2,4,6-tris(4-bromophenoxy)-1,3,5-triazine (BrPOT) features a channel size (11-12Å) allowing the inclusion of large guest molecules such as tetramethylpyrazine (TMPZ). TMPZ forms π-stacks (d: 3.5Å) along channels of BrPOT and shows rotational disorder for methyl positions. Co-inclusions of I2 resulted in a doped state where I2 molecules are oriented perpendicular to the channel axis with positional disorder as well. The particular orientation of I2 molecules is evident from the observed dichrois

Berger, Ricarda

Bonin, Michel

Couderc, Gaëtan

Hulliger, Jürg

Labat, Gaël

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ORIGINAL ARTICLEInclusion of tetramethylpyrazine in channels of the organic zeolite2,4,6-tris(4-bromophenoxy)-1,3,5-triazineGae¨tan Couderc Æ Michel Bonin Æ Gae¨l Labat ÆRicarda Berger Æ Ju¨rg HulligerReceived: 10 January 2008 / Accepted: 26 February 2008 / Published online: 15 March 2008 Springer Science+Business Media B.V. 2008Abstract 2,4,6-tris(4-bromophenoxy)-1,3,5-triazine(BrPOT) features a channel size (11–12 A˚) allowing theinclusion of large guest molecules such as tetramethyl-pyrazine (TMPZ). TMPZ forms p-stacks (d: 3.5 A˚) alongchannels of BrPOT and shows rotational disorder formethyl positions. Co-inclusions of I2 resulted in a dopedstate where I2 molecules are oriented perpendicular to thechannel axis with positional disorder as well. The particularorientation of I2 molecules is evident from the observeddichroism.Keywords Host–guest systems  Inclusion compounds Organic zeolitesThe triazine family [1] of channel inclusion compounds isof particular interest, because a channel size of about 10–12 A˚ opens up opportunities for hosting guest molecules ofa much larger diameter than possible for the 4–5 A˚ class ofmany other host compounds [2]. Given the large diameter,an intuitive view might assume that elongated prolate typemolecules based on trans disubstituted benzene rings(biphenyls, stilbenes, etc...) would enter the channel by apacking mode with overlapping guest species. However,this seems not to be the case, because it was found that thisfunctional class of molecules might only be included in thepresence of fitting solvent molecules. This applies as wellto C60 and C70 [3] for which no solvent free inclusions ine.g. 2,4,6-tris(4-bromo-phenoxy)-1,3,5-triazine (BrPOT)and 2,4,6-tris(4-bromo-3,5-difluorophenoxy)-1,3,5-triazine(Br-3,5-DFPOT) could be prepared so far. The moreinteresting is the fact that cylindrical types of molecules, suchas decamethyl-bis-cyclopentadienyl-metallate (M(cp*)2)molecules enter the channels without necessity of a solventco-inclusion. And most surprisingly the combination ofM(cp*)2 and C60, C70 does it as well, whereas C60(CH3)5-Fecp[3] requires again solvent co-inclusion. So, these triazinechannels obviously provide sites, where optimally (length)cylindrical molecules may allow 1D close packing beinginteresting for physical property generation (charge transport,magnetism).Here, we present the inclusion of tetramethylpyrazine(TMPZ), which represents a further guest, although not of aproper symmetry in respect to a trigonal or hexagonalchannel, which enters by a stacking of aromatic rings.Attempts were made to intersect this 1D stack with I2,showing, however, that only a low level I2 may substituteTMPZ entering the channel with the molecular axis at I2perpendicular to c.Preparation of crystals: Needle-shaped crystals (size:1.2 9 0.2 9 0.2 mm3) were obtained by slow cooling(1 C/h) of a toluene solution containing a mixture ofBrPOT and TMPZ. The nature of solvent and the quantityof TMPZ engaged in preparation were of crucial impor-tance: Butanone, mesitylene, and carbon disulfide did notyield crystals being stable against a loss of guests aftergetting out of the nutrient. Presumably, in the case of tol-uene we were obtaining a solvent free inclusion for TMPZ.Attempts to obtain a mixed chain of TMPZ and I2 or atleast a doped TMPZ chain were using particular relativeamounts in the nutrient (see Table 1).Electronic supplementary material The online version of thisarticle (doi:10.1007/s10847-008-9433-5) contains supplementarymaterial, which is available to authorized users.G. Couderc  M. Bonin  G. Labat  R. Berger  J. Hulliger (&)Department of Chemistry and Biochemistry, University ofBerne, Freiestrasse 3, Berne 3012, Switzerlande-mail: publication.hulliger@iac.unibe.ch123J Incl Phenom Macrocycl Chem (2008) 61:377–379DOI 10.1007/s10847-008-9433-5Samples A, B, D, and E were stable at long term andthus used for the analysis (DSC: decomposition above*120 C). C and F probably were co-inclusions with tol-uene accepting more iodine than others. Solution 1H-NMRshowed for A, B, D, and E a molar ratio of 1.0(1):1.0(1) forBrPOT/TMPZ and no presence of toluene. Thermogravi-metry confirmed these results (Fig. 1). The mass losscorresponded to a ratio of 1.0(1):1.0(1) and no significantamount of I2 was detected.The small concentration of I2 inside channels was mea-sured by ICP-MS: A few mg of crystals (B, D, E) weredestroyed in HNO3 (68%) and finally diluted in water to 1:10for being measured by an ICP-MS Varian 820 MS. The foundconcentrations for I2 of 320 ppm (B), 80 ppm (D), and50 ppm (E) scale well with the decreasing color intensity ofcrystals. A blank test for A showed no I2. To demonstrate thatI2 is really present within channels, the pronounced dichro-ism was used for confirmation. In Fig. 2, the maximumabsorption is obtained for a polarization perpendicular to thechannels. The optical absorption for a polarization along cwas not significant. Because of I2 perpendicular to c, a rota-tion of the needle around c might show an extinction of coloror not. In the first case, this would indicate ordering inthe (a,b) plan. However, the overall hexagonal symmetry ofthe inclusion (Table 2) would not support this. From obser-vation of a crystal rotated around the c-axis, we can concludeTable 1 Conditions and results of crystallization (1 ml solution oftoluene, cooling rate of 1 C/h starting from 70 C to roomtemperature)Sampleno.BrPOT/TMPZ /Iodine (molar ratio)Color RemarksA 1/13.3/0 Colorless Stable in airB 1/70.40/4.53 Yellow Stable in airC 1/3.25/0.96 Yellow Not stable in airD 1/34.11/1.59 Light yellow Stable in airE 1/4.19/1.14 Slight yellow Stable in airF 1/1.12/0.92 Orange Not stable in air024681012140 100 200 300 400 500T °CLoss of mass (mg)ABEDEvaporationof BrPOT TMPZ loss Fig. 1 Thermogravimetry for samples A, B, E, and D showing a lossof TMPZcyellowcolorless200 µmFig. 2 Dichroism of a crystal of type B BrPOT(TMPZ)(I2)x (x:320 ppm). The arrow shows the direction of polarization. (Colorpicture available on the web)Table 2 Crystal dataA BCrystallizationmethodSlow cooling Slow coolingEmpirical formula C21H12Br3N3O3 C21H12Br3N3O3C8H12N2 C8H12N2Formula wt.(g mol-1)730.26 730.26Crystal color Colorless YellowCrystal shape Prism PrismT (K) 293(2) 293(2)k (A˚) 0.71073 0.71073Crystal size (mm3) 0.20 9 0.18 9 0.16 0.51 9 0.17 9 0.13Crystal system Hexagonal HexagonalSpace group P63/m P63/ma (A˚) 15.695(2) 15.669(2)b (A˚) 15.695(2) 15.669(2)c (A˚) 7.1085(14) 7.1052(14)a () 90 90b () 90 90c () 120 120V (A˚3) 1516.4(4) 1510.7(4)Z 2 2q (g cm-3) 1.599 1.6052h max () 63.89 58.71l (MoKa/mm-1) 4.03 4.04Measured reflect 18474 14630Independent reflect 1876/I [ 2r(I) 1383 1479/I [ 2r(I) 1250Rint 0.0519 0.0394R1 I [ 2r(I) 0.0523/0.0780I [ 2r(I) 0.0444/0.0542wR2 0.1398 0.1243CCDC n 667809 667810Note: Cambridge Crystallographic Data Centre (CCDC) contains thesupplementary data for this paper. These data can be obtained free ofcharge from the CCDC via www.ccdc.cam.ac.uk/data_request/cif378 J Incl Phenom Macrocycl Chem (2008) 61:377–379123that no preferred I2 orientation in the (a, b) plane is evident forsample B.For a structural analysis, crystals of sample A, B, and Dwere mounted on a Stoe Mark II-imaging plate diffrac-tometer system [4] equipped with a graphitemonochromator. Data collection, using Mo-Ka radiation(k = 0.71073 A˚), was performed at -100 C for sample Band room temperature for sample A. Exposures wereobtained at an image plate distance of 80 mm with u = 0and 0 \x \ 180 for the crystal oscillating through 1 inx. The structure was solved by direct methods using theprogram SHELXS-92 [5] and refined by full matrix leastsquares on F2 with SHELXL-97 [6]. The hydrogen atomswere included in calculated positions and treated as ridingatoms. The diameter of the channel was estimated by usingthe Mercury visualization software [7]. The crystallo-graphic data are reported in Table 2.Both types of crystals, A, B (see Table 2) crystallize inthe hexagonal space group P63/m, typical for many triazineinclusion compounds. As the two-fold molecular symmetryof the TMPZ is incompatible with the 3-fold channelsymmetry (Fig. 3), rotational disorder is present. ThreeTMPZ’s share one site, each of them rotated by 120. Themain feature of the structural analysis reveals a stacking ofpyrazine moieties (stacking: 3.5 A˚) along the channels.There, the pyrazine is located at the center of the cavityformed by 3 bromo-phenoxy groups of host molecules.Obviously, this system is not adapting a mixed stack ofTMPZ and I2 as found in pyrazineI2 on pure crystals [8]and in the channels of tris(o-phenylenedioxy)cyclotri-phosphazene (TPP), where pyrazine and I2 form analternate pyrazineI2 pyrazine I2 packing [9].Acknowledgments This work was supported by the Swiss NationalFoundation, project Nr. 200021-113358/1. We thank Prof. U. Kra¨-henbu¨hl for ICP-MS measurements.References1. Saha, B.K., Jetti, R.K.R., Reddy, L.S., Aitipamula, S.: Halogentrimer-mediated hexagonal host framework of 2,4,6-tris(4-halo-phenoxy)-1,3,5-triazine: Supramolecular isomerism fromhexagonal channel (X = Cl, Br) to cage structure (X = I), Cryst.Growth Design. 5, 887–899 (2005); Saha, B.K., Aitipamula, S.,Banerjee, R., Nangia, A., Jetti, R.K.R., Boese, R., Lam, C.-K.,Mak, T.C.W.: Hexagonal host framework of syn-aryloxytriazinesstabilized by weak intermolecular interactions. Mol. Cryst. Liq.Cryst. 440, 295–316 (2005); Jetti, R.K.R., Xue, F., Mak, T.C.W.,Nangia, A.: 2,4,6-tris-4-(bromophenoxy)-1,3,5-triazine: a hexago-nal host framework assembled with robust Br...Br trimer synthons.Cryst. Eng. 2, 215–224 (1999); Reichenba¨cher, K., Su¨ss, H.I.,Stoeckli-Evans, H., Bracco, S., Sozzani, P., Weber, E., Hulliger, J.:Modification of channel structures by fluorination, New J. Chem.28, 393–397 (2004)2. Allrock, H.R., Siegel, L.A.: Phosphonitrilic compounds. III. 1Molecular inclusion compounds of tris(o-phenylenedioxy)phos-phonitrile trimer. J. Am. Chem. Soc. 86, 5140–5144 (1964);Hertzsch, T., Kluge, S., Weber, E., Budde, F., Hulliger, J.: Surfacerecognition of dipolar molecules entering channels of the organiczeolite tris(o-phenylenedioxy)cyclotriphosphazene, Adv. Mater.13, 1864–1867 (2001)3. Suess, H.I., Lutz, M., Hulliger, J.: Inclusion of fullerenes intochannels of 2,4,6-tris-4-(bromophenoxy)-1,3,5-triazine (BrPOT),Cryst. Eng. Comm. 4, 610–612 (2002); Reichenba¨cher, K., Neels,A., Stoeckli-Evans, H., Balasubramaniyan, P., Mu¨ller, K., Matsuo,Y., Nakamura, E., Weber, E., Hulliger J.: New fluorinated channel-type host compounds, Cryst. Growth Design. 7, 1399–1405 (2007);Bonin, M., Lu¨thi, T.A., Reichenba¨cher, K., Bu¨rgi, H.-B., Hulliger,J.: Inclusion of C60 into cages of 2,4,6-tris(4-iodophenoxy)-1,3,5-triazine and classification of known triazine related inclusionstructures, to be submitted4. Stoe & Cie.: IPDS Software, Stoe & Cie GmbH, Darmstadt,Germany, (2005)5. Sheldrick, G.: Phase annealing in SHELX-90: direct methods forlarger structures. Acta. Cryst. A46, 467–473 (1990)6. Sheldrick, G.: SHELXL-97, Program for crystal structure refine-ment, University of Go¨ttingen, Germany (1997)7. Mac Rae, C.F., Edgington, P.R., McCabe, P., Pidcock, E., Shields,G.P., Taylor, R., Towler, M., van de Streek, J.: Visualization andanalysis of crystal structures. J. Appl. Cryst. 39, 453–457 (2006)8. Bailey, R.D., Buchanan, M.L., Pennington, W.T.: Molecularcomplexes of 1,4-diazines with iodine. Acta Cryst. C48, 2259–2262 (1992)9. Couderc, G., Bonin, M., Neels, A., Hauser, J., Sozzani, P.,Hulliger, J.: Iodine-pyrazine chain inside the channel of tris(o-phenylenedioxy)cyclotriphosphazene, to be submittedFig. 3 Typical hexagonal packing layer of BrPOT(TMPZ). Forclarity only one possible orientation of three of the pyrazine guestmolecules is shownJ Incl Phenom Macrocycl Chem (2008) 61:377–379 379123

Inclusion of tetramethylpyrazine in channels of the organic zeolite 2,4,6-tris(4-bromophenoxy)-1,3,5-triazine

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Inclusion of tetramethylpyrazine in channels of the organic zeolite 2,4,6-tris(4-bromophenoxy)-1,3,5-triazine

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