摘要:

J O U R N A L O F C H E M I S T R Y Materials Hybrid molecular materials based on organic molecules and the inorganic magnetic cluster [M4(H2O)2(PW9O34)2]10- (M2+=Co, Mn)† Miguel Clemente-Leo�n,a Eugenio Coronado,*a Jose-Ramo�n Gala�n-Mascaro� s,a Carlos Gime�nez-Saiz,a Carlos J. Go�mez-Garcý�aa and Toribio Ferna�ndez-Oterob aDepartamento de Quý�mica Inorga�nica. Universidad de Valencia, 46100 Burjasot, Spain bL ab.Electroquý�mica, Fac. de Quý�mica, UPV, PO Box 1072, 20080 San Sebastian, Spain The synthesis and physical characterization of new organic–inorganic hybrids formed by conducting and magnetic networks are reported. The crystalline radical salts are formed by BEDT-TTF type donors as the organic part, and by large metal–oxide clusters of the type [M4(H2O)2(PW9O34)2]10- (M2+=Co, Mn) as the inorganic part.We also show how these magnetic clusters can be incorporated in conducting organic polymers to give hybrid organic–inorganic films.The search for new molecule-based materials combining con- of definite sizes and shapes which can accommodate one or more magnetic centers in their structures. The solubility of ducting and magnetic properties constitutes a current challenge in materials science, which only very recently has begun to be such clusters in both aqueous and non-aqueous solvents makes it possible to electrochemically oxidize the organic donor in explored.A convenient chemical approach to obtain such multiproperty materials is the so-called organic–inorganic the presence of these counter-ions so as to obtain crystalline salts of these hybrids.8 In this context, the most successful hybrid approach.1 It consists of using as building blocks organic molecules or polymers possessing itinerant electrons results have been obtained from the BEDT-TTF molecule (1 in Scheme 1) which has allowed the growth of crystals contain- and inorganic metal complexes possessing localized magnetic moments.ing polyoxometalates9 with metal nuclearities comprised between 6 and 18 [Fig. 1(a)–(c)]. Owing to the diYculty in As the organic part one can use p-electron donor molecules of the TTF type which are the basic ingredient for most of the crystallizing these salts as the complexity of the cluster is increased, obtaining crystalline radical salts containing larger molecular conductors and superconductors.2 Another interesting possibility is to use conducting polymers of the type clusters is a chemical challenge.polypyrrole or polyaniline. These polymers are relatively simple to obtain by chemical or electrochemical oxidative polymerization of the monomer molecules and they have considerable potential technological applications.3 As the inorganic part, a variety of anionic metal complexes of various nuclearities and dimensionalities can be chosen.Starting with the most simple magnetic anions one can find the mononuclear metal halides (FeCl4-, CuCl42-,…). These anions are being successfully combined with several organic donors to Scheme 1 give radical ion salts with coexistence of localized magnetic moments and itinerant electrons.4 Another important mono- With the aim of introducing clusters of higher nuclearities nuclear anion is the iron(III) tris(oxalato) complex, Fe(ox)33-, we have tried the reaction of BEDT-TTF with the magnetic which combined with the BEDT-TTF donor resulted in the polyoxoanions [M4(PW9O34)2]10- (M2+=Co, Mn) which preparation of the first molecular material with coexistence of have a metal nuclearity of 22 [Fig. 1(d)]. We present here the paramagnetic centers and superconductivity.5 Themost complex synthesis and physical characterization of these crystalline class of inorganic complexes we can use are polymeric. Anion hybrids. We also report how these magnetic clusters can be magnetic chains or layers are known that on paper can be incorporated in conducting organic polymers to give hybrid combined with cation radicals. From the magnetic point of organic–inorganic films.view, polymeric layered complexes such as, for example, the bimetallic oxalato-bridged complexes [MIIMIII(ox)3]- (MII= Mn, Fe, Ni, Co, Cu; MIII=Cr, Fe), are the most interesting since they can confer to the hybrid material cooperative magnetic properties such as ferromagnetism.6 However, these polymeric anions are not easy to handle in terms of the chemistry (extremely insoluble and only stable in the solid state).In fact, only discrete bimetallic oxalato complexes but not polymeric ones have been combined so far with organic donors.7 In between these two extreme cases one can find the polyoxometalate complexes. These are big metal–oxide clusters Fig. 1 Polyhedral representation of the: (a) Lindquist, [M2O19]2 (M= Mo, W), (b) Keggin [XM12O40]n- (M=Mo, W), (c) Dawson–Wells, † Presented at the 58th Okazaki Conference, Recent Development and Future Prospects of Molecular Based Conductors, Okazaki, Japan, [X2M18O62]n- (M=Mo, W) and (d) [M4 (H2O)2(PW9O34)2]10- (M2+=Co, Cu, Mn, Fe, Cr, Ni and Zn) polyanions 7–9 March 1997. J. Mater. Chem., 1998, 8(2), 309–312 309Fig. 3 Plot of xmT vs. T for the [Mn4(H2O)2(PW9O34)2]10- polyanion Fig. 2 Plot of xmT vs. T for the [Co4(H2O)2(PW9O34)2]10- polyanion in its K+ (×), BEDT-TTF+ (#) salts in its K+ (×), BEDT-TTF+ (#) and polypyrrole ($) salts No influence coming from the organic component on the Organic–inorganic crystalline materials based on magnetic coupling within or among the clusters is detected BEDT-TTF electron donors down to 2 K.Thus, in the Co derivative the product xmT shows a sharp increase below 50 K upon cooling and a The polyoxoanions [M4(PW9O34)2]10- are of magnetic intermaximum at ca. 6 K. Such a behavior is analogous to that est since they contain the tetranuclear magnetic clusters Co4 observed in the K+ salt (see Fig. 2) and unambiguously and Mn4 encapsulated in between two polyoxotungstate moietdemonstrates that the ferromagnetic cluster is maintained when ies [PW9O34] [see Fig. 1(d)]. In the cobalt case the ions are we change K+ to BEDT-TTF+. Furthermore, it is indicative ferromagnetically coupled giving rise to a magnetic ground of a lack of interactions between the two components as a state comprising 12 unpaired electrons,10 while in the mangaconsequence of the good insulation of the Co4 cluster provided nese one this exchange coupling is antiferromagnetic and by the polyoxotungstate framework.Low temperature EPR results in a non-magnetic ground state (S=0).11 Furthermore, spectra support such a conclusion (Fig. 4). We observe that at the type of exchange coupling is diVerent in both clusters. 4.2 K the two samples show the same spectrum: a very broad Thus, while high-spin octahedral Mn2+ has a fully isotropic and anisotropic signal mainly coming from the ground 6A1 ground state, high-spin octahedral Co2+ has an orbitally Kramers doublet of the cluster, centered around 1620 G (g= degenerate 4T1 ground state which is split into six anisotropic 4.1), which extends from 1000 to 4000 G.This signal has to Kramers doublets by the eVect of spin–orbit coupling and be attributed to the Co4 cluster. No signal coming from the distortions of the octahedron. As a consequence the exchange organic radical is observed at this temperature. This should interaction between Co2+ ions is highly anisotropic resulting indicate that the unpaired electrons located at the BEDT- in a complete splitting of the highly degenerate ground state TTF+ cations are strongly coupled in the solid so that they in spin doublets.In fact the ground state of this cluster is an are magnetically silent at low temperature. anisotropic Kramers doublet which is well separated in energy The similarity between the BEDT-TTF+ and K+ derivatives from the other excited doublets (the closest energy level is at is also evident in the Mn case (Fig. 3). Thus, the two magnetic ca. 14 cm-1).12 curves are coincident in the whole temperature range, within Black crystals of composition BEDT-TTF6H4[M4(H2O)2- the experimental error. This result proves that the antiferro- (PW9O34)2] (M 2 +=Co, Mn) have been obtainedcoupled Mn4 cluster is maintained intact in the crystallization.Although they are still not of suYcient quality radical salt. The close coincidence between the two magnetic to be studied by X-ray diVraction, a preliminary study of their unit cells indicates that they are isostructural.‡ In view of the stoichiometry of these salts (651), four protons had to be introduced in order to compensate the charges.With this assumption the six organic molecules should be completely charged (+1). Accordingly, the compounds are insulators (the electrical conductivity has been measured on pressed pellets). The magnetic properties of the BEDT-TTF salts are shown in Fig. 2 and 3 and compared to those of the potassium salts of the two polyanions. In both cases the low temperature magnetic behavior is dominated by the inorganic component.§ ‡ Unit cell of the cobalt(II) derivative (from indexation of 17 reflections): a=11.85(2), b=13.23(1), c=27.741(5) A ° , a=83.15(5), b= 87.17(4), c=73.85(9)°; unit cell of the manganese(II) derivative (from indexation of 16 reflections): a=11.79(1), b=13.23(1), c=27.48(1) A °, a=88.95(6), b=89.96(4), c=73.79(8)°.§ At high temperatures the magnetic moments of both the BEDT-TTF salt and the polypyrrole film are higher than that observed in the potassium salt (see Fig. 2). The origin of such diVerences may come from the large anisotropy of the magnetic cluster. Slightly diVerent octahedral distortions within the clusters can give rise to significant variations in the local Lande� tensors and therefore in the magnetic properties.In fact, if one compares the magnetic properties of the Co4 cluster encapsulated by the [PW9O34] ligands or by the [P2W15O56] ones, we observe that in the former case xmT varies from 14 emu K mol-1 at high T to 24 emu K mol-1 at 6 K, while in the latter this Fig. 4 EPR spectra of the [Co4(H2O)2(PW9O34)2]10- polyanion in variation is only from 10 to 15 emu K mol-1. However, the position of the characteristic maximum in xmT stays constant in both cases.its K+ and BEDT-TTF salts 310 J. Mater. Chem., 1998, 8(2), 309–312biggest ever used in the synthesis of radical cation salts, and (ii ) the salts constitute the first known examples of hybrid materials containing a magnetic cluster and an organic donor. In the second case we have shown that these magnetic clusters can be incorporated in polypyrrole films to give magnetic films having semiconducting properties.More hybrid films of this kind can now be prepared in which new functional properties can be introduced by playing for example with the electrochromic character of the polyoxometalate component. Another aspect that is being developed in this context in order to improve the properties of the film is that of creating well organized hybrid films by using the Langmuir–Blodgett technique.13 Experimental Fig. 5 Plot of the conductivity vs. T of a [Co4(H2O)2(PW9O34)2]10-– Single crystals of the radical salts BEDT-TTF6H4[M4- polypyrrole film (H2O)2(PW9O34)2] (M2+=Co, Mn) were obtained on a platinum wire electrode by anodic oxidation of the organic donor curves also shows that the presence of BEDT-TTF+ radicals ET (2×10-3 M in a 152 mixture of CH3CN–CHCl2CH2Cl) in does not aVect the magnetic coupling within or between the a U-shaped electrocrystallization cell under low constant cur- Mn4 clusters.As for the EPR spectra, these are dominated by rent (I=1.2 mA) in the presence of a solution of the polyanion a broad signal centered at g=2 arising from the Mn4 cluster.in toluene. After two weeks very small hexagonal plate-like A sharp signal of very weak intensity is superimposed onto single crystals were observed in the anode. They were collected, the cluster signal. This may be associated with paramagnetic washed with CH3CN and air dried. Found: C, 10.37; radical impurities. The above crystalline materials demonstrate H, 0.96; N, 0.16; S, 22.01.BEDT-TTF6H4[Co4(H2O)2- the ability of this type of large magnetic clusters to form (PW9O34)2]·(CH3CN)·5(H2O) requires C, 10.36; H, 0.90; N, crystalline organic–inorganic radical salts with the BEDT- 0.19; S, 21.40%. Found: C, 9.91; H, 1.05; N, 0.0; S, 20.85. TTF donor, despite its big size and charge. BEDT-TTF6H4[Mn4(H2O)2(PW9O34)2]·9H2O requires C, 10.02; H, 1.04; N, 0.0; S, 21.41%.The IR spectra of both salts are very similar and show all the characteristic bands of the Organic–inorganic films based on polypyrrole polyanion and BEDT-TTF molecules. In view of the stability of the above clusters in both aqueous The films of polypyrrole with the cobalt-containing polyand non-aqueous solutions we have examined the possibility of anion were prepared by electrochemical oxidation in a N2 obtaining conducting polymers incorporating this kind of magatmosphere of an aqueous solution of pyrrole (0.5 M) in the netic polyoxometalates.Preliminary results with the Co4 cluster presence of the polyanion (3.6×10-3 M). The intensity of the show that by aqueous electrochemical polymerization of pyrrole current was fixed at 5 mA and after several minutes the (2 in Scheme 1) in the presence of this polyoxometalate, organic– polypyrrole–polyanion films were collected from the anode.inorganic films containing ca. 80 pyrrole units per cobalt cluster can be obtained.¶ The magnetic properties are very close to We thank the Spanish DGICYT for founding this work (Grant those observed in the K+ salt (Fig. 2) indicating that the PB94–0998). M. C. L. and J. R. G. M. thank the Generalitat structure of the ferromagnetic cluster is maintained in the film. Valenciana for a predoctoral Grant. The electrical properties show a semiconducting behavior with an electrical conductivity at room temperature of ca. 0.1 S cm-1 (Fig. 5). The material constitutes a clear example of the ability References of large polyoxometalate clusters to be incorporated in polymer 1 E.Coronado, J. R. Gala�n Mascaro� s, C. Gime�nez-Saiz and films. It represents the first hybrid film formed by a high spin C. J. Go�mez-Garcý�a in Magnetism: A Supramolecular Function, ed. cluster embedded in a polypyrrole polymer in which the large O. Kahn, NATO ASI Ser. C, Kluwer Academic Publishers, magnetic moments localized on the polyoxometalate coexist Dordrecht, 1996, 484, 281 and references therein. 2 J.M.Williams, J. R. Ferraro, R. J. Thorn, K. D. Carlson, U. Geiser, with a delocalized electron framework. The strategy presented H. H. Wang, A. M. Kini and M. H. Whangbo in Organic here is general and can be extended to other kinds of magnetic Superconductors. Synthesis, Structure, Properties and T heory, polyoxometalates (such as the Mn4 derivative, for example) and Prentice Hall, Englewood CliVs, NJ, 1992.to other conducting films. 3 A. G. MacDiarmid, Synth.Met., 1997, 84, 27. 4 (a)M. Lequan, R.M. Lequan, C. Hauw, J. Gaultier, G.Maceno and P. Delhaes, Synth. Met., 1987, 19, 409; (b) T. Mori and H. Inokuchi, Concluding remarks Bull. Chem. Soc. Jpn., 1988, 61, 591; (c) P.Day, M. Kurmoo, T. Mallah, I. R. Marsden, R. H. Friend, F. L. Pratt, W. Hayes, In the attempt to obtain hybrid organic–inorganic materials D. Chasseau, J. Gaultier, G. Bravic and L. Ducasse, J. Am. Chem. with coexisting itinerant electrons and localized spins in the Soc., 1992, 114, 10 722, and references therein; (d) T. Enoki, J. I. same material, this contribution has illustrated the use of the Yamaura, N.Sugiyasu, K. Suzuki and G. Saito, Mol. Cryst. L iq. polyoxometalate clusters [M4(H2O)2(PW9O34)2]10- (M2+= Cryst., 1993, 233, 325; (e) J. A. Ayllo�n, I. C. Santos, R. T. Henriques, Co, Mn) as the magnetic component of new hybrids in which M. Almeida, E. B. Lopes, J. Morgado, L. Alca� cer, L. F. Veiros and M. T. Duarte, J. Chem.Soc., Dalton T rans., 1995, 3543; ( f ) the organic component can be either the electron donor BEDTH. Kobayashi, H. Tomita, T. Naito, A. Kobayashi, F. Sakai, TTF or polypyrrole. In the former case crystalline charge T.Watanabe and P. Cassoux, J. Am. Chem. Soc., 1996, 118, 368 and transfer salts containing these magnetic clusters have been refere) R. Kumai, A. Asamitsu and Y.Tokura, Chem. obtained. The resulting molecular materials are unprecedented L ett., 1996, 753; (h) E. Coronado, L. R. Falvello, J. R. Gala� nin several aspects: (i) this type of inorganic anions are the Mascaro� s, C. Gime�nez-Saiz, C. J. Go� mez-Garcý�a, V. N. Lauhkin, A. Pe� rez-Bený�tez, C. Rovira and J. Veciana, Adv.Mater., 1997, 9, 984. 5 M. Kurmoo, A. W. Graham, P.Day, S. J. Coles, M. B. Hursthouse, ¶ The given ratio pyrrole5polyanion has been determined by chemical analysis as well as by the magnetic measurements. The possibility of J. L. Caulfield, J. Singleton, F. L. Pratt, V. Hayes, L. Ducasse and P. Guionneau, J. Am. Chem. Soc., 1995, 117, 12209. obtaining other ratios by varying the experimental conditions (starting materials, intensity of the electrical current, times of reaction, etc.) is 6 (a) H. Tamaki, Z.J. Zhong, N. Matsumoto, S. Kida, M. Koikawa, N. Achiwa, Y. Hashimoto and H. Okawa, J. Am. Chem. Soc., 1992, being currently investigated. J. Mater. Chem., 1998, 8(2), 309–312 311114, 6974; (b) C. Mathonie`re, S. G. Carling, D. Yusheng and 12 (a) C. J. Go� mez-Garcý�a, E. Coronado, J. J. Borra�s-Almenar, M.Aebersold, H. U. Gu� del and H. Mutka, Physica B, 1992, 180, P. Day, J. Chem. Soc., Chem. Commun., 1994, 1551. 7 E. Coronado, J.R. Gala�n Mascaro� s, C. Gime�nez-Saiz, C. J. Go�mez- 181, 238; (b) J.M. Clemente, H. Andres, M. Aebersold, J. J. Borra�s- Almenar, E. Coronado, H. U. Gu� del, H. Bu�ttner and G. Kearly, Garcý�a, C. Ruiz-Pe�rez and S. Triki, Adv.Mater., 1996, 8, 737. 8 E. Coronado and C. J. Go�mez-Garcý�a, Comments Inorg. Chem., Inorg. Chem., 1997, 36, 2244. 13 (a) M. Clemente-Leo� n, B. Agricole, C. Mingotaud, C. J. Go�mez- 1995, 17, 255; Chem. Rev., in press. 9 E. Coronado, P. Delhaes, J. R. Gala�n-Mascaro� s, C. Gime�nez-Saiz Garcý�a, E. Coronado and P. Delhaes, L angmuir, 1997, 13, 2340; (b) M. Clemente-Leo�n, B. Agricole, C. Mingotaud, C. J. Go�mez- and C. J. Go�mez-Garcý�a, Synth.Met., 1997, 85, 1647. 10 C. J. Go�mez-Garcý�a, E. Coronado and J. J. Borra�s-Almenar, Inorg. Garcý�a, E. Coronado and P. Delhaes, Angew. Chem., Int. Ed. Engl., 1997, 36, 1114. Chem., 1992, 31, 1667. 11 C. J. Go�mez-Garcý�a, E. Coronado, P. Go�mez-Romero and N. Casan� -Pastor, Inorg. Chem., 1993, 32, 3378. Paper 7/0686

ISSN:0959-9428    

DOI:10.1039/a706864f

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Radical salts of the organic donor BET-TTF† with polyoxometalate clusters‡ Eugenio Coronado,*a Jose� R. Gala�n-Mascaro�s,a Carlos Gime�nez-Saiz,a Carlos J. Go�mez-Garcý�a,a Concepcio� Rovira,*b Judit Tarre�s,b Smail Trikia§ and Jaume Vecianab aDepartamento de Quý�mica Inorga�nica, Universidad de Valencia, E-46100 Burjasot, Spain bInstitut Ciencia deMaterials de Barcelona, CSIC, Campus de la U.A.B., E-08193 Bellaterra, Spain The synthesis, structures and physical characterizations of the first radical ion salts of the organic donor BET-TTF 1 with polyoxometalate clusters ([M6O19]2-; M=WVI, MoVI, 2) are reported.The 251 salts (BET-TTF+)2[M6O19]2- are formed by pairs of the BET-TTF+ radical cations surrounded by polyanions so as to form a 3D packing of anions and cations with short intermolecular contacts between the cation pairs.The synthesis, physical properties and main structural features of the first radical ion salts of the organic donor BET-TTF 1 with the polyoxometalate cluster [SiW12O40]4- 3 are also reported. The 451 salt (BET-TTF+)4[SiW12O40]4- is formed by a 2D hexagonal packing of anions and by isolated BET-TTF+ pairs.The compounds are insulators and diamagnetic. A current approach to obtaining new molecular conductors more than one compound can be formed in the same experiment. Despite this intrinsic diYculty we show herein that consists of combining organic electron donor molecules with large cluster anions. The so-called polyoxometalates oVer radical salts of 1 of suYcient quality for structural and physical characterization can be obtained using polyoxometalate clus- interesting structural and electronic characteristics in this context.1 ters as counterions.(i) These soluble metal–oxides show diVerent sizes, shapes and charges which are maintained in aqueous and non-aqueous Results and Discussion solvents as well as in the solid state.These features can induce new packings in the molecular constituents of the conducting The radical salts of BET with the Lindqvist anions [M6O19]2- (M=W and Mo) 4 and 5 part, leading to new band structures and therefore to unusual electrical properties.1,2 The two salts containing the [M6O19]2- anions were obtained (ii) They can have a magnetic character when they accommoas single crystals by electrocrystallization. Both salts are isodate magnetic ions or clusters in the structure, or when they structural and crystallize in the triclinic system P19 (see Table 1).act as electron acceptors giving rise to delocalized mixed- The unit cell is displayed in Fig. 1(a) and contains two BET valence clusters. These electronic features provide the opporcrystallographically equivalent molecules and one Lindqvist tunity to create systems combining magnetic and conducting anion located in the apexes of the unit cell.properties.3 The BET molecules present a disorder aVecting the sulfur The examples so far reported of organic donor–inorganic atoms external to the TTF core which are disordered over two cluster hybrids are almost exclusively based on the combination diVerent positions. These sites have a multiplicity of 0.5 for C of commercially available tetrathiafulvalene (TTF) or bis(ethyand 0.5 for S.This disorder may be due to the presence of two lenedithio)-TTF (BEDT-TTF or ET) with polyoxometalates diVerent orientations of the pure trans isomer of the BET having metal nuclearities of six (Lindqvist [M6O19]2-; M= molecule (starting material), or maybe to the possible isomeriz- WVI, MoVI),2,4 eight (octamolybdate b-[Mo8O26]4-), twelve {Keggin [XM12O40](8-n)- (Xn+=PV, SiIV, BIII, Fe 3 +, 2H+, Co2+, Cu 2 +, etc.; M=WVI, MoVI}5 and eighteen (Wells– Table 1 Relevant intramolecular distances of the BET molecule in the Dawson [P2W18O62]6-).6 With the aim of extending these salts BET2[M6O19] and calculation of its charge Q using the formula of Guionneau et al.;10 Q=6.347-7.463{(b+c)-(a+d)} studies to other organic donors we have combined the molecule bis(ethylenethio)-TTF (in short BET 1) with Lindqvist 2 (W and Mo derivatives) and Keggin 3 ([SiW12O40]4- anion) polyoxometalates.This organic donor has shown a good ability to form conducting radical salts with simple S S S S S S a d c b monoanions7 such as for example XF6- (X=P, As, Sb) or compound a/A ° b/A ° c/A ° d/A ° Qcalc SCN- with enhanced structural and electronic dimensionalities and also with magnetic anions8 of the type FeCl4-. However, BET2[W6O19] 1.38(1) 1.73(1) 1.74(1) 1.33(2) 0.95 in most cases the salts of 1 do not crystallize properly and 1.73(1) 1.72(1) 1.35(2) 1.72(1) 1.70(1) † BET-TTF=bis(ethylenethio)tetrathiafulvalene. 1.72(1) 1.70(1) ‡ Presented at the 58th Okazaki Conference, Recent Development and Future Prospects of Molecular Based Conductors, Okazaki, BET2[MoO19] 1.392(5) 1.724(3) 1.726(3) 1.348(5) 1.07 Japan, 7–9 March 1997. 1.730(3) 1.731(4) 1.353(5) § Permanent address: Laboratoire de Chimie, Electrochimie 1.734(3) 1.719(3) Mole`culaires et Chimie Analytique, URA CNRS 322, Universite� de 1.719(3) 1.717(4) Bretagne Occidentale. F-29285 Brest Cedex, France.J. Mater. Chem., 1998, 8(2), 313–317 313Fig. 1 (a) View of the unit cell of the salts 4 and 5; (b) two views of a dimer of BET molecules in 4 and 5 ation in solution of the cis–trans species during the electrooxidation. 9 The BET molecules are associated forming centrosymmetric face to face dimers with short contacts between the central C and S atoms [C(1)MC(1) 3.34 A ° , S(2)MS(3) 3.47 A ° ] although they are not eclipsed [Fig. 1(b)]. These dimers are surrounding the polyoxoanions so as to form a compact packing of anions and cations which is reminiscent of that of the NaCl salt. Thus, in the (1019) plane we observe that anions and dimeric cations are alternating along the directions [101] and [19219] [Fig. 2(a)]. However, due to the tendency of the organic donors to stack, the BET dimers are not completely isolated but show short contacts with the neighbouring dimers. In the above plane the shortest contacts occur in the b direction and involves two sulfur atoms (distance d3 in Fig. 2). Strong interdimer interactions are also observed along the a direction [Fig. 2(b)]. In view of the stoichiometry 251 of 4 and 5 the organic molecules are expected to be completely ionized (charge +1). This can be confirmed from the correlation between the intramolecular distances of the TTF skeleton and the oxidation degree Q proposed by Guionneau et al.10 for the BEDT–TTF molecule (see Table 2) that nicely fits to Q values of 0.95 and 1.07 for 4 and 5, respectively.A further support of this ionic charge is provided by the NIR–VIS spectra which exhibit a very strong and broad band centered at 7700 cm-1 which is Fig. 2 (a) View of the structure of 4 and 5 in the (1019) plane. Shortest intermolecular distances for 4 (5) in A ° : d1 [C(12)MC(12)]=3.69 (3.67), to be associated with the charge transfer between fully oxidized d2 [S(6)/C(8)MC(11)]=3.71 (3.71), d3 [S(6)/C(8)MC(8)/S(6)]=3.69 donors (B band), while the band associated with the electron (3.71), d4 [S(8)/C(10)MO(1)]=3.18 (3.16), d5 [C(11)MO(6)]=3.32 transfer between partially charged donors (A band) does not (3.29), d6 [S(4)MO(8)]=3.13 (3.12).(b) View of the structure in the appear.11 The IR spectrum is also typical of fully charged BET (012) plane.Shortest intermolecular distances for 4 (5) inA ° : d7 ions. In a mixed valence system broad bands associated with [S(7)/C(9)MS(1)]=3.53 (3.54), d8 [S(3)MS(3)]=3.61 (3.62), d9 the ag modes are observed in the region 800–1600 cm-1 arising [S(5)/C(7)MO(3)]=3.43 (3.42), d10 [O(3)MO(4)]=3.20 (3.21). from the coupling between delocalized electrons and vibrational modes of the double bonds.In the present case however only sharp bands are observed. The lack of a mixed charged BET molecules which have their spins antiferromagnetically coupled giving rise to a S=0 ground spin state. valence character in the organic part prevents the occurrence of electron delocalization. In fact, the transport properties Accoignal is observed in the EPR spectra of both salts.The thermal dependence of the intensity of this measured on single crystals (two-probe) indicate that both salts are insulators with low conductivity values [sRT= signal (proportional to the spin susceptibility) is plotted in Fig. 3. Note that this signal stays roughly constant in the 3.2×10-6 S cm-1] and high activation energies (Ea=240 meV in the range 240–300 K).The temperature dependent magnetic investigated temperature range. Such a behavior can not be attibuted to the exclusive presence of a paramagnetic impurity. susceptibility indicates that the two compounds are diamagnetic. This result is consistent with the dimerization of the The possibility of an excited triplet state thermally accessible 314 J. Mater. Chem., 1998, 8(2), 313–317Table 2 Crystallographic data for C20H16S12W6O19 4, C20H16S12Mo6O19 5 and C42H39NS24SiW12O42 6 chemical formula C20H16S12W6O19 C20H16S12Mo6O19 C42H39NS24SiW12O42 a/A ° 8.362(5) 8.352(6) 24.807(5) b/A° 10.925(6) 10.919(6) 24.194(5) c/A ° 11.664(4) 11.666(5) 14.357(3) a/degrees 65.28(3) 65.30(4) 90.00 b/degrees 79.11(2) 79.02(3) 90.00 c/degrees 80.73(3) 80.64(4) 90.00 V /A ° 3 946.5(8) 944.7(8) 8616.8(31) Z 1 1 3 M 2048.21 1520.75 4233.6(3) space group P19 (no. 2) P19 (no. 2) Pnma (no. 62) T /K 293(2) 293(2) 293(2) l/A ° 0.71073 0.71073 0.71073 Dc/g cm-3 3.593 2.673 3.704 m(Mo-Ka)/cm-1 18.896 2.672 24.248 R(F)a 0.0363 0.0228 0.0723 Rw(F)b 0.1214 0.0846 0.1937 aR=S[|Fo|-|Fc|]/S|Fo|; bRw=[Sw(|Fo|-|Fc|)2/Sw|Fo|2]1/2; w=4Fo2/[s2(|Fo|)-(0.07|Fo|2)].Fig. 3 Thermal dependence of the intensity of the EPR signal for the Fig. 4 View of the structure of 6 in the ac plane, showing the channels compounds BET2[W6O19] 4 and BET4[SiW12O40] 6 occupied by the disordered BET molecules BET molecules are occupying the hexagonal channels running can not be excluded. In fact, the data fit to the sum of a along the b axis created by the polyoxoanions.paramagnetic contribution, C/T , and a thermally activated Taking into account the stoiquiometry of 6 (451) and the contribution, (C¾/T ) exp(-J/kT ), with a coupling constant J charge of the anion [SiM12O40] (-4) the four BET molecules ca. 700 cm-1 and a 2% paramagnetic contribution. should be completely ionized (charge +1). This was confirmed by the absence of the characteristic ‘A’ band of mixed-valence The radical salt BET4[SiW12O40]·CH3CN·2H2O 6 species in the NIR spectrum.Accordingly the radical-cation salt is an insulator. The magnetic properties indicate a complete The preparation of radical salts of the BET donor with diVerent polyoxometalates having the Keggin structure {series coupling of the spins, which is in agreement with the association in dimers of the radical cations.In fact, the EPR spectra show [XM12O40] (X=PV, SiIV, BIII, Fe 3 +, 2H+, Co 2 +, Cu 2 +, etc.; M=W, Mo) and [XM(H2O)W11O39] (X=PV, SiIV; M=Ni2+, an extremely weak signal which, according to the thermal behavior, has to be attributed to the presence of a small Co2+, Cu2+, Cr3+, Fe3+)} was explored using the electrocrystallization technique.However, only the Si derivative gave amount of paramagnetic impurity (Fig. 3). single crystals suitable for a crystallographic study. The other polyanions do not gave any solid derivative and only in the Conclusions cases of PMo12 and PMnW11 was some powder deposited on the electrode. The first radical-cation salts of the electron donor molecule BET with Lindqvist and Keggin polyoxometalate clusters have Elemental analysis of 6 is consistent with the formula BET4[SiW12O40]·CH3CN·2H2O.Owing to the poor quality been prepared. The X-ray crystal structures of these salts show that in both cases the donor molecules are forming non- of the crystals only limited information about the crystal structure could be extracted by X-ray diVraction experiments. eclipsed dimers in the solid.However the diVerent size and charge of the two clusters have resulted in a diVerent packing Only the atoms of the Keggin anion as well as those of two of the four BET molecules could be found. The two remaining of these dimers with a significant extent of the intermolecular interactions in the Lindqvist derivatives, while quasi-insulated BET molecules are strongly disordered in the crystal and can not be localized (fragments of the central part of these mol- dimers are present in the Keggin derivative.Furthermore, EPR measurements suggest the presence of a thermally activated ecules have been localized in the Fourier maps). Fig. 4 shows a view of the structure in the ac plane. As we can see the triplet state in the [BET·+]2 dimers of the Lindqvist salts.In the reported salts the donor molecules have been found Keggin anions are forming hexagonal layers in this plane. The two BET molecules are located in between these anions and to be completely ionized and not surprisingly they are insulators with very low conductivity values. Compared with the are associated forming face to face dimers with a geometry which is similar to that found in the Lindqvist salts 4 and 5, equivalent BEDT–TTF radical salts we notice that a similar 251 insulating salt formed by [BEDT–TTF·+]2 dimers has but in this case the dimers are well isolated.The two disordered J. Mater. Chem., 1998, 8(2), 313–317 315Table 3 Atomic coordinates and isotropic or equivalent isotropic thermal parameters for the salt BET2[W6O19] atom x y z Ua /A ° 2 atom x y z Ua /A ° 2 W(1) 0.15295(5) 0.33787(4) -0.06422(4) 0.0274(1) C(3) 0.451(1) 0.179(1) 0.614(1) 0.031(2) W(2) -0.23398(5) 0.38887(4) 0.04408(4) 0.0293(1) C(4) 0.555(1) 0.194(1) 0.509(1) 0.034(2) W(3) 0.05657(5) 0.37228(4) 0.20745(4) 0.0275(1) C(5) 0.130(1) 0.764(1) 0.343(1) 0.032(2) O(1) 0.262(1) 0.2156(7) -0.1099(7) 0.040(2) C(6) 0.236(1) 0.780(1) 0.236(1) 0.035(2) O(2) 0.099(1) 0.2794(8) 0.3598(7) 0.042(2) C(7)b 0.4558(6) 0.0281(5) 0.7392(5) 0.045(1) O(3) -0.400(1) 0.3056(10) 0.0770(9) 0.051(2) C(8)b 0.6883(7) 0.0581(6) 0.5139(6) 0.052(1) O(4) -0.3089(9) 0.5414(7) 0.0887(7) 0.033(2) C(9)b -0.0158(5) 0.9004(4) 0.3318(4) 0.0281(8) O(5) -0.0668(9) 0.2821(7) -0.0183(7) 0.032(2) C(10)b 0.214(1) 0.9252(7) 0.1132(8) 0.078(2) O(6) 0.1671(9) 0.2662(7) 0.1130(7) 0.029(2) C(11) 0.618(2) -0.036(1) 0.667(2) 0.051(3) O(7) -0.075(1) 0.5284(7) 0.2196(7) 0.033(2) C(12) 0.023(2) 0.962(1) 0.166(2) 0.063(5) O(8) 0.232(1) 0.4833(7) 0.1315(7) 0.034(2) H(1)a 0.478(3) 0.034(1) 0.816(4) 0.050 O(9) -0.1413(9) 0.3062(7) 0.2004(7) 0.033(2) H(2)a 0.359(3) -0.019(1) 0.757(4) 0.050 O(10) 0.0000 0.5000 0.0000 0.024(2) H(3)a 0.672(3) 0.021(1) 0.455(4) 0.050 S(1) 0.3157(3) 0.3193(2) 0.6116(2) 0.0315(5) H(4)a 0.802(3) 0.076(1) 0.502(4) 0.050 S(2) 0.5486(3) 0.3477(3) 0.3815(3) 0.0356(6) H(5)a -0.126(3) 0.874(1) 0.367(4) 0.050 S(3) 0.1489(3) 0.6155(2) 0.4717(2) 0.0312(5) H(6)a 0.012(3) 0.960(1) 0.366(4) 0.050 S(4) 0.3809(3) 0.6501(3) 0.2409(2) 0.0334(5) H(7)a 0.226(3) 0.915(1) 0.033(4) 0.050 S(5)b 0.4558(6) 0.0281(5) 0.7392(5) 0.045(1) H(8)a 0.287(3) 0.989(1) 0.107(4) 0.050 S(6)b 0.6883(7) 0.0581(6) 0.5139(6) 0.052(1) H(9) 0.592(2) -0.121(1) 0.671(2) 0.050 S(7)b -0.0158(5) 0.9004(4) 0.3318(4) 0.0281(8) H(10) 0.708(2) -0.057(1) 0.716(2) 0.050 S(8)b 0.214(1) 0.9252(7) 0.1132(8) 0.078(2) H(11) -0.049(2) 0.924(1) 0.136(2) 0.050 C(1) 0.386(1) 0.4193(9) 0.4556(9) 0.028(2) H(12) -0.002(2) 1.059(1) 0.130(2) 0.050 C(2) 0.311(1) 0.5477(9) 0.396(1) 0.028(2) aUeq=(4/3)[a2B(1,1)+b2B(2,2)+c2B(3,3)+ab(cos c)B(1,2)+ac(cos b)B(1,3)+bc(cos a)B(2,3)]; H atoms with fixed U.bAtoms with multiplicity of 0.5. Table 4 Atomic coordinates and isotropic or equivalent isotropic thermal parameters for the salt BET2[Mo6O19] atom x y z Ua /A° 2 atom x y z Ua /A° 2 Mo(1) 0.15585(4) 0.33745(3) -0.06201(3) 0.03034(7) C(2) 0.3134(4) 0.5484(3) 0.3947(3) 0.0289(6) Mo(2) -0.23197(4) 0.38691(3) 0.04392(3) 0.03308(8) C(3) 0.4487(4) 0.1792(3) 0.6153(3) 0.0314(6) Mo(3) 0.05504(4) 0.37431(3) 0.20835(3) 0.03162(8) C(4) 0.5567(4) 0.1929(4) 0.5099(3) 0.0333(7) O(1) 0.2616(4) 0.2174(3) -0.1097(2) 0.0414(6) C(5) 0.1279(4) 0.7670(3) 0.3410(3) 0.0324(7) O(2) 0.0954(4) 0.2787(3) 0.3583(2) 0.0437(7) C(6) 0.2348(5) 0.7822(3) 0.2342(3) 0.0338(7) O(3) -0.3979(4) 0.3043(3) 0.0747(3) 0.0498(7) C(7)b 0.4562(2) 0.0280(2) 0.7409(2) 0.0502(4) O(4) -0.3100(3) 0.5403(3) 0.0910(2) 0.0350(5) C(8)b 0.690(1) 0.056(1) 0.513(1) 0.0476(4) O(5) -0.0667(3) 0.2834(2) -0.0232(2) 0.0347(5) C(9)b -0.014(1) 0.9002(9) 0.329(1) 0.0346(3) O(6) 0.1649(3) 0.2625(2) 0.1135(2) 0.0324(5) C(10)b 0.216(2) 0.928(1) 0.110(1) 0.0674(6) O(7) -0.0775(3) 0.5247(2) 0.2214(2) 0.0350(5) C(11) 0.6183(6) -0.0395(4) 0.6682(5) 0.055(1) O(8) 0.2362(3) 0.4809(3) 0.1310(2) 0.0359(5) C(12) 0.0224(2) 0.9645(2) 0.1649(2) 0.060(1) O(9) -0.1427(3) 0.3042(2) 0.2016(2) 0.0342(5) H(1)b 0.4799(2) 0.0342(2) 0.8165(2) 0.050 O(10) 0.0000 0.5000 0.0000 0.0253(6) H(4)b 0.672(1) 0.019(1) 0.454(1) 0.050 S(1) 0.3154(1) 0.31878(8) 0.61201(8) 0.0322(2) H(5)b 0.013(1) 0.9591(9) 0.364(1) 0.050 S(2) 0.5490(1) 0.3475(1) 0.38096(8) 0.0361(2) H(6)b -0.124(1) 0.8740(9) 0.363(1) 0.050 S(3) 0.1486(1) 0.61678(8) 0.47129(8) 0.0323(2) H(7)b 0.227(2) 0.917(1) 0.030(1) 0.050 S(4) 0.3807(1) 0.65015(9) 0.23974(8) 0.0340(2) H(8)b 0.290(2) 0.991(1) 0.103(1) 0.050 S(5)b 0.4562(2) 0.0280(2) 0.7409(2) 0.0502(4) H(9) 0.5887(6) -0.1231(4) 0.6709(5) 0.050 S(6)b 0.6903(2) 0.0571(2) 0.5136(2) 0.0476(4) H(10) 0.7077(6) -0.0633(4) 0.7181(5) 0.050 S(7)b -0.0152(2) 0.9025(2) 0.3304(2) 0.0346(3) H(11) -0.0496(2) 0.9261(2) 0.1352(2) 0.050 S(8)b 0.2135(2) 0.9290(2) 0.1114(2) 0.0674(6) H(12) -0.0032(2) 1.0619(2) 0.1300(2) 0.050 C(1) 0.3857(4) 0.4181(3) 0.4563(3) 0.0291(6) aUeq=(4/3) [a2B(1,1)+b2B(2,2)+c2B(3,3)+ab(cos c)B(1,2)+ac(cos b)B(1,3)+bc(cos a)B(2,3)]; H atoms with fixed U.bAtoms with multiplicity of 0.5. been found with the Lindqvist anions, although in this last Experimental case the structure is formed by alternating layers of the organic Synthesis donor and the anions,12 as is customarily observed in the BEDT–TTF salts. With the Keggin anions the diVerences All the radical salts were obtained on a platinum wire electrode between the BEDT–TTF salts and the BET ones are more by anodic oxidation of the organic donor 1 in a U-shaped pronounced. Thus, while the former donor forms a wide 851 electrocrystallization cell under low constant current (1.2 mA) family of semiconducting salts in which mixed-valence layers in the presence of the tetrabutylammonium (TBA+) salts of of the organic donor alternate with anion layers,5a the latter the polyanions as supporting electrolyte.The TBA+ salts of 2 salts exhibit a dimeric association of fully charged radical were prepared by metathesis from the Na+ salts,13 and recryscations. The lack of mixed valence states in the reported BET tallized from acetone or DMF. The TBA+ salt of 3 was salts may be then attributed to the larger tendency of these prepared by metathesis from the acid (commercial grade), and donors to form [BET·+]2 dimers.The preparation of related recrystallized from acetonitrile. The solvents were not pre- BET salts having higher electron delocalization and, eventually, viously dried. All the crystals were collected, washed with a magnetic component is now being explored.With this aim CH3CN, CH2Cl2 and/or DMF (to remove any portion of we are using Lindqvist and Keggin anions of diVerent charges neutral BET crystals or of the TBA+ salts of the polyanions), and air-dried. Good quality black prismatic crystals of containing magnetic centers. 316 J. Mater. Chem., 1998, 8(2), 313–317BET2[M6O19] (M=W 4, Mo 5) were obtained in DMF, and funding this work.J.R.G-M thanks the Generalitat Valenciana for a pre-doctoral grant. shiny black needle-like crystals of BET4[SiW12O40] 6, were obtained from CH3CN–CH2Cl2 (253). The stoichiometries of 4 and 5 were only determined from the X-ray structure. For 6 References the stoichiometry was determined from elemental analysis which indicated that the correct formula for 6 is 1 E.Coronado and C. J. Go�mez-Garcý�a, Chem. Rev., in press. 2 L. Ouahab, in Polyoxometalates: From Platonic Solids to Anti- BET4[SiW12O40]·CH3CN·2H2O (Found: C, 11.81; H, 0.94; N, Retroviral Activity, ed. M. T. Pope and A. Mu� ller, Kluwer 0.39; S, 16,91%. Calc.: C, 11.92; H, 0.97; N, 0.33; S, 18.18%). Academic, Dordrecht, 1994, p. 245. 3 (a) E.Coronado, J. R. Gala�n Mascaro� s, C. Gime�nez-Saiz and X-Ray crystallography C. J. Go�mez-Garcý�a, in Magnetism: A Supramolecular Function, NATO ASI Series, ed. O. Kahn, Kluwer Academic, Dordrecht, Crystals of the three salts, which are stable in air, were mounted 1996, vol. C484, p. 281; (b) E. Coronado, J. R. Gala�n-Mascaro� s, on an Enraf-Nonius CAD4 diVractometer equipped with a C.Gime�nez-Saiz and C. J. Go�mez-Garcý�a, Synth. Met., 1997, 85, graphite crystal, incident beam monochromator. Preliminary 1647. examination and data collection were performed with Mo-Ka 4 C. Bellito, D. Attanasio, M. Bonamico, V. Fares, P. Imperatori and S. Patrizio, Mater. Res. Soc. Symp. Proc., 1990, 173, 143. radiation. Cell constants and an orientation matrix for data 5 (a) C.J. Go� mez-Garcý�a, C. Gime�nez-Saiz, S. Triki, E. Coronado, collection were obtained from least-squares refinement, using P. Le Magueres, L. Ouahab, L. Ducasse, C. Sourisseau and the setting angles of 25 reflections. Lorentz, polarization and a P. Delhaes, Inorg. Chem., 1995, 4139; (b) J. R. Gala�n-Mascaro� s, semi-empirical absorption correction (y-scan method)14 were C. Gimenez-Saiz, S. Triki, C.J. Go�mez-Garcý�a, E. Coronado and applied to the intensity data. Other important features of the L. Ouahab, Angew. Chem., Int. Ed. Engl., 1995, 34, 1460. crystals are summarized in Table 2 with atomic coordinates and 6 E. Coronado, J. R. Gala�n-Mascaro� s, C. Gimenez-Saiz, C. J. Gomez-Garcý�a and V. N. Laukhin, Adv.Mater., 1996, 8, 801. thermal parameters for 4 and 5 listed in Tables 3 and 4.The X- 7 (a) J. Tarres, N. Santalo, M. Mas, E. Molins, J. Veciana, C. Rovira, ray crystal structures were determined for 4 and 5 (M=Mo, S. Yang, H. Lee, D. O. Cowan. M. L. Doublet and E. Canadell, W), which are isostructural as expected, and were solved by Chem. Mater., 1995, 7, 1558; (b) E. Ribera, J. Tarre�s, V. Laukhin, direct methods and developed with successive full-matrix least- E.Canadell, M. Mas, E. Molins, J. Veciana and C. Rovira, Synth. squares refinements and diVerence Fourier syntheses, which Met., 1997, 86, 2145. showed all the atoms of organic donors and polyanions. In 8 E. Coronado, L. Falvello, J. R. Gala�n-Mascaro� s, C. Gime�nez-Saiz, C. J. Go�mez-Garcý�a, V. Lauhkin, A. Pe�rez-Bený�tez, C. Rovira and contrast, the structure of 6 could not be fully determined and J.Veciana, Adv.Mater., 1997, 9, 984. only the atoms of polyanions and two BET molecules could be 9 C. Rovira, J. Veciana, N. Santalo� , J. Tarre�s, J. Cirujeda, E. Molins, found. This was owing to the presence of disorder aVecting the J. Llorca and E. Espinosa, J. Org. Chem., 1994, 59, 3307. position of the other two BET molecules in the formula, and to 10 P. Guionneau, C. J. Kepert, G. Bravic, D. Chasseau, M. R. Truter, the poor quality of the crystals, which prevented the assigment M. Kurmoo and P. Day, Synth.Met., 1997, 86, 1973. of peaks with Dr <2.53 e A ° -3. Full crystallographic details, 11 B. Torrance, B. A. Scott, B. Walter, F. B. Kaufman and P. E. Seiden, Phys. Rev. B, 1979, 19, 730. excluding structure factors, have been deposited at the 12 S. Triki, L. Ouahab and D. Grandjean, Acta Crystallogr., Sect. C, Cambridge Crystallographic Data Centre (CCDC). See 1991, 47, 645. Information for Authors, J. Mater. Chem., 1998, Issue 1. Any 13 (a) N. H. Hur, W. G. Klemperer and R. C. Wang, Inorg. Synth., request to the CCDC for this material should quote the full 1990, 27, 80; (b)M. Fournier, Inorg. Synth., 1990, 27, 77. literature citation and the reference number 1145/68. 14 A. C. T. North, D. C. Philips and F. S. Mathews, Acta Crystallogr., Sect. A, 1968, 24, 351. We thank the Ministerio de Educacio�n y Cultura (CICYT) and tper 7/06866B; Received 23rd September, 1997 J. Mater. Chem., 1998, 8(2), 313–317 317

ISSN:0959-9428    

DOI:10.1039/a706866b

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Synthesis, structure and properties of new dithiolene complexes containing a 1,3,5-trithiepin ring Masaki Takahashi,*a† Neil Robertson,a‡ Akiko Kobayashi,b Hermut Becker,c Richard H. Friendc and Allan E. Underhilla aDepartment of Chemistry, University of Wales, Bangor, Bangor, Gwynedd, UK L L 57 2UW bDepartment of Chemistry, School of Science, the University of T okyo, Hongo, T okyo 113, Japan cDepartment of Physics, University of Cambridge, Cavendish L aboratory,Madingley Road, Cambridge, UK CB3 0HE Mono-tetrabutylammonium salts of nickel, copper, and gold 1,3,5-trithiepin-6,7-dithiolato (ttdt) complexes 1a–c have been prepared and the structures of 1b and 1c determined by X-ray crystallography.Cyclic voltammograms of these complexes showed oxidation peaks in the range 0.23–0.46 V (vs.SCE). Partially oxidised salts of these complexes were obtained either as amorphous or polycrystalline solids. The electrical conduction properties are reported. The crystal structure of (TTF)[Au(ttdt)2] obtained from the reaction of 1c and TTF3(BF4)2 was determined by X-ray crystallography. Bis(dithiolene) transition metal complexes have been investi- Preparation of (R4N)[M(ttdt)2] gated extensively during the last two decades, because of their (R=Bun, Me; M=Ni, Cu, Au) potential for the preparation of molecular conductors or superconductors.1 Recently, large third order non-linear optical (Bun4N)[Ni(ttdt)2] was prepared starting from 1,3-dithiolo[4,5- f ][1,3,5]trithiepin-2-thione 2 by the reported method.4 K2(ttdt) properties have been found in some of these complexes, and some of these complexes are also of interest because of their 3 was prepared by the hydrolysis of thione 2 with an excess of potassium hydroxide in ethanol and isolated by filtration under unique magnetic behaviour.The crystal structures of these complexes which contain columnar stacks of anions and their nitrogen. K2(ttdt) was allowed to react with NiCl2·6H2O in methanol.Addition of tetrabutylammonium bromide to the associated cations play an important role in determining their solid state properties. reaction mixture followed by filtration and recrystallisation yielded the green–black solid product (Scheme 1). One area of current interest in the field of molecular conductors is to construct molecular systems in which either (Bun4N)[M(ttdt)2] (M=Cu 1b, Au 1c) were prepared similarly by using copper(II) chloride or potassium tetrachloroaurate.The donors and acceptors (or ions) or donors and donors are interlinked. This can be achieved for example, by introducing corresponding tetramethylammonium salts of 1a–c were prepared using a similar procedure with tetramethylammonium bromide. a hydrogen bonding network.2 From this point of view, the study of compounds which include non-conjugated group 16 All these complexes gave satisfactory analytical data.The IR spectra contain absorption bands corresponding to elements at the periphery of donors (or acceptors) are important. Studies of TTF derivatives which have peripheral seven- the weakened CNC bond at around 1380 cm-1 for all the complexes and the absorption band corresponding to the CMS membered rings including SCH2OCH2S and SCH2SCH2S group have been reported recently.3 The radical cation salts bond appeared around 850 cm-1.Complexes 1b and 1c exhibited a singlet in 1H NMR spectra due to the SCH2 group at d ca. 4.0. of these donors showed relatively high room temperature conductivities (10-1–102 S cm-1) and also exhibited metal-like electrical conduction properties down to 4.2 K.Crystal structure of (Bun 4N)[M(ttdt)2] In contrast to these cationic salts, metal dithiolene complexes (M=Au, Cu) containing these moieties will give rise to anionic partially oxidised salts and therefore the lone pairs of electrons on the The crystal structures of the copper and gold complexes (1b, peripheral heteroatoms could interact favourably with counter- 1c) were determined by X-ray crystallography.The crystal cations in charge transfer salts. Kato et al. reported the preparation and the structure of the nickel bis(dithiolate) 1a.4 Although the platinum and palladium complexes of this ligand were prepared by Faulmann et al., the preparation of partially oxidised salts of these complexes was unsuccessful.5 Therefore, we have studied the preparation and the properties of bis(dithiolene) complexes 1a–c (Scheme 1) in which the metals (nickel, copper and gold) are coordinated by the 1,3,5-trithiepin-6,7- dithiolato ligand (ttdt) having the 1,3,5-trithiodimethyl group in the periphery of the molecule [M(ttdt)2]x-.† Present address; Centre for Instrumental Analysis, Ibaraki University, 2–1-1, Bunkyo, Mito 310, Japan. ‡ Present address; Department of Chemistry, University of Edinburgh, King’s Buildings, West Main Road, Edinburgh, Scotland, UK S M S S S S S S S S S S S S S S S SK SK S S S 1 2 2 3 2 K2(ttdt) KOH EtOH 2 3 1) metal salt* / MeOH 2) Bun 4NBr (a: M = Ni, b: M = Cu, c: M = Au) c: KAuCl4 b: CuCl2 (Bun 4N) * a: NiCl2 .6H2O Scheme 1 EH9 3JJ. J.Mater. Chem., 1998, 8(2), 319–324 319S M S S2 C2 C1 S1 NC NC CN CN S M S S2 C2 C1 S1 S4 C3 S3 S S S S S M S S2 C2 C1 S1 S S S4 S3 C4 C3 S M S S2 C2 C1 S1 S S S S5 C4 S4 C3 S3 S M S S S S S S S S M S S S S O S S O S [M(mnt)2] [M(dmit)2] [M(dddt)2] [M(ttdt)2] [M(ddtdt)2] [M(diod)2] Fig. 1 Compounds under study structures of these complexes are shown in Fig. 2 and 3. The bond lengths and SMMMS angles found in 1a–c and related complexes are summarized in Table 1. The crystal structures of 1a–c are similar and the structural Fig. 3 Molecular structure of [Au(ttdt)]- in the crystal of parameters of outer trithiepin rings are nearly the same. The (Bun4N)[Au(ttdt)2] 1c diVerences observed between the structures of these complexes are associated with the structural parameters of the inner but slightly shorter than that found for [Cu(dddt)2]- (1.39 A ° ) metallocycles because of the diVerent central metal atoms.The or [Cu(dmit)2]2- (1.36 A ° ). The exo-CMS bond lengths of the structures of these complexes are nearly planar about the metal ligand at 1.753–1.764 A ° , are close to the CMS bond lengths of atom and the outer trithiepin rings take up a chair-like the metallocycle (1.743–1.764 A ° ) and similar to the correspond- conformation. ing distances in related copper complexes (1.75–1.76 A ° ).These The copper complex 1b has basically a planar metallocycle values are in between the usual CNS bond length (1.71 A ° ) and with a slight twist associated with the two dithiolene planes CMS bond length (1.81 A ° ), suggesting that the CMS bonds (four sulfur atoms around the copper atom are deviated from on the dithiolene planes are delocalized.The CuMS bond their mean plane by 0.09–0.17 A ° ). This basically planar struclengths of between 2.181 and 2.190 A° , resemble those in ture is also observed for [Cu(mnt)2]- (the deviations of sulfur [Cu(mnt)2]- (2.170 A ° ) and [Cu(dddt)2]- (2.181 A ° ).The CMS atoms from the mean plane were 0.05–0.11 A ° )6a but is in sharp bond length present in the peripheral trithiepin ring is ca. contrast with the fact that the dithiolene planes in the crystal 1.80 A° , slightly longer than the CMS bonds of [Cu(dddt)2]- of [Cu(dddt)2]- (Bun4 salt) and [Cu(dmit)2]2- are twisted to (1.75 and 1.77 A ° ). 29° 6b and 57°,6c respectively. The CNC bond length of the The structure of the gold complex 1c is similar to those of metallocycle, 1.325 A ° , is a little longer than that of a usual the nickel and copper complexes (1a, 1b), having basically a CNC bond and similar to the value in [Cu(mnt)2]- (1.32 A ° ) planar structure around the gold atom with a chair-like bent peripheral trithiepin rings.The bond lengths and SMAuMS angle are close to the corresponding values of other gold complexes of related ligands (Tables 1 and 2). Redox potentials of (Bun 4N)[M(ttdt)2] (M=Ni, Cu, Au) Cyclic voltammetry measurements were carried out on 1a–c in acetonitrile using a standard calomel electrode with 0.1 M tetrabutylammonium hexafluorophosphate as the electrolyte.The redox potential of these complexes and other complexes are shown in Table 3. The nickel and gold complexes (1a, 1c) showed reversible oxidation peaks at +0.21 and +0.46 V (vs. SCE) respectively, whereas the copper complex 1b showed an irreversible oxidation peak at +0.45 V. The reversible oxidation waves observed for 1a and 1c disappeared on repetitive scans when the potential was increased to >1.5 V.Reversible reduction waves were observed for 1a–c (-0.59, -0.63, -0.91 V, respectively). The oxidation potential of the nickel complex 1a is 0.61 V lower than that of [Ni(mnt)2]-, 0.15 V higher than that of [Ni(dddt)2]- and is close to those of [Ni(dmit)2]- and [Ni(ddtdt)2]-. It therefore appears that nickel complexes of ligands containing seven-membered outer rings are slightly Fig. 2 Molecular structure of [Cu(ttdt)]- in the crystal of (Bun4N)[Cu(ttdt)2] 1b more diYcult to oxidise to the neutral complex than the 320 J. Mater. Chem., 1998, 8(2), 319–324Table 1 Bond distances (A° ) and bond angles (degrees) of some ammonium salts of nickel, copper and gold bis(dithiolene) complexes complex MMS1 C1MS1 C1NC2 S1MMMS2 C1MS3 S3MC3 C3MS4 [Ni(mnt)2]- a 2.149 1.72 1.37 92.5 [Ni(dmit)2]- b 2.156 1.72 1.35 93.2 [Ni(dddt)2]- c 2.132 1.75 1.28 91.1 1.77 1.81, 1.89 [Ni(ttdt)2]- d 2.141 1.72 1.37 91.3 1.76 1.81 1.81, 1.82 [Cu(mnt)2]- e 2.170 1.72 1.32 92.4 [Cu(dmit)2]2- f 2.272 1.73 1.36 94.0 1.75 [Cu(dddt)2]- g 2.181 1.73 1.39 91.5 1.76 1.75, 1.77 [Cu(ttdt)2]- 2.183(1) 1.752(5) 1.332(6) 91.68(6) 1.758(5) 1.805(5) 1.799(5) [Au(mnt)2]- h 2.317 1.75 1.33 90.5 [Au(dmit)2]- i 2.323 1.75 1.31 91.5 1.75 [Au(dddt)2] c 2.304 1.70 1.39 89.2 1.77 1.78, 1.88 [Au(ttdt)2]- 2.312(1) 1.750(5) 1.334(7) 89.35(6) 1.766(4) 1.810(5) 1.780(6) 1.809(6) The numbering of the atoms is as shown in the compounds.References: aA. Kobayashi and Y. Sasaki, Bull. Chem. Soc. Jpn., 1977, 50, 2650.bC. T. Vance, R. D. Bereman, J. Bordner, W. E. Hatfield and J. H. Helms, Inorg. Chem., 1985, 24, 2905. cA. J. Schultz, H. H. Wang, L. C. Soderholm, T. L. Sifter, J. M. Williams, K. Beckgaard and M.-H. Whangbo, Inorg. Chem., 1987, 26, 3757. dRef. 4. eRef. 6(a). fRef. 6(c). gRef 6(b). hP. Kuppusamy, N. Venkatalakshmi and P. T. Manoharan, J. Cryst. Spectrosc. Res., 1985, 15, 629. iG.Matsubayashi and A. Yokozawa, J. Chem. Soc., Dalton T rans., 1990, 3535. Table 2 Bond distances (A ° ) and bond angles (degrees) of [Au(ttdt)2]x- and [Au(dddt)2]x- complexes complex MMS1 C1MS1 C1NC2 S1MMMS2 C1MS3 S3MC3 C3MS4 (Bun4N)[Au(ttdt)2] 2.312(1) 1.750(5) 1.334(7) 89.35(6) 1.766(4) 1.810(5) 1.780(6) 1.809(6) TTF[Au(ttdt)2] 2.318(2) 1.754(5) 1.340(10) 90.78(6) 1.768(5) 1.810(5) 1.805(6) TTF[Au(dddt)2]a 2.304 1.78 1.29 89.8 1.77 1.77, 1.93 TTF[Au(dddt)2]a 2.303 1.76 1.37 89.8 1.76 1.68, 1.81 Reference: aU.Geiser, A. J. Schultz, H. H. Wang, M. A. Beno and J. M. Williams, Acta Crystallogr., Sect. C, 1988, 44, 259. Table 3 Redox potentials of nickel, copper and gold bis(dithiolene) Electrochemical oxidation of (R4N)[M(ttdt)2] complexes The electrochemical oxidation of 1a–c in the presence of alkali E1/V E2/V DE/V metal salts or TTF derivatives was investigated.A variety of complex -1P0 -2P-1 (E1-E2) solvent, electrode solvent systems and current densities were investigated. No crystals were obtained in the electrochemical crystallisation of [Ni(mnt)2]- a +0.82 (irr.) -0.14 0.96 MeCN, Ag/Ag+ the nickel complex 1a but an amorphous solid was obtained [Ni(dmit)2]- b +0.22 (irr.) -0.13 0.37 MeCN, SCE [Ni(dddt)2]- b +0.06 -0.69 0.75 MeCN, SCE on the anode in every experiment.Electrochemical oxidation [Ni(ddtdt)2]- b +0.16 -0.71 0.87 MeCN, SCE of the copper complex 1b aVorded only a small amount of a [Ni(ttdt)2]- +0.21 -0.59 0.80 MeCN, SCE mixture of products on the anode. Experiments involving the gold complex 1c resulted in the production of a polycrystalline [Cu(mnt)2]- a +0.96 (irr.) -0.03 0.99 MeCN, Ag/Ag+ product on the anode.The analytical results obtained for the [Cu(dddt)2]- c +0.38 (irr.) -0.49 0.87 DMF, Ag/Ag+ products obtained from (R4N)[Ni (ttdt)2] suggested a stoichi- [Cu(ttdt)2]- +0.45 (irr.) -0.63 1.08 MeCN, SCE ometry close to that of the neutral [Ni (ttdt)2] complex but [Au(mnt)2]- d +1.15 -0.88 2.03 CH2Cl2, Ag/Ag+ containing a small quantity of the counter-cation.From the [Au(dmit)2]- +0.35 -0.60 0.95 MeCN, SCE analytical data it was very diYcult to determine whether or [Au(dddt)2]- e +0.41 -1.32 1.73 CH2Cl2, SCE not partially oxidised products were obtained. For the nickel [Au(ttdt)2]- +0.46 -0.91 1.37 MeCN, SCE complexes, room temperature conductivities in the range 10-4–10-5 S cm-1 were obtained for products produced by Irr.=irreversible.References: aL. Persaud and C. H. Langford, Inorg. Chem., 1985, 24, 3562. bRef. 4. cRef. g in Table 1. dJ. C. Fitzmaurice, electrocrystallisation in the presence of alkali metal cations. A A. M. Z. Slawin, D. J. Williams, J. D. Woollins and A. J. Lindsay, higher conductivity of 10-1 S cm-1 was observed for the Polyhedron, 1990, 9, 1561.eRef. c in Table 1. product obtained in the presence of Me4N+ ions and whose composition was close to (Me4N)0.5[Ni(ttdt)2] from elemental analysis. These results are somewhat diVerent from those complexes of ligands containing six-membered outer rings. The reported by Cassoux who obtained the neutral nickel complex potentials are rather close to those of [Ni(dmit)2]- which directly from electrochemical and chemical oxidation of 1a.5 contains a conjugated CNS bond.The diVerence between the For the gold complexes, conductivities of around 10-3 S cm-1 oxidation and reduction potentials (DE) of 1a is 0.80 V, which were obtained for products obtained in the presence of alkali is considerably larger than DE of [Ni(dmit)2]-, but is close metal, Bun4N+, Me4N+ cations and BEDT-TTF.to the values of [Ni(dddt)2]- and [Ni(ddtdt)2]- and smaller Partially oxidised salts of [M(dmit)2]- (M=Ni, Au) than that of [Ni(mnt)2]-. The gold complex 1c is more have been shown to exhibit high room temperature conducdi Ycult to oxidise than [Au(dmit)2]- by 0.11 V and has a tivities {room temperature conductivity=101 S cm-1 for larger DE value than [Au(dmit)2]-. The copper complex 1b (Bun4N)0.29[Ni(dmit)2],7 102 S cm-1 for K0.5[Au(dmit)2],8 can be oxidised at a potential lower by 0.51 V compared with 10-1 S cm-1 for TTF0.67[Au(dmit)2]9} whereas the partially oxidised salts of [M(diod)2]- and [M(ttdt)2]- 1 complexes [Cu(mnt)2]-, but DE of 1b is similar to that of [Cu(mnt)2]-. J.Mater. Chem., 1998, 8(2), 319–324 321show relatively lower conductivities {room temperature con- dipotassium salt was added a methanolic solution (10 ml ) of NiCl2 6H2O (133 mg, 0.85 mmol). After stirring the reaction ductivity=10-2 S cm-1 for BEDT-TTF0.17[Ni(diod)2] (compressed pellets)10}. It seems that the bulk or the flip motion of mixture overnight at room temperature, air was bubbled through it for 15 min.The precipitate formed in the reaction the peripheral chair-like seven-membered rings on these ligands interferes with the packing of the anions and makes the was filtered oV and the filtrate was added to a methanolic solution (20 ml ) of tetrabutylammonium bromide (0.90 g, formation of partially oxidised products less likely. 2.8 mmol).The precipitate of 1a was collected by filtration (190 mg, 31%). Dark green crystals of 1a were obtained by Metathesis experiments recrystallisation from acetone and propan-2-ol under vacuum (mp 176.0–176.5 °C). DiVusion controlled metathesis experiments involving (TTF)3(BF4)2 and 1a–c in acetonitrile were carried out. Anal. Calc. for C24H44NS10Ni: C, 39.90; H, 6.11; N, 1.94; S, 44.17.Found: C, 40.28; H, 6.67; N, 1.92; S, 44.99%. IR (KBr Fine needle-shaped crystals were obtained for the nickel and gold complexes (1a, 1c), but no crystals were obtained using disk): 1479, 1453, 1385, 1212, 1164, 1120, 886, 850, 719 cm-1. UV–VIS (CH2Cl2): 395 nm (e=14 300 dm3 mol-1 cm-1), 340 the copper complex 1b. The structure of the gold complex was successfully determined by X-ray crystallography and revealed (e=28 200).near-IR (CH2Cl2): 911 (e=8200). that the product obtained was the 151 salt, TTF[Au(ttdt)2]. Some of the structural parameters are shown in Tables 2 and Preparation of (Bun 4N)[Cu(ttdt)2] 1b 4. In the crystal, a pair of TTF molecules are surrounded by a pair of gold complexes (Fig. 4), an arrangement also seen in A procedure similar to that used in the preparation of 1a the crystal packing of TTF[Au(dddt)2].The structure of was adopted using CuCl2 (130 mg, 1.0 mmol) instead of [Au(ttdt)2]- is very similar to that in (Bun4N)[Au(ttdt)2] and NiCl2 6H2O. The reddish black powder of 1b was obtained the structure of the TTF molecule is similar to that found in (508 mg, yield 72%). Deep red crystals were obtained by TTF[Au(dddt)2] (Tables 2 and 4). recrystallisation from acetone and propan-2-ol under vacuum Too little product was obtained from the experiment involv- (mp 140.5–141.0 °C).ing 1a for elemental analysis and the crystals were too thin for Anal. Calc. for C24H44NS10Cu: C, 39.44; H, 6.07; N, 1.92; S, an X-ray structure determination. 43.87. Found: C, 38.69; H, 6.12; N, 1.82; S, 42.98%.IR (KBr The electrical conductivity of the crystals of TTFx[Ni (ttdt)2] disk): 1481, 1452, 1373, 1213, 1164, 1120, 881, 850, 718 cm-1. obtained from the metathesis experiment of 1a was measured. 1H NMR (CDCl3): d 1.05(12 H, t), 1.45(16 H, m), 3.13(8 H, The room temperature conductivity was ca. 4.7×10-4 S cm-1 t), 4.01(8 H, s, SCH2). UV–VIS (CH2Cl2): 441 nm (e= and the band gap was 0.19 eV over the temperature range 22 200 dm3 mol-1 cm-1). 295–210 K. Preparation of (Bun 4N)[Au(ttdt)2] 1c Conclusion A procedure similar to that used in the preparation of 1a was The preparation, redox electrical properties of [M(ttdt)2]x- adopted using potassium tetrachloroaurate(III) (320 mg, complexes (M=Ni, Cu, or Au) have been described. The 0.85 mmol) instead of NiCl2 6H2O.Air was not bubbled crystal structure of the Cu and Au complexes have been through the solution. A black powder of 1c was obtained determined. Attempts to prepare partially oxidised products (115 mg, yield 16%). Yellow crystals were obtained by recrysby electrocrystallisation resulted in products which behaved tallisation of the product from acetone and propan-2-ol under as semiconductors from room temperature down to 200 K.vacuum (mp 197.0–198.5 °C). The yield of 1c was improved to The compound TTF[Au(ttdt)2] was prepared by metathesis. 35% when the reaction of K2(ttdt) with KAuCl4 was carried out at 50 °C over 2 days. Anal. Calc. for C24H44NS10Au: C, 33.36; H, 5.13; N, 1.62; S, Experimental 37.10. Found: C, 33.14; H, 4.88; N, 1.62; S, 38.46%. IR (KBr All the reaction were carried out under nitrogen.All the disk): 1482, 1374, 1213, 1164, 1120, 951, 872, 850, 719 cm-1. solvents used in the experiments were purified by published 1H NMR (CDCl3): d 1.03(12 H, t), 1.45(16 H, m), 3.12(8 H, methods. Melting points were uncorrected. A Perkin Elmer t), 3.95(8 H, s, SCH2). UV–VIS (CH2Cl2): 345 nm (e= 1600 series FTIR spectrophotometer was used for IR measure- 27 000 dm3 mol-1 cm-1).ment, a Carlo Erba elemental analyser 1106 was used for elemental analysis and a Bruker AC250 instrument was used Preparation of (Me4N)[M(ttdt)2] (M=Ni, Cu, Au) for 1H NMR measurements. UV–VIS spectra were recorded on Hitachi 200–10 spectrophotometer and near-IR spectra The tetramethylammonium salts were prepared by using was recorded on a Perkin Elmer Lambda 9 spectrophotometer.a similar procedure to that used in the preparation of Cyclic voltammograms was performed using a Polarographic corresponding tetrabutylammonium salts 1a–c. Tetramethyl- Analyser Model 264A. ammonium bromide was used instead of tetrabutylammonium bromide [yield: 49% (M=Ni), 36% (M=Cu), 50% Preparation of (Bun 4N)[Ni(ttdt)2] 1a (M=Au)]. Thione 2 (0.51 g, 2 mmol) was allowed to react with potassium hydroxide (0.90 g, 16 mmol) in 10 ml ethanol for 1.5 h at (Me4N)[Ni(ttdt)2].mp: 182.5–184.0 °C. Anal. Calc. for C12H20NS10Ni: C, 25.85; H, 3.62; N, 2.51; S, 57.50. Found: C, 40–60 °C. The resulting gray precipitate of K2(ttdt) was isolated by filtration under nitrogen. To a methanolic solution of the 26.68; H, 3.63; N, 2.30; S, 52.08%.Table 4 Bond distances (A ° ) and bond angles (degrees) of TTF in TTF[Au(ttdt)2] and TTF[Au(dddt)2] complex C5NC5 S6MC5MS7 C5MS6 S6MC6 C6NC7 TTF[Au(ttdt)2] 1.40(1) 115.3(4) 1.705(8), 1.725 (8) 1.716(7) 1.33(2) TTF[Au(dddt)2]a 1.51 115 1.63, 1.73 1.74 1.36 The numbering of the atoms is as shown in Fig. 4. Reference: aRef. a in Table 2. 322 J. Mater. Chem., 1998, 8(2), 319–324Fig. 4 Crystal structure of TTF[Au(ttdt)2]: (a) molecular structure of [Au(ttdt)2]x- in TTF[Au(ttdt)2]; (b) molecular structure of TTFx+ in TTF[Au(ttdt)2]; (c) crystal packing of TTF[Au(ttdt)2] (Me4N)[Cu(ttdt)2].mp: 152.0–153.0 °C. Anal. Calc. for 0.710 69 A ° ) and 12 kW rotating anode generator. Azimuthal scans of several reflections indicated no need for an absorption C12H20NS10Cu: C, 25.62; H, 3.58; N, 2.49; S, 56.99.Found: C, 24.65; H, 3.45; N, 2.34; S, 55.23%. correction. The data were corrected for Lorenz and polarization eVects. The structure was solved by heavy atom Patterson methods (PATTY) and expanded using Fourier techniques. (Me4N)[Au(ttdt)2]. mp: 145.0–146.0 °C. Anal. Calc. for C12H20NS10Au: C, 20.71; H, 2.90; N, 2.01; S, 46.08.Found: C, The refinement was carried out against F. The non-hydrogen atoms were refined anisotopically. The final cycle of full-matrix 21.40; H, 2.96; N, 1.90; S, 47.85%. least squares refinement was based on 3141 observed reflections [I>3.00s(I)] and 325 variable parameters with R(Rw)=0.052 X-Ray crystallography (0.037). All calculations were performed using teXsan crys- Crystal data for 1b.C24H36NS10Cu, M=722.70, primitive tallographic software package of Molecular Structure monoclinic cell, space group P21/n (no. 14), a=12.108(2), b= Corporation.11 17.141(1), c=16.813(2) A ° , b=102.16(1)°, V=3411.1(8) A ° 3, Z=4, Dc=1.407 g cm-3, m=12.68 cm-1. The intensity data (2h<55°) were collected on a Rigaku AFC5R diVractometer Crystal data for 1c.C24H44NS10Au, M=864.18, primitive monoclinic cell, space group P21/n (no. 14), a=12.155(4), with graphite monochromated Mo-Ka radiation (l= J. Mater. Chem., 1998, 8(2), 319–324 323b=17.230(4), c=16.974(3) A° , b=102.51(2)°, V=3470(1) A° 3, We thank the Ramsay Memorials Fellowships Trust and the Ministry of Education, Science and Culture in Japan for the Z=4, Dc=1.654 g cm-3, m=48.72 cm-1.The intensity data (2h<55°) were collected on a Rigaku AFC7R diVractometer support towards M. T. We also thank the British Council (to A. E. U.) and the EPSRC (to N. R.) for support. with graphite monochromated Mo-Ka radiation (l=0.710 69 A ° ). An empirical absorption correction based on azimuthal scans of several reflections was applied which resulted in References transmission factors ranging from 0.6145 to 1.0000. The data were corrected for Lorentz and polarization eVects.The struc- 1 P. Cassoux and L. Valade, Inorganic Materials, ed. D. W. Bruce ture was solved by heavy-atom Patterson methods (SAPI91) and D. O’Hare, John Wiley and Sons Inc., Chichester, 1992, ch. 1, pp. 1–58. and expanded using Fourier techniques. The refinement was 2 For example; (a) T.K. Hansen, T. Jørgensen, P. C. Stein and carried out against F. The non-hydrogen atoms were refined J. Becher, J. Org. Chem., 1992, 57, 6403; (b) T. K. Hansen, anisotopically. The final cycle of full-matrix least squares T. Jørgensen, F. Jensen, P. H. Thygesen, K. Christiansen, refinement was based on 3813 observed reflections M. B. Hursthouse, M. E.Harman, M. A. Malik, B. Girmay, [I>3.00s(I)] and 325 variable parameters with R(Rw)=0.046 A. E. Underhill, M. Begtrup, J. D. Kilburn, K. Belmore, (0.036). All calculations were performed using teXsan crys- P. RoepstorV and J. Becher, J. Org. Chem., 1993, 58, 1359. 3 (a) H. Mu� ller and Y. Ueba, Bull. Chem. Soc. Jpn., 1993, 66, 1773; tallographic software package of Molecular Structure (b) T.Mori, H. Inochi, A. M. Kini and J. M. Williams, Chem. Corporation.11 L ett., 1990, 1279; (c) H. Nakano, K. Yamada, T. Nogami, Y. Shirota, A. Miyamoto and H. Kobayashi, Chem. L ett., 1990, 2129; (d) H. Mu� ller and Y. Ueba, Synth. Met., 1995, 70, 1181; Crystal data for TTF[Au(ttdt)2]. C14H12S14Au, M=826.06, (e) H. Nakano, S. Ikegawa, K. Miyawaki, K. Yamada, T. Nogami primitive triclinic cell, space group P19 (no. 2), a=12.349(3), and Y. Shirota, Synth.Met., 1991, 41–43, 2409. b=13.438(3), c=7.387(2) A ° , a=124.54(2), b=120.88(2), c= 4 R. Kato, H. Kobayashi, A. Kobayashi and Y. Sasaki, Bull. Chem. 101.24(1)°, V=629(1) A ° 3, Z=1, Dc=2.179 g cm-3, m= Soc. Jpn., 1986, 59, 627. 70.27 cm-1. The intensity data (2h<55°) were collected on a 5 (a) C.Faulmann, A. Errami, B. Donnadieu, I. Malfant, J.-P. Legros, P. Cassoux, C. Rovira and E. Canadell, Inorg. Chem., 1996, 35, Rigaku AFC7R diVractometer with graphite monochromated 3856; (b) P. Cassoux, L. Brossard, M. Tokumoto, H. Kobayashi, Mo-Ka radiation (l=0.710 69 A ° ) and 18 kW rotating anode A. Moradpour, D. Zhu, M. Mizuno and E. Yagubskii, Synth. Met., generator. The linear absorption coeYcient, m, for Mo-Ka is 1995, 71, 1845. 70.3 cm-1. An empirical absorption correction based on azi- 6 (a) J. D. Forrester, A. Zalkin and D. H. Templeton, Inorg. Chem., muthal scans of several reflections was applied which resulted 1964, 3, 1507; (b) C. T. Vance, J. H. Welch and R. D. Bereman, in transmission factors ranging from 0.8003 to 0.9995. The Inorg. Chim. Acta, 1989, 164, 191; (c) G. Matsubayashi, K.Takahashi and T. Tanaka, J. Chem. Soc., Dalton T rans., 1988, data were corrected for Lorentz and polarization eVects. The 967. structure was solved by direct methods (SHELX86) and 7 P. Cassoux, L. Valade, H. Kobayashi, A. Kobayashi, R. A. Clark expanded using Fourier techniques. The refinement was carried and A. E. Underhill, Coord. Chem. Rev., 1991, 110, 115. out against F. The non-hydrogen atoms were refined anisotop- 8 L. Valade, J. P. Legros, C. Tejel, B. Pomarede, B. Garreau, ically. The final cycle of full-matrix least squares refinement M. F. Bruniquel, P. Cassoux, J. P. Ulmet, A. Audouard and was based on 2723 observed reflections [I>3.00s(I)] and L. Brossard, Synth. Met., 1991, 41–43, 2268. 9 C. E. A. Wainwright and A. E. Underhill, Mol. Cryst. L iq. Cryst., 128 variable parameters with R(Rw)=0.063 (0.077). All calcula- 1993, 234, 193. tions were performed using teXsan crystallographic software 10 (a) A. E. Underhill, N. Robertson and D. L. Parkin, Synth. Met., package of Molecular Structure Corporation.11 1995, 71, 1955; (b) C. F. Cleary, N. Robertson, M. Takahashi, Full crystallographic details, excluding structure factors, A. E. Underhill, D. E. Hibbs, M. B. Hursthouse and have been deposited at the Cambridge Crystallographic Data K. M. A. Malik, Polyhedron, 1997, 16, 1111. Centre (CCDC). See Information for Authors, J. Mater. Chem., 11 teXsan, Crystal Structure Analysis Package, Molecular Structure Corporation, The Woodlands, TN, 1985 & 1992. 1998, Issue 1. Any request to the CCDC for this material should quote the full literature citation and the reference number 1145/73. Paper 7/05966C; Received 14th August, 1997 324 J. Mater. Chem., 1998, 8(2), 319–3

ISSN:0959-9428    

DOI:10.1039/a705966c

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Synthesis of fullerene- and fullerol-containing polymers Liming Dai,*a Albert W. H. Maua and Xiaoqing Zhangb aCSIRO, Division of Chemicals and Polymers,† Private Bag 10, RosebankMDC, Clayton, VIC 3169, Australia bDepartment of Chemical Engineering, T he University of Melbourne, Parkville, VIC 3052, Australia Fullerenes have been covalently attached along polydiene chains via a lithiation reaction.Ultraviolet–visible (UV–VIS), Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) measurements, together with thermal gravimetric analyses (TGA), indicate that both highly soluble and crosslinked polymeric fullerene derivatives can be prepared under appropriate reaction conditions. Furthermore, an aqueous methanol solution of hydrochloric acid is shown to be an eYcient reagent for the conversion of the polymer-bound fullerenes to fullerols.Introduction Experimental Materials Fullerenes have attracted a great deal of interest since the discovery that [60]fullerene, C60, has a soccer-ball like While cis-1,4-polybutadiene (98% cis, Mw=2 500 000) was structure—a truncated icosahedron.1 Fullerenes and their purchased from Aldrich, the cis-1,4-polyisoprene was anionderivatives have been shown to possess unusual photonic, ically synthesised in cyclohexane at room temp.(20 °C) using electronic, superconducting and magnetic properties.2 The n-butyllithium as the initiator. The synthesis and characterizlarge- scale synthesis of fullerenes3 has made C60 readily ation of the cis-1,4-polyisoprene have been previously reported available and chemical modification of fullerenes has since in detail elsewhere.20–23 The fullerene sample was purchased attracted considerable attention.4–14 In particular, the combifrom Aldrich, as were the analytical grade tetramethylethylenenation of the unique molecular characteristics of fullerenes diamine (TMEDA), BusLi (supplied in cyclohexane), cyclohexwith good processability of certain polymers through chemical ane and methanol.Hydrochloric acid in water (36 mass%) modification has proved promising for making advanced was used as supplied by Ajax Chemicals. polymeric materials with novel physicochemical properties. In this regard, fullerenes have been chemically bonded onto some tractable polymer chains either as pendant groups or as Synthesis constituent units of the polymer backbones.For instance, the In a typical experiment, we carried out the grafting reaction chemical or photo-polymerization of C60 has been demonshown in Scheme 1 (reactions 1–3) by dissolving 100 mg of strated to produce polymer backbones containing C60 enticis- 1,4-polyisoprene or cis-1,4-polybutadiene in 10 ml of dry ties,15 while the amine addition of amino-polymers into cyclohexane (or benzene) under an argon atmosphere at room fullerene double bonds16 and the cycloaddition reaction of temp.Then, a predetermined amount of BusLi was added with functionalized polymers with C6017,18 have been shown to stirring,24 and to the stirred solution TMEDA was subgenerate fullerene-grafted polymer chains.sequently injected at a 151 molar ratio with respect to BusLi We have recently demonstrated that C60 can also be (TMEDA was used to enhance the eYciency of the metallation covalently attached onto 1,4-polydiene chains, such as 1,4- of diene polymers19). The colour of the reaction mixture polybutadiene and 1,4-polyisoprene, through lithiation of the changed from pale-yellow to dark-red in a few minutes, as the polymer chains with sec-butyllithium (BusLi), followed by reaction progressed. The reaction mixture was further stirred chemically bonding fullerenes onto the lithiated polymer at room temp.for about 2 h before a selected amount of C60 chains and quenching with MeOH. Preliminary results, (pre-dissolved in toluene or benzene) was added at a fixed previously reported in a short communication,19 have shown molar ratio of BusLi to C60, depending on whether a soluble that the resulting C60-functionalized polydiene materials with or a crosslinked form of the final product was desired.24 multiple pendant fullerenes dispersed along their polymer Consequently, a colour change from dark-red to dark-brown backbones are highly soluble and thermally processable, was observed. Thereafter, the fullerene-functionalized polywhich could open up novel applications for fullerenes.In our meric adduct was quenched and precipitated by addition of further investigation on fullerene-containing polymers, we methanol. The soluble C60-grafted polymer was then redisfound that C60-crosslinked polydiene elastomers can also be solved into THF and this was followed by centrifugation to prepared via the lithiation reaction under certain reaction remove unreacted C60 (if any), as the solubility of free fullerenes conditions.Furthermore, an aqueous methanol solution of in THF is negligibly low.25 The soluble C60-grafted polymer hydrochloric acid was shown, for the first time, to be an was finally separated into THF as a brass-coloured solution.eYcient reagent for the conversion of the polymer-bound In cases where C60-crosslinked polymer gels were produced, fullerenes to fullerols. In this paper, we present these new any unreacted C60 and uncrosslinked polymer chains were findings, together with the details of syntheses and spectroremoved by thoroughly washing with pure benzene.scopic characterization of the fullerene- and fullerol-contain- Fullerol-containing polydienes were prepared in two diVeing polymers. rent ways. Method 1: during the synthesis of the C60-containing polydienes, the lithiated C60-containing intermediate (i.e. Product III of Scheme 1) was terminated by an undegassed aqueous HCl (36 mass%)–methanol solution (151 v/v) instead † Currently renamed as: CSIRO Molecular Science.J. Mater. Chem., 1998, 8(2), 325–330 325Fig. 1 UV–VIS absorption spectra of (a) C60 in cyclohexane; (b) the purified MeOH-terminated C60-grafted polybutadiene diluted in THF Scheme 1 Lithiation of polydienes followed by reaction with fullerene and its subsequent conversion to fullerols (The exact position and number of the hydroxy group(s) in Product VI are yet to be determined).Reagents and conditions: (1) Bu s Li, TMEDA; (2) C60; (3) MeOH; (4) HCl, H2O, MeOH (O2); (5) HCl, H2O, MeOH (O2). of methanol alone (reaction 4 of Scheme 1). Method 2: the purified C60-grafted polymers (i.e. Product IV of Scheme 1) were treated with the undegassed aqueous HCl–MeOH solution at room temp. (reaction 5 of Scheme 1).Characterization Fig. 2 GPC chromatograms of (a) the pristine cis-1,4-polyisoprene in The ultraviolet–visible (UV–VIS) spectroscopic measurements THF recorded by the refractive index detector; (b) C60-grafted polywere carried out using a Hewlett-Packard HP-8451A spec- isoprene in THF recorded by the refractive index detector trometer. FTIR spectra were measured on polymer samples cast on a KRS-5 crystal, using a Mattson Alpha Centauri a continuous red-shift in the UV–VIS spectrum. The UV–VIS FTIR spectrometer with a resolution of 4 cm-1.Solution spectra of pure C60 and the resulting brass-coloured solution NMR measurements were performed on a Bruker AC-200 of C60-grafted polydienes diluted in THF are shown in Fig. 1(a) NMR spectrometer using deuterated chloroform (99.8% D) as and (b), respectively.Comparison of curve (b) with curve (a) solvent. High-resolution solid state 13C NMR spectra of dried shows the appearance of several new absorption bands. This samples were collected on a Varian Unity Inova-300 specis accompanied by the disappearance of the characteristic trometer at resonance frequency 75.4 MHz under conditions peaks of fullerene at 213 and 329 nm,26 suggesting the formaof magic angle sample spinning (MAS) and high-power dipolar tion of polymeric fullerene derivatives.A similar decrease in decoupling (DD) by using either a single 90° pulse sequence the absorption at 329 nm observed for calixfullerene was with a repetition time of 2 s or the cross-polarization (CP) attributed to the isolation of C60 by the intramolecularly linked pulse sequence at a contact time of 2 ms and a repetition time calix[8]arene,27 while the appearance of peaks at 213, 248, of 3 s.The 90° pulse-width was of 3.7 ms while the rate of MAS 257, 308 and 326 nm had been taken as evidence for monowas 9–10 kHz. The chemical shift of 13C spectra was deteraddition of fullerenes in other cases.6,16,28 The expected absorpmined by taking the carbonyl carbon of solid glycine tion characteristic of the fullerene mono-adduct in the region (176.03 ppm relative to SiMe4) as an external reference stan- 415–435 nm16,29 was very weak, with respect to those peaks dard.Gel permeation chromatographic (GPC) measurements in the UV region, and became apparent only after scaling up were made on a Waters Associates GPC unit using tetrahydrothe axis of absorbance as was the case for C60-capped vinyl furan (THF) as solvent and a polystyrene standard.All the ether oligomers.29 The other newly appeared weak absorption spectroscopic measurements were made at room temp. unless bands seen in Fig. 1(b), however, may indicate the occurrence otherwise stated. Thermal analyses were made using a thermal of slightly higher degrees of addition onto traces of C60.gravimetric analyser (TGA, Mettler TG50). The grafting reaction shown in Scheme 1 (reactions 1–3) was also followed by GPC measurements. The GPC chromato- Results and Discussion grams for the pristine polyisoprene [curve (a)] and a purified C60-grafted polyisoprene [curve (b)] recorded with a refractive Soluble fullerene-containing polymers index (RI) detector are shown in Fig. 2. As can be seen in Fig. 2(a), the anionically polymerized polyisoprene has a very Soluble fullerene-functionalized polydiene chains were prepared according to the reactions shown in Scheme 1 (reactions narrow molecular mass distribution (Mw/Mn=1.1) with a weight-average molar mass (polystyrene equivalent) Mw= 1–3) at low molar ratios of BusLi to C60 (i.e.[BusLi]/ [C60]<1).24 The lithiation reaction was reflected by a color 44 000 g mol-1. Fig. 2(b), however, shows the appearance of a shoulder at higher molecular mass while the peak correspond- change from colorless, through pale-yellow, to dark-red, and 326 J. Mater. Chem., 1998, 8(2), 325–330ing to that of Fig. 2(a) remained unshifted. As a result, new pristine polybutadiene chains are observed at 1445 cm-1 and 2700–3000 cm-1, respectively.31–33 For the C60-grafted polybu- values ofMw=95 000 g mol-1 andMw/Mn=1.8 were obtained for the modified polymer. A similar change in GPC chromato- tadiene after being terminated by pure MeOH [Fig. 3(b)], the absorption band characteristic of MCH2M deformation grams has previously been observed for the cycloaddition of C60 onto azido-substituted polystyrenes with mono-addition vibration at 1445 cm-1 changed shape considerably. This was accompanied by the appearance of several broad absorption being the dominant process.17 Thus, the reasonably small value of the polydispersity (i.e.Mw/Mn=1.8) for the C60-grafted peaks centered at 1470, 1140 and 500 cm-1 which are assigned to [60]fullerene, with the expected peaks26,34 at 1428, 1181, polyisoprene suggests that cross-linking, if any, was insignifi- cant at the low ratio of [BusLi]/[C60] although gel formation 578 and 528 cm-1 shifted somewhat as a result of chemical interactions with the polymer backbone. However, almost no was observed for the grafting reactions carried out at high degrees of lithiation and a low molar ratio of C60, as we shall detectable change was observed for the characteristic absorption bands of the CNC bonds at 715 and 1670 cm-1.These see later. The corresponding GPC result measured by a UV–VIS detector at l=326 nm, a wavelength at which only spectroscopic changes confirm the occurrence of the intended coupling reaction (Scheme 1) with C60 being attached onto the fullerene absorbs,21,22,26 confirms that the higher molecular mass species associated with the shoulder in Fig. 2(b) corre- saturated aliphatic carbons along the polydiene chains. spond to the fullerene-grafted polyisoprene chains, as only the species of higher molar masses were observed by the UV–VIS Fullerene-crosslinked polymer gels detector.As a control, GPC measurements were also made on A sol–gel transformation occurred when the grafting reaction the lithiated, fullerene-free polyisoprene, after it had been (reactions 1–3 of Scheme 1) was carried out at a high molar quenched by MeOH in the same manner as for the fullereneratio of BusLi to C60 (i.e. [BusLi]/[C60]>1). The mass% of grafted polyisoprene.No change in the molecular mass with C60 incorporation into the fullerene containing polymers was respect to the polyisoprene precursor was found. Therefore, measured by TGA analyses. Fig. 4 shows the mass loss for the diVerences between curves (a) and (b) in Fig. 2 can be both the pristine cis-1,4-polybutadiene [curve (a)] and the C60- attributed to the grafting reaction of C60 onto the polymer crosslinked polybutadiene elastomer [curve (b)].Comparing chains. curve (b) with curve (a) of Fig. 4 shows that polybutadiene The presence of the peak corresponding to the cis-1,4- backbones in the C60-containing polymer sample completely polyisoprene precursor in Fig. 2(b), however, indicates that a decomposed at 350–500 °C with no mass loss for C60 up to significant amount of the polyisoprene chains did not react 650 °C.As a result, about 51 mass% incorporation of C60 with C60 in this particular case, presumably due to a low was obtained. eYciency of lithiation and/or the aggregation of polyisoprenyl- The degree of swelling for the as-synthesized C60-crosslinked lithium chains30 which could physically trap some of the ‘living’ cis-1,4-polybutadiene in benzene was determined according to: lithium sites away from the grafting reaction.It is also worth (wet mass-dry mass)/dry mass,35 from which a value of about pointing out that GPC measures the hydrodynamic volume of 9000% was obtained for the sample with 51 mass% C60 a macromolecular chain rather than its absolute molar mass. incorporation. The resultant dry C60-crosslinked cis-1,4- From the GPC results, therefore, a calculation of the molar polybutadiene elastomers were studied by high-resolution percentage of C60 in the host polymeric chains cannot be made solid-state NMR spectroscopy, and the results are shown in without detailed information on changes in the polymer confor- Fig. 5. A single 90° pulse sequence with a repetition time of mation upon the grafting reaction.10 Nevertheless, the percent- 2 s, together with MAS–DD techniques, was used to measure age incorporation of C60 into the polydiene chains can be the 13C spectra for the pristine cis-1,4-polybutadiene and estimated from the thermal gravimetric analyses (see below).17 mobile regions of the C60-crosslinked polybutadiene, as the The purified C60-grafted polydiene chains (Product IV of resonances from C60 or rigid domains adjacent to C60- Scheme 1) were analysed by FTIR measurements.As shown crosslinking sites were unobservable due to long 13C relaxation in Fig. 3(a), the band at 715 cm-1 is characteristic of the NCH times.36 The 13C signals of C60 and those polybutadiene out of plane (bending) deformation of the pristine polybutadisegments near to the C60-crosslinking sites were, however, ene, while the band at 1670 cm-1 corresponds to the stretching detected by the cross-polarization (CP) method under vibration of the isolated CNC bonds.31–33 The deformation MAS–DD conditions.In this case, the 13C resonances from and stretching vibration of MCH2M/MCHM bonds in the mobile segments in the C60-crosslinked polymer sample became unobservable due to their weak capability of cross-polarization, as also was the case for the pristine (amorphous) cis-1,4- polybutadiene. For comparative purposes, Fig. 5(a) and (b) show the MAS–DD 13C NMR spectrum for the pristine cis- 1,4-polybutadiene and the C60-crosslinked polybutadiene, Fig. 3 FTIR spectra of (a) the pristine cis-1,4-polybutadiene; (b) C60- Fig. 4 TGA mass loss data of (a) cis-1,4-polybutadiene; (b) C60- crosslinked cis-1,4-polybutadiene. Scanning rate, 10 °C min-1. grafted cis-1,4-polybutadiene terminated by MeOH J. Mater. Chem., 1998, 8(2), 325–330 327Fig. 6 FTIR spectra of (a) the pristine cis-1,4-polybutadiene; (b) C60- grafted cis-1,4-polybutadiene terminated by an undegassed aqueous HCl (36 mass%)–MeOH solution (151 v/v) rigid regions.Several new resonances were also observed as compared to Fig. 5(b). The resonances at 43.7 and 39.6 ppm are attributed to the aliphatic carbons at and next to the C60- grafting sites, respectively, as shown in the structural unit of MCH(C60)MCH2M.31,32 The band with a chemical shift around 143.4 ppm was assigned to unreacted olefinic carbons on the polymer-bound C60 moieties.26,37,38 The appearance of weak resonances at about 71.9 and 168.4 ppm may suggest a partial conversion of the polymer-bound fullerenes to fullerols (see below) and further rearrangements to ketone–hemiketal moieties.37–40 Fullerol-containing polymers Previously reported syntheses of fullerols from fullerenes have involved the use of strong acids, such as sulfuric acid and nitric acid, at a relatively high temperature (typically, Fig. 5 Solid state 13C NMR spectra of (a) the unreacted cis-1,4- polybutadiene (MAS–DD); (b) C60-crosslinked cis-1,4-polybutadiene 85–115 °C).34,37–42 However, we found that an aqueous HCl– (MAS–DD); (c) C60-crosslinked cis-1,4-polybutadiene (CP–MAS–DD) methanol solution is an eYcient reagent for the conversion of the polymer-bound fullerenes to fullerols even at room temperature.Fig. 6 reproduces FTIR spectra for cis-1,4-polybuta- respectively. The similar overall appearance of the narrow resonances seen in Fig. 5(a) and (b) indicates that the major diene before and after the C60-grafting, followed by quenching with an undegassed aqueous HCl(36 mass%)–MeOH (151 v/v) contribution to the mobile regions in the C60-crosslinked sample is from those non-crosslinked or lightly crosslinked solution (Method 1).Comparing spectrum (b) with (a) of Fig. 6 shows a strong hydroxy absorption band around 3400 cm-1, polybutadiene segments. The ratio of aliphatic carbons to olefinic carbons was assessed by integration of the resonance together with several other new absorption bands characteristic of fullerols centred at 1595, 1392 and 1084 cm-1.37 peaks at 27.8 and 129.8 ppm.31 This ratio was found to reduce from 1.00 [Fig. 5(a)] to 0.95 [Fig. 5(b)] upon grafting with Further evidence for the C60 grafting reaction and/or the subsequent conversion from the polymer-bound fullerenes to C60, indicating, once again, that C60 was grafted onto the aliphatic carbons. Assuming that the loss of the aliphatic fullerols was obtained by NMR measurements.The solution 1H NMR spectra for the pristine cis-1,4-polybutadiene and a carbon resonance at 27.8 ppm resulted fully from the grafting reaction, it can be estimated that the percentage incorporation soluble C60-grafted cis-1,4-polybutadiene after having been terminated by an undegassed aqueous HCl–MeOH solution of C60 should be about 57 mass% for a mono-addition, 40 mass% for a bis-addition, and 30 mass% for a tris-addition are given in Fig. 7. By referring to Fig. 7(a), the peaks at 2.08 and 5.40 ppm seen in Fig. 7(b) correspond to the aliphatic and onto each of the C60 entities. The observed value of 51 mass% from the TGA measurement on the crosslinked sample, which olefinic protons in the cis-1,4-polybutadiene chains.31 The weak, broad peaks centred at about 2.70 and 5.60 ppm may was also used for the NMR measurement, indicates that the polymer-gel contains a significant amount of mono-func- be attributed to the expected aliphatic and olefinic proton resonances of MCH(C60)M and NCHMC(C60)M, respec- tionalized C60 dangling groups in addition to various multiattached fullerenes at the crosslinking sites.These mono- tively. The observed downfield shift for these 1H NMR peaks of the 1,4-polybutadiene upon grafting with C60 is consistent functionalized C60 pendant groups should allow the final product to retain the physicochemical properties characteristic with an electron-withdrawing influence from the grafted fullerenes. 5,6 The broad bands centred at ca. 3.95 ppm may arise of C60. The 13C CP–MAS–DD spectrum of the C60-crosslinked from those hydroxy protons on the polymer-bound fullerols. 37–40 The sharp peaks at about 7.25 and 3.40 ppm are polybutadiene (Fig. 5(c)) shows rather wide linewidths for almost all resonances, suggesting a broad chemical-shift iso- attributable to impurities associated with CHCl3 and MeOH, respectively.32 tropic distribution of the resonances associated with rather 328 J.Mater. Chem., 1998, 8(2), 325–330on the lithiated, fullerene-free polybutadiene, after it had been quenched by MeOH in the same manner as for the C60-grafted polybutadiene. No change in the FTIR spectrum with respect to that of the pristine polybutadiene was observed. Therefore, Fig. 8 clearly suggests a conversion from fullerenes to fullerols for the unsymmetrically perturbed, polymer-bound C60 under the mild conditions.Prolonged acid treatment, however, may cause subsequent rearrangements from the newly formed fullerols to ketone–hemiketal moieties.37–40 Conclusions In summary, we have demonstrated that fullerenefunctionalized polydienes with multiple pendant fullerenes dispersed along their polymer backbones can be prepared by firstly lithiating polydienes with BusLi, which was followed by covalently grafting C60 onto the lithiated polymer chains.Both highly soluble C60-grafted polymers and C60-crosslinked polydiene elastomers can be prepared by properly controlling the reaction conditions. Furthermore, an aqueous methanol solution of hydrochloric acid is shown to be an eYcient reagent for the conversion of the polymer-bound fullerenes to fullerols at room temperature.Given that the lithiation reaction is a very versatile method for preparation of organolithium materials,43 the grafting Fig. 7 1H NMR spectrum, measured in CDCl3, of (a) cis-1,4-polybutadiene; (b) soluble C60-grafted cis-1,4-polybutadiene terminated by an reaction described in this paper should have important impliundegassed aqueous HCl (36 mass%)–MeOH solution (151 v/v) cations for covalent grafting of fullerenes onto various polymer chains.44–46 While the soluble and/or crosslinked fullerenecontaining polymers thus prepared may open up novel appli- The above results prompted us to investigate the conversion cations for the fullerenes, the acid treatment is expected to be between the polymer-bound fullerenes to fullerols in a more of use for making a wide range of new polymer-modified controllable manner by using the C60-grafted polybutadiene fullerene derivatives from the fullerol-containing polymers via after having been terminated with MeOH (i.e.Product IV of reactions characteristic of hydroxy groups.Scheme 1) as the starting material for the treatment in an aqueous HCl–MeOH solution (Method 2). Fig. 8 shows FTIR spectra for the MeOH-terminated C60-grafted polybutadiene References before and after the acid treatment. As mentioned above, the 1 H. W. Kroto, J. R. Heath, S. C. O’Brien, R. F. Curl and broad absorption peaks centred at 1470, 1140 and 500 cm-1 R. F. Smalley, Nature, 1985, 318, 162.seen in Fig. 8(a) characterize the polymer-bound fullerene C60 2 See, for example: Acc. Chem. Res., 1992, 25 (special issue on fuller- in the starting material. Upon treating it with an undegassed enes); A. F. Hebard, Ann. Rev. Mater. Sci., 1993, 23, 159; aqueous HCl (36 mass%)–MeOH (151 v/v) solution at room R. M. Baum, CE News, 1993, Nov. 22, 8; A. Hirsch, Angew.Chem., temperature [Fig. 8(b)], the strong hydroxy absorption bands Int. Ed. Engl., 1993, 32, 1138; ed. H. W. Kroto, J. E. Fischer and characteristic of fullerols developed, notably at 3424 and D. E. Cox, T he Fullerenes, Pergamon, Oxford, 1993; ed. K. M. Kadish and R. S. RuoV, Recent Advances in the Chemistry and 1084 cm-1, while the bands centred at 1470, 1140 and 500 cm-1 Physics of Fullerenes and Related Materials, The Electrochemical corresponding to the polymer-bound C60 decreased signifi- Society Inc., Pennington, NJ, 1994; ed.W. Andreoni, T he Chemical cantly. As a control, the same acid treatment was carried out Physics of Fullerenes 10 (and 5) Years L ater, NATO ASI Ser. E, 316, Kluwer Academic, Dordrecht, 1996. 3 W. Kratschmer, L. D. Lamb, K.Fostiropolous and D. R. HuVman, Nature, 1990, 347, 354. 4 For recent reviews see: F. Wudl, Acc. Chem. Res., 1992, 25(3), 157; A. Hirsh, Adv.Mater., 1993, 5, 859; A. Hirsch, T he Chemistry of the Fullerenes, Thieme Verlag, Stuttgart, 1994; F. Diederich, L. Isaacs and D. Philp, Chem. Soc. Rev., 1994, 23, 243; ed. R. Taylor, The Chemistry of Fullerenes, World Scientific, Singapore, 1995; F.Diederich and C. Thilgen, Science, 1996, 271, 317; M. Prato, J.Mater. Chem., 1997, 7, 1097. 5 A. Hirsch, Q. Li and F. Wudl, Angew. Chem., Int. Ed. Engl., 1991, 30(10), 1309. 6 A. Hirsch, A. Soi and H. R. Karfunkel, Angew. Chem., Int. Ed. Engl., 1992, 31(6), 766. 7 P. J. Fagan, P. J. Krusic, D. H. Evans, S. A. Lerke and E. Johnston, J. Am. Chem. Soc., 1992, 114, 9697. 8 D. A. Loy and R. A. Assink, J. Am. Chem. Soc., 1992, 114, 3977. 9 R. Seshadri, A. Govindaraj, R. Nagarajan, T. Pradeep and C. N. R. Rao, T etrahedron L ett., 1992, 33(15), 2069. 10 E. T. Samulski, J. M. DeSimone, M. O. Hunt, (Jr.), Y. Z. Menceloglu, R. C. Jarnagin, G. A. York, K. B. Labat and H.Wang, Chem. Mater., 1992, 4, 1153. 11 P. J. Fagan, P. J. Krusic, C. N. McEwen, J. Lazar, D.H. Parker, N. Herron and E. Wasserman, Science, 1993, 262, 404; and refer- Fig. 8 FTIR spectra of (a) C60-grafted cis-1,4-polybutadiene terminated ences therein. 12 M. Prato, Q. Chan and F.Wudl, J. Am. Chem. Soc., 1993, 115, 1148. by MeOH; (b) the MeOH-terminated C60-grafted cis-1,4-polybutadiene after having been treated in an undegassed aqueous HCl (36 13 A. O. Patil, G. W. Schriver, B.Carstensen and R. D. Lundberg, Polym. Bull., 1993, 30, 187. mass%)–MeOH solution (151 v/v) for 35 min J. Mater. Chem., 1998, 8(2), 325–330 32914 W. K. Fullagar, I. R. Gentle, G. A. Haeth and J. W. White, J. Chem. 32 See, for example: T he Aldrich L ibrary of NMR Spectra, Vol. II(1), Soc., Chem. Commun., 1993, 525; C. J. Hawker, P. M. Saville and ed. C. J. Pouchert, Aldrich Chemical Company, Inc., Wisconsin, J.W. White, J. Org. Chem., 1994, 59, 3503. 1983; T ables of Spectral Data for Structure Determination of 15 See, for example: A. Hassanien, T. Mrzel, P. Venturini, F. Wudl, Organic Compounds, ed. W. Fresenius, J. F. K. Huber, E. Pungor, D. Mihailovic, J. Gasperic, B. Kralj, D. Zigon, S. Milicev and G. A. Rechnitz, W. Simon, and Th. S. West, Springer-Verlag, A.Demsar, in Electronic Properties of Fullerenes; Springer Ser. Berlin, 1989. Solid-State Sci., 1993, 117, 316; N. Zhang, S. R. Schricker, F.Wudl, 33 L. Dai, H. J. Griesser, X. Hong, A. Mau, T. H. Spurling, Y. Yang M. Prato, M. Maggini and G. Scorrano, Chem. Mater., 1995, 7(3), and J. W. White,Macromolecules, 1996, 29, 282. 441. 34 L. Y. Chiang, R. Upasani, J.W. Swirczewski and K. Creegan, 16 K. E. Geckeler and A. Hirsch, J. Am. Chem. Soc., 1993, 115, 3850; Mater. Res. Soc. Symp. Proc., 1992, 247, 285. C. Weis, C. Friedrich, R. Mu�lhaupt and H. Frey, Macromolecules, 35 S. Wibullucksanakul, K. Hashimoto and M. Okada, Macromol. 1995, 28, 403. Chem. Phys., 1996, 197, 1865. 17 C. J. Hawker, Macromolecules, 1994, 27, 4836. 36 H. Ajie, M. M.Alvarez, S. J. Anz, R. D. Beck, F. Diederich, 18 K. I. Guhr, M. D. Greaves and V. M. Rotello, J. Am. Chem. Soc., K. Fostiropoulos, D. R. HuVman, W. Kra�tschmer, Y. Rubin, 1994, 116, 5997. K. E. Schriver, D. Sensharma and R. L. Whetten, J. Phys. Chem., 19 L. Dai, A. W. H. Mau, H. J. Griesser, T. H. Spurling and 1990, 94, 8630. J. W. White, J. Phys. Chem., 1995, 99, 17 302. 37 L. Y.Chiang, R. B. Upasani, J. W. Swirczewski and S. Soled, J. Am. 20 L. Dai and J. W. White, J. Polym. Sci., Part B, 1993, 31, 3. Chem. Soc., 1993, 115, 5453. 21 L. Dai and J. W. White, Polymer, 1991, 32, 2120. 38 L. Y. Chiang, R. B. Upasani and J. W. Swirczewski, J. Am. Chem. 22 L. Dai, J. Phys. Chem., 1992, 96, 6469. Soc., 1992, 114, 10 154. 23 L. Dai,Macromol. Chem. Phys., 1997, 198, 1723. 39 L. Y. Chiang and L.-Y. Wang, TRIP, 1996, 4, 298. 24 The molar ratio of BusLi to C60 determines the number of attach- 40 L. Y. Chiang, L.-Y. Wang, J. W. Swirczewski, S. Soled and ment points onto a single C60 entity. With [BusLi]/[C60]>1, mul- S. Cameron, J. Org. Chem., 1994, 59, 3960. tiple addition could occur leading to the formation of C60- 41 L. Y. Chiang, L.-Y. Wang and C. S. Kuo, Macromolecules, 1995, crosslinked polydiene gels. 28, 7574. 25 A. O. Patil, G. W. Schriver and R. D. Lundberg, ACS Polym. Prep., 42 L. Y. Chiang, J. W. Swirczewski, C. S. Hsu, S. K. Chowdhury, 1993, 34(2), 592. S. Cameron and K. Creegan, J. Chem. Soc., Chem. Commun., 1992, 26 H. W. Kroto, A. W. Allaf and S. P. Balm, Chem. Rev., 1991, 91, 1791. 1213. 43 B. Mudryk and T. Cohen, J. Am. Chem. Soc., 1993, 115, 3855. 27 M. Takeshita, T. Suzuki and S. Shinkai, J. Chem. Soc., Chem. 44 A. J. Chalk, J. Polym. Sci., Part B, Polym. Phys., 1968, 6, 649; Commun., 1994, 2587. A. J. Plate, M. A. Jampolskaya, S. L. Davydova and V. A. Kargin, 28 T. Suzuki, Q. Li, K. C. Khemani, F. Wudl and O. Almarsson, J. Polym. Sci., Part C, 1969, 22, 547; H. Tomita and R. A. Register, Science, 1991, 254, 1186. Macromolecules, 1993, 26, 2791, and references therein. 29 H. Okamura, M. Minoda, K. Komatsu and T. Miyamoto, 45 M. D. Guiver and G. P. Robertson,Macromolecules, 1995, 28, 294. Macromol. Chem. Phys., 1997, 198, 777. 46 D. E. Bergbreiter, H. N. Gray and B. Srinivas, Macromolecules, 30 J. N. Hay, D. S. Harris and M. Wiles, Polymer, 1976, 17, 613; 1993, 26, 3245. C. A. Ogle, F. H. Strickler and B. Gordon III, Macromolecules, 1993, 26, 5803, and references cited therein. 31 L. Dai, A. W. H. Mau, H. J. Griesser and D. A. Winkler, Macromolecules, 1994, 27, 6728. Paper 7/03764C; received 30thMay, 1997 330 J. Mater. Chem., 1998, 8(2), 325&ndash

ISSN:0959-9428    

DOI:10.1039/a703764c

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials The synthesis and mesomorphism of di-, tetra- and hexa-catenar liquid crystals based on 2,2¾-bipyridine Kathryn E. Rowe and Duncan W. Bruce* Department of Chemistry, University of Exeter, Stocker Road, Exeter, UK EX4 4QD 2,2¾-Bipyridines are known to coordinate to a wide variety of metal centres. In this paper, liquid-crystalline two-chained (dicatenar), four-chained (tetracatenar) and six-chained (hexacatenar) bipyridines are synthesised and their mesomorphism is described.For the tetracatenar bipyridines, a full homologous series, from tetramethoxy to tetratetradecyloxy, was synthesised, and the phase diagram showed a classic progression from nematic and smectic C phases at short chain length, through a cubic phase to a columnar phase. 2,2¾-Bipyridines are some of the most versatile ligands used in synthesise several more examples and in particular, we examined tetracatenar (four-chain) and hexacatenar (six-chain) the construction of metal coordination complexes,1 having been used to make dendrimers,2 helical structures,3 photoactive derivatives. The syntheses and liquid crystal properties of these new bipyridines are now described.systems,4 and a wide range of other supramolecular structures.5 Their attractiveness comes form their synthetic versatility and from their ability to coordinate to a very wide variety of Synthesis of the bipyridines metal centres. In recent publications, we have reported that by suitable Four diVerent types of bipyridine were synthesised, shown in choice of anisotropic ligand, it is possible to form rod-like Scheme 1, and their synthesis is now described.Reaction of liquid crystals based on metals with octahedral stereochemis- methyl 4-hydroxybenzoate, or ethyl 3,4-dihydroxy- or 3,4,5- try.6 The approach is based on the assumption that such a trihydroxybenzoate with bromoalkane under basic conditions high coordination number metal centre perturbs the anisotropy led to the related mono-, di- or tri-alkoxybenzoic acid, after of the ligand to which it binds and leads to complexes with alkaline hydrolysis and an acidic workup.For the mono- and low aspect ratios. Consequently, it is necessary to use rather di-alkylations, butanone was used as the solvent, while pentahighly anisotropic ligands to screen out the perturbing eVects none was preferred for the trialkylation reaction.These acids of the metal complex. We have demonstrated that this is were then esterified with hydroquinone which was monopropossible with imines orthometallated to MnI 7 and ReI,8 and tected with either tetrahydropyran (THP) or with a benzyl with diazabutadienes coordinated to ReI.9 It is, however, of group.Benzyl protection was initially used and was subinterest to note that low aspect ratios appear not to be so sequently readily removed by hydrogenolysis. However, hydromuch of a disadvantage in the design of columnar mesogens, genolysis of the di- and tri-alkoxy esters was painfully slow, as evidenced by the synthesis by Swager10 of mesomorphic which led us to change to THP-protection, where the deproteccomplexes based on octahedral metal centres bound to poly- tion using oxalic acid in methanol at reflux gave essentially substituted b-diketones.quantitative yields. However, we subsequently found that Subsequently, we used the same approach in an eVort to addition of a small amount of triethylamine during the hydroincorporate bipyridines as ligands in metal-based liquid crys- genolysis of the benzyl-protected system led to complete deprotals. 11 Thus, we reported the synthesis and mesomorphism of tection within minutes for any of the systems we studied, diesters of 2,2¾-bipyridine-5,5¾-dicarboxylic acid,12 simul- indicating a clearly preferential route, especially as mono THPtaneously with reports of mesomorphic bipyridines based on protected hydroquinone is obtained in four steps from hydrounsymmetrically substituted 5,5¾-disubstituted bipyridines.13 quinone. After deprotection, the resulting phenol was then However, when complexed to a whole range of metal centres, esterified with 2,2¾-bipyridine-5,5¾-dicarbonyl dichloride.This the liquid crystallinity of the bipyridines was lost.14 Curious was the lowest-yielding step of the whole procedure and despite to understand the absence of mesomorphism in these systems, our best eVorts which included evaluation of other possible we reasoned that by comparison with our own work and with esterification methods, we could not obtain more than about that of Deschenaux with 1,3-disubstituted ferrocenes,15 it 30% yield for this reaction.However, we would recommend seemed necessary to have, in addition to the core of the making the diacid chloride just before it is required as under molecules, an additional four phenyl rings in order to realise these circumstances, yields were consistently higher.mesomorphic metal complexes. Thus, when complexed, the For the sake of later clarity, the bipyridines (Scheme 1) will 2,2¾-bipyridine unit represented part of the core and, according be abbreviated as follows.The two-chain (or dicatenar) bipyrito our idea, four extra rings were required. It was therefore dines, will be labelled Dn, where n denotes the number of necessary to synthesise a six-ring bipyridine to fulfil this design carbon atoms in the alkoxy chains. Similarly, the four-chain criterion, and subsequent complexation to ReI eventually led (tetracatenar) and six-chain (hexacatenar) bipyridines will be to a liquid crystalline complex.16 abbreviated as Tn and Hn, respectively.Having shown that two-chained, six-ring derivatives of 2,2¾- The two-chained bipyridines were found to be highly insolbipyridine could lead to mesomorphic complexes of ReI, we uble making purification diYcult, and while an analytically were keen to pursue the synthesis of further examples as pure sample was obtained for the octyloxy derivative, D8, the bipyridines have enormous potential for coordination to a other derivatives gave carbon values which were low by very wide range of metal centres.Therefore, we proceeded to approximately 1%, despite numerous recrystallisations; compound R8 behaved in a similar fashion.Further purification involved attempts to convert the dicatenar ligands to the * E-mail: d.bruce@exeter.ac.uk J. Mater. Chem., 1998, 8(2), 331–341 331(OH) OH (OH) RO2C (OCnH2 n+1) OCnH2 n+1 (OCnH2 n+1) HO2C (OCnH2 n+1) OCnH2 n+1 (OCnH2 n+1) O O HO N N O O O O (OCnH2 n+1) OCnH2 n+1 (OCnH2 n+1) O O O (C nH2 n+1O) CnH2 n+1O O (C nH2 n+1O) (OCnH2 n+1) OCnH2 n+1 (OCnH2 n+1) O O BzO (i) (v) (ii) Monoalkoxy Dialkoxy Trialkoxy Monoalkoxy Dialkoxy Trialkoxy 456 Monoalkoxy Dialkoxy Trialkoxy 9 10 11 D n T n H n Monohydroxy R = CH3 Di- or tri-hydroxy R = C2H5 (iii) (iv) Dicatenar Tetracatenar Hexacatenar 123 Scheme 1 Synthesis of the polycatenar bipyridines.Reagents and conditions: (i) CnH2n+1Br, KHCO3; (ii) KOH/EtOH; (iii) BzOH, DCC, DMAP; (iv) H2, Pd/C; (v) 2,2¾-bipyridine-5,5¾-dicarbonyl dichloride, toluene, Et3N. corresponding hydrochloride salt, in order to achieve higher lower phase (M1) being unidentified.However due to decomposolubility thus aiding purification. Unfortunately this was also sition occurring at these elevated temperatures it was not accompanied by decomposition, and so was unsuitable.possible to obtain a clear texture of the lower mesophase on Compound T1 was also very insoluble and we could not cooling making identification impossible. Furthermore, this obtain good analytical data. However, we are not unduly meant that only data from the first DSC cycle could be used. disturbed by this as neither of the first two homologues was The butoxy bipyridine, D4, showed only a nematic phase, mesomorphic.while the longer chain length derivatives, D8, D12 and D14, showed a smectic C phase before giving way to the nematic Synthesis of bipyridine, R8 phase at higher temperatures. The temperature of the SC–N transition was found to vary with heating rate, which is One example of a bipyridine with one of the ester groups attributed to decomposition occurring in the upper reaches of reversed was synthesised to examine the eVect on mesomorphthe SC phase and rapidly accelerating in the nematic phase.ism. The route is shown in Scheme 2. Thus, benzyl 4-hydroxy- Despite this, the SC phase range was found to increase with benzoate was first protected with 3,4-dihydro-2H-pyran under increasing chain length, as is expected with calamitic materials.acid-catalysed conditions at room temperature in ethyl acetate, On both the heating and cooling cycles of the DSC, D12 before the benzyl group was cleaved, in quantitative yield, with showed another mesophase (M2) between the crystal and SC hydrogen over a palladium-on-charcoal catalyst. This carphase. By microscopy, with careful cooling, this transition was boxylic acid 11 was reacted with 4-octyloxyphenol, using a observed, but persisted for only a degree or so before crystallis- standard DCC–DMAP esterification, and the THP group was ation occurred.Due to decomposition occurring in the nematic subsequently cleaved under acidic conditions, at reflux in phase, it was not possible to obtain a good optical texture for methanol.The resulting phenol 13 was reacted with 2,2¾- the SC phase, and therefore for the M2 phase, too. However, bipyridine-5,5-dicarbonyl dichloride at reflux in toluene conthe relative magnitude of both the entropy and enthalpy taining a few drops of triethylamine, to give the reversed ester, changes (obtained on cooling) leads to a tentative assignment R8. In common with the dicatenar bipyridines above, this as a crystal smectic phase.compound was found to be highly insoluble, again making As this additional phase first appeared in the dodecyloxy purification diYcult. derivative it was hoped that its phase range would increase with increasing alkoxy chain length. Hence, the tetradecyloxy Mesomorphism of the dicatenar bipyridines, Dn derivative, D14, was subsequently synthesised as a direct attempt to elucidate the nature of this mesophase.Five dicatenar 2,2¾-bipyridine ligands were synthesised with Unfortunately, the range of the phase was found to be equally n=1, 4, 8, 12 and 14; the thermal data for these compounds short and once more, a good optical texture could not be are collected in Table 1. The methoxy derivative was found to exhibit two mesophases, the upper one being nematic, but the obtained, leaving the mesophase unidentified. 332 J. Mater. Chem., 1998, 8(2), 331–341HO O OBz O O OBz O O O OH O O O OC8 H17 O O O O OC8 H17 HO N N O O O O O O O O OC8H17 C8H17O 10 11 12 13 R8 (i) (ii) (iii) (iv) (v) Scheme 2 The synthesis of the ‘reversed ester’ ligand. Reagents and conditions: (i) 3,4-dihydro-2H-pyran, HCl(g); (ii ) H2, Pd/C; (iii) 4- octyloxyphenol, DCC, DMAP; (iv) oxalic acid, MeOH; (v) 2,2¾-bipyridine-5,5¾-dicarbonyl dichloride, toluene, Et3N.Table 1 Thermal data for the dicatenar bipyridines conventional discoid molecules. Conventional disc shaped molecules stack on top of each other to form a column, these n Transitiona T °/C DH/kJ mol-1 DS/J K-1 mol-1 columns being packed in a two-dimensional array.However, in the polycatenar systems, between two and four molecules 1 Cr�M1 237 —b —b come together to form what is, in eVect, a disc-like repeat unit M1�N 264 —b —b representing a slice through the columns, which are then N�decomp. >264 — — themselves packed in a two-dimensional array. 4 Cr�N 269 45.8 84 Probably the most interesting of the polycatenar systems N�decomp. 350 — — are the tetracatenar compounds which can display lamellar, 8 Cr�SC 231 52.3 104 cubic and columnar mesophases. Generally, lamellar meso- SC�N 328c —b —b phases are observed at short chain lengths while columnar N�decomp. >328 — — mesophases are observed at longer chain lengths. At intermedi- 12 Cr�M2 210 2.1d 4d ate chain lengths, this competition can result in the formation M2�SC 212 35.5d 75d of a frustrated phase, namely the cubic phase. This polymor- SC�N 341c —b —b phism arises due to the fact that in the mesophase, segregation N�decomp.>341 — — of the aromatic and aliphatic parts of the molecule occurs, and 14 Cr�M2 209 0.5d 1d as such these molecules can be regarded as amphiphilic in M2�SC 211 49.0 102 nature.Indeed, their observed polymorphism is similar to that SC�N 355c 4.2 7 N�I 368c —b —b of lyotropic systems in the sense that two-dimensional oblique or rectangular columnar phases, or three-dimensional cubic aM1 and M2 are unidentified mesophases (see text). phases can be inserted in between lamellar and hexagonal bNot seen by DSC. columnar phases. Also, like lyotropic systems, this segregation cThese temperatures are sensitive to the thermal history of the sample of molecular parts results in curvature at the aromatic–ali- due to decomposition occuring in the SC phase. phatic interface.This helps to explain the correlation between dThe thermodynamic data for these transitions are taken from the cooling cycles on the DSC. mesophase type and the length of the aliphatic chain, for as the chain length is increased so the curvature is increased, resulting in the columnar mesophases being stabilised at the expense of the lamellar mesophases.Mesomorphism of the tetracatenar bipyridines, Tn Because of the potential for such rich mesomorphism in Polycatenar liquid crystals17,18 are those which contain, typi- these systems, we undertook the synthesis of a complete cally, three or more chains and a rather extended core.They homologous series from n=1–14. We believe that this is the are classified both by the number of terminal chains they first time that such an homologous series has been investigated possess (tri-, tetra-, penta- and hexa-catenar) and also by the for tetracatenar mesogens, and the results are presented as a way these are distributed on the terminal benzene rings.phase diagram in Fig. 1, while the thermal data are collected The hexa- and penta-catenar compounds are found to in Table 2. exhibit columnar phases, while the tricatenar compounds show This series of compounds exhibits a phase behaviour that lamellar and cubic mesophases. The columnar phases result is very typical for tetracatenar species, namely nematic from a strong curvature at the aromatic–aliphatic interface in and lamellar phases at short chain lengths, columnar at long a way similar to that observed in lyotropic liquid crystals.The chain lengths, with the changeover being accompanied by the structure of the columnar mesophase formed from polycatenar observation of a cubic phase at intermediate chain lengths.species has been shown by dilatometry studies and X-ray Until the pentyloxy derivative, T5, only nematic phases were observed at elevated temperatures, with decomposition measurements to be slightly diVerent from those formed by J. Mater. Chem., 1998, 8(2), 331–341 333occurring in the upper regions of these phases, beginning above 300 °C and accelerating rapidly above 350 °C.Thus, for the methoxy (T1) and ethoxy (T2) derivatives, no clearing point was observed. While the propoxy (T3) and butoxy (T4) derivatives did clear to the isotropic, this temperature was not found to be reproducible on subsequent runs as it was accompanied by extensive decomposition. Nevertheless, the clearing point decreased quite markedly as the chain length increased.In initial microscopy studies, it appeared that T2–T4 melted over a large temperature range. DSC data showed that there was a crystal–crystal transition immediately prior to melting into the nematic mesophase. Further microscopy allowed the melting temperature to be ascertained; however by DSC the first transition was almost complete before the compounds melted into the nematic phase; hence, the thermodynamic data associated with these melting points are only N I Colh Cub Sc Cr carbon chain length 0 2 4 6 8 10 12 14 350 300 250 200 150 T/°C approximate.Fig. 1 Phase diagram for the tetracatenar bipyridines (Cr=crystal; An additional phase, namely SC, was introduced at the N=Nematic, SC=smectic C; Cub=cubixy chain length and was readily characterised by its onal); D, Cr–N; 1, Cr–SC ; 2, Cr–Colh; $, SC–N; #, SC–Cub; *, optical texture.Thus, the aliphatic chain was now of suYcient Cub–N; +, Cub–Colh; %, N–I; &, Cub–I; x, Colh–I length to stabilise lamellar mesophases. The derivatives T6–T8 represent the change over from lamellar to hexagonal columnar Table 2 Thermal data for the tetracatenar bipyridines mesophases, and as is often typical in tetracatenar systems this is achieved via the cubic phase.Thus, the cubic phase (charac- n Transition T /°C DH/kJ mol-1 DS/J K-1 mol-1 terised by its optical anisotropy, by the slow formation of such 1 Cr�N 259 62.6 117 a texture via the characteristic appearance of square edges N�decomp. >300 — — growing across the preceding texture, its high viscosity and 2 Cr�Na 262 52.4 99 the accompanying appearance of misshapen air bubbles) first N�decomp.>300 —c —c appears in the hexyloxy derivative, between the SC and N phases, giving one of very few well-authenticated examples of 3 Cr�Na 263 55.7 104 N�Ib 345 —c — a cubic phase below a nematic.19 In the heptyloxy derivative, a monotropic columnar hexagonal phase was observed and 4 Cr�Na 242 55.6 109 by the octyloxy derivative we had a compound that exhibited N�Ib 325 —c —c enantiotropic lamellar, cubic and hexagonal columnar phases. 5 Cr�SC 221 61.8 126 We believe that this is also unique in tetracatenar systems. SC�N 229 3.2 6 From T9 onwards, only columnar mesomorphism was N�I 294 1.0 2 observed, with both the melting and clearing temperatures 6 Cr�SC 196 55.8 120 remaining remarkably constant, irrespective of chain length.SC�Cub 220 1.7 14 The optical textures of these hexagonal columnar phases was Cub�N 239 4.0 8 (Cub�SC) (203) —c —c highly characteristic, exhibiting beautiful focal conic monodo- (SC�Cub) (224) —c —c mains and areas of homeotropic orientation. These columnar (N�SC) (229) —c —c mesophases have been identified as disordered hexagonal N�I 272 0.5 1.0 columnar mesophases by X-ray diVraction studies which will 7 Cr�SC 184 59.2 130 be published in due course as part of a much larger structural SC�Cub 197 2.9 6 study of the phase diagram.20 Thus, spacings in the ratio 1, (Col�Cub) (228) (3.6) (7.0) Ó3, Ó4 were seen and, for example, T12 gave d001=43.8 A ° .(I�Col) (234.5) —c —c This phase diagram is absolutely ‘text-book’ for the behav- Cub�I 239 3.8 7 iour of tetracatenar mesogens and is, to our knowledge, the 8 Cr�SC 173 56.0 126 first time that a full homologous series of tetracatenar mesog- SC�Cub 188 2.4 5 ens, from methoxy upwards, has been synthesised. Thus, the Cub�Colhd 229 — — nematic and smectic C phases observed at short chain lengths Colhd�I 237 4.0 8 pass through an ‘intermediate’ cubic phase before giving way 9 Cr�Colhd 171 35.6 4 to a columnar phase. By contrast, in a related piece of work Colhd�I 238 3.9 8 where we complexed two dicatenar alkoxystilbazoles in a trans 10 Cr�Colhd 166 45.2 103 fashion across a PtCl2 centre, the mesomorphism changed Colhd�I 237 4.3 9 suddenly from smectic C to columnar on passing from the 11 Cr�Colhd 165 48.2 110 dodecyloxy derivative (SC only) to the tridecyloxy derivatice Colhd�I 236 5.31 11 (columnar only), without any sign of a cubic phase and without 12 Cr�Colhd 161 48.6 112 any of the homologues showing both lamellar and columnar Colhd�I 234 5.8 11 phases.21 The sensitivity of polycatenar mesogens to their core 13 Cr�Colhd 161 47.7 110 structure has been commented on previously.22 Colhd�I 229 6.6 12 Close examination of the phase diagram reveals some interesting possibilities.For example, there is a direct nematic–cubic 14 Cr�Colhd 161 48.9 113 Colhd�I 230 6.5 13 transition which ought to allow for the production of a cubic monodomain from an aligned nematic, leading to unequivocal aThe DSC data are only approximate due to an incomplete crystal– assignment of the symmetry of the cubic phase, as reported crystal transition immediately prior to melting.previously by us for mesomorphic complexes of silver(I ).23 bThese temperatures are sensitive to the thermal history of the sample Furthermore, we have in T8, a compound with the enanti- due to decomposition occurring in the upper regions of the otropic phase sequence Colh =Cub=SC, previously found nematic phase.cNot seen by DSC. only monotropically and not before in symmetric, tetracatenar 334 J. Mater. Chem., 1998, 8(2), 331–341systems.20We have recently carried out a detailed investigation Thus, while on cooling from the nematic phase the cubic phase is thermodynamically preferred, the nematic can supercool due of polycatenar complexes of silver(I )24 using X-ray scattering, freeze–fracture electron microscopy,25 and dilatometry, in to these slow kinetics, allowing the appearance of the SC phase.As this phase is thermodynamically unstable with respect to which we confirmed an epitaxial relationship between the columnar and cubic phase, and have proposed a model for the the cubic, then the latter eventually appears, once more giving way to the (now thermodynamically stable) SC phase on columnar-to-cubic transition.26 We now have the possibility of extending this approach to look at the epitaxy of the columnar- further cooling. A similar situation exists with T7, where the heating and to-cubic-to-smectic C transitions in the same material, which we hope will give further information on transitions to cubic cooling phase sequences are as shown below: phases. These studies are already underway and will be Col�Cub�I Heating reported in due course.The mesomorphism of the hexyloxy and heptyloxy deriva- I�Col�Cub�Col Cooling tives were found to be particularly interesting and are now Very similar arguments can be invoked here, with a thermodiscussed in some detail.Thus, on heating, T6 showed the dynamically unstable columnar phase appearing on cooling following phase sequence: the isotropic due to the slow kinetics of cubic phase formation. Cr�SC�Cub�N�I Mesomorphism of the hexacatenar 2,2¾-bipyridines However, on cooling the nematic phase gives way to a SC phase rather than a cubic phase. A cubic phase then grows As the mesomorphism displayed with the hexacatenar 2,2¾- into the SC phase and persists until the SC phase reappears bipyridine systems was found to be predominantly columnar, once more.Thus, the phase sequence on cooling is: only four ligands were synthesised with n=1, 4, 8 and 12. Thermal data are collected in Table 3. I�N�SC�Cub�SC�Cr The mesomorphism observed in these compounds is typical We were initially perplexed by this behaviour, but following of hexacatenar systems, namely columnar mesophases, with discussions with Dr Antoine Skoulios of the IPCMS in the exception of the methoxy derivative which exhibits a rather Strasbourg, we feel we can oVer an explanation.The behaviour diVerent phase sequence. Thus, the butoxy derivative was is best explained by considering a schematic free energy found to show a columnar phase.The cooling cycle of the diagram for the system as shown in Fig. 2. DSC only gave the isotropic–columnar transition, but the Thus, on increasing the temperature and minimising G, crystal–columnar transition was reproducibly obtained on transitions would be expected (and are observed) from subsequent heating cycles, following a cold crystallisation SC�Cub�N�I.On cooling, the reverse would clearly be exotherm. The octyloxy and dodecyloxy derivatives exhibited expected, but the behaviour is modified due to the very slow similar mesomorphism. In both derivatives, the first heating kinetics generally found for the formation of cubic phases. cycle on the DSC gave two transitions prior to clearing into the isotropic.On cooling, neither sample crystallised, and consequently on subsequent heating cycles, the melting transition was no longer obsero crystallise, with the texture that first appeared from the isotropic remaining until solidification.As a result, the mesophase–mesophase transition (reproducible obtained by DSC), was not initially observed by microscopy. On careful reexamination of the dodecyloxy derivative by microscopy, it was possible on the first heat to see a subtle textural change in the highly birefringent sample, from a smooth to a finely grained, less focused surface. However, the textures observed by the first heat were not suYcient for characterisation.The natural texture of the upper phase observed on cooling was characteristic of a columnar phase, and the small change in enthalpy required in the mesophase–mesophase transition combined with the lack of any observed textural change on cooling, suggests that the lower phase is also columnar. X-Ray Table 3 Thermal data for the hexacatenar bipyridines n Transition T /°C DH/kJ mol-1 DS/J K-1 mol-1 1 Cr�Cub 203 —a —a Cub�SA 211 —a —a SA�N 217 —a —a N�I 292 —a —a 4 Cr�Col 143 26.7 64 Col�I 176 3.5 8 8 Cr�Colb 85 45.2 126 Col�Col¾ 157 0.2 1 Col�I 165 6.4 15 12 Cr�Colb 54 38.6 114 Col�Col¾ 142 0.3 1 Col¾�I 151 5.7 14 Fig. 2 Schematic representation to show the thermodynamic relationship between the mesophases in compounds T6 (a) and T7 (b) aNot seen by DSC.bThis transition is only observed on the first heat. J. Mater. Chem., 1998, 8(2), 331–341 335studies are now in progress in order to ascertain the exact opposing each other, therefore they are now serving to stabilise lamellar interactions. nature of these mesophases (and the other analogues in this series). The methoxy derivative was remarkable in showing the phase sequence: Conclusions Cr�Cub�SA�N�I A number of di-, tetra- and hexa-catenar six-ring 2,2¾-bipyri- While transitions from both SA to cubic and nematic to cubic dines have been synthesised.These were found to be novel are known, we are not aware of the I�N�SA�Cub phase liquid-crystalline materials that exhibited a rich polymorphism. sequence having been observed before.All of the phases were Thus, the dicatenar compounds were found to exhibit readily assigned on the basis of optical microscopy, although nematic and SC phases, with the SC phase being stabilised at bizarrely, no thermal changes could be observed by DSC. We the expense of the nematic phase with increasing chain length. have come across this problem before in other studies and This was the only lamellar phase observed, leading to the have usually found that by changing the experimental method observation reported previously15 that the 2,2¾-bipyridine core slightly, it was possible to obtain reproducible data.However, seems to strongly promote SC phase formation in these types in this case it was to no avail. of compounds. This observation was also borne out when the direction of the terminal ester functionality was reversed, as only a SC phase was observed. Mesomorphism of ligand, R8 The tetracatenar system, in particular displayed the most Thermal data for R8 and D8 are collected in Table 4.It is well interesting mesomorphism as these compounds were found to known that the direction of an ester functionality can have a exhibit nematic and lamellar phases at short chain lengths, profound eVect on the observed mesomorphism.27 The six-ring and hexagonal columnar phases at long chain lengths, with a 2,2¾-bipyridines described so far have their ester groups cubic phase appearing at intermediate chain lengths at the arranged so that their dipoles oppose one another (see Fig. 3), transferral point between the lamellar and columnar leading to net lateral dipoles which can be regarded as being mesophases.mutually repulsive and therefore, promoting nematic phases, Finally, the mesomorphism of hexacatenar species synas observed. However, if the outer ester groups are reversed, thesised was found to be essentially columnar, with the excepthen the dipoles would be arranged as a kind of ‘outboard’ tion of the methoxy derivative which behaved as a calamitic dipole which should promote smectic phases.Similar eVects mesogen. are seen on the introduction of fluoro substituents into mesomorphic systems.28 Reversal of the terminal ester group was found to promote SC phase formation by destabilising both the crystal and the Experimental nematic phase. Nematic phase formation was suppressed to Elemental analysis were determined by the University of the extent that it was no longer observed and the melting SheYeld Microanalysis Service.Mass spectra were recorded point was lowered by some 34 °C. This is unsurprising as the using the Fast Atom Bombardment technique (FAB), at the dipole moments of the ester functionalities are now no longer University of SheYeld.Infrared spectra were measured using a Nicolet MAGNA 550 FTIR infrared spectrometer; UV–VIS spectroscopy was carried out using a ATI Unicam UV4 Table 4 Thermal data for D8 and the ‘reversed’ ester, R8 machine. NMR spectra were recorded on either a Bruker Comp. Transition T /°C DH/kJ mol-1 DS/J K-1 mol-1 ACF-300 or a Bruker DRX-400 spectrometer, where the chemical shifts are reported relative to the internal standard R8 Cr�SC 197 37.3 80 of the deuterated solvent used.J values are in Hz. Analysis by SC�decomp. >280 — — DSC was carried out on a Perkin-Elmer DSC7 instrument D8 Cr�SC 231 52.3 104 using heating and cooling rates of either 5 or 10 K min-1. SC�Na 328 — — Analysis by hot stage microscopy was carried out using a Zeiss N�decomp.a >328 — — Labpol, or Olympus BH40 microscope equipped with a Link- Am HFS91 hot stage, TMS92 controller and LNP2 colling aThese temperatures are sensitive to the thermal history of the sample due to decomposition occurring in the SC phase.unit. Silica gel particle size was 40–63 mm. N N O O O O OCnH2 n+1 O O O O CnH2 n+1O 2 3 4 7 8 9 10 5 6 11 12 13 14 16 15 D8 N N O O O O O OC8 H17 O C8H17O O O 12 13 14 15 16 3 4 9 10 11 8 6 7 5 R8 Fig. 3 Diagram to show the relative dispositions of dipoles in the dicatenar compounds and the related ‘reversed ester’ 336 J. Mater. Chem., 1998, 8(2), 331–341Synthesis of the 3,4-dialkoxybenzoic acids All derivatives were prepared similarly and one example is given. All other derivatives were obtained in yields ranging from 80–95%.OCH2CH2(CH2)5CH3 O O O 1 3 4 5 6 7 8 9 I0 2 11 12 14 13 15 16 22 4c 4-(4-Octyloxybenzoyloxy)-1-benzyloxybenzene 4c. 4-Octyloxybenzoic acid (5 g, 0.02 mol), 4-benzyloxyphenol (4 g 0.02 mol), and dicyclohexylcarbodiimide (4.1 g, 0.02 mol), were dissolved OCH2CH2(CH2)5CH3 OCH2CH2(CH2)5CH3 HO2C 1 2 3 4 7b 8b 5 6 7a 8a 14a 14b 2h in dichloromethane. To this N,N-dimethylaminopyridine (0.25 g 0.002 mol) was added and the reaction was stirred at 3,4-Bis(octyloxy)benzoic acid 2h.Ethyl-3,4-dihydroxy- room temp. for 24 h. The colourless precipitate was removed benzoate (5 g, 0.027 mol), potassium carbonate (15.15 g, by filtration and the solvent was evaporated. Crystallisation 0.1 mol) and 1-bromooctane (10.6 g, 0.055 mol) were placed in from ethanol (2×) gave the product as a colourless solid.butanone (150 cm3), and the reaction heated at reflux for 84 h. Yield: 6.8 g (80%); dH (CDCl3): 8.05 (2H, AA¾XX¾, H12, JAA¾XX¾ Water (100 cm3) was added and the aqueous phase extracted 9), 7.35 (5H, m, H1–3), 7.05 (2H, AA¾XX¾, H8, JAA¾XX¾ 9), 7.05 against dichloromethane (3×100 cm3). The organic extracts (2H, AA¾XX¾, H13, JAA¾XX¾ 9), 6.87 (2H, AA¾XX¾, H7, JAA¾XX¾ were combined, dried over MgSO4, filtered and evaporated to 9), 5.00 (2H, s, H5), 3.95 (2H, t, H15, 3JHH 6.5), 1.75 (2H, qt, give a brown solid.A solution of potassium hydroxide (3.07 g, H16), 1.40 (2H, m, H17), 1.25 (8H, m, H18–21), 0.80 (3H, t, H22); 0.055 mol) in ethanol (95%, 100 cm3) was added and the dC (CDCl3): 165.3(C10), 163.5(C14), 156.4(C6), 144.8(C9), reaction heated at9(C4), 132.3(C12), 128.6, 128.0, 127.5(C1–3), 122.6(C8), and the solution acidified with HCl (conc., 10 cm3). The 121.6(C11), 115.5(C7), 114.3(C13), 70.5(C5), 68.3(C15), 31.8, resulting colourless precipitate was collected and crystallised 29.4, 29.3, 29.1, 26.0, 22.7(C16–21), 14.1(C22). twice from ethanol to give 3,4-bis(octyloxy)benzoic acid as a colourless solid.Yield: 9.12 g (88%); dH (CDCl3): 7.72 (1H, dd, Synthesis of the 4-(3,4-dialkoxybenzoyloxy)-1-benzyloxybenzenes H6, 3JHH 8.5, 4JHH 2), 7.60 (1H, d, H2, 4JHH 2), 6.89 (1H, d, H5, 3JHH 8.5), 4.07 and 4.05 (4H, t, H7a and b), 1.85 (4H, qt, H8), All derivatives were prepared similarly and one example is 1.30 (20H, m, H8–13), 0.90 (6H, t, H14) given.All other derivatives were obtained in yields ranging from 58% to quantitative. Synthesis of the 3,4,5-trialkoxybenzoic acids All derivatives were prepared similarly and one example is given. All other derivatives were obtained in yields ranging from 55–70%. OCH2CH2(CH2)5CH3 OCH2CH2(CH2)5CH3 O O O 6 7 8 9 10 11 12 13 14 15 16 17b 18b 24b 1 2 3 4 5 17a 18a 24a 5h 4-[3,4-Bis (octyloxy)benzoyloxy]-1-benzyloxybenzene 5h.This was prepared from 3,4-bis(octyloxy)benzoic acid using OCH2CH2(CH2)5CH3 OCH2CH2(CH2)5CH3 OCH2CH2(CH2)5CH3 HO2C 1 2 3 4 5b 6b 12b 5a 6a 12a 3c the procedure given for 4c. This gave the product as a colourless solid. Yield: 3 g (80%); dH (CDCl3): 7.82 (1H, dd, 3,4,5-Tris(octyloxy)benzoic acid 3c. Methyl 3,4,5-trihydroxy- H16, 3JHH 8.5, 4JHH 2), 7.68 (1H, d, H12, 4JHH 2), 7.40 (5H, m, benzoate (5 g, 0.027 mol), potassium carbonate (22.5 g, H1–3), 7.13 (2H, AA¾XX¾, H8, JAA¾XX¾ 9), 7.01 (2H, AA¾XX¾, 0.16 mol) and 1-bromooctane (15.65 g, 0.082 mol), were placed H7, JAA¾XX¾ 9), 6.93 (1H, d, H15, 3JHH 8.5), 5.09 (2H, s, H5), in pentan-3-one (150 cm3), and the reaction heated at reflux 4.09 and 4.08 (4H, t, H17a and b), 1.87 and 1.86 (4H, qt, H18a for 84 h.Water (100 cm3) was added and the aqueous phase and b), 1.51 (4H, m, H19), 1.35 (16H, m, H20–23), 0.91 (6H, t, extracted against dichloromethane (3×150 cm3). The organic H24); dC (CDCl3): 165.4(C10), 156.4(C6), 153.8(C14), 148.7(C13), extracts were combined dried over MgSO4, filtered and evapor- 144.8(C9), 136.9(C4), 128.6, 128.0, 127.5(C1–3), 124.3(C8), ated to give a brown oil.A solution of potassium hydroxide 122.6(16C), 121.8(C11), 115.5(C7), 114.7(C12), 112.1(C15), (3.04 g, 0.054 mol) in 95% ethanol (150 cm3) was added and 70.5(C5), 69.4&69.1(C17a and b), 31.8, 29.4, 29.3, 29.2, 29.1, 26.0, the reaction heated at reflux for 2.5 h. Water (100 cm3) was 22.7(C18–23), 14.1(C24). added and the solution acidified with conc.hydrochloric acid (20 cm3). The resulting colourless precipitate was collected and Synthesis of the 4-(3,4,5-trialkoxybenzoyloxy)- crystallised (2×) from ethanol to give 3,4,5-tris(octyloxy)ben- 1-benzyloxybenzenes zoic acid as a colourless solid. Yield 11 g (54%); dH (CDCl3): 7.30 (2H, s, H2), 4.00 and 4.03 (6H, t, H5a and b), 1.84 (6H, qt, All derivatives were prepared similarly and one example is H6), 1.50 (6H, m, H7), 1.30 (24H, m, H8–11), 0.85 (9H, t, H12); given.All other derivatives were obtained in yields ranging dC (CDCl3): 172.0(CO2H), 152.8(C3), 143.1(C4), 123.7(C1), from 65–89%. 108.5(C2), 73.6(C5a), 6.2(C5b), 31.9, 31.8, 30.3, 29.5, 29.4, 29.3, 26.1, 22.7 (C6–11), 14.1(C12). Synthesis of the 4-(4-alkoxybenzoyloxy)-1-benzyloxybenzenes All derivatives were prepared similarly and one example is given.All other derivatives were obtained in yields ranging from 70–83%. OCH2CH2(CH2)5CH3 OCH2CH2(CH2)5CH3 O O O 6 7 8 9 10 11 12 13 14 15b 16b 22b 1 2 3 4 5 15a 16a 22a OCH2CH2(CH2)5CH3 6c J. Mater. Chem., 1998, 8(2), 331–341 3374-[3,4,5-Tris(octyloxy)benzoyloxy]-1-benzyloxybenzene 6c. 116.2(C2), 114.6(C7), 112.0(C10), 69.4 and 69.1(C12a and b), 31.8, 29.4, 29.3, 29.2, 29.0, 26.0, 22.7(C13–18), 14.1(C19). This was prepared from 3,4,5-tris(octyloxy)benzoic acid using the procedure described for 4c. The crude product was purified by crystallisation from ethanol (250 cm3), to give the pure Synthesis of the 4-(3,4,5-trialkoxybenzoyloxy)phenols product as a colourless solid.Yield: 0.88 g (65%); dH (CDCl3): All derivatives were prepared similarly and one example is 7.40 (5H, m, H1–3), 7.38 (2H, s, H12), 7.10 (2H, AA¾XX¾, H8, given. All other derivatives were obtained in yields ranging JAA¾XX¾ 9), 7.00 (2H, AA¾XX¾, H7, JAA¾XX¾ 9), 5.06 (2H, s, H5), from 80–95%. 4.05 (6H, m, H15), 1.82 and 1.80 (6H, qt, H16a and b), 1.50 (6H, m, H17), 1.30 (24H, m, H18–21), 0.85 (9H, t, H22).Synthesis of the 4-(4-alkoxybenzoyloxy)phenols All derivatives were prepared similarly and one example is given. All other derivatives were obtained in yields ranging from 76% to quantitative. O HO OCH2(CH2)6CH3 OCH2(CH2)6CH3 OCH2(CH2)6CH3 8 9 O 10a 21a 1 2 3 4 5 6 7 10b 21b 11c 4-[3,4,5-Tris(octyloxy)benzoyloxy]phenol 11c. Compound 6c (3.9 g, 5.7 mmol) was dissolved in freshly distilled THF (150 cm3) and triethylamine (1 cm3) and 10% wet Degassu OCH2CH2(CH2)5CH3 O O HO 1 2 3 4 5 6 7 8 9 10 11 21 9c Pd/C catalyst (0.05 g) was added.The reaction flask was evacuated and placed under hydrogen (three times), before 4-(4-Octyloxybenzoyloxy)phenol 9c. 4-(4-Octyloxybenzoy- being stirred at room temp. under an atmosphere of hydrogen.loxy)-1-benzyloxybenzene (6.6 g, 0.015 mol) was dissolved in After the calculated amount of hydrogen had been taken up freshly distilled THF (150 cm3) and triethylamine (1 cm3), and the catalyst was removed by filtration through Celite and the 10% wet Degassu Pd/C catalyst (0.05 g) was added. The solvent was evaporated. The crude product was purified by reaction flask was evacuated and placed under hydrogen flash chromatography on silica gel using THF as the eluent.(repeated three times), before being stirred at room temp. Yield: 3.37 g (quantitative); dH (CDCl3) 7.38 (2H, s, H7), 7.03 under an atmosphere of hydrogen. After 223 cm3 of hydrogen (2H, AA¾XX¾, H3, JAA¾XX¾ 9), 6.83 (2H, AA¾XX¾, H2, JAA¾XX¾ 9), had been taken up the catalyst was removed by filtration 5.18 (1H, s, OH), 4.02 (6H, t, H10), 1.80 and 1.75 (6H, qt, through Celite and the solvent was evaporated, to give a H11a and b), 1.45 (6H, m, H12), 1.30 (24H, m, H13–16), 0.85 (9H, colourless solid as the product. Yield: 4.7 g (90%); dH (CDCl3): t, H17); dC (CDCl3): 166.2(C5), 153.8(C1), 152.9(C8), 144.1(C4), 8.12 (2H, AA¾XX¾, H7, JAA¾XX¾ 9), 7.02 (2H, AA¾XX¾, H3, 142.8(C9), 123.9(C6), 122.5(C3), 116.2(C2), 108.5(C7), JAA¾XX¾ 9), 6.95 (2H, AA¾XX¾, H8, JAA¾XX¾ 9), 6.80 (2H, AA¾XX¾, 73.7(C10a), 69.3(C10b), 31.9, 31.8, 31.6, 30.3, 29.5, 29.4, 29.3, H2, JAA¾XX¾ 9), 5.38 (1H, s, OH), 4.02 (2H, t, H10, 3JHH 6.5), 26.9, 26.1, 22.7 (C11–16), 14.1(C17). 1.80 (2H, qt, H11), 1.45 (2H, m, H12), 1.30 (8H, m, H13–16), 0.85 (3H, t, H17); dC (CDCl3): 166.2(C5), 163.7(C9), 153.7(C1), Synthesis of the bis[4-(4-alkoxybenzoyloxy)phenyl] 2,2¾- 144.2(C4), 132.4(C7) 122.5(C3), 121.4(C6), 116.3(C2), 114.3(C8), bipyridine-5,5¾-dicarboxylates 68.4(C10), 31.8, 29.3, 29.2, 29.1, 26.0, 22.7(C11–16), 14.1(C17). All derivatives were prepared similarly and one example is given.Yields and elemental analyses are collected in Table 5. Synthesis of the 4-(3,4-dialkoxybenzoyloxy)phenols No 13C NMR data could be obtained for any of these materials due to poor product solubility.All derivatives were prepared similarly and one example is given. All other derivatives were obtained in yields ranging from 80–95%. Table 5 Yields and analytical data (Calc. %) Found % n Yield (%) C H N D1 20 (69.0) 67.6 (4.1) 4.0 (4.0) 4.2 D4 15 (70.8) 69.5 (5.2) 5.2 (3.6) 3.5 OCH2CH2(CH2)5CH3 OCH2CH2(CH2)5CH3 O O HO 1 2 3 4 5 6 7 8 9 10 11 12b 13b 23b 12a 13a 23a 10h D8 18 (72.6) 72.4 (6.3) 6.3 (3.1) 3.0 D12 12 (74.1) 73.2 (7.2) 7.2 (2.8) 2.8 D14 12 (74.7) 74.3 (7.6) 7.5 (2.6) 2.7 T1 20 (66.7) 64.4 (4.3) 4.2 (3.7) 3.6 4-[3,4-Bis(octyloxy)benzoyloxy]phenol 10h.Compound 5h T2 15 (68.0) 67.4 (5.0) 5.0 (3.5) 3.3 (6.6 g, 0.0118 mol) was dissolved in freshly distilled THF T3 8 (69.1) 68.9 (5.6) 5.6 (3.2) 3.2 (150 cm3) and triethylamine (1 cm3) and 10% wet Degassu T4 18 (70.1) 69.6 (6.1) 6.1 (3.0) 3.0 Pd/C catalyst (0.05 g) was added.The reaction flask was T5 8 (71.0) 71.0 (6.6) 6.7 (2.9) 2.8 evacuated and placed under hydrogen (three times), before T6 22 (71.8) 71.8 (6.9) 7.1 (2.7) 2.6 being stirred at room temp. under an atmosphere of hydrogen. T7 22 (72.5) 72.3 (7.4) 7.2 (2.5) 2.5 T8 25 (73.1) 73.3 7.7 7.9 (2.4) 2.5 After the calculated amount of hydrogen had been taken up T9 19 (73.7) 73.4 (8.0) 7.9 (2.3) 2.3 the catalyst was removed by filtration through Celite and the T10 10 (74.3) 74.0 (8.3) 8.2 (2.2) 2.2 solvent was evaporated.The crude product was purified by T11 32 (74.9) 74.6 (8.6) 8.5 (2.1) 2.1 crystallisation from ethanol, to give a colourless solid as the T12 5 (75.2) 75.0 (8.8) 8.7 (2.0) 2.0 product.Yield: 5.25 g (95%); dH (CDCl3): 7.74 (1H, dd, H11, T13 5 (75.2) 75.2 (9.2) 9.0 (2.0) 2.0 3JHH 8.5, 4JHH 2), 7.57 (1H, d, H7, 4JHH 2), 6.95 (2H, AA¾XX¾, T14 18 (76.0) 75.7 (9.2) 9.0 (1.9) 1.8 H1 20 (64.7) 64.4 (4.4) 4.5 (3.4) 3.5 H3, JAA¾XX¾ 9), 6.85 (1H, d, H10, 3JHH 8.5), 6.75 (2H AA¾XX¾, H4 12 (69.6) 69.4 (6.8) 6.9 (2.6) 2.6 H2, JAA¾XX¾ 9), 5.15 (1H, s, OH), 4.01 and 4.00 (4H, t, H12), H8 18 (72.6) 72.4 (6.3) 6.3 (3.1) 3.0 1.80 (4H, qt, H13), 1.40 (4H, m, H14), 1.25 (16H, m, H15–18), H12 12 (73.5) 73.2 (8.6) 8.9 (2.0) 2.0 0.83 (6H, t, H19); dC (CDCl3): 166.1(C5), 153.9(C1), 153.7(C9), R8 24 (72.6) 71.6 (6.3) 6.1 (3.1) 3.4 148.6(C8), 144.2(C4), 124.5(C3), 122.5(C11), 121.5(C6), 338 J.Mater. Chem., 1998, 8(2), 331–341N N O O O O OCnH2 n+1 O O O O CnH2 n+1O 2 3 4 7 8 9 10 5 6 11 12 13 14 16 15 D8 N N O O O O OCnH2 n+1 O O O O CnH2 n+1O OCnH2 n+1 CnH2 n+1O 2 3 4 7 8 9 10 5 6 11 12 13 14 16 15 17 18 T8 Bis[4-(4-octyloxybenzoyloxy)phenyl] 2,2¾-bipyridine-5,5¾- hot through Celite. The colourless solution was evaporated and the solid recrystallised (×2) from 1,4-dioxane, giving the dicarboxylate D8.The apparatus was flame dried prior to use. 2,2¾-Bipyridine-5,5¾-dicarboxylic acid dichloride (2.4 g, product as a cream solid. Yield: 0.62 g (17%); dH (CDCl3): 9.43 (2H, dd, H6, 4JHH 2, 5JHH 1), 8.65 (2H, dd, H3, 3JHH 8.5, 5JHH 3.6 mmol), and 4-(4-octyloxybenzoyloxy)phenol (1.74 g 7.1 mmol) were placed in freshly distilled toluene (50 cm3). 1), 8.55 (2H, dd, H4, 3JHH 8.5, 4JHH 2), 7.78 (2H, dd, H18, 3JHH 8.5, 4JHH 2), 7.60 (2H, d, H14, 4JHH 2), 7.29 and 7.22 (8H, Triethylamine (1 cm3) was added and the reaction heated at reflux, under nitrogen overnight. The solvent was evaporated AA¾XX¾, H9 and 10, JAA¾XX¾ 9), 6.88 (2H, d, H17, 3JHH 8.5), 4.03 and 4.02 (8H, t, H19a and b), 1.60 (8H, m, H20), 1.43 (8H, m, and dichloromethane added. This was extracted against 10% ammonia solution.The aqueous phase was then extracted with H21), 1.30 (32H, m, H22–25), 0.95 (12H, t, H26); dC (CDCl3): 164.9(C12), 163.7(C7), 158.7(C2), 153.9(C16), 151.2(C6), 148.9 dichloromethane (2×100 cm3), the organic extracts combined and the solvent evaporated to give a crude dark brown solid.and 148.6, 147.8(C8,11 and 15), 138.8(C4), 125.8(C5), 124.4(C3), 122.9 and 122.5(C9 and 10), 121.6(C18), 121.2(C13), 114.5(C14), The solid was placed in ethyl acetate, heated to reflux, allowed to cool to room temp. and the solid collected by centrifugation 111.9(C17), 69.3 and 69.1(C19a and b), 31.8, 29.4, 29.3, 29.1, 29.0, 26.0, 22.7 (C20–25), 14.1(C26). (×2). The solid was then heated to reflux in 1,4-dioxane and collected (×2), giving the product as a cream solid.dH (CDCl3) 9.40 (2H, dd, H6, 4JHH 2.5, 5JHH 1), 8.64 (2H, dd, H3, 3JHH 8.5, The synthesis of the bis[4-(3,4,5-trialkyloxybenzoyloxy)- phenyl] 2,2¾-bipyridine-5,5¾-dicarboxylates 5JHH 1), 8.54 (2H, dd, H4, 3JHH 8.5, 4JHH 2.5), 8.06 (4H, AA¾XX¾, H14, JAA¾XX¾ 9), 7.22 (8H, AA¾XX¾, H9 and 10), 6.90 (4H, AA¾XX¾, All derivatives were prepared similarly and one example is H15, JAA¾XX¾ 9); The alkyl region was unresolvable.given. Yields and elemental analyses are collected in Table 5. Synthesis of the bis[4-(3,4-dialkoxybenzoyloxy)phenyl] 2,2¾- Bis{4-[3,4,5-tris(octyloxy)benzoyloxy]phenyl} 2,2¾-bipyribipyridine- 5,5¾-dicarboxylates dine-5,5¾-dicarboxylate H8. The apparatus was flame dried prior to use. 2,2¾-Bipyridine-5,5¾-dicarboxylic acid dichloride All derivatives were prepared similarly and one example is given. Yields and elemental analyses are collected in Table 5. (0.25 g, 0.9 mmol), and 4-[3,4,5-tris(octyloxy)benzoyloxy]- phenol (10.6 g 1.8 mmol) were placed in freshly distilled toluene (50 cm3). Triethylamine (1 cm3) was added and the reaction Bis{4-[3,4-bis(octyloxy)benzoyloxy]phenyl} 2,2¾-bipyridine- 5,5¾-dicarboxylate T8.The apparatus was flame dried prior to heated at reflux, under nitrogen overnight. The solvent was evaporated and dichloromethane added. This was extracted use. 2,2¾-Bipyridine-5,5¾-dicarboxylic acid dichloride (0.9 g, 3.2 mmol), and 4-[3,4-bis(octyloxy)benzoyloxy]phenol (3 g, against 10% ammonia solution. The aqueous phase was then extracted with dichloromethane (2×100 cm3), the organic 6.4 mmol) were placed in freshly distilled toluene (50 cm3).Triethylamine (1 cm3) was added and the reaction heated at extracts combined and the solvent evaporated to give a crude dark brown solid. The solid was placed in ethyl acetate, heated reflux, under nitrogen overnight. The solvent was evaporated and dichloromethane added.This was extracted against 10% to reflux, allowed to cool to room temp. and the solid collected by centrifugation (×2), before being crystallised from 1,4- ammonia solution. The aqueous phase was then extracted with dichloromethane (2×100 cm3), the organic extracts combined dioxane. The crude product was placed in chloroform, heated to reflux and filtered hot through Celite.The colourless solution and the solvent evaporated to give a crude dark brown solid. The solid was placed in ethyl acetate, heated to reflux, allowed was evaporated and the solid recrystallised (×2) from 1,4- dioxane, giving the product as a cream solid. Yield: 0.23 g to cool to room temp. and the solid collected by centrifugation (×2), before being crystallised from 1,4-dioxane. The crude (19%); dH (CDCl3): 9.50 (2H, dd, H6, 4JHH 2, 5JHH 1), 8.73 (2H, dd, H3, 3JHH 8.5, 5JHH 1), 8.63 (2H, dd, H4, 3JHH 8.5, 4JHH product was placed in chloroform, heated to reflux and filtered N N O O O O OCnH2 n+1 O O O O CnH2 n+1O OCnH2 n+1 CnH2 n+1O CnH2 n+1O OCnH2 n+1 2 3 4 7 8 9 10 5 6 11 12 13 14 16 15 H8 J.Mater. Chem., 1998, 8(2), 331–341 3392), 7.42 (4H, s, H14), 7.35 and 7.30 (8H, AA¾XX¾, H9 and 10, JAA¾XX¾ 9), 4.08 and 4.06 (12H, t, H17a and b), 1.86 and 1.80 (12H, m, H18a and b), 1.49 (12H, m, H19), 1.30 (48H, m, H20–23), 0.90 (18H, t, H24); dC (CDCl3): 164.9(C12), 163.6(C7), 158.8(C2), 153.0(C15), 151.1(C6), 148.8 and 148.0(C8 and 11), 143.3(C16), 138.7(C4), 125.9(C5), 123.6(C13), 122.9 and 122.5(C9 and 10), 121.7(C3), 108.7(C14), 73.6(C17a), 69.3(C17b), 31.9, 31.8, 30.4, O O 1 2 3 4 5 6 7 8 9 O 10 O OCH2CH2(CH2)5CH3 11 12 13 14 15 16 22 12 29.5, 29.4, 29.3, 26.1, 22.7 (C18–23), 14.1(C24). 4-Octyloxyphenyl 4¾-(tetrahydropyran-2-yloxy)benzoate 12.Synthesis of the reversed ester, R8 Compound 11 (2.5 g, 0.012 mol), 4-octyloxyphenol (2.5 g 0.012 mol), and dicyclohexylcarbodiimide (DCC) (2.32 g 0.012 mol) were dissolved in dichloromethane (80 cm3). 4- (N,N-Dimethylamino)pyridine (0.14 g 1.2 mmol) was then added and the reaction stirred at room temp. overnight. The colourless precipitate was removed by filtration and the solvent evaporated. Crystallisation from ethanol (×2) gave the product as a colourless solid. Yield: 4 g (84%); mp 81 °C (sublimes); dH (CDCl3): 8.13 (2H, AA¾XX¾, H8, JAA¾XX¾ 9), 7.10 (2H, AA¾XX¾, H7, JAA¾XX¾ 9), 7.15 (2H, AA¾XX¾, H13, JAA¾XX¾ 9), 6.90 (2H, O O 1 2 3 4 5 6 7 8 9 O 10 O 11 12 13 15 14 10 AA¾XX¾, H12, JAA¾XX¾ 9), 5.55 (1H, t, H5, 3JHH 3), 3.95 (2H, t, H15, 3JHH 6.5), 3.88 (1H, m, H1eq), 3.62 (1H, m, H1ax), 2.05, Benzyl 4-(tetrahydropyran-2-yloxy)benzoate 10. 3,4- 1.90 and 1.70 (6H, m, H2,3 and 4), 1.78 (2H, m, H16), 1.45 (2H, Dihydro-2H-pyran (20 cm3, 0.22 mol) and ethyl acetate satum, H17), 1.30 (8H, m, H18–21), 0.90 (3H, t, H22); dC (CDCl3): rated with HCl(g) (3.5 cm3) was added to a solution of benzyl 165.3(C10), 161.4(C6), 156.8(C14), 144.4(C11), 132.1(C8), 4-hydroxybenzoate (10 g, 0.044 mol) in ethyl acetate (100 cm3). 122.7(C9), 122.4(C12), 116.1(C7), 115.1(C13), 96.1(C5), The reaction was stirred at room temp.for 12 h before the 68.5(C15), 62.0(C1), 30.1(C4), 25.1(C2), 18.5(C3), 31.8, 29.4, solvent was removed. Flash chromatography on neutral alum- 29.3, 29.2, 26.1, 22.7(C16–21), 14.1(C22). ina using dichloromethane as the eluent gave the product as a colourless oil which solidified on standing. Yield: 12 g (88%); mp 68–71 °C (decomp.); dH (CDCl3): 8.03 (2H, AA¾XX¾, H8, JAA¾XX¾ 9), 7.40 (5H, m, H13–17), 7.06 (2H, AA¾XX¾, 7H, JAA¾XX¾ 9), 5.50 (1H, t, H5, 3JHH 3), 3.88 (1H, m, H1eq), 3.62 (1H, m, H1ax), 2.01, 1.90 and 1.70 (6H, m, H2,3 and 4); dC (CDCl3): HO 1 2 3 4 O 5 O OCH2CH2(CH2)5CH3 6 7 8 9 10 11 17 13 166.2(C10), 161.0(C6), 136.4(C12), 131.6(C8), 128.6, 128.12 and 128.07(C13–15), 123.3(C9), 115.9(C7), 96.1(C5), 66.4(C11), 4-Octyloxyphenyl 4-hydroxybenzoate 13.Compound 12 (4 g, 62.0(C1), 30.1(C4), 25.1(C2), 18.5(C3). 9.4 mmol) and oxalic acid (50 mg) were placed in methanol– water (100 cm3; 951), and the reaction was heated at reflux for 72 h. The reaction was cooled to room temp. and the resulting colourless needles collected and washed with ethanol– water (151), to give the pure product. The mother liquor was evaporated and the resulting colourless solid crystallised from ethanol–water to give more product as colourless needles.O O 1 2 3 4 5 6 7 8 9 OH 10 O 11 Yield: 2.95 g (95%); mp 159 °C; dH (CDCl3): 8.10 (2H, AA¾XX¾, H3, JAA¾XX¾ 9), 7.10 (2H, AA¾XX¾, H7, JAA¾XX¾ 9), 6.89 and 6.93 (4H, AA¾XX¾, H2 and 8, JAA¾XX¾ 9), 5.80 (1H, s, OH), 3.95 ( 2H, 4-(Tetrahydropyran-2-yloxy)benzoic acid 11.To a solution t, H10, 3JHH 6.5), 1.78 (2H, qt, H11), 1.45 (2H, m, H12), 1.30 of compound 10 (11.5 g, 0.037 mol) in freshly distilled THF, (8H, m, H13–16), 0.90 (3H, t, H17); dC (CDCl3): 165.5(C5), wet Degassu Pd/C catalyst was added (10%, 50 mg). The 162.3(C1), 156.7(C9), 144.5(C6), 132.3(C3), 122.5(C7), reaction was placed under vacuum and hydrogen (×3) before 120.6(C4), 115.5, 115.0(C2 and 8), 68.4(C10), 31.8, 29.3, 29.2, being left to stir under an atmosphere of hydrogen at room 26.0, 22.6(C11–16), 14.1(C17).temp. After hydrogen (900 cm3) had been used the reaction was filtered through Celite and the solvent evaporated. The crude product was crystallised from ethanol to give a colourless Bis[(4-octyloxybenzoyloxy)phenyl] 2,2¾-bipyridine-5,5- dicarboxylate R8.This was prepared from compound 13 using solid as the product. Yield: 6 g (73%); mp 159 °C (decomp.); dH (CDCl3): 8.05 (2H, AA¾XX¾, H8, JAA¾XX¾ 9), 7.10 (2H, the procedures for esterification with 2,2¾-bipyridine-5,5¾-dicarboxylic acid dichloride described above. This gave the product AA¾XX¾, 7H, JAA¾XX¾ 9), 5.55 (1H, t, H5, 3JHH 3), 3.88 (1H, dt, H1eq), 3.62 (1H, m, H1ax), 2.01, 1.90 and 1.70 (6H, m, as a cream solid.Analytical data are found in Table 5. dH (CDCl3): 9.51 (2H, dd, H6, 4JHH 2, 5JHH 1), 8.75 (2H, dd, H3, H2,3 and 4); dC (CDCl3): 172.0(C10), 161.6(C6), 132.2(C8), 122.4(C9), 116.0(C7), 96.1(C5), 66.4(C11), 62.1(C1), 30.1(C4), 3JHH 8.5, 5JHH 1), 8.64 (2H, dd, H4, 3JHH 8.5, 4JHH 2), 8.33 (4H, AA¾XX¾, H10, JAA¾XX¾ 9), 7.44 (4H, AA¾XX¾, H9, JAA¾XX¾ 9), 25.1(C2), 18.5(C3).N N O O O O O OC8 H17 O C8H17O O O 12 13 14 15 16 3 4 9 10 11 8 6 7 5 R8 340 J. Mater. Chem., 1998, 8(2), 331–34112 D. W. Bruce and K. E. Rowe, L iq. Cryst., 1995, 18, 161. 7.14 (4H, AA¾XX¾, H14, JAA¾XX¾ 9), 6.95 (4H, AA¾XX¾, H15, 13 L. Douce, R. Ziessel, R. Seghrouchni, E. Campillos, A. Skoulios JAA¾XX¾ 9), 3.98 (4H, t, H17, 3JHH 6.5), 1.85 (4H, qt, H18), 1.50 and R.Deschenaux, L iq. Cryst., 1995, 18, 157. (4H, m, H19), 1.27 (16H, m, H20–23), 0.90 (12H, t, H24); MS 14 K. E. Rowe and D. W. Bruce, L iq. Cryst., 1996, 20, 183. m/z: [M+] 892.39; no 13C NMR data could be obtained due 15 See e.g. R. Deschenaux and J. W. Goodby, in Ferrocenes, ed to the product’s insolubility. A. Togni and T. Hayashi, VCH, Weinheim, 1995, ch. 9. 16 K. E. Rowe and D. W. Bruce, J. Chem. Soc., Dalton T rans., 1996, 3913. Support from the EPSRC and the University of Exeter is 17 J. Mathe�te, H.-T. Nguyen and C. Destrade, L iq. Cryst., 1993, 13, gratefully acknowledged. 171. 18 H.-T. Nguyen, C. Destrade and J. Malthe�te, Adv. Mater., 1997, 9, 375. References 19 D. W. Bruce and S. A. Hudson, J. Mater. Chem., 1994, 4, 479; W. Weissflog, G. Pelzl, I. Letko and S. Diele, Mol. Cryst., L iq. 1 E. C. Constable, Adv. Inorg. Chem. Radiochem., 1984, 30, 69. Cryst., 1995, 260, 157. 2 G. X. Liu and R. J. Puddephatt, Organometallics, 1996, 15, 5257. 20 B. Heinrich and D. Guillon, unpublished results. 3 J.-M. Lehn and A. Rigault, Angew. Chem., Int. Ed. Engl., 1988, 21 B. Donnio and D. W. Bruce, J. Chem. Soc., Dalton T rans., 1997, 27, 1095. 2745. 4 V. Balzani, A. Juris, M. Venturi, S. Campagna and S. Serroni, 22 W. Weissflog, I. Letko, S. Diele and G. Pelzl, Adv. Mater., 1996, Chem. Rev., 1996, 96, 759. 8, 76. 5 See e.g. J.-M. Lehn, Supramolecular Chemistry, VCH, Weinheim, 23 D. W. Bruce, B. Donnio, S. A. Hudson, A.-M. Levelut, S. Megtert, 1995. D. Petermann and M. Veber, J. Phys. II Fr., 1995, 5, 289. 6 D. W. Bruce, Adv.Mater., 1994, 6, 699. 24 D. W. Bruce, B. Donnio, D. Guillon, B. Heinrich and M. Ibn- 7 D. W. Bruce and X.-H. Liu, J. Chem. Soc., Chem. Commun., 1994, Elhaj, L iq. Cryst., 1995, 19, 537. 729. 25 B. Donnio, D. W. Bruce, H. Delacroix and T. Gulik-Krzywicki, 8 D. W. Bruce and X.-H. Liu, L iq. K., 1995, 18, 165. L iq. Cryst., 1997, 23, 147. 9 S. Morrone, G. Harrison and D. W. Bruce, Adv. Mater., 1995, 7, 26 B. Donnio, D. W. Bruce, B. Heinrich, D. Guillon, H. Delacroix 665; S. Morrone, D. Guillon and D. W. Bruce, Inorg. Chem., 1996, and T. Gulik-Krzywicki, Chem. Mater., 1997, in press, B. Donnio, 35, 7041. PhD T hesis, University of SheYeld, 1996. 10 H. Zheng and T. M. Swager, J. Am. Chem. Soc., 1994, 116, 27 G. W. Gray, T hermotropic L iquid Crystals, Wiley, Chichester, 761 T. M. Swager and H. Zheng, Mol. Cryst., L iq. Cryst., 1995, 1987. 260, 301. 28 M. A. Osman, Mol Cryst, L iq. Cryst., 1985, 128, 45; G. Nestor, 11 See also: K. Hanabusa, J.-I. Higashi, T. Koyama, H. Shira, N. Hojo G. W. Gray, D. Lacey and K. J. Toyne, L iq. Cryst., 1990, 7, 669; and A. Kurose, Makromol. Chem., 1989 190, 1; T. Kuboki, D. W. Bruce and S. A. Hudson, J. Mater. Chem., 1994, 4, 479; K. Araki, M. Yamada and S. Shiraishi, Bull. Chem. Soc. Jpn., 1994, G. W. Gray, M. Hird and K. J. Toyne, Mol. Cryst., L iq. Cryst., 67, 984; D. W. Bruce, J. D. Holbrey, A. R. Tajbakhsh and 1991, 204, 91. G. J. T. Tiddy, J. Mater. Chem., 1993, 3, 905; A. Elgayoury, L. Douce, R. Ziessel, R. Seghrouchni and A. Skoulios, L iq. Cryst., 1996, 21, 143. Paper 7/06400D; Received 2nd September, 1997 J. Mater. Chem., 1998, 8(2), 331–341

ISSN:0959-9428    

DOI:10.1039/a706400d

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Induction of liquid crystalline phases in linear polyamines by complexation of transition metal ions Hartmut Fischer,b Thomas Plesnivy,a Helmut Ringsdorfa and Markus Seitz*,a,† aInstitut fu� r Organische Chemie, J. J. Becherweg 18–20, Johannes Gutenberg-Universita� t, 55099 Mainz, Germany bT echnische Universiteit Eindhoven, Polymer Chemistry & T echnology 5600MB Eindhoven, Netherlands In this paper, we describe the preparation and characterization of polyamine–copper complexes based on N-alkylated polyethyleneimines which were obtained by polymer analogous reduction of the corresponding N-acylated polymers.Liquid crystalline properties of the originating linear polyamides are lost in the resulting polyamines which show a higher conformational mobility.In analogy to low molecular mass azacrown derivatives, the complexation of transition metal ions, here copper(II), may reinduce liquid crystalline behavior. The structure formation in the liquid crystalline state is discussed based on X-ray investigations. The generation of well-defined macroscopic structures by non- cyclene derivative peracylated with 4-dodecyloxybenzoyl chloride.15 covalent interaction of two or more individual components is In general, the use of suitable side groups—e.g.the 3,4- of great interest in liquid crystalline research, and more generdialkoxybenzoyl unit16—provides the formation of columnar, ally in the so-called field of ‘supramolecular chemistry’.1–3 For especially discotic hexagonal mesophases (Dh) for a large instance, two diVerent molecular subunits that do not show number of substituted macrocyclic oligoamides.This was any mesomorphic properties themselves may interact to form related to their discoidal molecular geometry, which in turn a liquid crystalline ‘supramolecule’. The self-organization of had been associated with the restricted conformational mobility such systems may take place either in solution, in the solid or of the central macrocycle by N-acylation with benzoic or even in the liquid crystalline state by various kinds of molecular cinnamoic acid derivatives.17–19 As a consequence, discotic interactions such as hydrogen bonding, donor–acceptor interazacrown derivatives lose their mesomorphic properties by actions or the complexation of transition metal ions.4–9 The complete reduction to the N-alkylated macrocycle, due to the induction of liquid crystalline phases in polymeric materials more flexible linkage of the side chains.8 However, a confor- by means of low molecular mass ‘dopants’, such as electron mational fixation of the N-alkylated core and thus the reinduc- acceptor molecules or small cations that act as central units tion of a columnar mesophase may be achieved by coordination for a complex subunit is particularly interesting.10–12 of the central core with transition metal ions,8,17,20 as shown Inorganic as well as organic amino compounds, especially in Fig. 1 for tetrasubstituted cyclam derivatives. In a similar multivalent (‘polydentate’) amino ligands such as linear and fashion, even the salts of protonated cyclic oligoamines may branched oligomers of the aminoethylene unit (dien and trien be enabled to form thermotropic mesophases.21 etc.), have played an outstanding role in the development of Considering azamacrocycles as cyclic oligomers of ethy- coordination chemistry.13 In the context of the work presented leneimine, well-known principles relating structure and proper- here, macrocyclic amino ligands (azacrowns)14 are of particular ties of N-substituted azacrowns can be applied to N-substituted interest.Their principal ability to serve as a central unit of polyethyleneimines. In particular, the formation of thermo- thermotropic liquid crystals was first recognized for a hexatropic hexagonal columnar mesophases by N-benzoylated as well as N-cinnamoylated azamacrocycles was also realized for * E-mail: seitm@engineering.ucsb.edu the equivalent linear polymers.22–24 The particular packing † Present address: Department of Chemical Engineering, University of behavior of N-3,4-acylated ethyleneamine fragments results in California, Santa Barbara, CA 93106, USA.a nearly identical thermotropic phase behavior for cyclic and ‡ The structure shown was obtained by first minimizing the steric linear oligomers as well as for linear polymers (Fig. 2).24 energy of the decamer of N-dimethoxybenzoylethyleneimine starting For the linear polyamide 3 (PEI-3,4), based on miscibility both, from a ‘prefolded’ chain or a zig-zag conformation (2/1-helix). studies and entropic considerations it has been proposed that The final replacement of the methoxy substituents by decyloxy chains in the second step of the energy minimization gave rise to only gradual the columnar aggregates would consist of single helically folded changes in the position of the atoms in the polymer main chain. polymer chains surrounded radially by the alkyl chains.22,24 However, this structure which was obtained using a standard software The polymer backbone of such a possible energetically favored package (CSC Chem3D for Macintosh) should not be viewed as the conformation is shown in Fig. 3. One helix turn is formed by result of an extensive modelling calculation. It rather provides a refined four to five repeat units resulting in a column center with a and reasonable model that we found very useful for the discussion of diameter of about 5 A ° adopting a shape similar to the tetraaza- the packing requirements along the polymer main chain.Nevertheless, cycles; the pitch height in this model is 7.3 A ° .‡ it is in good agreement with earlier molecular modeling calculations in which a 14/3-helical conformation has been proposed for polyoxazol- Based on the N-substituted alkyleneamine fragment one ines containing chiral centers in the main chain (cf.Y. S. Oh, may think of a variety of diVerent molecular architectures, T. Yamazaki and M. Goodman, Macromolecules, 1992, 25, 6322). In such as branched or dendrimeric structures.24–26 In this context, this context, a discussion of the induction of a helical main chain the phase separation in a hydrophilic central region surrounded conformation by the sterical requirements of tapered side groups has by hydrophobic alkyl groups has been discussed as the main been presented recently (cf.V. Percec, D. Schlueter, J. C. Ronda, driving force for the hexagonal columnar mesomorphism G. Johansson, G. Ungar and J. P. Zhou, Macromolecules, 1996, 29, 1464). observed in dendrimeric polymers of higher generation.27 J.Mater. Chem., 1998, 8(2), 343–351 343N N N N CO CO R R R CO R CO N N N N CH2 CH2 R R CH2 R CH2 R N N N N CH2 CH2 R R CH2 R CH2 R OC10H21 OC10H21 OC10H21 Cu2+ Cu(NO3)2 (1:1) c 196 i red. R = c 105 i c 18 Dh 180 (decomp.) lc 96 Dh 132 i * c1 39 c2 52 i g 67 i R = Fig. 1 Induction of columnar mesophases by transition metal ion complexation as observed for CuII complexes of N-alkylated cyclam derivatives (cf.refs. 8 and 17) Synthesis The synthesis of N-acylated polyethyleneimine derivatives by polymer analogous conversion of linear polyethyleneimine has been extensively described elsewhere.22,24 Also, the reduction of N-acylated polyethyleneimines to poly(N-alkylethyleneimines) has been investigated already by Saegusa and Kobayashi.29 In general, the use of lithium aluminium hydride can lead to a decrease in the degree of substitution due to a CMN cleavage in the transition state of the reaction.30 This side reaction had been attributed to a stabilization of the transition state by the lithium counterion,31 and could thus be suppressed by using AlH3 which was freshly prepared from LiAlH4 with concentrated sulfuric acid in THF solution.8,31,32 A CMN cleavage resulting in a degradation of the polymer main chain was not observed.During this work, the polyamides 3 (PEI-3,4) and 4 (PEI-4) could be completely reduced to the polyamines 6 (PA-3,4) and 5 (PA-4), respectively, using a fivefold excess of aluminium hydride (Scheme 1). reaction was followed by IR spectroscopy, monitoring the disappearance of the CNO stretching band at ca. 1640 cm-1 as the reaction proceeded. In addition, 1H NMR spectra of the polyamines in chloroform solution indicated their higher conformational mobility; the signals of the aromatic protons in the side group CH2 CH2 N C R O R C N N N C C N C R R O O O O R OC10H21 OC10H21 R C N HN N C C NH C R R O O O O R 22 3 g 61 fh 120 i R = 2 c 99 (fh 93) i 1 c 108 Dh 154 i which could only be detected as single broad peaks for the Fig. 2 Thermal phase behavior of cyclic and linear oligoamides as polyamides were now split into doublets. Similar behavior has well as linear polymers based on the same N-benzoylated ethyleneimine been observed for the corresponding azacrown derivatives.19 unit (in °C, g=glassy; c=crystalline; wh=hexagonal columnar; i= isotropic) Poly(N-4-decyloxybenzylethyleneimine), 5 (PA-4).LiAlH4 in THF (Aldrich) (1 M; 10 ml ) was stirred under a dry stream of It was supposed that further typical mesomorphic features nitrogen at 0 °C. After dropwise addition of concentrated of substituted macrocyclic oligoamides may be transferred to H2SO4 (0.26 ml) the mixture was stirred for an additional hour the analogous linear polymers.24 In an earlier communication, during which time the evolution of hydrogen could be observed, we have already addressed this point and briefly described the and a white precipitate was formed.This freshly prepared induction of liquid crystalline phases in linear polyamines via AlH3 solution was filtered under argon. Then, 400 mg complexation of transition metal ions.28 Continuing this work, (1.32 mmol) of poly(N-4-decyloxybenzoylethyleneimine), 4 we now present a more detailed discussion of this concept (PEI-4, n=85), in dry THF was added slowly, and the resulting in combination with the first structural studies by X-ray reaction mixture was stirred at room temp.overnight. The diVraction. next day, excess of AlH3 was destroyed by the addition of 3 ml THF–H2O (151 v/v), the solvent was distilled oV, and the white residue dissolved in a 151 mixture of 1 M NaOH and Experimental dichloromethane.The organic layer was washed with water, Materials dried with sodium sulfate, and concentrated by evaporating most of the solvent. The white polymer was precipit- The chemicals and solvents (p.a. grade) used for synthesis were ated in cold acetone.Yield: 265 mg (69%); dH (CDCl3, purchased from Merck and were used as obtained without 200 MHz) 0.87 [t, 3H, CH3(CH2)9O], 1.15–1.5 [br, 14H, further purification unless explicitly stated. THF used for the CH3(CH2)7CH2CH2O], 1.68 [t, 2H, CH3(CH2)7CH2CH2O], polymer analogous reduction of linear polyamides was freshly 2.40 [br, 4H, CH2NCH2], 3.35 [br, 2H, NCH2Ar], 3.81 [t, distilled after refluxing over potassium in a nitrogen atmosphere for several hours. 2H, CH3(CH2)8CH2O], 6.70 (d, 2H, Ar H-3,5), 7.02 (d, 2H, Ar 344 J. Mater. Chem., 1998, 8(2), 343–351Fig. 3 Helical arrangement of the N-acylated polyethyleneimine 3 (PEI-3,4) in a possible energetically favored conformation (for matters of simplification only the atoms of the polymer backbone are shown; thus note that most of the apparent free volume in the center of the column is actually filled with hydrogen atoms) CH2 CH2 N C O OC10H21 CH2 CH2 N CH2 OC10H21 R R CH2 CH2 N CH2 OC10H21 R n n i n ii Cu2+/4 PEI-3,4 3 R = OC10H21 PEI-4 4 R = H PA-4 5 R = H PA-3,4 6 R = OC10H21 PCu-4/NO3 7 R = H, X– = NO3 – PCu-4/OAc 8 R = H, X– = CH3COO– PCu-3,4/OAc 9 R = OC10H21, X– = CH3COO– Scheme 1 Reagents and conditions: i, AlH3, THF, 0 °C, 16 h; ii, copper(II) nitrate (7) or copper(II) acetate (8, 9), THF or CH2Cl2–H2O, room temp., 1–3 d H-2,6); nmax (KBr)/cm-1 2956, 2923, 2852, 2826 (CH2), 1617, (C/N=26.82); degree of substitution calculated from C/N ratio >95%]. 1511, 1464 (CNC), 1246 (CMO) [Calc. for C19H31NO: C, 78.84; H, 10.79; N, 4.84 (C/N=16.29).Found: C, 78.11; H, 10.93; N, 5.07% (C/N=15.41); degree of substitution calculated Preparation of polyamine–copper complexes from C/N ratio: ca. 93%]. The binding of Cu2+ and Ni2+ to branched polyethyleneimine, resulting in the first known polyamine–metal complexes, was Poly[N-3,4-bis(decyloxy)benzylethyleneimine], 6 (PA-3,4). The reaction proceeded in the same way as described for 5 described in 196333 and has recently been reviewed.34 In the work presented here, the complexes were prepared as described (PA-4), starting from 1.0 g (2.2 mmol) of poly[N-3,4-bis- (decyloxy)benzoylethyleneimine], 3 (PEI-3,4, n=85), 15 ml earlier for N-benzylated azamacrocycles,8 by adding a solution of the polyamine in THF or dichloromethane to an excess of (15 mmol) of 1 M LiAlH4-solution in THF and 0.25 ml of concentrated H2SO4. Yield: 620 mg (63%); dH (CDCl3, the metal salt (Scheme 1).The latter was either dissolved in water or used as a solid (which for the cases of nitrates and 200 MHz) 0.85 [t, 6H, CH3(CH2)9O], 1.15–1.5 [br, 28H, CH3(CH2)7CH2CH2O], 1.70 [m, 2H, CH3(CH2)7CH2CH2O], acetates, which are partially soluble in THF, yielded a homogeneous reaction mixture).The resulting mixtures were stirred 2.35 ( br, 4H, CH2NCH2), 3.30 (br, 2H, NCH2Ar), 3.80 [m, 4H, CH3(CH2)8CH2O], 6.5–6.65 (m, 2H, Ar H-2,5), 6.7 (br, for one to several days, although in most cases the complexation was indicated by a dark blueish or greenish color of 1H, Ar H-6); nmax (KBr)/cm-1 2935, 2849 (CH2); 1525, 1469 (CNC); 1260 (CMO) [Calc. for C29H51NO2: C, 78.15; H, 11.53; the organic phase almost instantaneously. After removal of the solvent, the resulting residues were dissolved in dichloro- N, 3.14 (C/N=24.89).Found: C, 76.18; H, 11.10; N, 2.84% J. Mater. Chem., 1998, 8(2), 343–351 345methane and washed with water several times, and filtered observed using an Ortholux II POL-BK (Leitz) microscope. For the photographs of the observed textures Olympus SC 35 through a 0.45 mm Teflon filter to remove traces of the metal salt.After distillation, the solid complexes were dissolved in (type 12) and Kodak-Ektachrome 400 ASA film material was used. DiVerential scanning calorimetry (DSC) measurements benzene, filtered again and finally freeze-dried. As an example, the analytical data of 7 (PCu-4/NO3) were performed with a DSC-7 (Perkin-Elmer) microcalorimeter using an Epson-PC and DSC-7 multitasking software (Perkin- obtained by reaction of polyamine 5 (PA-4) with copper(II) nitrate are as follows: blue–green powder; dH (CDCl3, Elmer) for data evaluation.Calibration standards were indium and lead. Prior to the measurements, 3–10 mg of the substances 200 MHz) 0.87 [t, 3H, CH3(CH2)9O], 1.15–1.50 [br, 14H, CH3(CH2)7CH2CH2O], 1.70 [t, 2H, CH3(CH2)7CH2CH2O], were sealed in aluminium pans.Observed peak maxima are given as the first order transition temperatures; the inflection 2.60–3.40 ( br, 4H, CH2NCH2), 3.25–4.10 [br, 4H, NCH2Ar and CH3(CH2)8CH2O], 6.70 (d, 2H, Ar H-3,5), 7.01 (d, 2H, points for the DSC traces are taken as the glass transitions.X-Ray structural investigations were performed with Cu-Ka- Ar H-2,6); nmax (KBr)/cm-1 2953, 2923, 2850 (CH2), 1612, 1514, 1468 (CNC), 1385 (NMO, nitrate counterion), 1305, radiation (l=0.1541 nm). The diVracted radiation was analyzed using a graphite monochromator and a Siemens X-1000 1252 (CMO), 1163, 1030, 818; l (THF)/nm 665 (e= 40 l mol-1 cm-1) [Found: C, 67.44; H, 9.49; N, 6.30% (C/N= flat plate detector or a flat picture camera at diVerent sample– detector distances.The temperature of the samples was con- 10.71]. Assuming nitrate as the only counterion 21.7% copper( II ) ions per repeating unit were calculated, resulting in an trolled with an accuracy of 0.1 °C by a Linkam THM 600 heating stand. average composition of CuL4.7 (L=amino ligand).§ For the complexation of diVerent central ions (Ni2+, Co2+, UO22+) and the use of other counterions (SO42-, Cl-, BF4-) Results and Discussion during this work, the procedure as described above was used.Complexation of transition metal ions by N-alkylated However, it seems that this approach cannot be generalized: polyethyleneimines using copper chloride, copper sulfate or copper tetrafluoroborate which are not soluble in suitable organic solvents, the The complexation of the polyamines 5 (PA-4) and 6 (PA-3,4) reaction had to be performed in heterogeneous media.Also, was followed using diVerent spectroscopic techniques, as will most complexation attempts with other metal cations (regardbe discussed for the single-chain substituted polyamine–copper less of the counterion) failed so far, both in homogeneous as system 7 (PCu-4/NO3).Fig. 4(a) shows the FT-IR spectra of well as in heterogeneous reaction media. Only for the system the complex and of the pure polyamine ligand 5 (PA-4). As in 5 (PA-4)/Ni(NO3)2 was the preparation of a polymer–metal the case of low molecular mass azacrown derivatives,8 the CHcomplex achieved in THF solution.The optimization of the stretching band at n=2830 cm-1 disappeared, which can be experimental conditions to promote the polymer–metal comrelated to the methylene group next to the amino donor in the plex formation has yet to be investigated.¶ polymer main chain. The influence of the complexation was also seen in the 1H NMR spectrum [Fig. 4(b)]. As compared Characterization to the relatively high mobility of the polyamine ligand, which in that case led to narrower peaks as well as to a doublet 1H NMR spectra were recorded with a 200 MHz FT–NMR splitting of the aromatic signals, the bands were significantly Spectrometer AC-200 (Bruker).Infrared (IR) spectra were broadened for the metal complex. This was particularly pro- recorded from KBr pellets of the materials with an FT-IR nounced for the resonances of the amino methylene protons spectrometer 5DXC (Nicolet).UV–VIS absorption spectra which, in addition, are shifted to lower field. For the pure were measured in quartz cuvettes (Hellma) with a Lambda 5- polyamine ligand 5 (PA-4) they were detected at d=2.4 (main spectrometer (Perkin-Elmer) using UVASOL grade solvents chain) and d=3.4 (side chain), whereas for the complex 7 (Merck).For polarizing microscope investigations, thin films (PCu-4/NO3) two broad signals were found at d=2.6–3.4 and of the compounds prepared on microscopic slides were d=3.4–4.0. Finally, the ligand–metal interaction could be observed by § The authors wish to apologize for an error in the elemental analysis UV–VIS spectroscopy (spectra not shown here).A broad data given for complex 7 (PCu-4/NO3) in ref. 28. By mistake, the shoulder (l=310 nm) of the aromatic absorption band (lmax= calculated data for the ligand 5 (PA-4) instead of the experimental 275 nm) as well as a very weak d–d band of the central atom data for the complex were reported there. This error has been corrected at l=665 nm (e=40 l-1 mol-1 cm-1) were detected. Because here.Also note that, although found useful for the determination of the average copper–ligand ratio in the complexes with nitrate coun- an exact determination of the coordination number of the terion, the same calculation for the compounds obtained with cop- central ions could not be achieved in all cases,§ it should be per(II ) acetate did not yield meaningful values.From the analytical mentioned that several remarks on the complexation of transdata of 8 (PCu-4/OAc) an average composition CuL2 was calculated. ition metal cations with branched and linear polyethyleneimine Despite repeated filtration the complex seemingly still contains traces have been given in the literature.33–35 Based on this, the low of copper(II) acetate.This also resulted in two sharp reflections in the molar extinction coeYcient may be explained by the polymeric wide angle region of the X-ray diVraction pattern as well as in a very weak first order transition at 116 °C in the DSC scans corresponding nature of the ligand resulting in a less defined complexation to the melting point of the copper salt. However, for 9 (PCu-3,4/OAc) of the CuII ions, since in addition to the expected fourwhich evidently does not contain inorganic impurities an even higher coordination, a possible five-coordination has to be taken into value for the copper content was evaluated.Obviously, the basic account as well.34,36,37 assumption for the calculation, accounting for only one counterion species, does not hold for the complexes obtained from copper acetate.Characterization of thermal phase behavior ¶ Interestingly, the extraordinary stability of complexes formed by copper and branched polyethyleneimine even in acidic solution has In analogy to the cyclic low molecular mass derivatives,8 the been reported in this context (cf. B. L. Rivas and K. E. Geckeler, Adv. corresponding polyamines 5 (PA-4) and 6 (PA-3,4) obtained Polym.Sci., 1992, 102, 173), which even served for the separation of Cu2+ from other metal ions (cf. K. E. Geckeler, E. Bayer, G. A. by polymer analogous reduction from the polyamides 4 (PEIVorob’eva and B. Y. Spivakov, Anal. Chim. Acta, 1990, 230, 171). As 4) and 3 (PEI-3,4), respectively, are partially crystalline matein general, metal complexes of branched polyethyleneimine are con- rials that do not form liquid crystalline phases before melting siderably more stable than those of the linear polymer (cf.S. Kobayashi, into an isotropic liquid (Fig. 5). As in the case of the cyclic K. Hiroishi, M. Tokunoh and T. Saegusa, Macromolecules, 1987, 20, oligomers, this can be attributed to the higher conformational 1496), the observed problems for most metal ions may be explained flexibility of the N-alkylated polymers as compared to the and thus also point to the stability of the copper–polyethyleneimine coordination compounds.N-acylated compounds. 346 J. Mater. Chem., 1998, 8(2), 343–351The latter model resembles the proposed structure for the observed hexagonal columnar mesophase of the corresponding linear polyamides,22,24 and would be comparable with the helical crystal structures of metal complexes formed, e.g.by oligopyridine ligands.38,39 On the other hand, a lamellar layered structure would be in agreement with smectic mesophases observed for diVerent organometal complexes of CuII.40 Due to the observed decomposition of the complex nitrate at elevated temperatures, the introduction of the acetate ion was investigated.Although the thermal stability of the obtained compound 8 (PCu-4/OAc) was only slightly improved, this approach proved successful in so far as the simultaneous decrease of the clearing point below the decomposition temperature now allowed the heating of the material to the isotropic state. On first heating under the polarizing microscope (by 10 °C min-1), the complex formed an unspecific texture which slowly cleared at ca. 94°C (last anisotropic domains disappeared at ~105 °C). On decreasing the temperature, the sample showed a considerable supercooling of the clearing point to 72 °C. The growth of typical ba�tonets41 which eventually resulted in the formation of a fan-shaped texture (Fig. 7) at that temperature points to the existence of a smectic mesophase.In addition, the sample could be sheared easily even after cooling down to 40 °C, until at room temperature a marked increase of the viscosity of the material was observed. The behavior was reversible in the following heating and cooling cycles. The copper complex 9 (PCu-3,4/OAc) obtained from the double side chain polyamine 6 (PA-3,4) and copper(II) acetate was obtained as a highly viscous and sticky material.Under the polarizing microscope, a Schlieren texture indicating a nematic mesophase was observed [Fig. 8(a)] at room temperature. On cooling from the isotropic liquid phase (T ca. 75°C), typical ‘Maltese crosses’ were formed within an almost completely homotropically oriented sample [Fig. 8(b)]. In DSC measurements, 8 (PCu-4/OAc) showed a glass transition at ca. 10°C and two first order transitions at 67 and 98 °C [in addition, a very weak signal at 116 °C was detected Fig. 4 Complexation of copper(II) ions by N-alkylated polyethylene- which can be related to residual traces of copper(II) acetate]. imines as follow by spectroscopic investigations on 7 (PCu-4/NO3); Whereas the latter corresponds to the microscopically deter- (a) 1H NMR spectrum (200 MHz, CDCl3, room temp.); (b) FT-IR mined transition to the isotropic melt, the nature of the first spectrum (KBr pellet) transition could not be completely clarified.As the material could be easily sheared in the microscopic investigations at 40 °C, the first peak may be related to a transition between Based on the results for the low molecular mass derivatives (Fig. 1) where a columnar mesophase was found for complexes two liquid crystalline mesophases. On cooling however, only one peak at 70 °C was detected next to the glass transition. formed from the macrocyclic ligand bearing a single-chained 4-alkoxybenzoyl substituent and copper nitrate,8 the investi- Considering the higher cooling rate used in the DSC measurements (10 °C min-1), this is in good agreement with the gation of the polymeric complex 7 (PCu-4/NO3) appeared most promising.Indeed, thermotropic liquid crystalline observations under the polarizing microscope, where a supercooling of the clearing point and the growth of a fan-shaped behavior was observed for this complex as described in an earlier communication.28 Under the polarizing microscope, a texture at ca. 72°C were seen. Thus, the anisotropic domains observed on heating above 72 °C could also be related to a rather unspecific, but shearable texture was observed above the determined glass transition at 53 °C. However, decompo- biphasic behavior of the material above that temperature. The curves of 9 (PCu-3,4/OAc) showed a first order melting trans- sition of the material was observed above 160 °C, and the observed texture completely disappeared at 173 °C.A more ition in the same temperature region in which the glass transition of 8 (PCu-4/OAc) was detected. The clearing tem- detailed analysis of the phase behavior by microscopic investigation was thus not possible. perature of 68 °C agreed with the microscopic observations.The transition temperatures of the copper(II ) complexes 7 By X-ray diVraction, the existence of a thermotropic liquid crystalline phase for 7 (PCu-4/NO3) now could be ultimately (PCu-4/NO3), 8 (PCu-4/OAc), and 9 (PCu-3,4/OAc) as determined from DSC are listed in Table 1. proven. However, the exact determination of the phase type still remains unclear. In the diVraction pattern, next to a broad X-Ray investigations on a powder sample of 8 (PCu-4/OAc) cooled from the isotropic phase to room temperature proved halo at ~4.6 A ° which corresponds to the disordered alkyl side chains, only a first order Bragg peak was found which allowed the liquid crystalline character of the material.Next to the first order Bragg reflection with a corresponding lattice param- calculation of the lattice parameter as d001 ~35.5 A ° .For this material, the absence of mixed or higher order reflections still eter d001=34.9 A ° , two very weak signals were detected in the low angle region of the flat camera picture [Fig. 9(b)]. Their prevents the experimental distinction between a lamellar mesophase structure [Fig. 6(b)] and a cylindrical complex structure, corresponding spacings of 17.5 A ° (ca.d001/2) and ca. 11.5 A ° (ca. d001/3) identify them as the (002) and (003) reflections of as resulting for instance from a helical arrangement of the polyamine main chain around the central copper ions a lamellar structure in which the copper ions are complexed by the amino head groups of polyamine bilayers. In the wide [Fig. 6(c)]. J. Mater. Chem., 1998, 8(2), 343–351 347Fig. 5 Thermotropic phase behavior of N-alkylated polyethyleneimines 5 (PA-4) and 6 (PA-3,4) (in °C, taken from second DSC heating scan, scan rate: 10 °C min-1); g=glassy; c=crystalline; i=isotropic. * The sample could be sheared under the polarizing microscope below the detected first order transition, proving the semicrystalline nature of the polymer, so that a glass transition has to be assumed below 40 °C (not unambiguously detected in the DSC scans).Fig. 6 Schematic representation of possible structures of the polyamine–copper complex 7 (PCu-4/NO3) within the thermotropic mesophase; (a) layered structure; (b) columnar structure. angle region [Fig. 9(a)], a broad halo of the alkyl chains with diVractogram of the polyamine–copper complex 9 (PCu- 3,4/OAc) measured at room temperature [Fig. 10(a)] exhibited a maximum at ca. 4.8 A ° was found. In addition, 8 (PCu- 4/OAc) showed two additional sharp reflections at 2h ca. 29° a rather broad, but pronounced Bragg peak in the small angle region at 2h ca. 2.7° from which a spacing of ca. 32.8 A° was and ca. 44° (ca. 3.0 and ca. 2.0 A° , respectively) which can be attributed to residual traces of copper acetate (compare dis- calculated; mixed or higher order reflections were not found.In the flat camera picture shown in Fig. 10(b), next to the cussion of DSC results). Contrary to expectations which were based on the nematic Bragg peak (from which a slightly higher value of ca. 34A ° was determined) and the halo related to the alkyl chains at texture observed in polarizing microscopy, the X-ray 348 J.Mater. Chem., 1998, 8(2), 343–351Fig. 7 Microscopic texture of 8 (PCu-4/OAc) after cooling to 70 °C from the isotropic phase with 1 °C min-1 Fig. 9 X-Ray flat camera picture of 8 (PCu-4/OAc) after cooling from the isotropic phase to the liquid crystalline state: (a) complete picture; (b) low angle region 4.4 A ° (halo 2), an additional weak halo at ca. 7.3 A ° (halo 1) was measured. This is particularly interesting as this distance coincides with the proposed pitch height of a helically wound polymer main chain in the model shown in Fig. 2 for the mesomorphic linear polyamide 3 (PEI-3,4). Based on the X-ray data, a layered structure also seems possible for 9 (PCu-3,4/OAc). However, considering the comparably high width of the Bragg peak and the microscopic textures observed, the results point to a nematic columnar phase.This assumption appears reasonable since in comparison with the complexes 7 (PCu-4/NO3) and 8 (PCu-4/OAc) of the polyamine ligand 5 (PA-4) which bear only one side chain per Fig. 8 Microscopic textures of 9 (PCu-3,4/OAc): (a) room temperature, polymer repeating unit, and which both form layered structures directly after preparation; (b) after cooling to 42 °C from the isotropic [Fig. 11(a)], a higher number of side chains have to be phase with 1 °C min-1 incorporated in the aggregates of the double chain derivative Table 1 Phase transition temperatures of copper(II)-polyamine complexes 7(PCu-4/NO3), 8(PCu-4/OAc), and 9(PCu-3,4/OAc) given in °C (taken from the second DSC heating scan measured with a scan rate of 10 °C min-1, for 8(PCu-4/OAc) the thermal transitions in the first cooling curve are also shown): g, glassy; c, crystalline; SX, unidentified smectic/lamellar structure; SA, smectic A/lamellar; NC, nematic columnar; i, isotropic DSC scan T / °C 7 from 5 (PA-4) and Cu(NO3)2 2nd heating g 53 lc 173 (decomp.) 8 from 5 (PA-4) and Cu(OAc)2 2nd heating g 11 c/SX 67 SA 98 i 1st cooling g 10 SA 70 i 9 from 6 (PA-3,4) and Cu(OAc)2 2nd heating c 12 NC 68 i J.Mater. Chem., 1998, 8(2), 343–351 349be wound helically around the central copper ions. On the other hand, more than one polymer chain may constitute the columnar packing which may even result in a crosslinked structure, in which single polymer chains may participate in more than one column.However, based on the observed low viscosity of the material within the mesophase the latter model appears least likely. On the other hand, the packing of several polymer chains in the second model would aVord a much higher order than a single more or less helically folded chain. In addition, although in each model the additional halo found at 7.3 A ° in the flat camera picture could correspond to an average distance of copper atoms in the center of complex sub-units along such columns, the obvious similarity of this distance with the pitch height in the helical model discussed for N-substituted linear polyethyleneimines (Fig. 3) lets us favor the first structural model. Conclusions By polymer analogous reduction of the benzamide group in linear polyamides, N-alkylated polyethyleneimines were obtained which, due to their high conformational mobility cannot form liquid crystalline mesophases.As in the case of azamacrocycles, a mesophase is formed by the materials after the coordination of the polyamine to CuII. Whereas the discoid molecular structure of cyclic oligomers only allows discotic phases, based on the higher flexibility of the polyamine main chain, the polymeric complexes may also adopt layered structures.In addition, even for a higher side chain density for which a loss of mesomorphic features was observed in the case of macrocyclic complexes, now a presumably nematic columnar Fig. 10 X-Ray diVraction patterns of 9 (PCu-3,4/OAc) at room temmesophase is found.Although detailed information about the perature: (a) goniometer scan; (b) flat camera picture conformation of the polymeric ligands in the liquid crystalline complexes has yet to be elucidated, the general principle of mesophase induction by metal ion complexation could be proven for the materials discussed. The results described again show the analogy between low molecular mass cyclic derivatives and linear polymers composed of the same basic monomer unit and are therefore of general interest in polymer liquid crystal research.In addition, based on their complex nature, numerous interesting possibilities for tailoring the physical properties of mesomorphous polymer systems appear. For instance, by simple variation of structural features such as the metal ion, the side chain density or by the introduction of chiral centers into the polyamine ligand, physical parameters such as thermotropic phase behavior and also the optical properties of the materials could be tuned.References 1 (a) J.-M. Lehn, Angew. Chem., Int. Ed. Engl., 1988, 27, 89; (b) J.-M. Lehn, Angew. Chem., Int. Ed. Engl., 1990, 29, 1304; (c) J.-M.Lehn, Supramolecular Chemistry, VCH Verlagsgesellschaft, Weinheim, 1995. 2 F.Vo� gtle, Supramolecular Chemistry, Wiley, New York, 1991. 3 E. C. Constable, Nature, 1990, 346, 314. 4 M.-J. Brienne, J. Gabard, J.-M. Lehn and I. Stibor, J. Chem. Soc., Chem. Commun., 1989, 1868. Fig. 11 Schematic representation of the possible structures of polyam- 5 (a) T. Kato and J. M.J. Fre� chet, J. Am. Chem. Soc., 1989, 111, 8533; ine–copper(II ) complexes within their thermotropic mesophases: (a) (b) T. Kato and J. M. J. Fre� chet, Macromolecules, 1989, 22, 3818. smectic mesophase of 8 (PCu-4/OAc); (b) nematic columnar mesophase 6 (a) G. Lattermann and G. Staufer, L iq. Cryst., 1989, 4, 347; (b) of 9 (PCu-3,4/OAc) M. Ebert, R. Kleppinger, M. Soliman, M.Wolf, J. H. WendorV, G. Lattermann and G. Staufer, L iq. Cryst., 1990, 7, 553. 9 (PCu-3,4/OAc). This is in agreement with the findings 7 W. Paulus, H. Ringsdorf, S. Diele and G. Pelzl, L iq. Cryst., 1991, for the corresponding N-acylated polyethyleneimines where 9, 807. 8 A. Liebmann, C. Mertesdorf, T. Plesnivy, H. Ringsdorf and lamellar crystals or hexagonal columnar mesophases were J.H. WendorV, Angew. Chem., Int. Ed. Engl., 1991, 30, 1375. observed for mono- or bis-decyloxysubstituted side groups, 9 C.M. Paleos and D. Tsiourvas, Angew. Chem., Int. Ed. Engl., 1995, respectively.24 34, 1696. As has been discussed before for the original mesomorphic 10 H. Ringsdorf, R. Wu� stefeld, E. Zerta, M. Ebert and J. H. WendorV, polyamides,24 the formation of the complex columnar aggre- Angew.Chem., Int. Ed. Engl., 1989, 28, 914. gates may be explained by several diVerent structural models 11 (a) V. Percec, G. Johansson, J. Heck, G. Ungar and S. V. Batty, J. Chem. Soc., Perkin T rans. 1, 1993, 1411; (b) V. Percec, [Fig. 11(b)]. For instance, a single polymer main chain may 350 J. Mater. Chem., 1998, 8(2), 343–351G. Johansson, D. Schlueter, J.C. Ronda and G. Ungar,Macromol. 30 V. M. Micovic and M. L. Mihailovic, J. Org. Chem., 1953, 18, 1190. 31 N. M. Yoon and H. C. Brown, J. Am. Chem. Soc., 1968, 90, 2927. Symp., 1996, 101, 43. 12 J. L. M. van Nunen, R. S. A. Stevens, S. J. Picken and 32 T. Saegusa, S. Kobayashi and M. Ishiguro, Macromolecules, 1974, 7, 958. R. J. M. Nolte, J. Am. Chem. Soc., 1994, 116, 8825. 13 (a) D. A. House, in Comprehensive Coordination Chemistry, ed. 33 H. Thiele and K.-H. Gronau,Makromol. Chem., 1963, 59, 207. 34 (a) A. von Zelewsky, L. Barbosa and C. W. Schla�pfer, Coord. Chem. G. Wilkinson, Pergamon Press, Oxford, 1987, p. 23; (b) F. A. Cotton and G. Wilkinson, Advanced Inorganic Chemistry, Rev., 1993, 123, 229; (b) B. L. Rivas and K. E. Geckeler, Adv. Polym. Sci., 1992, 102, 173.Wiley, New York, 1988. 14 R. D. Hancock and A. E. Martell, Chem. Rev., 1989, 89, 1875. 35 S. Kobayashi, K. Hiroishi, M. Tokunoh and T. Saegusa, Macromolecules, 1987, 20, 1496. 15 J. M. Lehn, J. Malthe�te and A. M. Levelut, J. Chem. Soc., Chem. Commun., 1985, 1794. 36 U. Stebani, G. Lattermann, M. Wittenberg and J. H. WendorV, Angew. Chem., Int. Ed. Engl., 1996, 35, 1858. 16 G. Lattermann, L iq. Cryst., 1989, 6, 619. 17 S. Bauer, T. Plesnivy, H. Ringsdorf and P. Schuhmacher, 37 (a) J. Arago� , A. Bencini, A. Bianchi, E. Garcia-Espan� a, M. Micheloni, P. Paoletti, J. A. Ramirez and P. Paoli, Inorg. Chem., Makromol. Chem., Macromol. Symp., 1992, 64, 19. 18 C. Mertesdorf and H. Ringsdorf, Molecular Engineering, 1992, 2, 1991, 30, 1843; (b) B. J. Hathaway and A.A. G. Tomlinson, Coord. Chem. Rev., 1970, 5, 1. 189. 19 D. Tatarsky, K. Banerjee and W. T. Ford, Chem. Mater., 1990, 38 (a) J. M. Lehn, A. M. Rigault, J. Siegel, J. Harrowfield, B. Chevrier and D. Moras, Proc. Natl. Acad. Sci. USA, 1987, 84, 2565; (b) 2, 138. 20 G. Lattermann, S. Schmidt, R. Kleppinger and J. H. WendorV, J.-M. Lehn and A. Rigault, Angew. Chem., 1988, 100, 1121; (c) U. Koert, M. M. Harding and J.-M. Lehn, Nature, 1990, 346, 339; Adv. Mater., 1992, 4, 30. 21 G. Lattermann, S. Schmidt and B. Gallot, J. Chem. Soc., Chem. (d) E. C. Constable, S. M. Elder, J. Healy, M. D. Ward and D. A. Tocher, J. Am. Chem. Soc., 1990, 112, 4590. Commun., 1992, 1091. 22 H. Fischer, S. S. Ghosh, P. A. Heiney, N. C. Maliszewskyj, 39 (a) A. F. Williams, C. Piguet and G. Bernardinelli, Angew. Chem., Int. Ed. Engl., 1991, 30, 1490; (b) C. Piguet, G. Bernardinelli, T. Plesnivy, H. Ringsdorf and M. Seitz, Angew. Chem., Int. Ed. B. Bocquet, A. Quattropani and A. F. Williams, J. Am. Chem., Soc., Engl., 1995, 34, 795. 1992, 114, 7440; (c) A. Williams, Chem. Eur. J., 1997, 3, 15. 23 U. Stebani and G. Lattermann,Macromol. Rep., 1995, A32, 385. 40 (a) C. Carfagna, U. Caruso, A. Roviello and A. Sirigu, Makromol. 24 M. Seitz, T. Plesnivy, K. Schimossek, M. Edelmann, H. Ringsdorf, Chem., Rapid Commun., 1987, 8, 345; (b) U. Caruso, A. Roviello H. Fischer, H. Uyama and S. Kobayashi, Macromolecules, 1996, and A. Sirigu, Macromolecules, 1991, 24, 2606; (c) K. Hanabusa, 29, 6560. J.-I. Higashi, T. Koyama, H. Shirai, N. Hojo and A. Kurose, 25 U. Stebani and G. Lattermann, Adv. Mater., 1995, 7, 578. Makromol. Chem., 1989, 190, 1; (d) L. Oriol and J. L. Serrano, Adv. 26 U. Stebani, G. Lattermann, M. Wittenberg and J. H. WendorV, Mater., 1995, 7, 348. J.Mater. Chem., 1997, 7, 607. 41 (a) D. Demus and L. Richter, T extures of L iquid Crystals, VEB 27 J. H. Cameron, A. Facher, G. Lattermann and S. Diele, Adv. Deutscher Verlag fu� r GrundstoYndustrie, Leipzig, 1978; (b) Mater., 1997, 9, 398. G. W. Gray and J. W. G. Goodby, Smectic L iquid Crystals: 28 H. Fischer, T. Plesnivy, H. Ringsdorf and M. Seitz, J. Chem. Soc., T extures and Structures, Leonard Hill, Glasgow, 1984. Chem. Commun., 1995, 1615. 29 T. Saegusa, A. Yamada, H. Taoda and S. Kobayashi, Macromolecules, 1978, 11, 435. Paper 7/05592G; Received 1st August, 1997 J. Mater. Chem., 1998, 8(2),

ISSN:0959-9428    

DOI:10.1039/a705592g

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials EVects of nitro substituents on the properties of a ferroelectric liquid crystalline side chain polysiloxane Magnus Svensson,a Bertil Helgee,*a Kent Skarpb and Gunnar Anderssonb aDepartment of Polymer T echnology, Chalmers University of T echnology, S-412 96 Go�teborg, Sweden bDepartment of Physics, Chalmers University of T echnology, S-412 96 Go�teborg, Sweden The syntheses of chiral liquid crystalline side chain polysiloxanes with lateral nitro substituents in the mesogenic core are described. The influence of the substituents and substituent positions on phase behaviour and electro-optical properties are investigated and compared.The lateral nitro groups strongly aVect the phase behaviour of the side chain precursors as well as the liquid crystalline polymers.Properties in smectic A and C* phases are discussed with respect to substituent position. One side chain precursor exhibits very large spontaneous polarization of ~700 nC cm-2. The possibility of designing and using chiral liquid crystalline acid moiety. The nitro group is introduced at the 2- and 3- side chain polymers for technical applications in the future position in the phenyl ester and at the 3¾-position in the depends on the understanding of structure–property relation- biphenyl part.The side-chain precursors are attached to a ships. A vast number of new molecules, architectures and poly(dimethyl-co-methylhydrogen)siloxane backbone. It was concepts of chiral liquid crystalline side chain polymers have found that the introduction of substituents changes the phase been synthesized, examined and reported1,2 since the first behaviour dramatically depending on position.One of the ferroelectric liquid crystalline polymer was prepared by Shibaev side-chain precursors only exhibits a 10 °C temperature interval et al.3 in 1984. Research on the eVects of structural changes in of the N*-phase but in the corresponding polymer smectic the diVerent parts of the mesogens like the chiral centre,4,5 phases over a temperature range of 70 °C are again obtained.mesogenic core6–8 and alkyl chain9–11 has been carried out. Another side-chain precursor shows very large spontaneous The influence of the polymer main-chain on properties has polarization (nearly 700 nC cm-2).25,26 The same system shows also been investigated.12–17 Nevertheless, a large part of today’s interesting NLO-properties reported earlier,27 where a controlinformation on structure–property relationships in chiral liquid lable SHG-intensity in the smectic A phase was described for crystalline polymers relies on extrapolations from research on the first time.For the reference system (without nitro substitulow molar mass liquid crystals performed during the 1970s.ent), both the low molar mass mesogen and the polymeric Concerning lateral substituents Osman18 has shown that liquid crystal have been described in detail previously.24,28 steric eVects and thereby the van der Waals volume of the substituent are usually more important with respect to phase Experimental behaviour than dipolar interactions.The more detailed influences of lateral substituents depend on the structure of the Techniques rigid core and the position of the substituent. Generalizations 300 MHz 1H NMR spectra were obtained using a Varian are diYcult, since the eVects diVer between polar and non- VXR300 spectrometer. All spectra were run in CDCl3 or [2H6] polar mesogens and probably also change from low molar mass to polymer liquid crystals.Using electron attracting DMSO solutions. Infrared spectra were recorded on a Perkinsubstituents Masuda et al.19 showed that substituents in the Elmer 2000 FT-IR spectrophotometer using KBr pellets. The centre of the mesogenic core not only increased the intermol- phase behaviour of the diVerent materials was identified by ecular distance, thus destabilizing the liquid crystal behaviour, combining optical microscopy, diVerential scanning calorbut also hindered the formation of smectic phases.With imetry and electro-optical measurements. Optical microscopy multiple substituents where the second and/or third does not was performed using a Mettler FP82HT hot stage, Mettler increase the steric eVect but adds possibilities for polar inter- FP80HT central processor and an Olympus BH-2 polarizing actions the smectic phases can be regained.20 A study by Hird microscope.DSC measurements were recorded on a Perkinet al.21 shows the same tendencies. Elmer DSC 7 diVerential scanning calorimeter. The nitro group with its large dipole moment and electron attracting power oVers a way to drastically change the electron Materials distribution in the aromatic core.This has been used to Materials and reagents were of commercial grade quality and enhance NLO-eVects such as second harmonic generation used without further purification unless otherwise noted. Dry (SHG) in liquid crystals and in liquid crystalline polymers.22,23 toluene and methylene chloride were obtained by passing the In the present paper we have studied the eVect of introducing solvents through a bed of aluminium oxide (ICN Alumina a nitro substituent at various aromatic positions in a 4¾- N-Super I).(+)-2-(4-Hydroxyphenoxy)propionic acid was gen- alkoxybiphenyl-4-carboxylic acid phenyl ester mesogen. The erously provided by BASF. Poly(dimethylsiloxane-co-methyl- nitro group was chosen to increase the spontaneous polarizhydrosiloxane) with a copolymer ratio 2.7/1 and a degree of ation in the chiral smectic C phase.We were particularly polymerization of ca. 30 (according to manufacturer) and interested in how a strong dipole at diVerent locations in the the hydrosilylation catalyst dicyclopentadienylplatinum(II) polarizable aromatic core would change phase behaviour and dichloride were obtained from Wacker Chemie.Size-exclusion electro-optical properties of a ferroelectric liquid crystalline chromatography (SEC) analysis in chloroform of the copoly- polymer24 having a very broad smectic C* phase and good alignment properties. The chiral group is a substituted lactic mer performed at 30 °C on a Waters WISP712 instrument J.Mater. Chem., 1998, 8(2), 353–362 353HO CH3O CH3 O O CH3O O OH CH3O O OH NO2 HO O OH NO2 HO O OH O O OH O O OH NO2 i ii iii iv v vi v vi 1 2 3 4 5b 5a 6a 6b Scheme 1 Reagents: i, MeI, KOH, DMF; ii, AcCl, AlCl3, CH2 Cl2; iii, Br2, KOH, 1,4-dioxane; iv, HNO3, AcOH; v, HBr, AcOH; vi, undecenyl bromide, KI, EtOH equipped with three commercial Styragel columns and Waters boxylic acid 3 following closely the procedure reported by Percec et al.29 410 refractive index detector gave M : n=2.6·103 g mol-1 and M : w=5.4·103 g mol-1 with reference to polystyrene standards. 4¾-Methoxy-3¾-nitrobiphenyl-4-carboxylic acid 4. 4¾- Methoxybiphenyl-4-carboxylic acid 3 (0.01 mol, 2.28 g) in Synthesis acetic acid (50 ml ) was refluxed with concentrated nitric acid The synthesis of polymers 14a–d was carried out according to (6 ml) for 15 min.The reaction mixture was poured into water the reactions in Schemes 1–4. All structures were verified by and the precipitate was filtered oV. The product recrystallized 1H NMR spectroscopy and NMR data were in accordance from ethanol to yield 2.2 g (80%). dH ([2H6] DMSO) 3.98 (s, with the structures in all cases. 3 H), 7.48 (d, 1 H), 7.85 (d, 2 H), 8.02 (d, 2 H), 8.07 (dd, 1 H), 8.26 (d, 1 H). 4¾-Hydroxybiphenyl-4-carboxylic acid 5a. The acid was synthesized from 4-hydroxybiphenyl via 4-methoxybiphenyl 1, 4- 4¾-Hydroxy-3¾-nitrobiphenyl-4-carboxylic acid 5b. The acid 5b was synthesized as for 5a starting from 4. dH ([2H6] DMSO) acetyl-4¾-methoxybiphenyl 2 and 4¾-methoxybiphenyl-4-car- O Cl OH HO O O OH O O OH NO2 + HO O OH O * O O O NO2 O O * HO O OH O * NO2 HO O O O * NO2 HO O O O * HO O O O * HO O OH O * NO2 NO2 12a 11 12c 9 10 12b 7 8 i v v ii ii iii iv v Scheme 2 Reagents: i, pyridine, CH2Cl2, N2; ii, HNO3, AcOH, <35 °C; iii, (S)-ethyl lactate, PPh3, diethyl azodicarboxylate, THF, N2; iv, aq.KOH, EtOH; v, BuOH, HCl(g) 354 J. Mater. Chem., 19982), 353–3626a + 12a i (CH2)9 O O O O O H3C O * 13a 6a + 12b i (CH2)9 O O O O O H3C O * 13b NO2 6a + 12c i (CH2)9 O O O O O H3C O * 13c NO2 6b + 12a i (CH2)9 O O O O O H3C O * 13d NO2 Scheme 3 Reagents: i, DCC, DMAP, CH2Cl2 7.25 (d, 1 H), 7.81 (d, 2 H), 7.95 (dd, 1 H), 8.00 (d, 2 H), 8.22 (d, 1 H), 11.3 (s, 1 H). 4¾-( Undec-10-enyloxy)biphenyl-4-carboxylic acid 6a. The hydroxy-acid 5a (0.090 mol, 19.3 g) was dissolved in hot ethanol (1500 ml) and water (75 ml ) together with potassium hydroxide 86% (11.5 g) and a few crystals of potassium iodide.Undec-10-enyl bromide (0.18 mol) was added and the mixture was refluxed for 24 h. To hydrolyse any ester formed a 10% solution of potassium hydroxide in 70% ethanol was added and refluxing was continued for an additional 3 h.The reaction mixture was allowed to cool and was acidified with concentrated hydrochloric acid. The solid formed was recrystallized from acetic acid and ethanol to yield 22.2 g of product (69%). dH ([2H6] DMSO) 1.2–1.5 (m, 12 H), 1.72 (quintet, 2 H), 2.00 (q, 2 H), 4.00 (t, 2 H), 4.96 (m, 2 H), 5.79 (m, 1 H), 7.03 (d, 2 H), 7.67 (d, 2 H), 7.75 (d, 2 H), 7.98 (d, 2 H). 3¾-Nitro-4¾-(undec-10-enyloxy)biphenyl-4-carboxylic acid 6b.The acid 6b was synthesized as for 6a starting from 5b. dH ([2H6] DMSO) 1.2–1.5 (m, 12 H), 1.73 (quintet, 2 H), 2.00 (q, 2 H), 4.21 (t, 2 H), 4.96 (m, 2 H), 5.78 (m, 1 H), 7.47 (d, 1 H), O Si O Si CH3 H CH3 CH3 n m O Si O Si CH3 CH3 CH3 n m + 13a–d m/ n = 2.7 O O O O O O H3C * NO2 14a–d Scheme 4 7.85 (d, 2 H), 7.98–8.06 (m, 3 H), 8.24 (d, 1 H). 4-Hydroxyphenyl benzoate 7. A mixture of hydroquinone (0.15 mol, 16.5 g) and pyridine (0.15 mol) in dry methylene concentrated nitric acid (11 ml ) was added dropwise. The temperature of the reaction mixture was kept below 35 °C. chloride was stirred at room temp. Nitrogen was bubbled through and benzoyl chloride (0.14 mol, 19.6 g) was added After 50 min the reaction mixture was poured into 700 ml of water.The precipitate was collected and purified on a silica slowly. After 2 h additional stirring the solvent was evaporated. The solid was washed with water to remove unreacted hydro- gel column using light petroleum–ethyl acetate (251) as eluent. Yield 5.28 g (51%). dH (CDCl3) 7.24 (d, 1 H), 7.49 (dd, 1 H), quinone and then treated with diethyl ether to dissolve the product; the diester remained as it is less soluble in diethyl 7.55 (t, 2 H), 7.67 (m, 1 H), 8.01 (d, 1 H), 8.19 (dd, 2 H), 10.5 (s, 1 H).ether. After evaporation of solvent the product was recrystallized from ethanol with increasing amounts of water. Yield 18.0 g (60%). dH ([2H6] DMSO–CDCl3) 6.87 (d, 2 H), 7.00 (d, 3-Nitro-4-[(1R)-1-ethoxycarbonylethoxy]phenyl benzoate 9 [2-(4-benzoyloxy-2-nitrophenoxy)propanoic acid ethyl ester]. 3- 2 H), 7.52 (t, 2 H), 7.65 (t, 1 H), 8.16 (d, 2 H), 9.1 (s, 1 H). Nitro-4-hydroxyphenyl benzoate 8 (0.016 mol, 4.15 g), S-ethyl lactate (0.016 mol, 1.89 g) and triphenylphosphine (0.020 mol) 3-Nitro-4-hydroxyphenyl benzoate 8. To hydroquinone monobenzoate 7 (0.04 mol, 8.6 g) in 100 ml of acetic acid, were placed in dry glass equipment with dry THF (100 ml) as J.Mater. Chem., 1998, 8(2), 353–362 355solvent. N2 gas was bubbled through the mixture at room (DMAP) in dry methylene chloride was treated with 4 mmol (0.83 g) of dicyclohexylcarbodiimide (DCC) at 0 °C. The tem- temp. and diethyl azodicarboxylate (0.020 mol) was added during 30 min. After 3 h of additional stirring at room temp.perature was allowed to rise to room temp. and stirring was continued for 3 h. Urea was filtered oV and the filtrate was the solvent was evaporated from the reaction mixture. The resulting solid was dissolved in ethyl acetate and on adding evaporated to dryness. Column chromatography on silica gel with light petroleum–ethyl acetate (951) as eluent gave 1.0 g four times the volume of light petroleum, triphenylphosphine oxide was precipitated.The solution was evaporated to dryness of pure product (80%). [a]D22-28.7 (CHCl3). dH (CDCl3) 0.89 (t, 3 H), 1.2–1.5 (m, 14 H), 1.6 (m, 2H), 1.69 (d, 3 H), 1.80 and the product recrystallized from light petroleum, 4.76 g (83%). dH (CDCl3) 1.26 (t, 3 H), 1.71 (d, 3 H), 4.23 (m, 2 H), (quintet, 2 H), 2.02 (q, 2 H), 4.00 (t, 2 H), 4.15 (m, 2 H), 4.82 (q, 1 H), 4.95 (m, 2 H), 5.80 (m, 1 H), 6.98 (d, 2 H), 7.03 (d, 1 4.84 (q, 1 H), 7.05 (d, 1 H), 7.40 (dd, 1 H), 7.53 (t, 2 H), 7.67 (t, 1 H), 7.79 (d, 1 H), 8.18 (d, 2 H).H), 7.38 (dd, 1 H), 7.58 (d, 2 H), 7.68 (d, 2 H), 7.78 (d, 1 H), 8.18 (d, 2 H). 2-(2R)-(4-Hydroxy-2-nitrophenoxy)propanoic acid 10. To 0.008 mol (2.87 g) of 9 in ethanol (120 ml), 0.016 mol of 4-[(1R)-1-Butoxycarbonylethoxy]-2-nitrophenyl 4¾-(undec- 10-enyloxy)biphenyl-4-carboxylate 13c.From 6a and 12c as for potassium hydroxide in a few millilitres of water was added. The mixture was stirred overnight at room temp. Ethanol was 13b. [a]D22+21.7 (CHCl3). dH (CDCl3) 0.93 (t, 3 H), 1.24–1.43 (m, 12 H), 1.48 (m, 2 H), 1.64 (m, 2 H), 1.69 (d, 3 H), 1.82 evaporated and the product was extracted from methylene chloride with water.Water was evaporated and the solid was (quintet, 2 H), 2.05 (q, 2 H), 4.02 (t, 2 H), 4.21 (t, 2 H), 4.82 (q, 1 H), 4.97 (m, 2 H), 5.82 (m, 1 H), 7.01 (d, 2 H), 7.23 (dd, dissolved in ethyl acetate. The insoluble part was filtered oV and the filtrate was evaporated to dryness and used without 1 H), 7.30 (d, 1 H), 7.6 (d+d, 3 H), 7.70 (d, 2 H), 8.22 (d, 2 H).further purification. dH ([2H6] DMSO) 1.47 (d, 3 H), 4.89 (q, 1 H), 7.01 (dd, 1 H), 7.07 (d, 1 H), 7.19 (d, 1 H), 9.9 (s, 1 H). 4-[(1R)-Butoxycarbonylethoxy]phenyl-3¾-nitro-4¾-(undec-10- enyloxy)biphenyl-4-carboxylate 13d. From 6b and 12a as for 13b. [a]D22+16.0 (CHCl3). dH (CDCl3) 0.92 (t, 3 H), 1.2–1.55 2-(2R)-(4-Hydroxy-3-nitrophenoxy)propanoic acid 11.To a solution of 2-(2R)-(4-hydroxyphenoxy)propanoic acid (m, 16 H), 1.64 (d, 3 H), 1.88 (quintet, 2 H), 2.05 (q, 2 H), 4.17 (m, 4 H), 4.75 (q, 1 H), 4.97 (m, 2 H), 5.82 (m, 1 H), 6.94 (d, 2 (0.027 mol, 5.0 g) in acetic acid (100 ml) concentrated nitric acid (1.5 ml) was added dropwise. The temperature of the H), 7.14 (d, 2 H), 7.18 (d, 1 H), 7.69 (d, 2 H), 7.80 (dd, 1 H), 8.13 (d, 1 H), 8.26 (d, 2 H).reaction mixture was kept below 35 °C. After 30 min the reaction mixture was poured into water. The product was Polymers 14a–d. Dry equipment was used. 0.26 g of poly(di- extracted from the aqueous phase using diethyl ether. No methyl-co-methylhydrogen)siloxane (2.751) (corresponding to further purification was done. Yield 5.1 g (80%).dH ([2H6] 1.0 mmol Si-H) and 1.1 mmol of 13a-d were dissolved in dry DMSO) 1.53 (d, 3 H), 4.89 (q, 1 H), 7.11 (d, 1 H), 7.24 (dd, 1 toluene (2 ml). Catalyst solution [0.8 ml; dicyclopentadienyl- H), 7.39 (d, 1 H), 10.6 (s, 1 H). platinum(II) chloride in dry toluene; 0.1 mg ml-1] was added and the reaction flask was sealed with a septum and heated to Butyl 2-(2R)-(4-hydroxyphenoxy)propanoate 12a.A solution 110 °C. After 2 d an additional 0.8 ml of catalyst solution was of 2-(2R)-(4-hydroxyphenoxy)propanoic acid (0.01 mol, 1.9 g) added and heating was continued. The reaction was monitored in butanol (150 ml) was treated with hydrogen chloride gas by IR spectroscopy and further addition of catalyst continued until no further heat was evolved. The reaction mixture was until the SiMH signal at ca. 2155 cm-1 was constant relative evaporated to dryness. The product was separated by column to the CNO signal at ca. 1740 cm-1. The reaction mixture chromatography on silica gel with light petroleum–ethyl acetwas added dropwise to methanol (400–800 ml) during vigorous ate (251) as eluent. Yield 1.6 g (64%). [a]D22+33.9 (CHCl3). stirring. The product was collected by centrifugation.dH (CDCl3) 0.88 (t, 3 H), 1.30 (m, 2 H), 1.6 (d+m, 5 H), 4.14 Reprecipitation from chloroform in methanol was continued (m, 2 H), 4.65 (q, 1 H), 6.72 (m, 4 H). until no free side-chain could be detected by thin layer chroma- Esters 12b and c were synthesized as for 12a starting from tography. Treatment of the product by dissolving it in ethyl 10 and 11 respectively.acetate and passing the solution through a 0.2 mm Teflon filter often reduced the amount of remaining SiMH drastically. Yield Butyl 2-(2R)-(4-hydroxy-2-nitrophenoxy)propanoate 12b. 0.5–0.8 g. 1H NMR spectra of the polymers show broader [a]D22-84 (CHCl3). dH (CDCl3) 0.90 (t, 3 H), 1.31 (m, 2 H), signals than those of the side chain precursors, but are other- 1.60 (m, 2 H), 1.66 (d, 3 H), 4.16 (m, 2 H), 4.74 (q, 1 H), 6.94 wise very similar except that the signals from methyl groups (d, 1 H), 6.97 (dd, 1 H), 7.32 (d, 1 H).attached to silicon at d 0–0.16 and a methylene group attached to silicon at d 0.5 are present, while the olefinic protons at d Butyl 2-(2R)-(4-hydroxy-3-nitrophenoxy)propanoate 12c. 4.95–4.97 and d 5.80–5.82 are absent.A SiMH signal appeared [a]D22+77.1 (CHCl3). dH (CDCl3) 0.92 (t, 3 H), 1.35 (m, 2 H), at d 4.7, equivalent to 10–15% unreacted hydrogens. 1.64 (d+m, 5 H), 4.18 (m, 2 H), 4.73 (q, 1 H), 7.10 (d, 1 H), 7.27 (dd, 1 H), 7.48 (d, 1 H), 10.3 (s, 1 H). 14a [a]D22+13.8 (CHCl3). The last reaction step to the mesogenic side-chain precursors 14b [a]D22-10.0 (CHCl3). 13a–d was similar for all and is described for 13b. 14c [a]D22+15.3 (CHCl3). 4-[(1R)-Butoxycarbonylethoxy]phenyl 4¾-(undec-10- 14d [a]D22+10.0 (CHCl3). enyloxy)biphenyl-4-carboxylate 13a. From 6a and 12a as for 13b. [a]D22+18.0 (CHCl3). dH (CDCl3) 0.90 (t, 3 H), 1.2–1.5 (m, 14 H), 1.6 (d+m, 5 H), 1.81 (quintet, 2 H), 2.04 (q, 2 H), 4.00 (t, 2 H), 4.17 (m, 2 H), 4.74 (q, 1 H), 4.97 (m, 2 H), 5.81 Sample preparation and electric measurements (m, 1 H), 6.92 (d, 2 H), 7.00 (d, 2 H), 7.13 (d, 2 H), 7.58 (d, 2 H), 7.68 (d, 2 H), 8.21 (d, 2 H).For the study of physical properties such as electro-optic eVects in smectic liquid crystals, the achievement of well aligned samples is essential. Our standard shear cell,30 built for 4-[(1R)-Butoxycarbonylethoxy]-3-nitrophenyl 4¾-(undec-10- enyloxy)biphenyl-4-carboxylate 13b.From 6a and 12b. Dry measurements on low molar mass ferroelectric liquid crystals, has proved very useful for obtaining aligned polymer samples glassware was used. A mixture of 2 mmol (0.73 g) of 12b, 2 mmol (0.57 g) of 6a and 15 mg of dimethylaminopyridine and was used for all polymeric liquid crystals and some low 356 J. Mater. Chem., 1998, 8(2), 353–362Fig. 1 Experimental set-up and cell geometry molar mass liquid crystal compounds in this study. The sample Fig. 2 Phase behaviour of side-chain precursors and polymers is applied to the lower glass plate and melted into the isotropic phase to cover the whole glass area. Then the upper glass plate is put on and the shear cell is assembled. Orientational shear third chiral group (compound 12b) was synthesized via a was applied in the smectic A phase close to the isotropic phase.Mitsunobu reaction of (S)-ethyl lactate with nitrohydroquinone A special electrode pattern ensures that the active area is monobenzoate. The reaction was performed under standard always 16.8 mm2, independent of shear position. Spacers con- Mitsunobu conditions and proceeds with inversion of consist of thermally evaporated 2 mm SiO2, and the orientation of figuration.31 In the final step of the side chain precursor the smectic layers is such that the layer normal (k� ) is perpen- synthesis, the biphenylcarboxylic acids were esterified with the dicular to the shear direction, cf.Fig. 1. A 1000 A° protective chiral propanoic ester derivatives using dicyclohexylcarbodiim- SiO2 layer covers the ITO electrodes.The shear alignment cell ide (Scheme 3). The side chain liquid crystalline polymers were is mounted in a Mettler FP52 hot stage for temperature finally obtained by a hydrosilylation reaction (Scheme 4). The control and put in a Zeiss Photomicroscope equipped with a extent of reaction was monitored by FT-IR. Attempts to fast electro-optic recording system.The sample temperature is quantify the optical purity of the mesogens by 1H NMR using independently measured by a Pt 100 resistor element placed a chiral shift reagent, (+)-praseodymium tris (3-heptafluorobuin the sample holder close to the sample. For some of the low tyrylcamphorate), have been made. Addition of the chiral shift molar mass samples good alignment could also be achieved in reagent caused no observable separation of peaks, although standard commercial surface-coated cells with 4×4 mm active this has been reported by others.32 Materials up to three years area and 4 mm thickness, obtained from EHC.old show no reduction in the specific optical rotations due to The measurement of the spontaneous polarization Ps was racemization.done with either the bridge method or the triangular wave method. The measured polarization is taken from a series of Liquid crystal properties hysteresis curves, where the reading of the amplitude of the The system used as reference24 (13a, 14a) is easy to handle loop directly gives the spontaneous polarization by eqn. (1), during physical measurements and shows typical ferroelectric behaviour.The introduction of a strong electron attracting Ps= 1 2A kDU G C1 (1) group at diVerent aromatic positions in the mesogenic core was thought to give indications of the importance of electric where A is the active sample area, k is a correction factor for dipoles in the mesogen. The influence on spontaneous polarizthe SiO2 protective layer (k=1.1 for the shear cell glasses), G ation in the chiral smectic C phase was of special interest.is the gain of the instrumental amplifier, DU is the amplitude of the loop and C1 is the reference capacitor in series with the Phase behaviour. The nitro substituent aVected the phase ferroelectric LC sample. In order to measure the smectic tilt behaviour markedly for the low molar mass materials as can angle H in the C* phase, we applied a low frequency square be seen in Table 1 and Fig. 2.The lateral substituent lowers wave field and determined the two extinction orientations by the clearing temperature in all cases, a well-known eVect. rotating the sample between crossed polarizers. To investigate Furthermore the nitro group alters the type of liquid crystalline the electroclinic eVect, measurements of induced tilt angle and phase that appears, depending on substituent position.Only optical response time were carried out as a function of applied in mesogen 13b is the smectic C* phase retained and a field and temperature. comparison of ferroelectric behaviour can be made with the reference system, 13a. In mesogen 13c the smectic phases are Results and Discussion lost and only in a narrow temperature interval does a chiral nematic phase remain.The nitro group ortho to the central Synthesis ester linkage probably induces greater order and thereby causes crystallization. This can be explained by an increase in attract- The synthetic route to these side chain liquid crystalline polymers consists of four parts as already shown in Schemes ive forces by dipole–dipole interactions between mesogens or by a decrease in intramolecular mobility on introduction of 1–4.The synthesis of 4¾-hydroxybiphenyl-4-carboxylic acid9,29 and its etherification also including the 3¾-nitro derivatives the nitro group in this position. The observed drastic lowering of the clearing temperature would at first make the former were straightforward (see Scheme 1).Scheme 2 shows the route to the chiral groups of which two were made from (+)-2-(4- explanation less probable but dipole–dipole interactions are known to be strongly temperature dependent33 and rotation hydroxyphenoxy)propionic acid kindly supplied by BASF. The J. Mater. Chem., 1998, 8(2), 353–362 357about the molecular long axis could be restricted by steric or electronic interactions involving the nitro group or by an increased moment of inertia.The location of the substituent towards the centre of the mesogenic core hinders the formation of layered phases. With a diVerent chiral group Walba22 described similar behaviour although the smectic phases were not completely lost. With the nitro group in the biphenyl as in 13d a broad smectic A phase and aarrow nematic region are observed (Fig. 2). Compared to 13a the core is broadened by the nitro substituent which according to Goodby disfavours formation of a smectic C phase.34 It also reduces the anisotropy of molecular polarizability and increases the polarizability perpendicular to the long molecular axis. This is known to diminish liquid crystalline order,6 as is also seen in system 13d.The changes in phase behaviour when the side-chain precursors are attached to the polysiloxane backbone follows the general expectations. All clearing temperatures are raised by 25–45 °C and crystallization is prohibited (Fig. 2). The stability of the smectic phases is increased at the expense of the nematic phases which disappears.In the polysiloxane systems, microphase separation of main chain and side chains exerts an extra Fig. 3 Spontaneous polarization of side-chain precursors versus tem- driving force for this formation of layered structures. In the perature with reference to SA–SC* phase transition: (+) 13a and (#) 13b case of 13b the smectic C* phase cannot be detected when going to polymer 14b which is somewhat unexpected.Naciri et al.26 reported a smectic C* phase ranging from Tg to 37 °C which have the polar lateral substituents at the end of the stiV core. The formation of distinct smectic layers is more favour- for a polymer similar to 14b with one methylene unit less in the spacer and a diVerent co-polymerization ratio in the able than polar interactions between mesogens giving a small overlap of the stiV cores.The intermesogenic interactions are siloxane backbone. It is possible that polymer 14b possesses a smectic C* phase but that it has a very short helical pitch reduced and a nitro substituent at the end of the core in the polymeric liquid crystals would favour a smectic A phase over which we have not succeeded in unwinding. Therefore the sample behaves as a smectic A phase.Comparing polymer 14a a smectic C*. In the case of 14c the formation of distinct smectic layers arranges the mesogens to give large overlap of without a lateral substituent in the mesogenic core with 14b–d containing a nitro group, it can be seen that the clearing the stiV cores although a disturbing substituent is positioned in the central part of the core. Without the restricting polymer temperatures are lowered by the substituent eVect.In 14b and 14d the isotropic transition is moved by 15 and 20 °C, respect- sublayers this substituent causes a longitudinal shift of the mesogens to give only a nematic phase, 13c. Liquid crystalline ively. In 14c the substituent in the central part of the core gives a more drastic eVect and the lowering of the transition phase behaviour seems to depend on a very delicate balance between attractive and repulsive intermesogenic forces.The temperature is 60 °C. Another striking diVerence is that 14b and 14d only exhibit very broad smectic A phases while 14c distance between the mesogens, which is a key parameter, is aVected by geometry, electron distribution and polarizability has a broad smectic C* phase as well as a smectic A phase.In order to rationalize this let us consider the layer structures of of the mesogen. All these factors change when substituents are introduced or varied and this of course complicates the under- the polymers in relation to the low molar mass mesogens. In most cases of smectic phases of low molar mass mesogens, the standing of lateral substituent eVects in liquid crystals.layer structure is not especially well defined. This is seen in Xray studies which then only give the first order reflection. The Electro-optical properties, SmC* phase. The desired evaluation of the influence on ferroelectric behaviour exerted by the mesogens are thus able to make use of the most favourable intermesogenic interactions regardless of how much the mesog- nitro group in the mesogenic core becomes rather limited since the smectic C* phase is present only in 13b and 14c of the ens overlap each other.In a polymer liquid crystal with smectic phases there is a much more distinct layer structure. This is nitro-containing systems. Nevertheless interesting observations can be made.In Fig. 3 the spontaneous polarizations (Ps) of evident from X-ray diVraction studies where many polymeric smectic A phases show more than one order of reflection.35 In 13a and 13b are shown and one particularly interesting eVect of the nitro substituent can be seen. To our knowledge a Ps a polysiloxane system the backbone is confined to sublayers between the liquid crystalline layers because of the microphase value of ca. 700 nC cm-2 is the highest reported for a system with one chiral centre. One possible explanation could be the separation. This reduces the freedom of mesogen arrangement. The intermesogenic interactions that were favourable in the increased double bond character of the phenyl ether bond caused by the nitro group in an ortho position. This restricts low molar mass smectic phase may not give the lowest energy arrangement anymore.This can be the case in 14b and 14d rotational mobility around the ether linkage. Table 1 Phases and transition temperatures material phase sequence/°C 13a SX 30 SC* 74 SA 106 I 13b -5 SC* 52 SA 70 I 13c K 35 N* 45 I 13d -5 SA 59 N* 70 I 14a -5 SC* 105 SA 130 I 14b 0 SA 115 I 14c 0 SC* 61 SA 70 I 14d -10 SA 110 I 358 J.Mater. Chem., 1998, 8(2), 353–362Fig. 6 Tilt angle of polymers versus temperature with reference to Fig. 4 Spontaneous polarization of polymers versus temperature with SA–SC* phase transition: (6) 14a and (&) 14c reference to SA–SC* phase transition: (6) 14a and (&) 14c smectic A transition polymer 14c speeds up and response times In Fig. 4 the spontaneous polarization of the polymers are as low as 10 ms are recorded.The greater temperature depen- presented and 14c shows values up to twice as high as for 14a dence of dipole–dipole interactions is a possible explanation at the same reduced temperatures. Measured tilt angles are a for these latter observations. few degrees higher for the nitro containing systems as presented in Fig. 5 and 6. When comparing spontaneous polarization Electro-optical properties, SmA phase. Some details of the and tilt angle for a system, they usually exhibit the same electro-optical behaviour in the smectic A phase have been temperature behaviour, but as is seen in the figures this does examined for the side-chain precursors 13a, b, d. In Fig. 9 the not apply for 13a and 14a.The analysis of 13c and 14c was temperature dependence of the induced tilt shows the usual limited by the easily hydrolysed central ester linkage in the steep increase close to the SA–SC* transition for 13a and b, mesogen. while 13d has a smaller temperature dependence because of Optical response times (tr) are also of interest since they the diVerent phase sequence. The variations in induced tilt relate to collective side-chain dynamics, and from Fig. 7 and 8 with applied field are shown in Fig. 10 at 15 °C below the it is clear that for 13b and 14c with a nitro substituent in the Iso–SA transition temperature. Linear dependencies were mesogen, tr have a stronger temperature dependence than 13a obtained for all three systems. and 14a, respectively. 13b with a very high Ps has response The induced tilt as a function of temperature for the polymers times in the 100 ms region while 13a is ten times faster.It is (Fig. 11) does not give the usual behaviour for 14d. The curve evident that the stronger mesogenic interactions in 13b, which can be divided into three parts with diVerent slopes. As the are responsible for the high spontaneous polarization, are slowing the reorientation of the side-chains.The polymers are slower and show tr in the millisecond range but near the Fig. 7 Response times in the smectic C* phase of side-chain precursors versus temperature with reference to SA–SC* phase transition, at a field Fig. 5 Tilt angle of side-chain precursors versus temperature with of 8 V mm-1. For comparison the measured values of 13b were recalculated to this field (tr 3 1/E).(+) 13a and (#) 13b reference to SA–SC* phase transition: (+) 13a and (#) 13b J. Mater. Chem., 1998, 8(2), 353–362 359Fig. 10 Induced tilt as a function of applied field for side-chain Fig. 8 Response times in the smectic C* phase of polymers versus precursors at 15 °C below the I–SA phase transition (T-Ttr=-15 °C): temperature with reference to SA–SC* phase transition, at a field of (+) 13a, (#) 13b and (1) 13d 8 V mm-1.For comparison the measured values of 14c were recalculated to this field (tr 3 1/E). (6) 14a and (&) 14c. Other interesting properties. The side-chain precursor 13b phenomenon remains in a plot of the response time as a with its very large spontaneous polarization was of course of function of inverse temperature (Fig. 12) it cannot be regarded interest for NLO measurements. The results from these investias a viscosity eVect, if the viscosity is assumed to follow an gations have been reported earlier.27 From the SHG-intensity Arrhenius type of behaviour. Are there changes in the meso- in the smectic C* phase, a deff value of 0.055 pm V-1 was genic interactions through the temperature span of the smectic estimated.Furthermore, for the first time a field-controllable A phase? In Fig. 13 polymers 14b and d show large electroclinic SHG-intensity in the smectic A* phase dependent on the square coeYcients at low temperatures. This could indicate a smectic of the applied electric field was reported. C* phase at lower temperatures, but this has not been con- firmed. Further investigations of the polymers show response Conclusions times independent of applied field (Fig. 14). At the same reduced temperatures the response times were within the same We have studied the eVect of introducing nitro substituents order of magnitude for polymers 14a, b and d. When comparing in the mesogenic core, and have found it to be considerable. 14b and 14d at low temperatures (Fig. 13 and 14), polymer Drastic changes in phase behaviour with substituent position 14b shows larger electroclinic coeYcient and faster response. are observed. In one position the nitro group reduces the As the phase sequences are identical these observations can be transition temperatures for the low molar mass compound explained by the diVerence in position of the nitro group which and more than doubles the maximum spontaneous polarizmay cause a larger transverse dipole moment in 14b compared ation to a value of ca. 700 nC cm-2. Moving the nitro to 14d. substituent one position in the aromatic ring gives a mesogen Fig. 9 Induced tilt as a function of temperature with reference to I–SA Fig. 11 Induced tilt as a function of temperature with reference to I–SA phase transition, for polymers.Applied field 16.2, 53.5 and phase transition, for side-chain precursors. Applied field 7.5, 16.5 and 12.5 V mm-1 for (+) 13a, (#) 13b and (1) 13d, respectively. 23.8 V mm-1 for (6) 14a, ($) 14b and (2) 14d, respectively. 360 J. Mater. Chem., 1998, 8(2), 353–3622.4 2.6 2.8 3.0 3.2 3.4 3.6 10-3 10-2 10-1 100 101 102 103 104 response time/ms T–1/10–3 K–1 Fig. 12 Response times as a function of inverse temperature. Applied Fig. 14 Response times in the smectic A phase of polymers: (6) 14a, field 53.5 and 23.8 V mm-1 for ($) 14b and (2) 14d respectively. The ($) 14b and (2) 14d. Ttr refers to the I–SA transition. The lines are lines are linear regressions of the diVerent parts of the 14d plot.only a guide to the eye. Financial support from The Swedish Natural Science Research with no smectic phases. The position of the lateral nitro Council, The Swedish Research Council for Engineering substituent has a more pronounced eVect in the low molar Sciences and The Swedish Defence Research is gratefully mass compounds than in the polymer liquid crystals. In the acknowledged.polymers the phase separation of the polymer backbone is a driving force for smectic layer formation and this reduces the eVect of the substituents. References The presence of a nitro substituent results in larger tilt 1 V. P. Shibayev and S. V. Byelyayev, Polym. Sci. USSR, 1990, angles and stronger temperature dependence of the response 32(12), 2384. time in the smectic C* phase.The comparison of the investi- 2 P. Le Barny and J. C. Dubois, in Side Chain L iquid Crystal gated properties in the smectic A phase is complicated by the Polymers, ed. C. B. McArdle, Blackie, Glasgow, and Chapman and Hall, New York, 1989, p. 130. diVerences in phase sequence of the systems caused by the 3 V. P. Shibaev, M. V. Kozlovsky, L. A. Beresnev, L. M. Blinov and nitro substituents.The nitro group introduces both steric and N. A. Plate�, Polym. Bull., 1984, 12, 299. electronic eVects. Apart from changing the geometry of the 4 N. Shiratori, A. Yoshizawa, I. Nishiyama, M. Fukumasa, mesogen it also changes the dipole moment and the polariz- A. Yokoyama, T. Hirai and M. Yamane, Mol. Cryst. L iq. Cryst., ability of the mesogen. Depending on substituent position the 1991, 199, 129.total eVect on phase behaviour and electro-optical properties 5 J.W. Goodby and I. Nishiyama, J.Mater. Chem., 1993, 3(2), 149. 6 G. W. Gray, in Adv. L iquid Crystals, ed. G. H. Brown, Academic varies over a considerable range. Press, New York, 1976, p. 1. 7 E.M. Averyanov, L iq. Crystals, 1987, 2(4), 491. 8 G. W. Gray, J. S. Hill and D. Lacey, Makromol. Chem., 1990, 191, 2227. 9 G. W. Gray, J. B. Hartley and B. Jones, J. Chem. Soc., 1955, 1412. 10 T. Inukai, S. Saitoh, H. Inoue, K. Miyazawa, K. Terashima and K. Furukawa,Mol. Cryst. L iq. Cryst., 1986, 141, 251. 11 M. Svensson, B. Helgee, K. Skarp, G. Andersson and D. Hermann, Ferroelectrics, 1996, 181, 319. 12 N. F. Cooray, M.-a. Kakimoto, Y. Imai and Y.-i. Suzuki, Polym. J., 1993, 25, 863. 13 H. Stevens, G. Rehage and H. Finkelmann, Macromolecules, 1984, 17, 851. 14 V. Percec and A. Keller,Macromolecules, 1990, 23, 4347. 15 M. Dumon, H. T. Nguyen, M. Mauzac, C. Destrade, M. F. Achard and H. Gasparoux,Macromolecules, 1990, 23(1), 355. 16 H. Poths, E. WischerhoV, R. Zentel, A. Scho� nfeld, G. Henn and F. Kremer, L iq. Cryst., 1995, 18(5), 811. 17 R. Zentel and H. Poths, L iq.Cryst., 1994, 16(5), 749. 18 M. A. Osman, Mol. Cryst. L iq. Cryst., 1985, 128, 45. 19 Y. Masuda, Y. Sakurai, H. Sugiura, S. Miyake, S. Takenaka and S. Kusabayashi, L iq. Cryst., 1991, 10(5), 623. 20 C. J. Booth, J. W. Goodby, J. P. Hardy, O. C. Lettington and K. J. Toyne, J.Mater. Chem., 1993, 3(9), 935. 21 M. Hird, K. J. Toyne, P. Hindmarsh, J. C. Jones and V. Minter, Mol. Cryst. L iq. Cryst., 1995, 260, 227. 22 D. M. Walba, M. B. Ros, N. A. Clark, R. Shao, K. M. Johnson, M. G. Robinson, J. Y. Liu and D. Doroski, Mol. Cryst. L iq. Cryst., Fig. 13 Induced tilt as a function of applied field for polymers: 1991, 198, 51. 23 M. Ozaki, M. Sakuta, K. Yoshino, B. Helgee, M. Svensson and (6) 14a, ($) 14b and (2) 14d. Ttr refers to the I–SA transition. The lines are only a guide to the eye. K. Skarp, Appl. Phys. B, 1994, 59, 601. J. Mater. Chem., 1998, 8(2), 353–362 36124 B. Helgee, T. Hjertberg, K. Skarp, G. Andersson and F. Gouda, 30 K. Skarp and G. Andersson, Ferroelectrics L ett., 1986, 6, 67. 31 O. Mitsunobu, Synthesis, 1981, 1. L iq. Cryst., 1995, 18(6), 871. 32 C. J. Booth, G. W. Gray, K. J. Toyne and J. Hardy, Mol. Cryst. 25 M. Svensson, B. Helgee and K. Skarp, Conference paper (presen- L iq. Cryst., 1992, 210 31. tation), in International conference on liquid crystal polymers, 1994, 33 M. A. Osman, Z. Naturforsch. T eil A, 1983, 38a, 693. Beijing, China. 34 J. W. Goodby, in Ferroelectricity and related phenomena, vol. 7, 26 J. Naciri, B. R. Ratna, S. Baral-Tosh, P. Keller and R. Shashidhar, Ferroelectric liquid crystals: Principles, properties and applications, Macromolecules, 1995, 28, 5274. ed. G. W. Taylor, Gordon and Breach, 1991, p. 99. 27 K. Kobayashi, T. Watanabe, S. Uto, M. Ozaki, K. Yoshino, M. 35 P. Davidson and A. M. Levelut, L iquid Crystals, 1992, 11(4), 469. Svensson, B. Helgee and K. Skarp, Jpn. J. Appl. Phys., 1996, 35, L104. 28 R. Shashidhar, J. Naciri, G. P. Crawford and B. R. Ratna, Ferroelectrics, 1993, 148, 297. 29 V. Percec, Q. Zheng and M. Lee, J.Mater. Chem., 1991, 1(4), 61aper 7/04918H; Received 11th July, 1997 362 J. Mater. Chem., 1998, 8(2), 353–362

ISSN:0959-9428    

DOI:10.1039/a704918h

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials EVect of heteroaromatic spacers on the structure and electrical properties of cation radical salts of tetrathiafulvalene analogs Jean-Franc�ois Favard,a Pierre Fre`re,*a Ame�de�e Riou,a Amina Benahmed-Gasmi,b Alain Gorgues,a Michel Jubaulta and Jean Roncalia aInge�nierie Mole�culaire et Mate�riaux Organiques, UMR 6501, Universite� d’Angers, 49045 Angers, France bL aboratoire de Chimie Organique, Universite� d’Oran, Es-Senia, 31000, Alge�rie The X-ray crystal structure of single crystals of electrocrystallized cation radical salts of 2,5-bis(1,3-dithiol-2-ylidenemethyl)- thiophene and -furan 1 and 2 have been analysed.Both cation radicals adopt a syn conformation stabilized by strong intramolecular interactions. Bond length analysis reveals that the positive charge is delocalized over the whole molecule with enhanced delocalization for 2 + containing the less aromatic furan cycle. Whereas 2 + cation radicals are uniformly stacked along the c axis with interstack interactions, 1 + forms weakly interacting dimers stacked along the b axis.In agreement with an enhanced charge delocalization and increased dimensionality, 2 BF4 shows a conductivity ca.three orders of magnitude higher than 1 ClO4. Since the discovery of the conducting properties of charge- 2 ClO4 and 2 BF4, were grown whereas with the anion PF6- transfer complexes and cation radical salts (CRSs) of the p only powders were obtained. The 151 stoichiometry of 1 ClO4 donors of the tetrathiafulvalene (TTF) series,1 much eVort has and 2 BF4 was determined by X-ray crystallography.The been invested in the design of new p-donors by modification quality of the single crystals of 2 ClO4 has not allowed us to of the TTF framework.2 The main objective of this research is obtain a structural resolution but the unit cell indicates that the increased dimensionality and hence improved charge trans- it is isostructural with 2 BF4.port properties anticipated for the corresponding CRSs.3,4 A As shown in Figs. 1 and 2, both cation radicals adopt a syn recent trend in this area consists of the insertion of a conjugated conformation stabilized by two strong intramolecular interspacer between the two 1,3-dithiole rings in order to stabilize actions, S,S for 1 + and S,O for 2 +, between the the cation radical state by the enhanced delocalization of the heteroatom of the middle heterocycle and a S atom of each positive charge.3 Moreover, the decrease of the molecular 1,3-dithiole ring.The non-bonded lengths d1=3.11; d2=3.06 A ° charge density and the increase of p-interactions may allow for 1 + and d1=2.956; d2=2.926 A ° for 2 + are much shorter better intra- and inter-stack contacts between the donor mol- than the sum of the van der Waals radii (rwS=1.8 and ecules and hence an increased dimensionality for the corre- rwO=1.5 A ° ) but larger than a covalent single bond length sponding CRS.Based on these considerations, a new (SMS=2.04 and SMO=1.75 A ° ). superconducting CRS has recently been obtained from a fused Such 1,5-intramolecular interactions between thiophene or TTF with an ethylenic spacer.5 Linearly extended TTFs with furan rings and 1,3-dithiole rings have already been observed,7,8 a heterocyclic spacer have been synthesized almost simul- in particular for the neutral donor 1 which adopts the same taneously by four groups.6 However, the preparation and syn conformation.9 The similarity of the d1 and d2 lengths for characterization of the corresponding CRSs have not yet 1 (d1=3.11; d2=3.13 A ° ) and 1 + shows that oxidation does been reported.not significantly aVect the strength of these 1,5-intramolecular In this paper the preparation and X-ray diVraction structural stabilizing interactions. characterization of two CRSs with thiophene 1 and furan 2 In contrast, marked diVerences are observed between 1 and spacers are reported and the relationships between their struc- 1 + in the bond lengths along the p-conjugated path and in ture and electrical properties are discussed.particular for the exocyclic bonds x, x¾ and y, y¾ (Table 2). For the neutral molecule 1, the lengths of the bonds x, x¾ and y, y¾ are consistent with localized double and single bonds respectively while the diVerences between C(sp2)–C(sp2) bond lengths Dl and Dl¾ are close to the value expected for alternate single and double bonds (0.16 A ° ).Oxidation of 1 into 1 + produces a lengthening of bonds x and x¾ and a shortening of y and y¾, resulting in a decrease of Dl and Dl¾ and also in an inversion of the sign of Dl. The decrease in Dl and Dl¾ provides conclusive evidence for extensive delocalization of the positive charge Results and Discussion over the whole 1 + molecule (Scheme 1) while the inversion of Dl is consistent with an important contribution of the semi- Compounds 1 and 2 were synthesized using a known proquinoid geometry (B form in scheme 1) in the cation radical.cedure.6 As already demonstrated, the insertion of a hetero- Compared with 1 +, Dl and Dl¾ for the furan analog 2 + cyclic spacer into the TTF core results in a negative shift of decrease to ca. 0.01 and 0.02 A° . This bond length equalization the two oxidation potentials and in the decrease of their suggests that the lower aromatic resonance energy of the furan diVerence.6 Electrocrystallizations of 1 and 2 under galvanosring allows a better delocalization of the positive charge over tatic condition have been performed in the presence of ClO4-, the whole cation radical 2 + than for 1 +.This enhanced BF4- and PF6- as counter anions. The main results are presented in Table 1. Green single crystals, namely 1 ClO4, delocalization is further favored by the better planarity of 2 + J. Mater. Chem., 1998, 8(2), 363–366 363Table 1 Experimental conditions for galvanostic electrocrystallization on platinum wire (diameter: 0.5 mm; length: 1.5 cm) of donors 1 and 2.ACN: acetonitrile, EtOH: ethanol, THF: tetrahydrofuran donor 1 1 1 2 2 2 anion ClO4- BF4- PF6- ClO4- BF4- PF6- solvent ACN (10 ml ) ACN (10 ml ) ACN THF (20 ml ) THF(20 ml ) EtOH (20 ml ) EtOH (20 ml ) EtOH (10 ml ) EtOH (10 ml ) EtOH (10 ml ) current/mA 1 1 0.8 1 1 0.5 T /°C 0 0 2 5 5 5 results crystals small crystals green solution crystals crystals green solution and and powder powder Table 2 Exocyclic bond lengths in A ° of neutral molecule 19 and cation radicals 1 + and 2 + x x¾ y y¾ Dl=y-x Dl¾=y¾-x¾ 1 (X=S) 1.34(1) 1.28(1) 1.46(1) 1.45(1) 0.12 0.17 1 + (X=S) 1.43 (2) 1.37(2) 1.37(2) 1.40(2) -0.06 0.03 2 + (X=O) 1.379(5) 1.370(5) 1.390(4) 1.392(4) 0.01 0.02 Scheme 1 Fig. 1 ORTEP view of cation radical 1 + Fig. 2 ORTEP view of cation radical 2 + as shown by the decrease of the dihedral angles between the plane containing the middle heterocycle and those containing the 1,3-dithiole rings from 1.9° and 1.3° for 1 + to 1.12° and 0.24° for 2 +. The packing of 1 + ClO4- and 2 + BF4- is characterized by a head-to-tail overlap of radical cations (Figs. 3 and 4). In 1·ClO4, dimers of cation radicals stack along the b axis. As shown in Fig. 3(b), several S,S intermolecular contacts are observed in the centrosymmetric dimer. The strongest inter- Fig. 3 X-Ray crystal structure of 1 ClO4: (a) packing of the molecules and anions and (b) overlap mode of cation radicals 1 + in the dimer action occurs between the sulfur atoms of thiophene with a 364 J.Mater. Chem., 1998, 8(2), 363–366single crystal only gave values of 7×10-5, 4×10-2 and 10-2 S cm-1 for 1 ClO4, 2 ClO4 and 2 BF4 respectively. The isomorphous crystals 2 ClO4 and 2 BF4 have analogous conductivities whereas the ca. three orders of magnitude larger value obtained for 2 BF4 in comparison with 1 ClO4 is in fair agreement with the enhanced charge delocalization and increased dimensionality indicated by X-ray data.Conclusion The first X-ray structures of cation radical salts of extended tetrathiafulvalenes with a thiophene and furan spacer have been described. Both cation radicals adopt the synilized by strong intramolecular interactions, previously observed for the neutral state.Compared to 1 ClO4, the better electronic delocalization over the whole radical cation 2 + and above all the increased dimensionality of the crystal structure of 2 BF4 confer greater conductivity on this material. On the other hand, it is worth noting that the conductivity of 2 BF4 appears rather high for a CRS of 151 stoichiometry which should in principle behave as an insulator.This result suggests that the extension of charge delocalization allowed by the insertion of the heterocyclic spacer increases the probability of intermolecular charge transport. Work now in progress on more extended CRSs should permit us to confirm this hypothesis. Experimental Electrocrystallization Donors were dissolved in degassed solvent (Table 1) containing Fig. 4 X-Ray crystal structure of 2 BF4: (a) packing of the molecules the electrolyte and placed in the anode compartment of a and anions and (b) overlap mode of cation radicals 2 + 50 ml H-shaped electrocrystallization cell, separated from the cathode compartment by a porous glass frit. A constant current short distance d3=3.42 A ° . The sulfur atoms of the 1,3-dithiole was applied for 10–12 d.rings are in weaker contact with d4=3.61 and d5=3.76 A ° . Weak interactions are found between the dimers along the b X-Ray crystallography axis (3.81 A ° ) and no interstack contact is observed. In sharp contrast, for 2 BF4 the cation radicals are uniformly Single crystals were mounted on an Enraf-Nonius MACH3 diVractometer with a graphite monochromator and Mo–Ka stacked along the c axis with an overlap of the furan and 1,3- dithiole rings stabilized by regular S,S and weak S,O (l=0.71073 A ° ) radiation at T=294 K.Data collection was performed with the v/2h scan technique. intermolecular interactions with d6=3.70 and d7=3.35 A ° respectively [Fig. 4(b)]. Interstack contacts are observed with The structures were solved by direct methods (SIR) and refined by full-matrix least-squares techniques using MOLEN di=3.76 A ° [Fig. 4(a)]. Two-probe conductivity measurements performed on a software. Non-H atoms were refined anisotropically. The Table 3 Crystallographic data compound 1 ClO4 2 BF4 2 ClO4 symmetry monoclinic triclinic triclinic space group P21/n P19 P19 a/A ° 7.096(5) 7.964(2) 7.929(2) b/A° 25.193(7) 10.341(2) 10.391(2) c/A ° 9.765(4) 10.683(1) 10.820(3) a(°) 90 118.07(1) 117.97(2) b(°) 105.08(6) 100.99(1) 101.45(2) c(°) 90 94.12(2) 94.28(2) V /A ° 3 1685(2) 748.7(2) 757.1(4) Z 4 2 2 formula C12H8O4S5Cl C12H8OS4BF4 C12H8O5S4Cl M 411.97 383.26 395.90 Dc/g cm-3 1.62 1.70 1.74 F(000) 836 386 402 m/cm-1 8.31 6.47 7.98 hmin 2 2 hmax 28 30 h, k, l 0<h<9, 0<k<33, -12<l<12 0<h<11, -14<k<14, -15<l<15 data unique 4117 4634 data observed, I>3s(I ) 1229 3227 no.of variables 199 223 R 0.095 0.05 Rw 0.121 0.07 J. Mater. Chem., 1998, 8(2), 363–366 3656 (a) U. Scho� berl, J. Salbeck and J. Daub, Adv. Mater., 1992, 4, 41; hydrogen atoms were found by Fourier diVerence in 2 BF4 (b) A. S. Benahmed-Gasmi, P. Fre` re, B. Garrigues, A. Gorgues, and refined with fixed isotropic thermal parameters.In 1 ClO4, M. Jubault, R. Carlier and F. Texier, T etrahedron L ett., 1992, 33, the positions of hydrogen atoms were calculated using the 6457; (c) T. K. Hansen, M. V. Lakshmikantam, M. P. Cava, HYDRO program. Crystal data and experimental details are R. E. Niziurski-Mann, F. Jensen and J. Becher, J. Am. Chem. Soc., listed in Table 3 and data (excluding structure factors) for 1992, 114, 5035; (d) K.Takahashi, T. Nihira, M. Yoshifuji and K. Tomitani, Bull. Chem. Soc. Jpn., 1994, 66, 2330. 1 ClO4 and 2 BF4 have been deposited at the Cambridge 7 (a) Y. Yamashita, S. Tanaka, K. Imaeda, H. Inokuchi and M. Sano, Crystallographic Data Centre. (See Information for Authors, J. Org. Chem., 1992, 57, 5517; (b) Y. Misaki, T. Sasaki, T.Ohta, Issue No. 1; quote reference 1145/63 in any request to the H. Fujiwara and T. Yamabe, Adv. Mater., 1996, 8, 804; (c) A. Ohta CCDC). and Y. Yamashita, J. Chem. Soc., Chem. Commun., 1995, 557; (d) A. Ohta and Y. Yamashita, J. Chem. Soc., Chem. Commun., 1995, 1761; (e) A. Ohta and Y. Yamashita, Heterocycles, 1997, 1, 263. References 8 T. K. Hansen, M. R. Bryce, J.A. K. Howard and D. S. YYt, J. Org. Chem., 1994, 59, 5324; (b) E. H. Elandaloussi, P. Fre`re, 1 (a) J. M. Williams, J. R. Ferraro, R. J. Thorn, K. D. Carlson, A. Benahmed-Gasmi, A. Riou, A. Gorgues and J. Roncali, J. Mater. U. Geiser, H. H. Wang, A. M. Kini and M. H. Whangbo, Organic Chem., 1996, 12, 1859; (c) A. Benahmed-Gasmi, P. Fre` re, Superconductors (Including Fullerenes), Prentice Hall, Englewood E. H. Elandaloussi, J. Roncali, J. Orduna, J. Garin, M. Jubault, CliVs, NJ, 1992; (b) Organic Conductors. Fudamentals and A. Riou and A. Gorgues, Chem. Mater., 1996, 8, 2291. Applications, ed. J. P. Farges, Marcel Dekker, New York, 1994. 9 J. Roncali, L. Rasmussen, C. Thobie-Gautier, P. Fre` re, H. Brisset, 2 (a) G. Shukat, A. M. Richert and E. Fanghanel, Sulfur Rep., 1987, 7, M. Salle�, J. Becher, O. Simonsen, T. K. Hansen, A. Benahmed- 155; (b) G. Shukat and E. Fanghanel, Sulfur Rep., 1993, 14, 245. Gasmi, J. Orduna, J. Garin, M. Jubault and A. Gorgues, Adv. 3 M. Adam and K. Mu� llen, Adv. Mater., 1994, 6, 439. Mater., 1994, 6, 841. 4 M. R. Bryce, J.Mater. Chem., 1995, 5, 1491. 5 Y. Misaki, N. Higuchi, H. Fujiwara, T. Yamabe, T. Mori, H. Mori and S. Tanaka, Angew. Chem., Ind. Ed. Engl., 1995, 34, 1222. Paper 7/06948K; Received 25th September, 1997 366 J. Mater. Chem., 1998, 8(2), 363&nda

ISSN:0959-9428    

DOI:10.1039/a706948k

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Low temperature crystal structure of the organic metal ([2H8]BEDT–TTF)4Cl2·6D2O [BEDT–TTF= bis(ethylenedithio)tetrathiafulvalene] Philippe Guionneau,*†a Cameron J. Kepert,b Matthew Rosseinsky,b Daniel Chasseau,a Jacques Gaultier,a Mohamedally Kurmoo,c‡ Michael B. Hursthoused and Peter Dayc aL aboratoire de Cristallographie et Physique Cristalline, Universite� Bordeaux I, 351 cours de la L ibe�ration, F-33405 Talence Cedex, France bInorganic Chemistry L aboratory, South Parks Road, Oxford, UK OX1 3QR cT he Royal Institution of Great Britain, 21 Albemarle Street, L ondon, UK W1X 4BS dSchool of Chemistry and Applied Chemistry, University College of Wales, CardiV, UK CF1 3TB ([2H8]BEDT–TTF)4Cl2·6D2O [BEDT–TTF=bis(ethylenedithio)tetrathiafulvalene] exhibits a transition from semimetal to semiconductor at T=160 K (Rosseinsky et al., J.Mater. Chem., 1993, 3, 801). This electronic transition is accompanied by a structural transition that is characterized by the reversible appearance of superstructure reflections corresponding to the doubling of the cell parameter b and a change in space group from Pcca to Pbcn.The crystal structures are very similar above and below T and the calculated intermolecular transfer integrals scarcely change. In contrast, from the diVerence in intramolecular bond lengths, it is clear that the two crystallographically independent BEDT–TTF molecules carry diVerent charges at low temperature, suggesting that a degree of ionicity arising in the BEDT–TTF layer is responsible for the change in electrical behaviour.Progress in understanding the relation between the structures diVerent from those of other ET chloride salts. They belong to the orthorhombic space group Pcca. The structural arrange- and properties of molecular materials has required the development of many new methods. For example, structure refinement ment consists of columns of dimerized ET parallel to c that form layers parallel to the bc plane separated by anion sheets by X-ray diVraction at low temperatures or high pressures is needed to shed light on the crystal structure at the points in (Fig. 1). The main characteristic of the stacks is the alternation of parallel ET with twisted ET, the angle between dimers being the phase diagram where transformation takes place in physical properties.While high pressure X-ray investigations are still about 30° (Fig. 2). The structure is therefore nearer to that of the a¾-ET phase than that of the other ET salts with Cl anions. very rare,1 low temperature crystal structure determination is increasingly accessible as a result of the introduction of area The intermolecular interactions are strong both within the chains and between adjacent stacks, indicating a strong 2D detectors, as evidenced by several recent publications.2 BEDT–TTF (C10H8S8, also ET) salts have attracted great electronic behaviour.The Cl and O atoms of the anion layer create an unusual two-dimensional network formed by hydro- interest because of their diversity in physical properties due to extensive structural polymorphism.The chloride salts form gen bonds. In a previous paper,9 we noted the need for structural information at low temperature to explain the an interesting set, ET3Cl2·2H2O,3 ET4Cl2·4H2O4 and ET3Cl2.5·H5O2 5 are metallic under ambient conditions and mechanism of the electronic transition in this compound. Here, we present the temperature dependence of the crystal struc- undergo a transition towards a less conducting state at low temperature (Tc=100, 50 and 70 K respectively), the 352 salt ture and the intermolecular electronic interactions of ([2H8]ET)4Cl2·6D2O. becoming superconducting at 5 K on applying a pressure of up to 0.5 GPa.The recently reported salt ET3Cl2·5H2O6 behaves as a semiconductor. ([ 2H8]ET)4Cl2·6D2O behaves as Experimental a semimetal7 from room temperature (s=40 Scm-1) to 160 K where a transition occurs towards a semiconducting state with The quality of each crystal was checked by X-ray diVraction on films before use.The crystals studied were black needles of a maximum activation energy of 30 meV. On applying pressure, the conductivity increases and the transition temperature approximate dimensions 1.4×0.4×0.2 mm,2 all of which had a small fraction of twinning.decreases until the transition is suppressed at pressures greater than 2.4 GPa. The thermopower decreases linearly from room The low temperature structural investigation of this salt was performed in two steps. temperature to 160 K and then increases slightly. The magnetic susceptibility is low at room temperature and scarcely increases from 150 K to 50 K but then rises sharply down to 5 K.The room temperature crystal structure has been solved simultaneously by two groups showing that the deuterated salt, ([2H8]ET)4Cl2·6D2O,7 and the hydrogenated salt, ET4Cl2·6H2O,7 are isostructural but with structures very *E-mail: Philippe.Guionneau@durham.ac.uk † Durham Chemical Crystallography Group, Chemistry Department, Durham, UK DH1 3LE.‡ Institut de Physique et Chimie des Materiaux de Strasbourg, CNRSFig. 1 View of the unit cell of ([2H8]ET)4Cl2·6D2O along b UMR 0046, 23 rue du Loess, 67037 Strasbourg Cedex, France. J. Mater. Chem., 1998, 8(2), 367–371 367At the University of Bordeaux I, evolution of the unit cell parameters was followed from 293 to 18 K with a three circle diVractometer equipped with a closed cycle helium cryostat. The angular positions of sets of eighteen Bragg reflections were determined at five fixed temperatures on cooling and refined to give the cell parameters. Fifteen sets were collected on warming.Data collection of the Bragg reflections was performed at 18 K, but the very low accuracy of the structural resolution factor (R=16%), attributed to the quality of the crystals and to a technical problem leading to temperature fluctuations, does not permit us to present these results.At the University College of Wales, CardiV, we used a four circle diVractometer equipped with a nitrogen vapour jet cooling device operating down to 110 K and with a chargecoupled device (CCD) area detector.Strong superstructure reflections corresponding to the doubling of the b parameter Fig. 3 Temperature dependence of the relative intensities of three were seen at low temperature during a fast preliminary investisuperstructure reflections I=f (T ) and I/Imax=f (T /Tc) gation. Extended studies were performed on two crystals, in each case collecting complete structural data sets at 110 K and We note that the conventional space group corresponding performing scans in w at 5 K temperature increments to obtain to the double cell is Pbcn but, in order to compare the the temperature-dependence of the superstructure intensities. structures at low and high temperatures, it is more convenient Results for the two crystals were identical.The structure at to use the non-standard space group Pnca that arises from 110 K was determined starting from the ambient temperature Pbcn by rotating the axes.coordinates using SHELX76.10 The D atoms of the ET extremities were fixed in theoretical positions and those of Lattice parameter evolution D2O were refined from the room temperature positions. The moderately large magnitudes of the R and Rw factors (Table 1) Fig. 4 shows the temperature dependence of the simple cell and standard deviations of atomic coordinates may be attriparameters of the title compound. There are no observable buted to the small fraction of twinning in the crystal. diVerences between the cell parameter values obtained on cooling or warming. Results and Discussion As shown previously for ET salts,1,9,11 the main characteristic of the temperature dependence of the cell parameters is the Superstructure reflections anisotropy. Here, the relative variation of the parameter c (corresponding to the intrastack separation) is the highest, Analysis of the temperature-dependent intensities of more than about twice as large as that for the interstack direct b.The 100 superlattice reflections shows that the transition displays a parameter, which is perpendicular to the organic layers, no structural hysteresis. The temperature of appearance and remains nearly constant over the temperature range studied.disappearance of the reflections is about 165 K (Fig. 3), corre- The fact that the intrastack parameter decreases more than sponding to the change in electrical behaviour (Tc=160 K).At the interstack parameter mirrors the behaviour of a¾-ET2X9 110 K, the temperature of the crystal structure determination, and ET3CuBr2Y2 (Y=Cl or Br)1 even if in those cases the the superstructure reflection intensities are comparable to those most significant changes in conductivity occur in the interstack of the main reflections. Hence, the crystal structure at 110 K direction.correctly represents the structural evolution in the double cell. The temperature variation of the cell parameters changes The variation of I/Imax of representative reflections with markedly between 160 and 200 K with the onset of the (T /Tc) (Fig. 3) must be interpreted with caution because the superstructure reflections, so the choice of the temperature values of Imax are estimated from the incomplete curve I= intervals is important in calculating the isobaric tensor.Thus f (T ). The variation is quite steep when compared to the spinthe isobaric tensor was calculated over two temperature inter- Peierls system a¾-ET2X [X=Ag(CN)2 and AuBr2].9,11 vals (18–150 and 200–293 K) on either side of the transition zone. The principal components of the isobaric thermal expansion tensor are shown as a function of temperature in Fig. 5. The cell is orthorhombic and so the principal directions of expansion lie along the crystallographic axes. The amplitudes, Table 1 Crystal and experimental data ([2H8]ET)4Cl2·6D2O temperature: 110 K Crystal system orthorhombic reflections: Space group Pnca for the cell 85 ET/cell 16 measured 19841 independent ET 2 independent 4838 a/A ° 32.411(4) observed 3158 b/A ° 13.283(3) parameters 349 c/A ° 14.656(2) I/s(I ) 3 V /A ° 3 6309(4) Rint 0.050 D/Mg m-3 1.808 R(Fo) 0.064 F(000) 3464 vR(Fo) 0.061 Dimensions/mm 1.4×0.4×0.2 l/A ° (Mo-Ka) 0.71069 observation: twinned crystals m/mm-1 1.162 Fig. 2 View of the ET layer showing the ribbons of twisted dimers 368 J. Mater. Chem., 1998, 8(2), 367–371Fig. 4 Temperature dependence of the normalised lattice parameters: (%) a/a0, (#) b/b0, (6) c/c0 and ($) V/V0. Room temperature values are a0=32.497(15), b0=6.722(8), c0=14.826(8) A ° and V0=3238(8) A ° 3. Fig. 5 Temperature dependence of components of the thermal expansion tensors aa, ab and ac vary very little from 293 to 200 K but change abruptly between 150 and 18 K.The three amplitudes become nearly zero at 18 K showing that the crystal is no longer van der Waal distances) and the angles formed by the SMS thermally compressible. direction and the average ET plane. We recall that angles near At room temperature, the bulk modulus (aV-1) is high, zero lead to antibonding interactions.11 The b interactions, indicating a low compressibility. The value for the title com- corresponding to angles between the long axes of the ET pound (5300 K) is close to those of the a¾-ET2X salts (around molecules of around 30°, are quite weak and do not change at 6000 K)9 and much lower than that of ET3CuBr4 (9000 K).1 110 K so the asymmetry introduced by b and b¾ does not appear to be significant.The c interactions correspond to short Crystal structure at low temperature distances that decrease at 110 K, the diVerence between c and c¾ being significant but weak.The f interactions correspond to Below the structural transition temperature the unit cell is short distances and favourable angles for strong interactions. doubled without any change in the degree of symmetry. The The transfer integrals corresponding to f and f ¾ are similar at transition therefore leads to the emergence of two crystallolow temperature.Hence, the intermolecular interactions appear graphically independent ET molecules, labelled A and B. At a little stronger at low temperature, the salt retains its layer low temperature the ET stacks formed an …ABABA… character and any irregularity caused by the structural diVersequence.In the simple cell there are five significant near entiation between the two ET is minor. neighbour interactions within each layer (Fig. 6) (a1, a2, b, c, The anionic layer consists of a two-dimensional network: Cl f ). It should be noted that the interactions of the type (x, y, and O atoms linked by H-bonds form chains connected to z)-(1-x, -0.5+y, 0.5-z) are not considered significant each other by short OMCl contacts.At low temperature, the owing to the very large intermolecular distances involved. The distances within these chains scarcely decrease as the interchain number of major interaction modes increases to eight in the OMCl distances increase (Fig. 7). There are no close contacts doubled cell due to the existence of the two independent ET between anions and cations either at room or low temperature, (a1, a2, b, c, f, b¾, c¾, f¾).The stacks remain based on alternation of a1 and a2 in a manner that hardly changes from room temperature to 110 K: the averaged interplanar distances Table 3 Shortest intermolecular SMS distances (A ° ) with the contact between the ET decrease from 3.69(1) to 3.63(1) A ° (a1) and angles [°] between ET of adjacent stacks.Standard deviations are less than 0.005 A ° and 1.0° from 3.68(1) to 3.60(1) A ° (a2) and the torsion angles from 0° to 1(1)° (a1) and 32(1)° to 30(1)° (a2). Table 3 lists the short Interactions 293 K 110 K interstack SMS distances ( less than 1.2 times the sum of the b 4.046 [54.9] 3.938 [53.2] b¾ as for b 3.969 [53.2] Table 2 Averaged intramolecular bond lengths (A ° ) and charge for the 4.026 [51.1] two independent ET, A and B, at 110 K c 3.951 [5.8] 3.892 [7.9] 3.466 [4.0] 3.492 [6.1] 3.468 [4.6] 3.346 [6.4] 3.892 [7.3] 3.839 [8.1] 3.578 [11.1] 3.582 [12.1] 3.476 [9.9] 3.434 [9.8] c¾ as for c 3.932 [8.1] 3.384 [6.2] 3.533 [6.0] 3.880 [7.8] 3.528 [11.9] 3.503 [9.7] f 4.054 [52.3] 4.034 [52.3] 3.709 [57.1] 3.675 [58.1] 3.858 [58.0] 3.909 [58.4] a b c d d charge 3.729 [64.5] 3.618 [65.3] f ¾ as for f 4.024 [51.0] 293 K: 1.363 1.740 1.744 1.341 0.780 0.52 110 K: 3.686 [57.1] 3.773 [57.4] A 1.358 1.734 1.744 1.346 0.774 0.60 B 1.348 1.748 1.753 1.346 0.807 0.38 3.655 [63.2] J.Mater. Chem., 1998, 8(2), 367–371 369Fig. 6 Labelling scheme adopted for the ET layer in the double cell and the symmetry operations Fig. 7 Detail of the anion network and interatomic distances (A ° ) at contrary to the situation found in the a¾-ET2X series or in 293 (italic) and 110 K ET3CuBr4. Electronic interactions and the bond lengths are closer to the theoretical values. Such an ordering has been also observed in the a¾-ET2X series9 and The transfer integrals between neighbouring ET molecules in ET3Cl2·3H2O.13 have been calculated from the Hu� ckel method using a double- The central SMC and CNC bond lengths are quite diVerent f basis set12 for both the room temperature and the low in A and B (Fig. 9). Recently we established a correlation temperature structures (Table 4). between these intramolecular bond lengths and the charge of Results for the room temperature structure indicate that the the ET.14 This method, based on the parameter d= intrachain interactions are quite strong but the degree of (b+c)-(a+d) where b, c are the SMC and a, d the CNC dimerization is high (a1/a2=2.1) and of the same order as that averaged bond lengths of the central TTF (Table 2), enables in the a¾-ET2X series.The interstack transfer integrals between the charge to be estimated with an accuracy of about 0.1 e.coplanar ET are negative and comparable to the smaller The structure refinement is good enough to use this method intrachain one. The high value of the interstack transfer integral in the present case (lt;8% and standard deviations on bond f confirms the two dimensional nature of this salt. It is lengths less than 0.01 A ° ). At room temperature the existence interesting to note the coexistence between an intrachain of a single crystallographically independent ET requires that dimerization tendency and a 2D character.At low temperature, the transfer integrals increase slightly. The intrastack dimerization does not increase below the transition, in contrast to ET3Cl2·2H2O where the dimerization is more pronounced at low temperature.The emergence of two independent ET has little eVect: the diVerences between f, f ¾ and c, c¾ are quite small (20 meV) but agree with the change in electrical behaviour. The diVerence in the site energy of the two ET is an intermediate result in the dimer splitting calculations and arises from the diVerence in charge carried by the two ET. At room temperature this diVerence is zero because all the cations are identical, but at low temperature it increases to 60 meV as a result of the diVerence between A and B molecules.A similar variation has been found in the a¾-ET2X series and interpreted as the appearance of a degree of ionicity in the ET layers. ET conformations and bond lengths At room temperature, the two ethylene extremities of the ET are strongly disordered, as evidenced by the small bond lengths (1.381 and 1.389 A ° instead of 1.53 A ° ) and large atomic thermal coeYcients (Beq>10 A ° 2) (Fig. 8). At 110 K, the ethylene groups Fig. 8 Thermal ellipsoids (90% probability) of the ET molecules at (a) of A and B are ordered indicating that the disorder observed 293 and (b) 110 K at high temperature is dynamic: the values of these coeYcients correspond to those expected at this temperature (Beq<2.8 A ° 2) Table 4 Values of the intermolecular transfer integrals (meV) interactions 293 K 110 K intrastack a1 148 148 a2 70 76 interstack b 30 36 b¾ 30 40 c -80 -100 c¾ -80 -80 Fig. 9 Intramolecular bond lengths of the two independent ET (A and f 207 223 B) in ([2H8]ET)4Cl2·6D2O at 110 K. All standard deviations are less f ¾ 207 205 than 0.008 A ° . 370 J. Mater. Chem., 1998, 8(2), 367–371all the molecules carry a charge of +1/2, in agreement with in the ethylenic extremities and a change in the charge distribution. the charge calculated by the d-method [+0.52(10)]. We also note that the sum of the calculated charge for A and B at We are grateful to Simon Coles for his help in CardiV and to 110 K corresponds to that expected (A+B=+0.98 instead of Laurent Ducasse for the transfer integrals calculation program.+1). At 110 K, the SMC bonds in molecule A become shorter Financial support was received from the EPSRC (UK), the and the CNC longer than in B, corresponding to a diVerence European Community (HCM network) and the Re�gion in charge. From the d-method we estimate that the charges in Aquitaine (France).A and B at 110 K are respectively +0.60(10) and +0.38(10), a diVerence that is quite suYcient to open a gap at the Fermi energy and cause the transition from semimetal to semicon- References ductor. An analogous phenomenon is observed in the a¾-ET2X 1 P. Guionneau, J. Gaultier, D. Chasseau, G. Bravic, Y. Barrans, series where a partial localization of the charges leads to L.Ducasse, D. Kanazawa, P. Day and M. Kurmoo, J. Phys. I Fr., similar values of the cation charges (in this case: 0.66 for one 1996, 6, 1581. ET and 0.33 for the other at 120 K) below the transition 2 See for example: T. Burgin, T. Miebach, J. C. HuVman, towards a less conducting state. L. K. Montgomery, J. A. Paradis, C. Rovira, M.-H.Whangbo, S. N. Magonov. S. I. Khan, C. E. Strouse, D. L. Overmyer and J. E. Schirber, J. Mater. Chem., 1995, 5(10), 1659; H. Kobayashi, K. Kawano, T. Naito and A. Kobayashi, J. Mater. Chem., 1995, Conclusions 5(10), 1681. 3 M. J. Rosseinsky, M. Kurmoo, D. R. Talham, P. Day and The semimetal to semiconductor transition in ([2H8]- D. Watkin, J. Chem. Soc. Chem. Commun., 1988, 88.BEDT–TTF)4Cl2·6D2O is associated with a structural trans- 4 R. P. Shibaeva, R. M. Lobkovskaya, L. P. Rozenberg, L. I. Burarov, A. A. Ignatiev, N. D. Kushch, E. E. Laukhina, ition [(Pcca, a, b, c)<(Pnca, a, 2b, c)] that gives rise to an M. K. Makova, E. B. Yagubskii and A. V. Zvarykina, Synth. Met., overall increase in the strength of the intermolecular inter- 1988, 27, 189. actions; the two dimensional character remains at low tempera- 5 T.Mori and H. Inokuchi, Bull. Chem. Soc. Jpn., 1988, 61, 591. ture. The change in physical properties is not caused by a 6 G. Ono, A. Izuoka, T. Sugawana and Y. Sugawana, Mol. Cryst. molecular rearrangement but by the onset of a diVerence in L iq. Cryst., 1996, 285, 63. 7 M. J. Rosseinsky, M. Kurmoo, P. Day, I. R. Marsden, R.H.Friend, ionicity between the two independent ET. Indeed, the main D. Chasseau, J. Gaultier, G. Bravic and L. Ducasse, J. Mater. structural change resulting from the electronically driven trans- Chem., 1993, 3, 801. ition is the distribution of bond lengths within the ET unit, 8 M. B. Inoue, M. A. Bruck, M. Carducci and Q. Fernando, Synth. which splits into two crystallographically independent units at Met., 1990, 38, 353.low temperature. We believe that it is the separation in energy 9 P. Guionneau, J. Gaultier, M. Rahal, G. Bravic, J. M. Mellado, D. Chasseau, L. Ducasse, M. Kurmoo and P. Day, J.Mater. Chem., between the two independent ET, rather than any major 1995, 5, 1639 changes in the intermolecular interactions, that is important 10 G.M. Sheldrick, SHELX 76, University of Cambridge, 1976. in the development of a semiconducting band structure. The 11 D. Chasseau, J. Gaultier, G. Bravic, L. Ducasse, M. Kurmoo and proposed mechanism for the semimetallic to semiconducting P. Day, Proc. R. Soc. L ond. A, 1993, 442, 207. transition is a lowering of the free electron energy by band 12 A. Fritsch and L. Ducasse, J. Phys. I, 1991, 1, 855.narrowing, which accompanies the separation of charge in the 13 D. Chasseau, S. He�brard, G. Bravic, J. Gaultier, L. Ducasse, M. Kurmoo and P. Day, Synth.Met., 1995, 70, 947. ET layer. Such a mechanism is analogous to the charge- 14 P. Guionneau, C. J. Kepert, D. Chasseau, M. R. Truter and P. Day, density-wave induced metal to semiconductor transition. Synth.Met., 1997, 86, 1973. The analogy between the behaviour of the chloride and the 15 See e.g. ref. 2, 3, 9, 11, also V. E. Korotkov, V. N. Molchanov and a¾-ET2X series [X=Ag(CN)2 or AuBr2] is evident. R. P. Shibaeva, Kristallografiya, 1992, 37, 1437. M. Fettouhi, As the number of complete crystallographic studies at low L. Ouahab, D. Grandjean and L. Toupet, Acta Crystallogr., Sect. B., 1993, 49, 685. M. Fettouhi, L. Ouahab, D. Grandjean and temperature on this class of molecular conductors increases, it L. Toupet, Acta Crystallogr. Sect. B, 1992, 48, 275. M. Kurmoo, will be possible to correlate the transition in physical properties A. W. Graham, P. Day, S. J. Coles, M. B. Hursthouse, with the structural behaviour to extract general trends. From J. M. Caulfield, J. Singleton, L. Ducasse and P. Guionneau, J. Am. the results published up to now,15 it is clear that cooling Chem. Soc., 1995, 117(49), 12 209. strongly influences the intramolecular conformation of the ET, the general outcome being the disappearance of the disorder Paper 7/04818A; Received 7th July, 1997 J. Mater. Chem., 1998, 8(2), 367–371

ISSN:0959-9428    

DOI:10.1039/a704818a

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials A comment upon the aggregation of squaraine dyes GeoVrey J. Ashwell Centre for Molecular Electronics, Cranfield University, Cranfield, UK MK43 0AL The electrospray ionisation mass spectrum (ESI-MS) of 2,4-bis[4-(N-methyl-N-butylamino)phenyl]squaraine shows peaks which correspond to the fragmentation pattern of the dimeric aggregate (e.g. m/z=810 [2M+2H]+) and, although the molecule is centrosymmetric, solid solutions of the dye exhibit second-harmonic generation (SHG).In order to satisfy the structural requirement the nonlinear optical behaviour is attributed to the dimeric aggregate which must be non-centrosymmetric. In contrast, solid solutions of the tetrahydroxy analogue, 2,4-bis[4-(N-methyl-N-butylamino)-2,6-dihydroxyphenyl]squaraine, are SHG-inactive and the ESI-MS data are consistent with the formation of a heptameric aggregate (m/z=819 [1.75M]+O[7M]4+).The aggregation number is compound specific and an extensive study of fourteen anilino squaraines has shown direct correlation between the type of aggregate and the occurrence or absence of SHG. Squaraine dyes have properties which may be applied to electrophotographic devices,1 optical recording,2 third-order nonlinear optics3 and surprisingly, the frequency-doubling of light.4 The donor–acceptor–donor structure is centric but, in spite of this, SHG has been observed from Langmuir–Blodgett (LB) films of a variety of analogues with anilino4–7 and heterocyclic8,9 donors.The SHG is not inherent to the molecule and, furthermore, the intensity is too strong to be associated with the glass|LB interface.Instead, it is attributed to the aggregate which must be non-centrosymmetric. It is assumed that the molecules adopt a T arrangement and that the SHG arises from intermolecular charge transfer between the acceptor and donor moieties. There is evidence that the squaraine aggregates persist in solution and that the properties are dependent upon the type of association and the extent of the intermolecular donor– acceptor interaction.4,6 For example, Chen et al.10 have reported the inclusion of anilino squaraines as monomers in aqueous solutions of b-cyclodextrin and as dimers in the larger cavity of c-cyclodextrin, the absorption maximum being hypsochromically- shifted from 650 to 594 nm.McKerrrow et al.11 have observed two types of aggregate, J and H, by arrested crystallis- In this work, the aggregation of dye 1 has been reinvestigated ation from dimethyl sulfoxide–water mixtures. Using a Bernesi– and, in addition, the electrospray mass spectra and nonlinear Hildebrand analysis, Chen et al.12 have disclosed that the optical properties of several anilino squaraines are reported.supramolecular unit of the anilino squaraine is tetrameric and The results of Langley et al.13 have been reproduced by doping has a cyclic chiral structure. Furthermore, Langley et al.13 have with Na+ (or K+ to give the potassiated species) but importreported that the electrospray mass spectra of the 2,4-bis[4- antly, for solutions of the pure dye, none of the spectra shows (N,N-dialkylamino)phenyl]squaraines (dye 1) show aggregate evidence of metallation.Furthermore, the Cranfield ESI-MS peaks which may be assigned to [nM+Na]+ where 2n is an data reveal m/z values which may be assigned to dimeric (or integer and 42n9. They have suggested that the sodiation multiples of two for z>1), hexameric and heptameric aggreis a ‘true reflection of the behaviour of these species in solution’ gates.The association number is compound specific and there which, if correct, would have far reaching consequences on the is a direct correlation between the type of aggregate and the control of the aggregation for commercially relevant appli- SHG activity for dyes 1 to 5. cations. However, it is more likely that the sodiation is a consequence of contamination.Experimental Squaraine dyes were synthesised using published procedures14 and characterised by 1H NMR, elemental analysis and ESIMS. A VG Quattro quadrupole mass spectrometer (upgraded to Quattro II specifications) and MassLynx data system (VG Organic, Altrincham) were used in the positive ion electrospray mass spectrometry study at the Michael Barber Centre (UMIST).Experiments were performed with the electrospray source high-voltage lens at 0.32 kV and the source sampling cone voltage at 25 V. Electrospray data were collected in the mass range m/z 100–2500 for dilute solutions of the dye (10 mg cm-3) in (a) CH3CN, (b) a 451 mixture of CH3CN–H2O J. Mater. Chem., 1998, 8(2), 373–376 373and (c) a 451 mixture of CH3CN–H2O containing 0.1% formic acid.The spectra were averaged over 15 scans with a scan rate of 100 amu s-1 and a flow rate of 5 ml min-1. The spectrometer was calibrated using polyethylene glycol. Spun-coated films were obtained by spreading ca. 500 ml of a dilute chloroform solution of the dye and poly(vinyl acetate) onto a glass substrate and rotating the substrate at 500 rpm using a Headway spin-coater.SHG measurements were performed in transmission with the p-polarised laser beam (Nd5YAG, l=1064 nm) at an angle of 45° to the film. Results and Discussion Structure–property relationship LB films of the anilino squaraines exhibit strong SHG4–9 and the second-order properties result from the aggregate structure Fig. 2 Electrospray mass spectrum of 2,4-bis[6-(N-butyl-2,3,4-triwhich must be non-centrosymmetric and not from the centric hydroquinoloyl)]squaraine 4.Monomer: m/z=457 [M+H]+. molecule itself. Spun-coated films of some but not all of the Aggregate: m/z=913 [2M+H]+. squaraines in poly(vinyl acetate) are also SHG-active. The second-harmonic intensity increases with the concentration of dye but is weak in comparison with the signal from the LB monolayer.Nonetheless, its observation corroborates the persistence of the aggregates in solid solution and the noncentrosymmetry, necessary for second-order eVects, probably results from a partial orientation of the acentric species in the spinning process. The SHG-active films include several alkyl analogues of the anilino squaraine (1b–1g), the dihydroxy substituted derivatives (2a–2c), and the heterocyclic analogues (4 and 5).A common feature of their electrospray mass spectra is a high mass peak, or fragmentation pattern, which may be assigned to the dimeric aggregate (Fig. 1–3). An assignment of the m/z values for 2,4-bis[4-(N-methyl-Nhexylamino) phenyl]squaraine (dye 1c: R1=CH3, R2=C6H13) is given in the legend to Fig. 1. The monomeric species is observed as a dihydrogenated ion (m/z=462, [M+2H]+), this being previously reported by Law and co-workers15 for other Fig. 3 Electrospray mass spectrum of 2,4-bis(9-julolidinyl)squaraine anilino squaraines. Furthermore, a peak corresponding to the 5. Monomer: m/z=425 [M+H]+. Aggregate: m/z=850 [2M+2H]+. trihydrogenated dimeric aggregate (m/z=923 [2M+3H]+) is shown and the main fragmentation results from the progressive Table 1 Positive ion electrospray MS dataa loss of one to four (CH2)5 units.The N-methyl-N-butylamino to N-methyl-N-decylamino analogues of dye 1 also form aggregates (m/z) amino group dimeric aggregates (Table 1) but for the higher analogues, dye R1MNMR2 RMM [1.5M]+ [1.75M]+ [2M+nH]+ dodecyl to docosyl, fragmentation of the alkyl groups makes it diYcult to unambiguously assign the MS data.In contrast, 1a CH3MNMCH3 320 480 — — the spectra of the heterocyclic analogues (4 and 5) show a 1b CH3MNMC4H9 404 — — 811 single high mass peak which may be assigned to [2M+nH]+ 1c CH3MNMC6H13 460 — — 923 (Fig. 2 and 3). 1d CH3MNMC8H17 516 — — 1033 1e CH3MNMC10H21 572 — — 1146 1f C4H9MNMC4H9 488 — — 977 1g C5H11MNMC5H11 544 — — 1089 2a CH3MNMCH3 352 528 — — 2b CH3MNMC4H9 436 — — 873 2c C4H9MNMC4H9 520 — — 1041 3a CH3MNMC4H9 468 702 819 — 3b CH3MNMC6H13 524 786 917 — 4 — 456 — — 913 5 — 424 — — 850 aNone of the ESI-MS spectra showed significant peaks at m/z values greater than those listed.The tetrahydroxy substituted squaraines, 2,4-bis[4-(Nmethyl- N-alkylamino)-2,6-dihydroxyphenyl]squaraine (3), diVer in so far as their solid solutions do not exhibit SHG and the electrospray spectra show aggregate peaks which correspond to fractional values of the relative molecular mass: e.g.m/z=702 and 786 [1.5M]+ and 819 and 917 [1.75M]+ Fig. 1 Electrospray mass spectrum of 2,4-bis[4-(N-methyl-N-hexyl- respectively for the butyl and hexyl analogues (see Fig. 4). The amino)phenyl]squaraine 1c.Monomer: m/z=462 [M+2H]+. former may be assigned to the trimeric aggregate if z=2. Aggregate: m/z=923 [2M+3H]+; 867 [2M+3H-4CH2]+; 853 Alternatively, the peaks may be attributed to hexameric and [2M+3H-5CH2]+; 797 [2M+3H-9CH2]+; 783 [2M+3H- 10CH2]+; 726 [2M+2H-14CH2]+; 712 [2M+2H-15CH2]+. heptameric species respectively if z=4 and, although they may 374 J.Mater. Chem., 1998, 8(2), 373–376Table 2 Assignment of the aggregate fragmentation patterns of 2,4- bis[4-(N,N-dimethylamino)phenyl]squaraine (1a) and 2,4-bis[4-(N,Ndimethylamino)- 2-hydroxyphenyl]squaraine (2a) ESI-MS data (m/z) possible mass 1a 2a assignmenta (m/z) — 528 [6M]4+ 528 480 — [6M]4+ 480 456 455 [6M-7CH2]4+ 455.5 438 439 [6M-12CH2]4+ 438 424 — [6M-16CH2]4+ 424 415 414 [6M-6D]4+ 414 402 403 [6M-22CH2-7D]4+ 403 392 393 [6M-8D]4+ 392 370 368 [6M-10D]4+ 370 aThe two dyes show almost identical fragmentation patterns and, for simplicity, the listed MS fragments are for 1a; the fragments of dye 2a Fig. 4 Electrospray mass spectrum of 2,4-bis[4-(N-methyl-N-butyl- also exclude the oxygen atoms of the hydroxy groups. D= amino)-2,6-dihydroxyphenyl]squaraine 3a.Monomer: m/z=469 -N(CH3)2 (donor). [M+H]+. Aggregate: m/z=819 [1.75 M]+O[7M]4+; 702 [1.5M]+O[6M]4+. The peak at 818 [1.75M-H]+ is stronger and has been labelled instead of 819. abundant aggregate. However, using the method of McKerrow et al.,11 arrested crystallisation from solution has provided absorption maxima at ca. 650–700 nm for the SHG-active exist as separate entities, the lower aggregate may result from dyes, those which form dimeric aggregates, with the maxima the fragmentation of the heptamer.Furthermore, Chen et al.12 being hypsochromically shifted to 530–550 nm for the inactive have previously suggested the formation of a cyclic tetrameric species, the hexameric and heptameric aggregates. aggregate and, thus, it is feasible that the molecules of the Furthermore, correlation between the linear and nonlinear heptameric aggregate adopt a bicyclic arrangement in which optical properties and the aggregate structures of anilino two tetramers are fused.squaraines has been established for LB films.4–7 Significantly, The ESI-MS data for the N,N-dimethylamino analogues of transitions involving a hypsochromic shift of the LB absorption 1 and 2 also correspond to fractional values of the aggregate band invariably result in the loss of SHG6 and, typically, the mass (m/z=480 for 1a and 528 for 2a, [1.5M]+).The fragmen- SHG-inactive phase is associated with a narrow absorption at tation patterns are similar and may be assigned to the progressca. 530 nm and no significant higher wavelength shoulder.The ive loss of the CH2 and amino groups and, for the dihydroxy molecules probably adopt a parallel face-to-face arrangement derivative, the loss of both oxygens (Fig. 5; Table 2). Close whereas, for the SHG-active LB films and solution aggregates, scrutiny of the spectra suggests that the dyes probably form the structural requirement can only be met if there is non- the hexameric aggregate ([1.5M]+O[6M]4+) rather than the parallel alignment.It is therefore assumed that the molecules trimeric species ([1.5M]+O[3M]2+), the peaks at ca. 455.5 of the dimeric aggregate adopt a T arrangement with intermol- corresponding to the loss of 7CH2 for z=4 and a non-integral ecular charge transfer between the donor (anilino) and acceptor number for z=2. Furthermore, solid solutions of these dyes (C4O2) moieties.This was suggested in a previous report4 and are SHG-inactive and it is assumed that the aggregate structure the hypothesis has since been corroborated by the theoretical is centrosymmetric. In fact, none of the materials with m/z analysis of Bre�das and Brouye`re.16 values corresponding to fractional values of the relative molecular mass, i.e.[1.5M]+ or [1.75M]+, have thus far exhibited EVect of doping with Na+ and K+ SHG when deposited as spun-coated solid solutions. The solution spectra of these dyes typically display an Langley et al.13 reported ESI-MS data for three of the anilino intense monomer peak at ca. 635–665 nm with half widths at squaraines listed in Table 1 (labelled 1b, 1f and 1g) and half maximum of 7–13 nm and, additionally, a broad shoulder assigned the aggregate peaks to [nM+Na]+ where 2n is an which may be assigned to the aggregate.It is not possible to integer and 42n9. They proposed that the sodiation is a relate the nonlinear optical behaviour to the spectra because true reflection of the aggregates in solution whereas, in this the monomer absorption, albeit sharp, masks that of the less work, the ESI-MS data for dye 1 and several related squaraines clearly show that it is not.However, the metallated species may be obtained by doping with NaBr (or KBr to give the potassiated aggregate). The results are listed in Table 3 and, interestingly, the fine structure of the fragmentation pattern of Table 3 ESI-MS data of undoped and lightly doped samples of 2,4- bis[4-(N-methyl-N-alkylamino)phenyl]squaraine where the alkyl group is butyl (dye 1b) and hexyl (dye 1c) undoped (m/z) Na+ doped (m/z) K+ doped (m/z) assignmenta 1b 1c 1b 1c 1b 1c monomer [M+2H]+ 406 462 406 462 406 462 [M+H+A]+ — — 428 484 444 500 aggregate [2M+3H]+ 810 923 811 923 811 923 [2M+2H+A]+ — — 833 945 849 962 Fig. 5 Electrospray mass spectrum of 2,4-bis[4-(N,N-dimethylamino)- aA=alkali metal (Na+ or K+).Higher aggregates of general formula [ xM+yH+zA]+ have been observed but their occurrence is 2-hydroxyphenyl]squaraine 2a. Monomer: m/z=353 [M+H]+. Aggregate: m/z=528 [1.5M]+O[3M]2+ or [6M]4+. dependent upon the concentration of dopant. J. Mater. Chem., 1998, 8(2), 373–376 375K. Y. Law, J. Imaging Sci., 1987, 31, 83; K. Y.Law, Chem. Rev. 2,4-bis[4-(N-methyl-N-hexylamino)phenyl]squaraine is mim- 1993, 93, 449. icked by the sodiated and potassiated peaks with the m/z 2 V. P. Jipson and C. R. Jones, J. Vac. Sci. T echnol., 1981, 18, 105; values being shifted by 22 and 38 respectively. It is relevant D. J. Gravesteijn, C. Steenbergen and J. van der Ween, Proc. SPIE that Langley et al.13 used a mixture of NaI and CsI as the Int.Soc. Opt. Eng., 1983, 420, 327; A. H. Sporer, Appl. Opt., 1984, calibrant and this is a likely source of contamination of their 23, 2738. 3 C. Poga, T. M. Brown, M. G. Kuczyk and C. W. Dirk, J. Opt. Soc. ESI-MS data. The results of this study clearly indicate that Am B, 1995, 12, 531; J. H. Andrews, J. D. V. Khaydarov, K. D. the aggregates freely exist, even in dilute solution, and their Singer, D.L. Hull and K. C. Chuang, J. Opt. Soc. Am. B, 1995, 12, presence is manifested by the second-order properties. 2360; C. W. Dirk, W. C. Herndon, F. Cervantes-Lee, H. Selnau, S. Martinez, P. Kalamegham, A. Tan, G. Campos, M. Velez, J. Zyss, I. Ledoux and L. T. Cheng, J. Am. Chem. Soc., 1995, 117, 2214. Conclusion 4 G. J. Ashwell, G. JeVeries, D.G. Hamilton, D. E. Lynch, M. P. S. Squaraine dyes associate in solution and the ESI-MS analysis Roberts, G. S. Bahra and C. R. Brown, Nature, 1995, 375, 385; G. J. Ashwell, Adv.Mater. (Research News), 1996, 8, 248. has revealed m/z values which may be assigned to acentric 5 G. J. Ashwell, G. S. Bahra, C. R. Brown, D. G. Hamilton, D. E. dimeric aggregates (or multiples of two if z>1) which are Lynch and C.H. L. Kennard, J.Mater. Chem., 1996, 6, 23. SHG-active and to hexameric and/or heptameric aggregates 6 G. J. Ashwell, G. M. S. Wong, D. G. Bucknall, G. S. Bahra and which are not. The aggregation number is compound specific C. R. Brown, L angmuir, 1997, 13, 1629. and, for the anilino squarainesthe higher aggregates may be 7 G. J. Ashwell, G.JeVeries, N. D. Rees, P. C. Williamson, G. S. Bahra and C. R. Brown, L angmuir, submitted for publication. obtained by using hydroxy substituents and less sterically 8 G. J. Ashwell and P. Leeson, Electrical and Related Properties of hindered N,N-dialkylamino groups. It is assumed that hydro- Organic Solids (ed. R. W. Munn, A. Miniewicz and B. Kuchta), gen bonding and chromophore-dominated interactions play NATO ASI Series, 1997, 24, 297.an important role in determining the aggregate structure. 9 G. J. Ashwell, T. Handa, P. Leeson, K. Skjonnemand, G. JeVeries and A. Green, J.Mater. Chem., following paper. I am grateful to Gary JeVeries, Paul Leeson and Trish 10 H. Chen, W. G. Herkstroeter, J. Perlstein, K. Y. Law and D. G. Williamson (Cranfield) for technical assistance and Ian Fleet Whitten, J. Phys. Chem., 1994, 98, 5138. 11 A. J. McKerrow, E. Buncel and P. M. Kazmair, Can. J. Chem., and Lu Yu (UMIST) for providing the ESI-MS data. The 1995, 73, 1605. EPSRC (UK) and Defence Evaluation Research Agency (UK) 12 H. Chen, K. Y. Law, J. Perlstein and D. G. Whitten, J. Am. Chem. are also acknowledged for support of the nonlinear optics Soc., 1995, 117, 7257. programme on squaraine dyes. 13 G. J. Langley, E. Hecquet, I. P. Morris and D. G. Hamilton, Rapid Commun.Mass Spectrom., 1997, 11, 165. 14 K. Y. Law and F. C. Bailey, J. Org. Chem., 1992, 57, 3278. 15 K. Y. Law and F. C. Bailey, Can. J. Chem., 1993, 71, 494; K. Y. References Law, F. C. Bailey and L. J. Bluett, Can. J. Chem., 1986, 64, 1607. 16 J.-L. Bre�das and E. Brouye`re, personal communication. 1 R. J. Meiz, R. B. Champ, L. S. Chang, C. Chiou, G. S. Keller, L. C. Liclian, R. B. Neiman, M. D. Shattuck and W. J. Weiche, Photogr. Sci. Eng., 1977, 21, 73; A. C. Tam, Appl. Phys. L ett., 1980, 37, 978; Paper 7/05466A; Received 28th July, 1997 376 J. Mater. Chem., 1998, 8(2), 373–3

ISSN:0959-9428    

DOI:10.1039/a705466a

出版商:RSC    

年代:1998

数据来源: RSC