From Tectons to Composite Crystals

Pierre Dechambenoit, Sylvie Ferlay, and Mir Wais Hosseini*

Laboratoire de Chimie de Coordination Organique, UMR CNRS 7140,Universite Louis Pasteur, F-67000 Strasbourg, France

Received April 25, 2005

ABSTRACT: A combination of the tecton 12+ with [MII(CN)6]4- (M ) Fe, Ru) complex anions leads to the formationof analogous two-dimensional (2-D) H-bonded networks and isomorphous crystals. Based on the isomorphous natureof the two crystalline systems, the three-dimensional (3-D) epitaxial growth of composite crystals up to generationthree was achieved and visually demonstrated.

Introduction

Engineering composite crystals, that is, growing ad-ditional crystalline layers on preformed crystals, is atopic of current interest because of potential applicationsin optics and in magnetism, for example. To the best ofour knowledge, the epitaxial growth of molecular met-allo-organic single cocrystals with different compositionswas first described by MacDonald et al.,1 then by Stanget al.,2 and finally by us.3

The design of composite crystals1 may be achievedthrough the analysis of information contained in avail-able crystal structures. In particular, by spotting analo-gies such as isomorphism between crystalline systems,one may imagine procedures leading to the formationof such hierarchical crystalline systems.

Here we report the formation of a series of compositecrystals based on epitaxial growth of crystalline layerson preformed crystals.

During the course of our systematic investigations onthe formation of H-bonded molecular networks4 betweendicationic bisamidinium tectons and di-,5 tetra-,6 penta-,7 and hexacyanometalate6,8 complex anions, we havenoticed that the combination of the same organic tectonsuch as 12+ (Figure 1) with cyanometalate anions, suchas (i) dicyanoaurate and dicyanoargentate, (ii) tetracy-anonickelate, -palladate, and -platinate, (iii) hexacy-anoferrate or -cobaltate (M3+), and (iv) hexacyanoferrateor -ruthenate (M2+), leads within the same family toisomorphous crystalline materials.

In a previous contribution,3 we showed that compositecrystals may be obtained using crystals composed of thedicationic tecton 12+ and [MIII(CN)6]3- (M ) Fe or Co)anions. However, although we have been able to formthe first generation of composite crystals, the crystallinematerial obtained appeared to be rather fragile and didnot allow us to reach the fabrication of higher genera-tions.

Results and Discussion

Structural studies of combinations of the dicationictecton 12+ with [MII(CN)6]4- (M ) Fe or Ru) revealedthe formation of two analogous two-dimensional (2-D)H-bonded networks6,9 resulting from the interconnectionof octahedral anionic units [MII(CN)6]4- by two dicationic

tectons 12+ through both a chelate and a monohaptomode of H-bonding (Figure 1). Interestingly, both crys-tals are isomorphous (triclinic, P1h, Z ) 1), that is, theypresent rather close metrics (differences in a of 0.012Å, in b of 0.017 Å, in c 0.032 Å, in R of 0.008°, in â of0.02°, and in γ of 0.05°).6 Further more, the two robustcrystalline solids exhibit different colors: whereas [12+-Ru(CN)6

4-] crystals are colorless (Figure 2a), [12+-Fe-(CN)6

4-] crystals are orange (Figure 2c). We believedthat this difference in color would be appropriate todemonstrate visually the formation of composite crystals(see Table 1).* E-mail: hosseini@chimie.u-strasbg.fr.

Figure 1. Schematic representation of the 2-D H-bondednetwork obtained upon combining the dicationic tecton 12+ andhexacyanometalate anions. The arrows represent the transla-tions into two space directions.

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Starting with crystals of [12+-Ru(CN)64-] or [12+-

Fe(CN)64-], considered as generations G0(Ru) and G0-

(Fe), respectively, one could grow the next generation(G1(Ru,Fe) or G1(Fe,Ru)) by immersing the preformedcrystals G0 into a solution containing the same tecton12+ and the other cyanometalate anion. In an iterativefashion, one may proceed with crystals of the firstgeneration (G1(Ru,Fe) or G1(Fe,Ru)) and continue thefabrication process to generate the second generation(G2(Ru,Fe,Ru) or G2(Fe,Ru,Fe)) and further on; byrepeating the procedure, one should be able to form thethird generation (G3(Ru,Fe,Ru,Fe) or G3(Fe,Ru,Fe,Ru)),etc. (Figure 3).

Both G0(Ru) and G0(Fe) crystals were obtained uponslow diffusion of an EtOH solution of [12+-2TsO-]10 intoan aqueous solution of either [K4Ru(CN)6] or [K4Fe-(CN)6]. Starting with G0(Ru), the formation of G1(Ru,-Fe) was achieved by the growth of orange crystallinelayers on all faces of the seed crystal. The compositecrystal thus obtained was both visually observed at themacroscopic level and structurally analyzed at the

microscopic scale by X-ray diffraction. The cutting of thecomposed crystal clearly demonstrated the growth oforange crystalline system on the colorless seed crystal(Figure 4a). Interestingly, this microscopic pictureshows the same orientation of faces between the seedcrystal and the grown crystalline layers. To deal withthe structure of the composite crystal and the orienta-tion of the two crystalline systems, the composite crystalwas cut so as to isolate the colorless and the orangecrystalline zones. X-ray diffraction on both isolatedcrystals demonstrated their identity with the corre-sponding crystals, G0(Ru) and G0(Fe). X-ray diffractionon the composite crystal further revealed that the twocrystalline systems are oriented in the same spacedirections. However, some twinned reflections resultingfrom the slight difference in the cell parameters betweenthe two crystalline systems are observed.

Figure 2. Pictures of crystals of [12+-Ru(CN)64-] (a), [12+-

Fe(CN)64-] (c), and the solid solution obtained upon combining

both Ru(CN)64- and Fe(CN)6

4- with 12+ in a 1/1 Ru(CN)64-/

Fe(CN)64- ratio (b).

Table 1. Crystallographic Parameters of[12+-Ru(CN)6

4-], [12+-Fe(CN)64-], and

[12+-Fe0.5Ru0.5(CN)64-] Recorded at 173 K

[12+-Ru-(CN)6

4-][12+-Fe0.5Ru0.5-

(CN)64-]

[12+-Fe-(CN)6

4-]

space group P1h P1h P1ha (Å) 7.6658(2) 7.6598(2) 7.6538(2)b (Å) 10.9443(3) 10.9321(3) 10.9276(3)c (Å) 13.4958(4) 13.4753(3) 13.4639(3)R (deg) 70.252(2) 70.256(3) 70.260(5)â (deg) 75.065(2) 75.080(3) 75.085(5)γ (deg) 85.455(2) 85.463(3) 85.502(5)V (Å3) 1029.63(5) 1026.48(5) 1024.16(4)

Figure 3. Schematic representation of slices of crystalsgenerated from the generation Gn-1 used as seed crystals. Theprocedure starts with G0 consisting of pure crystals of [12+-Ru(CN)6

4-] or [12+-Fe(CN)64-], and the following generations

are obtained, in an iterative fashion, by immersing the crystalsof generation Gn-1 into a solution containing tecton 12+ andthe other cyanometalate anion.

Figure 4. Photographs of slices of crystals of generations G1

(a,b), G2 (c,d), and G3 (e,f). Colorless and orange zonescorrespond to [12+-Ru(CN)6

4-] and [12+-Fe(CN)64-] crystalline

layers, respectively.

From Tectons to Composite Crystals Crystal Growth & Design, Vol. 5, No. 6, 2005 2311

To challenge the robustness of the approach, thereverse situation was tested. As expected, again thethree-dimensional (3-D) epitaxial growth of colorlesscrystalline layers of [12+-Ru(CN)6

4-] on the orange seedcrystal G0(Fe) was achieved (Figure 4b). Furthermore,the generality of the process was demonstrated by therepetition of the procedure. Indeed, starting withG1(Ru,Fe) or G1(Fe,Ru), the second genrations G2(Ru,-Fe,Ru) (Figure 4c) and G2(Fe,Ru,Fe) (Figure 4d) wereobtained. Finally, starting with the latter generation,the third generation crystals of crystals G3(Ru,Fe,Ru,-Fe) (Figure 4e) and G3(Fe,Ru,Fe,Ru) (Figure 4f) werefabricated.

Whereas the formation of composite crystals is clearlya hierarchical process, we also explored the possibilityof forming a crystalline molecular alloy1,2,11 or a solidsolution resulting from statistical distribution of mo-lecular components in the crystal. As expected, uponslow diffusion of a solution of [12+-2TsO-] in EtOH intoan aqueous solution containing the potassium salts ofboth Fe(CN)6

4- and Ru(CN)64- anions (1/1 ratio), a

crystalline material was indeed obtained. The paleorange color of the latter (Figure 2b) is, as expected,intermediate between the color of G0(Ru) (colorless,Figure 2a) and G0(Fe) (orange, Figure 2c). Furthermore,for the solid solution, X-ray diffraction revealed inter-mediate cell parameters between those of G0(Ru) andG0(Fe) (Table 1).

In conclusion, we have demonstrated that upon usingtwo isomorphous crystalline systems, based on combi-nations of the tecton 12+ and [M(CN)6

4-] (M ) Fe orRu) anions leading to the formation 2-D H-bondedmolecular networks, one may fabricate crystallinemultilayered solids, also called composite crystals. Therobustness of the approach was demonstrated by gen-erating composite crystals up to the third generation.The formation of such hierarchical crystalline materialsbased on magnetic or fluorescent crystalline layers iscurrently under investigation.

Experimental Section

Single crystals of [(12+)-(Fe(CN)64-)‚8H2O] (orange) and

[(12+)-(Ru(CN)64-)‚8H2O] (colorless) were obtained as previ-

ously described.6

A colorless crystal of [12+-(Ru(CN)64-)] (approximately 0.1

× 0.06 × 0.02 mm3) was glued on a nylon wire before it wasimmersed or seeded on the surface of an aqueous solution (2mL) containing K4Fe(CN)6 (2.5 mM) and the ditosylate salt of12+ (5 mM). After 1 week, in addition to a few orange crystalsformed in solution corresponding to [12+-(Fe(CN)6

4-)], a 3-Depitaxial growth of orange crystalline layer on the surface ofthe seed crystals was observed. The same procedure wasrepeated starting with orange crystals, [12+-(Fe(CN)6

4-], asseeds and an aqueous solution containing K4Ru(CN)6 (0.8 mM)and the ditosylate salt of 12+ (1.6 mM). Again, in addition tocolorless crystals corresponding to [12+-(Ru(CN)6

4-)] formedin solution, a colorless crystalline layer was grown on all facesof the orange seed crystals. The same procedure was repeatedfor the fabrication of generations G2 and G3.

Acknowledgment. Universite Louis Pasteur, Insti-tut Universitaire de France, the Ministry of Educationand Research and CNRS are acknowledged for financialsupport. Thanks to J.-M. Planeix and N. Kyritsakas forX-ray diffraction studies.

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(3) Ferlay, S.; Hosseini, M. W. Chem. Commun. 2004, 788-789.

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