, Heidelberg.
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In/. Ed. Engl 1991, 30, 34, c) P o / ~ ~ o . ~ o n 7 r l a l from
u r r ~ .Plutonic So1rd.s 10 Antirrtroiwd A c / i v i / j (Eds.: M T. Pope, A. Muller), Kluwer, Dordrecht, 1994.
[2] C. J. Gomez-Garcia, L. Ouahah, C. Gimtnez-Saiz, S. Triki, E. Coronado,
P. Delhaes, Angeii.. Chem 1994, 106. 234. Angrw. Cl7mn. 1111. Ed. Engl. 1994.
33, 223.
[3] C. J. Ghmez-Garcia. C. Gimencz-Saiz, S. Triki, E.Coronado, P. Le Maguct-es,
L. Ouahab, L Ducassc, C. Sourisseau, P. Delhacs, 1nor.g. Chrm. 1995,34,4139.
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Coronado, L. Ouahab, A17gcw.Chem. 1995, 107, 1601; Angoi.. Chrm In/. Ed.
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[ S ] E.Coronado, C. J. Gomez-Garcia, Comm~n/.sInurg Chrm. 1995, 17, 255.
[6] T. Shimidzu, A. Ohtani, M. Aiba, K. Honda. .I Chem. Soc. Furudaj,Trans.
1988,84, 3941.
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[XI G Bidan, E. M. Genies. M. J. Lapkowski, J Chem. Soc. Chem Cunmiin. 1988,
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[14] Z . Kozarac, R. C Ahuja, D. Miibius. Langinuir 1995, 11, 568.
[15] M. Clementc-Leon, B. Agricolc. C. Mingotaud, C. J. Ghmer-Garcia. E. Coronado, P. Delhaes, Lungnzirir 1997, 13. 2340.
[16] C. Rocchiccioli-Deltchcff, M. Fournier. R. Franck, R Thouvenot. Inorg
Chem. 1983, 22,201.
[I71 R. L Carlin, MuRne/othenzi.,ir;~.Springer, Heidelberg 1986.
[18] V. C. Simmons, PhD thesis. Boston University (USA), 1963.
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[20] A. Teze, G. Herve, J Inorg. Nucl. Chem. 1977, 3Y, 999.
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1221 E. Dupart, B. Agrtcole. S. Ravaine, C. Mingotaud, 0 . Fichet, P. Delhacs, 1-1.
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Expevimen tal Sect ion
The following hcteropolyoxometalates were used: H,[SiW,,O,,]
H,(PW,,O,,] (Prolaho): K,H[CoW,,O,,,] and K,[BW,,O,,] were synthesized accordingly to litcrature proccdures.'i"zO1. Dimethyldioctadecylainmonium bro-
VCH l~,r./u,~.sgese/h~hcrftifift
mhH, 0-69451 Weinheim, 1997
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A n g m . C'hrm. Inr EX Eii,d 1997. 36. .\(I
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