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obviously a very stable state: the dye colloid can be heatedor stored for more than half a year at room temperaturewithout any flocculation.

The dispersion of 1a in water exhibits a deep red color(ruby-like; lmax = 499.0 nm, eeff = 31 830 M±1 cm±1; color co-ordinates: x = 0.4087, y = 0.3078, Y = 50.38 for 2�, normlightC, and UV-vis transmission Tmax = 0.1) and a moderatelyintense fluorescence (lmax = 544 nm). The UV-vis spectraof 1a are shown in Figure 2. It is remarkable that the fluor-escence excitation spectrum (lmax = 465 (sh), 496, and533 nm) differs from the absorption spectrum, which indi-cates that the major component is not the origin of fluores-cence, but some minor component, which may be even apartly disturbed lattice of 1a or especially oriented mol-ecules in the elementary cell.

Fig. 2. e vs. l for UV-vis absorption (solid line) and fluorescence (dashedline) and fluorescence excitation (dash±dot) spectra of a dispersion of 1a inwater. The dotted line is e vs. l for the absorption of 1a in chloroform (halfof the coefficient of extinction).

The formation of fluorescent colloids of dyes is of gener-al interest for scientific applications. Hydrophobic dyesmay thus be dispersed in water to form colloids of soliddyes. However, the preparation of such colloidal dyes re-quires special techniques. Problems such as sedimentationand flocculation occur, which diminish long-term stability.This may be compensated to some extend by employingprotective colloids. No such problems would be presentedif the colloid were a very stable state itself, which makesthe special value of dye 1a obvious. We are applying dye 1aas a tracer for the investigation of the movement of waterin order to answer geochemical questions. This is an inter-esting alternative to dissolved dyes as tracer because thereare no problems for dye 1a by adsorption in zeolites. Theresults of these investigations will be reported elsewhere.

Experimental

1a: Perylene-3,4:9,10-tetracarboxylic acid bisanhydride (270 mg,0.69 mmol), 2-aminomethyl-18-crown-6 (440 mg, 1.5 mmol), and imidazole(5 g) were heated at 140 �C for 1.5 h. 2N HCl (200 mL) was added, the mix-ture was stirred for 1 h at room temperature, and then extracted with

chloroform (600 mL). The chloroform extract was purified by column sepa-ration over Al2O3 (chloroform/ethanol 10:1), a second column separationover silica gel (chloroform/triethylamine 10:1), and filtration through a D4glass filter. It was then washed with diethyl ether and pentane and dried invacuo (0.01 torr, 24 h) to give 360 mg (55 %) of 1a. m.p. 290±291 �C; Rf (sil-ica gel, CHCl3/triethylamine 10:1) = 0.30; IR (KBr): n = 2911 m, 2865 m,1693 s, 1653 s, 1594 s, 1577 m, 1506 w, 1472 w, 1457 w, 1440 m, 1403 m, 1352m br., 1290 w, 1250 m, 1178 w, 1103 s br., 990 w, 959 w, 860 w, 835 w, 810 m,795 w, 747 m, 668 m cm±1; UV-vis (CHCl3): lmax (e) = 526 (82 700), 490(50 000), 459 (19 000) nm; Fluorescence (CHCl3): lmax = 533, 575 nm; 1HNMR (CDCl3): d = 3.63 (mc, 40 H, 20 CH2O), 3.87 (t, 4 H, 2 CH2O), 4.00(mc, 2 H, 2ÔCH<U->CH2), 4.31 (mc, 4 H, NCH2), 8.32 (d, J = 8.1 Hz, 4 H,perylene), 8.46 (d, J = 8.0 Hz, 4 H, perylene) ppm; 13C NMR (CDCl3): d =40.67, 69.72, 70.54, 70.58, 70.61, 70.73, 70.96, 72.70, 122.91, 122.97, 125.96,129.01, 131.18, 134.21, 163.23 ppm; MS (70 eV) m/z (%): 944 (20), 943 (58),942 (100) [M+], 912 (12), 898 (8), 854 (5), 810 (7), 798 (5), 766 (5), 723 (5),722 (5), 721 (6), 707 (9), 706 (12), 705 (19), 704 (16) [M+ ± C10H22O6], 693(8), 692 (14), 691 (8), 680 (8), 679 (13) [M+ ± C12H23O6], 487 (7), 486 (8), 485(9), 484 (6), 474 (6), 473 (10) [M+ ± 4 C2H4O ± C13H24O6 ± OH], 472 (9), 471(15), 470 (8), 460 (9), 459 (13), 458 (9), 457 (11), 456 (7), 455 (7), 447 (7), 446(19), 445 (10), 443 (11), 433 (6), 431 (6), 430 (9), 429 (17), 418 (7), 417 (9),416 (9) [M+ ± 2 C12H23O6], 415 (11), 404 (14), 403 (7) [M+ ± C13H24O6 ±C12H23O6], 391 (6), 390 (6) [M+ ± 2 C12H23O6], 275 (15), 175 (9), 149 (7), 133(15), 131 (11), 99 (9), 89 (37 (88 (5), 87 (84), 81 (7), 79 (9), 73 (17), 71 (6), 59(15), 45 (86) [C2H5O+]; C50H58N2O16 (943.0): calcd. C 63.68, H 6.20, N 2.97;found C 63.46, H 6.12, N 3.04.

Received: February 17, 1998Final version: April 29, 1998

±[1] H. Langhals, Heterocycles 1995, 40, 477.[2] H. Langhals, ªWater-Soluble Perylenetetracarboxylic Acid Bisimide

Fluorescent Dyesº, German Patent DE-3 703 513, 1987; Chem. Abstr.1988, 109, P212376w.

Multilayered Ferromagnets Based on HybridOrganic±Inorganic Derivatives**

By Valerie Laget, Claudie Hornick, Pierre Rabu,Marc Drillon,* Philippe Turek, and Raymond Ziessel

Molecular compounds with ferromagnetic propertieshave attracted considerable interest in recent years.[1] Re-markable results have been obtained by self-assemblingmolecular building units into compact structures,[2±4] suchas graphite or perovskite-like packing, which are moreusually observed in solid-state chemistry. Promising order-ing temperatures have been achieved in metal-based com-pounds; however, efforts to design high Curie temperatureorganic (radical-based) ferromagnets have not beencrowned with success to date, although strong intramolecu-lar ferromagnetic interactions have been reported between

±

[*] Dr. M. Drillon, Dr. V. Laget, Dr. C. Hornick, Dr. P. RabuInstitut de Physique et Chimie des MatØriaux de StrasbourgUMR 46 du CNRS23 rue du Loess, F-67037 Strasbourg (France)

Dr. P. TurekInstitut Charles Sadron, ULP6 rue Boussingault, F-67083 Strasbourg (France)

Dr. R. ZiesselLaboratoire de Chimie, d'Electronique et de Photonique MolØculairesECPM1 rue Blaise Pascal, F-67008 Strasbourg (France)

[**] The authors thank R. Poinsot and A. Derory very much for technicalassistance with magnetic measurements.

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p electrons in discrete molecules.[5] Intermolecular interac-tions between radicals do not appear to be very efficient atpromoting high ordering temperatures.[6,7]

The pioneering work on metal±radical-based complexes,made of alternating chains, has shown that significant ex-change coupling may occur between the two species.[8] Re-cently, exotic metal±radical rings and 2D systems havebeen reported, which confirm the existence of a significantcoupling through the p system of the bridging ligands.[9,10]

Consequently, the trend to develop hybrid organic±inor-ganic compounds is very appealing for the design of novel3D architectures in which the physical properties of the in-finite network and the radical species are closely related.Striking results have been obtained in photo-induced mag-netic and conducting materials[11,12] and in systems combin-ing two basic properties, conductivity and magnetism or op-tical properties and magnetism for instance.[13,14]

In previous papers, we have reported the correlations be-tween structure and properties of the anion exchangeablelayered compounds Co2(OH)3X, where X± is either an or-ganic (i.e., paraffinic chain) or an inorganic (i.e., halide) an-ionic spacer coordinated to the divalent metal ion.[15,16] Thestructure may be described as a two-dimensional (2D)triangular network of metal ions, held together through vander Waals interactions. The in-plane metal±metal distanceis close to 3.15 � whereas the interlayer spacing dependsstrongly on the size and stacking of the anionic spacers.The results have been shown to be very similar for cop-per(II) compounds.[17,18]

Ferromagnetic in-plane interactions usually dominatethe magnetic properties, while at low temperature thebehavior depends to a large extent on the interlayer spac-ing. For small spacing (less than 10 �) the interlayer inter-actions via hydrogen bonds stabilize 3D antiferromagnetic

order, and a metamagnetic transition occurs at low field.When the spacing is made larger, the compounds exhibit aspontaneous magnetization in zero field, even for spacingas large as 40 �.[19] Such a behavior has been explained byconsidering the dipolar through-space interactions betweenferromagnetic layers.[20] This interaction mechanism ismainly driven by the divergence of the in-plane spin±spincorrelation length as the ordering temperature is ap-proached. As a result, these materials may be viewed asgood prototypes of monolayer magnets interacting by aclassical mechanism of dipolar coupling to give a 3D ferro-magnet.

We report in this article the preparation and magneticproperties of the first hybrid cobalt(II)±radical-based com-pounds in which metal layers are interleaved with imino-nitroxide benzoate radical anions (para or meta, referred toas rad1 and rad2). Such novel compounds may be viewedas supramolecular multilayer magnets, which may be com-pared to the classical ferromagnetic metal-based superlat-tices.

Three compounds were obtained by exchange reactionof the nitrate groups in Co2(OH)3NO3 with the paramag-netic anions rad1 and rad2, and the diamagnetic bishy-droxyimidazolidine intermediate (prec1). During the ex-change process, the benzoate anions are coordinated to thecobalt(II) centers and nitrate anions are liberated, leadingto the desired multilayered material. The use of the non-magnetic radical precursor serves as an important controlsince it was anticipated, and later proved by experiment,that the structure of the resulting material (Co-prec1) wasclose to that obtained with the corresponding radical anion(Co-rad1). The synthesis of the host cobalt(II) compound,the organic derivatives, and the hybrid materials issketched in Figure 1.

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Fig. 1. Synthesis of the Co2(OH)3NO3 host compound, the 1,3-bishydroxyimidazolidine precursors precH1 and 2, the imino nitroxide benzoate radicals radH1and radH2, and the hybrid materials. The inorganic/organic exchange reaction was performed using a solution of radH1 (0.1 M) in water and a suspension ofCo2(OH)3NO3 in water at 50 �C and under argon. After 20 h, the resulting material was washed with water, dried under vacuum, and stored under argon.

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Co-rad1 and Co-rad2 are shown to be orange-brownwhile Co-prec1 is green. Chemical analysis confirms theCo2(OH)3.5(X)0.5×2H2O composition of the materials for X= prec1, rad1, and rad2, indicating the total exchange of ni-trate anions. The absence of residual nitrate groups waschecked by IR spectroscopy with the disappearance of therelated strongest bands (at 1424, 1340, and 1048 cm±1).Further, the small difference between the two characteris-tic carboxylate stretching vibrations (n(C=O) ± n(C±O) =150 cm±1) is consistent with a h-coordination of one oxygenatom to the cobalt center, and it is likely that the secondoxygen atom is involved in a hydrogen bond with the struc-tural water molecules.

Finally, the UV spectra indicate that the cobalt(II) ionslikely occupy both octahedral and tetrahedral sites in thethree hybrid compounds, as already mentioned for layeredtransition metal basic salts.[21,22] The comparison of the hk0reflections in the X ray powder patterns shows that thelayer structure and the Co±Co in-plane distance (a =3.15 �) are unchanged. In turn, the 00l reflections indicatea strong increase of the interlayer spacing, from d = 6.9 �in the hydroxide nitrate to 20.2 � for both Co-prec1 andCo-rad1, and 22.8 � for Co-rad2. This result is in goodagreement with the size and proposed stacking of the or-ganic molecules in between the layers (Fig. 1).

The magnetic properties of the hybrid compounds, re-corded on SQUID magnetometers (MØtronique and Quan-tum Design MPMS-XL), are given in Figures 2 and 3. Themagnetic behavior of the starting hydroxide nitrate is givenfor comparison.[23] The starting compound Co2(OH)3(NO3)exhibits features typical of a 2D ferromagnetic systemdown to T = 8.7 K, where long-range antiferromagnetic or-dering occurs due to small interlayer interactions. The in-plane (J) and out-of-plane (j) exchange interactions, calcu-lated by means of the Ising model, are shown to be J =7.4 K and j = ±0.2 K, respectively.

Fig. 2. Temperature dependence of the wT product for Co-rad1 (l), Co-rad2 (*) and the starting hydroxide nitrate (&). The susceptibility of Co-rad2 plotted in the inset shows the variation of the in-phase (w¢) and out-of-phase (w²) signals for an AC field of ±3.5 Oe.

Fig. 3. Temperature dependence of the remanent magnetization, normalizedto its T = 2 K value, for Co-rad1 (l), Co-rad2 (*), and Co-prec1 (^). Thevariation of magnetization with applied field is plotted for Co-rad2 in the in-set (T = 1.8 K).

The temperature dependence of the magnetic suscep-tibility (w) for the hybrid compounds Co-rad1 and Co-rad2differs drastically, as shown in Figure 2. Upon cooling fromroom temperature, the observed wT product shows a mini-mum around 60 K, and a strong divergence up to morethan 100 cm3 K/mol below 10 K. Then, a maximum of wToccurs, but in strong contrast with the hydroxide nitrate,neither compound orders antiferromagnetically. The ACmagnetic susceptibility (at 20 Hz and H = ±3.5 Oe) exhibitsan out-of-phase signal (plotted for Co-rad2 in the inset),which is the clear signature of a magnetic moment stabi-lized in the ground state. From the maximum of w¢, the or-dering temperatures are found to be 6.0 K for Co-rad1 and7.2 K for Co-rad2.

Field-dependent magnetization measurements confirmthese results. The magnetization against field, M(H), curvefor Co-rad2 (Fig. 3) exhibits a hysteresis loop characteristicof a ferromagnetic-like 3D order. At T = 1.8 K, the coer-cive field is found to be 510 Oe (340 Oe for Co-rad1), andthe remanent magnetization 1.18 mB mol±1 (1.15 mB mol±1

for Co-rad1), while the high field magnetization(~3.5 mB mol±1 at 8 tesla) is lower than expected for a com-plete ferromagnetic ordering of the moments. The simulta-neous presence of octahedral and tetrahedral symmetriesfor cobalt(II) ions may explain such a behavior by stabiliz-ing a ferrimagnetic ground state.

Accordingly, the cobalt(II) layers, which exhibit a net mo-ment in the ground state, may be viewed as supramolecularmagnets interacting at very large distance (>20 � apart)through a dipolar coupling mechanism responsible for the3D ordering.[20]

The thermal variation of the net magnetic moment showsclearly the similarity between Co-rad1 and Co-rad2(Fig. 3). Co-prec1, whose basal spacing is very close to Co-rad1, exhibits qualitatively the same behavior, but a muchhigher Curie temperature (T = 15.3 K) (Fig. 3).

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The presence of organic radicals grafted in between themetal-based inorganic sheets has a striking effect on thebulk behavior. The fact that the ordering temperature isstrongly affected suggests that a significant metal±radicalexchange interaction, rather than a simple polarization ofthe radicals by inorganic layers, takes place. The significantlowering of TC (by about 9 K) demonstrates that the coor-dination of cobalt(II) ions by nitroxide radicals modifiesconsiderably the interaction between inorganic layers.

The magnetic transition is clearly displayed in the firstderivative of the EPR absorption spectra in Co-prec1, Co-rad1, and Co-rad2, when recorded below the critical tem-perature (Fig. 4a). The broad feature appearing at low

field, below TC for all three compounds, is attributed to theCo layers coupling ferromagnetically to yield the 3D long-range order. Since the cobalt(II) layers are silent in electro-paramagnetic resonance (EPR) at higher temperature, thislow field hump corresponds to a ferromagnetic resonance.The polycrystallinity of the sample, without a well-definedshape of the crystallites, results in an ill-defined demagne-tizing field, hence an inhomogeneous broadening of thisresonance. Its decrease and shift as the temperature de-creases likely corresponds to the growth of the internalfield, as the magnetization is increasing in the ferromag-netic state.

As expected, the Lorentzian-shaped signal of the radicalis located close to the free-electron g-value at room tem-perature (see Fig. 4b). It is noteworthy that the radical lineobserved in the spectra of the radical-free precursor corre-sponds to unavoidable traces of radical impurities, whoseconcentration is estimated by EPR calibration to be 10±3

radical spins/mole. As observed in various radical-basedmagnets in the paramagnetic regime, the linewidth in-creases continuously and moderately, and the position ofthe resonance line, i.e., the g-factor, remains nearly un-changed from room temperature down to TC. Drasticchanges occur close to TC, as sketched in the low tempera-ture spectra of Figure 4b. A strong broadening of the EPRline and a large shift of the resonance field (see inset) aresimultaneously observed with the onset of bulk ferromag-netism. Therefore, the organic radical is actually probingthe cooperative alignment of the neighboring cobalt(II) mo-ments. The shift of the radical resonance means that theresonance field is no longer the applied Zeeman field. Inthe paramagnetic regime the spin Hamiltonian includes theZeeman interaction and the dipolar interaction with thesurrounding dipole moments. Added to these, the exchange

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Fig. 4. a) EPR spectra recorded at9.5 GHz, below the critical tempera-ture: upper trace, Co-rad2 at 4 K;middle trace, Co-rad1 at 4 K, lowertrace Co-prec1 at 10 K. Note thatthe magnitude of the trace is multi-plied by 250 for Co-prec1. b) EPRspectra of Co-rad2 showing the evo-lution of the line shape between 4 K(front spectrum) and 30 K (rearspectrum). The inset represents thetemperature-dependent shift of thecentral absorption signal (free radi-cal line) with respect to its positionat room temperature.

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interaction between i) radical spins, Jp±p, and ii) radical andcobalt spins, Jp±Co, must be considered. None of these isstrong enough to give striking effects at room temperature,e.g., strong exchange narrowing or line broadening due tofast relaxation processes. However, as TC is lower in theradical-based compounds, it appears that the sandwichedradical layer is actually counteracting the driving inter-action for the bulk ferromagnetic ordering.

The similarities in the physicochemical characterizationof the three compounds allow any significant structuralmodification between the radical derivatives and the pre-cursor compound to be excluded. The dipolar interactionHdip is assumed to be the driving interaction for the settingup of bulk ferromagnetism within the three compounds, asdemonstrated for alkyl-carboxylate parent compounds.[20]

It involves the in-plane spin±spin correlation function,which diverges critically as the layers order, thus promotingbulk ferromagnetism for the three materials. The loweringof the critical temperature for Co-rad1 and Co-rad2 com-pared to Co-prec1 must be attributed to the presence ofthe radical spins, since the interlayer distance is much thesame in the various compounds. Among the possible mech-anisms, it can be stated that the radical spins do not simplyline up within the internal field created when the cobalt(II)layers order, otherwise the net magnetic moment would in-crease up to saturation more rapidly for the radical deriva-tives. Moreover, the lowering of TC cannot be understoodwithin this scheme. Therefore, the observed effects aremore likely due to the exchange interaction Jp±Co. The co-balt(II) layers including the radical spins must order at low-er temperature than the radical-free compound, due to theeffect of Jp±Co.

In this respect, this new class of hybrid magnets differsmarkedly from the classical intercalated layer compounds,mostly because both sub-networks (inorganic and organic)are in strong interaction. This is very promising for the fu-ture design of multifunctional materials in which the prop-erties of the organic and inorganic networks are in closesynergy.

Received: March 6, 1998Final version: April 27, 1998

±[1] Proc. of the Conf. on Molecule-Based Magnets (Eds: K. Itoh, J. Miller,

T. Takui), Mol. Cryst. Liq. Cryst. 1997, 305±306.[2] S. Descurtins, H. W. Schmalle, P. Schneuwly, J. Ensling, P. Gütlich, J.

Am. Chem. Soc. 1994, 116, 9521.[3] V. Gadet, T. Mallah, I. Castro, P. Veillet, M. Verdaguer, J. Am. Chem.

Soc. 1992, 114, 9213.[4] H. O. Stumpf, L. Ouahab, Y. Pei, D. Grandjean, O. Kahn, Science

1993, 261, 447.[5] K. Matsuda, N. Nakamura, K. Takahashi, K. Inoue, N. Koga, H. Iwa-

mura, J. Am. Chem. Soc. 1995, 117, 5550.[6] M. Kinoshita, P. Turek, M. Tamura, K. Nozawa, D. Shiomi, Y. Nakaza-

wa, M. Ishikawa, M. Takahashi, K. Awaga, T. Inaba, Y. Maruyama,Chem. Lett. 1991, 1225.

[7] F. Romero, R. Ziessel, M. Drillon, J. L. Tholence, C. Paulsen, N. Kyrit-sakas, J. Fisher, Adv. Mater. 1996, 8, 826.

[8] A. Caneschi, D. Gatteschi, J. P. Renard, P. Rey, R. Sessoli, Inorg.Chem. 1989, 28, 2940.

[9] A. Caneschi, D. Gatteschi, J. Laugier, P. Rey, R. Sessoli, J. Am. Chem.Soc. 1988, 110, 2795.

[10] K. Inoue, H. Iwamura, J. Am. Chem. Soc. 1994, 116, 3173.[11] P. Gütlich, Mol. Cryst. Liq. Cryst. 1997, 305, 17.[12] Y. Sano, M. Tanaka, N. Koga, K. Matsuda, H. Iwamura, P. Rabu, M.

Drillon, J. Am. Chem. Soc. 1997, 119, 8246.[13] M. Kurmoo, A. W. Graham, P. Day, S. Coles, M. B. Hursthouse, J. L.

Caulfield, J. Singleton, F. L. Pratt, W. Hayes, L. Ducasse, P. Guion-neau, J. Am. Chem. Soc. 1995, 117, 12 209.

[14] R. ClØment, P. G. Lacroix, D. O'Hare, J. Evans, Adv. Mater. 1995, 6,794.

[15] M. Drillon, C. Hornick, V. Laget, P. Rabu, F. M. Romero, S. Rouba, G.Ulrich, R. Ziessel, Mol. Cryst. Liq. Cryst. 1995, 273, 125.

[16] V. Laget, S. Rouba, P. Rabu, C. Hornick, M. Drillon, J. Magn. Magn.Mater. 1996, 154, L7.

[17] P. Rabu, S. Rouba, V. Laget, C. Hornick, M. Drillon, Chem. Soc.Chem. Commun. 1996, 1107.

[18] W. Fujita, K. Awaga, Inorg. Chem. 1996, 35, 1915.[19] V. Laget, P. Rabu, C. Hornick, F. RomØro, R. Ziessel, P. Turek, M.

Drillon, Mol. Cryst. Liq. Cryst. 1997, 305, 291.[20] M. Drillon, P. Panissod, J. Magn. Magn. Mater., in press.[21] L. Markov, K. Petrov, V. Petkov, Thermochim. Acta 1986, 106, 283.[22] W. Stählin, H. R. Ostwald, Acta Crystallogr. B 1970, 26, 860. R. All-

mann, Z. Kristallogr. 1968, 126, 417.[23] P. Rabu, S. Angelov, P. Legoll, M. Belaiche, M. Drillon, Inorg. Chem.

1993, 32, 2463.

Crystallization of Mesoscale Particles overLarge Areas**

By Sang Hyun Park, Dong Qin, and Younan Xia*

Crystalline assemblies of mesoscale particles are usefulin many areas. For example, two-dimensional assemblieshave been used as arrays of microlenses in imaging[1] andas physical masks in microlithography;[2] three-dimensionalassemblies have been used as precursors in producing high-strength ceramics,[3] as templates in forming porous silicamembranes,[4] and as diffractive elements in fabricatingnew types of sensors,[5] optical components,[6] and photonicbandgap structures.[7] Although a number of methods havebeen demonstrated for assembling mesoscale particles,[8±13]

only two of them are capable of producing crystalline as-semblies with domain sizes of 1000 mm3 that are useful infabricating optical devices. One of the methods is based onsedimentation[10] and the other on electrostatic interactionof highly charged particles in appropriate solvents free ofelectrolytes.[12] The method based on sedimentation is ex-tremely slow; it usually takes several days or weeks to pro-duce a crystalline assembly, and it has almost no control

±

[*] Prof. Y. Xia, Dr. S. H. ParkDepartment of Chemistry, University of WashingtonSeattle, WA 98195-1700 (USA)

Dr. D. QinDepartment of Bioengineering and Washington Technology CenterUniversity of WashingtonSeattle, WA 98195-2141 (USA)

[**] This work has been supported in part by a New Faculty Award fromthe Dreyfus Foundation, a subcontract from the AFOSR MURI Cen-ter at the University of Southern California, and start-up funds fromthe University of Washington. It used the Microfabrication Laboratoryat the Washington Technology Center (WTC).

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