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J O U R N A L O F C H E M I S T R Y Materials Feature Article Developing an understanding of the processes controlling the chemical bath deposition of ZnS and CdS Paul O’Brien* and John McAleese Department of Chemistry, Imperial College of Science Technology and Medicine, South Kensington, London, UK SW7 2AY. E-mail: p.obrien@ic.ac.uk Received 24th June 1998, Accepted 3rd August 1998 The deposition of cadmium sulfide by chemical bath area which is well documented.10 Applications in optoelecmethods is straightforward and involves an alkaline solu- tronic or photovoltaic devices is another area receiving attention of a cadmium salt, a complexant and a chalcogen tion, see for example Squeiros et al.,11 but has yet to be fully source, often thiourea or thioacetamide.Supersaturation developed.In CdS based solar cells, the use of wider bandgap of the bath with respect to ‘Cd(OH)2’ is necessary for the materials such as ZnS or CdxZn1-xS could lead to decreases deposition of good quality films under a wide range of in window absorption losses and improvements in the short conditions. In contrast zinc sulfide is more difficult to circuit current of the cells. Saitoh et al.have discussed the use deposit. In this paper we discuss the literature concerning of ZnS in passive structures such as optical waveguides,12 the deposition of these chalcogenides and use equilibrium while Landis et al.13 have described the index-matching of models to rationalise many of the observations found in wide-bandgap epitaxial heterojunction windows including ZnS the literature.Strategies for the deposition of high quality for silicon based solar cells. On mercury cadmium telluride films of ZnS by CBD are discussed. (HgCdTe), ZnS films can be used as gate dielectric layers in infrared photodetectors for CCDs14 and hence have a Introduction potentially wide range of applications. There is considerable interest at present in the soft processing of materials.1 Zinc and cadmium sulfide are compound The CBD process semiconductors with a wide range of potential applications.Film deposition These materials have many similarities, both exist in cubic or hexagonal forms and are wide-, direct-bandgap In chemical bath deposition experiments, solid material is semiconductors. formed which means that the bath must be thermodynamically The chemical bath deposition (CBD) process uses a unstable with respect to precipitation of the solid phase controlled chemical reaction to eVect the deposition of a thin formed, i.e.supersaturated. There are two parent possible film by precipitation. In a typical experiment substrates are reactions leading to solid material, notably: (i) within the bulk immersed in an alkaline solution containing the chalcogenide of the solution (homogeneous precipitation); (ii) at a surface, source, the metal ion and added base.A chelating agent is the substrate or adventitious reaction on the reaction vessel also added to control the hydrolysis of the metal ion. The surface (heterogeneous precipitation). process relies on the slow release of S2- ions into an alkaline It is the second of these routes which leads to film formation.solution in which the free metal ion is buVered at a low There is a tendency in the literature to discuss the deposition concentration. The speciation of metal ions, in particular the of thin films in terms of two distinct mechanisms or models. free metal ion concentration, is controlled by the formation The models form end points in a complex series of potential of complex species, e.g.[Zn(NH3)6]2+. The supply of sulfide processes for the deposition of adherent films encompassing ions is controlled by the decomposition of an organic sulfur many diVerent possibilities (Fig. 1). The first of these is the containing compound, usually thiourea or thioacetamide. The solubility product of the compound in question helps maintain the stoichiometry of the deposited material, homogeneous compounds can be obtained as a result.A large number of physicochemical factors control the growth of the deposit under a specific set of reaction conditions. The supersaturation with respect to an individual phase is important as well as the kinetics of the growth processes.The technique has been used extensively to grow CdS and this is reflected in the numerous papers on the subject.2–8 CBD is the production method for the CdS component of the ‘Apollo’ (CdS/CdTe) series solar cells manufactured by BP Solar. The deposition of ZnS by CBD is a more diYcult proposition than that of CdS. In particular it is evident that there is a much wider range of conditions in which the concurrent deposition of zinc sulfide and oxide can occur.It would be useful to be able to deposit ZnS by CBD. There is a diverse range of applications for thin films of this semiconductor including as waveguides, heterojunction devices and in thin-film electroluminescent displays in which it is the most commonly used host material.9 The potential of ZnS layers in Fig. 1 Schematic representations of the processes which could lead to a thin film: ion-by-ion, cluster-by-cluster and mixed. blue light-emitting diodes (LEDs) and laser diodes is also an J. Mater. Chem., 1998, 8(11), 2309–2314 2309so-called ion-by-ion process in which the ions condense at the reacting surface to form the film. The second is termed the cluster-by-cluster process in which agglomeration of colloidal particles pre-formed in solution, by the homogeneous reaction, leads by absorption at the surface to particulate films.In practice both processes may occur and or interact, leading to films in which colloidal material is included in the growing films. The predominance of one mechanism over another is governed by the extent of heterogeneous and homogeneous nucleation.Key factors include the degree of supersaturation of the solution and the catalytic activity of the surface (substrate). 15 As indicated in (Fig. 1) there are several chemical reactions which can potentially be involved in each of these Fig. 2 Graph of growth rate vs. [ligand ]. processes. The mechanisms of CBD processes are really quite poorly The situation is diVerent for ZnS and Dona and Herrero21 understood and this is reflected in the literature.The actual have suggested that as the growth rate for ZnS appeared be processes leading to the formation of good quality adherent independent of stirring this allows the possibility of diVusion films are complex. The CdS system illustrates the point. Good control to be discarded.They found that graphs of growth quality (adherent) films are only obtained from baths which rate against [NH3] or [N2 H4] had similar profiles, see Fig. 2. are supersaturated with respect to the precipitation of cadmium There is an acceleration of growth rate with concentration up hydroxy species, irrespective of the substrate used. As the to an optimum concentration of the ligand (at molar concensupersaturation of Cd(OH)n species is a very important factor trations, 1.5–2.0 nm min-1) and then the rate rapidly declines.in the formation of adherent films, the processes that might Similar relationships are observed for both complexing agents. be important include: (i) the formation of clusters ‘CdxOHy’; Decreases in ligand concentration resulted in increases in the (ii) the absorption of these ‘nuclei’ at the surface; (iii) the free zinc metal ion concentration and therefore an enhancemetathetical reactions of surface bound ‘nuclei’ with sulfide ment of homogeneous precipitation.Increases in concentration ions or thiourea in a heterogeneous process to form good of either complexing ligand must reduce the amount of free quality CdS; and (iv) the formation and reactivity of pendant zinc ion in solution and therefore restrict the growth rates of OH groups on the surface.both homogeneous and heterogeneous precipitation. In early work, Kitaev et al. postulated16 that the presence Mokili et al.22 have hence proposed that the formation of of hydroxide particles in solution was necessary for the growth Zn(OH)2 must be minimised in order to obtain ZnS due to of good quality films, the decomposition of thiourea being possible competition between the formation of sulfide and stimulated by a solid phase such as cadmium hydroxide.This hydroxide in basic solutions [Zn(OH)2, Ksp=10-15.3 and ZnS, proposal was supported by the observations of Kaur et al.17 Ksp=10-23.8]. in that adherent films were only prepared in the presence of Froment and Lincot18 found ZnS films to be diVerent from ‘Cd(OH)2’ in solution.The importance of ‘Cd(OH)2’ species those of CdS and to be an aggregation of spherical particles, in the growth mechanism of CdS even in conditions where no in a more or less close packed structure. The distance between observable macroscopic precipitate is present is clear.Froment reticular planes revealed that the films were composed mainly and Lincot18 suggested that the mechanism of film formation, of cubic ZnS. Electron diVraction patterns are similar to those similar to that proposed by Parfitt,19 could be represented by for CdS colloids. Evidence like this indicates that the growth the following series of consecutive surface adsorption/reaction mechanism for ZnS is probably a colloid aggregation process.steps: Similar findings have been reported by Mokili et al.,22 TEM results revealing ZnS films composed of aggregated grains in Cd2+aq+site+2 OH-�Cd(OH)2,ads (1) an amorphous matrix. (NH2)2CS+Cd(OH)2,ads�C* (2) In contrast, Dona and Herrero21 suggest that the deposition process has its basis in the slow release of Zn2+ and S2- ions C*�CdS+site (3) in solution.These ions, it is suggested, condense on the where C* is a reaction intermediate. substrates. This idea suggests an ion-by-ion process, opposing The supersaturation limit for the formation of ‘Cd(OH)2’ the statement of others. Contradictory statements such as may be only coincidentaly signigficant as the pKa of surface these have prompted us to form the opinion that no proper, bound Cd2+ could be similar to that of the ion in solution.fundamental understanding of the process exists to date. The formation of surface bound hydroxy species could be the Table 1 summarises some typical chemical bath conditions important step which could serendipitously occur at a similar used in ZnS deposition. value of pH to the formation of a precipitate of the hydroxide.Various other sequences of these reactions could lead to Reaction kinetics adherent CdS. It is interesting to note that freshly precipitated Cd(OH)2 is readily metathesised to CdS in the presence of The kinetics of typical CBD processes (Fig. 3) appear to follow a sigmoidal profile similar to those observed for thiourea; this reaction appears not to happen with the zinc analogue.The solution species formed in the case of zinc are autocatalytic reactions.23,24 In solid state nucleation and growth processes, such evidently diVerent as is the degree of supersaturation. CdS has been reported to grow epitaxially on single crystals reactions are often described by a formal kinetic expression such as the Avrami equation: by CBD such as InP.20 This observation supports an ion-byion mechanism because of the register required between the a=1-e(-kt) (4) substrate and growing layers at the atomic level.Further evidence comes from an HRTEM18 study of material deposited where a is the fractional decomposition, t the time and k a rate constant. This is an expression of the rate of formation before coalescence of the CdS film. Monocrystalline nuclei (30 nm) are formed at the substrate surface with the c-axis of nuclei in the special case when there is completely random nucleation.25 If we consider such processes in a qualitative perpendicular to the surface. These crystallites coalesced to form a continuous film composed of microcrystallites (hexag- way the kinetics are dominated by three phases: (i) initiation, often nucleation, the initial step usually requiring a high onal, 20–80 nm). 2310 J. Mater. Chem., 1998, 8(11), 2309–2314Table 1 Some typical chemical bath conditions reported to have deposited ZnS Counter ion, Ligand 1, Ligand 2, Added base, Sulfiding agent, T / °C, Band gap/ Phase Ref. conc./M conc./M conc./M conc./M conc./M growth eV reported rate/A° min-1 sulfate, 0.14 NH3, 3.75 HZ, 0.508 Na2B4O7, 0.03 (NH2)2CS, 0.50 80, 10 34 90, 17 chloride, 0.20 NH4+/NH3, 2.00 TAA, 0.04 3.60 cubic 15 n-type chloride, 0.02 TAA, 0.02 4.10 cubic 15 >3.7 sulfate, 0.025 NH3, 1.00 HZ, 3.00 (NH2)2CS, 0.035 3.76 cubic 16 sulfate, 0.05 TEA, 0.20 2.2 ml pH 10 TAA, 0.04 17 NH3/NH4Cl sulfate, 0.05 TEA, 0.225 TAA, 0.02 17 19 sulfate, 0.025 NH3, 1.00 HZ, 3.00 (NH2)2CS, 0.035 3.76 cubic 21 acetate, HZ, 0.50–3.00 NH4+, 0.02 TAA, 0.001–0.1 <16.7 3.60–4.00 18 0.001–0.01 chloride, HZ, 1.10 (NH2)2CS, 25, 1.5 3.85 22 0.075–0.190 0.100–0.150 chloride, 0.20 HZ, 4.00 (NH2)2CS, 0.20 16.7 3.70–3.80 42 acetate/sulfate, HZ, 1.1–1.2 HZ, 3.00; (NH2)2CS, 0.035–0.1 25, 0.4 34 0.025–0.050 en, 0.2; TEA, 0.07 HZ, hydrazine (N2H4); TEA, triethanolamine; en, ethylenediamine; TAA, thioacetamide (CH3CSNH2).Glass substrates were used in all cases except ref. 17 where CuInSe2 substrates were also used. cadmium is extremely important in controlling the nature of the films deposited. There appears to be no such simple relationship for zinc sulfide deposition. The degrees of supersaturation in any system will depend on various factors including pH, ligand concentration and temperature.It is interesting to compare the speciation in similar chemical baths for cadmium and zinc. If we take the ethylenediamine system as an example, a bath modestly supersaturated with respect to cadmium hydroxide is readily obtained at a 251 ligand to metal ratio ([Cd]=180 mmol dm-3, [en]= 360 mmol dm-3), Fig. 4(a) pH> ca. 9.5. In contrast a similar Fig. 3 Kinetic profile for a generalized autocatalytic process, fraction of reaction (a) vs. time. activation energy in which reactive centres which catalyse the reaction are formed; (ii) the main phase of the reaction, sometimes zero order in which a number of reactive sites gives rise to a lower activation energy pathway, autocatalysis in a general sense, but in a heterogeneous reaction the growth of nuclei; and (iii) a termination step in which the reagent becomes depleted and the reaction begins to slow and eventually stops.Intuitively this kind of general model is attractive for CBD processes and one thing which is interesting is that many CBD processes show a substantial linear portion in their kinetic profile (see for example ref. 18). This observation may suggest that in this phase of the reaction the process is controlled by a constant number of saturated reaction sites. There is an analogy here with the growth of thin films by MOCVD which is often arranged to be in a diVusion limited regime. Equilibrium considerations The metal ions zinc and cadmium are both labile, so it is reasonable to assume that in stirred solutions equilibria will be rapidly established, hence equilibrium models are useful in assessing the starting points of these chemically reactive baths.In any reaction which involves precipitation, the state of supersaturation of the system will be crucial and equilibrium Fig. 4 Speciation diagram to illustrate the fundamental diVerences calculations help to assess its extent.It is known in the between cadmium and zinc complexation: (a) cadmium, (b) zinc. In deposition of CdS that the supersaturation of the reacting each case [M]=180 mmol dm-3 and [en]=100 mmol dm-3 (equilibrium constant values are at 50 °C and from references 8 and 26). chemical bath with respect to hydroxy/oxy complexes of J. Mater. Chem., 1998, 8(11), 2309–2314 2311released. In a typical deposition experiment (90 °C, 1 h), a conformal film ca. 0.6 mm thick was deposited. It would be interesting to look at the possibility for ternary material deposition from such baths which operate at much lower pH values than are typical for CBD. The films deposited by this method had bandgaps close to that expected for ZnS. Nature of the films deposited in ZnS experiments Electronic properties.Another important issue concerns ndgaps of films deposited from ammonia free baths discussed above27 which are close to that expected for bulk ZnS (3.6 eV). Films deposited from ammonia containing baths have been reported to have bandgaps (4.1–3.9 eV) consistently higher than the bulk value,28 Table 1. There has been speculation that this eVect is due to quantum confinement in the very small (grain size 3–6 nm) crystallites of which these films Fig. 5 Limiting solubility lines for ‘M(OH)2’ {[M]/mol dm-3 (for were composed.29 In essence, a 3-D quantum size eVect is supersaturation) vs. pH, M=Cd or Zn} and corresponding supersaturation line ([S-]/mol dm-3 vs. pH) [for illustration pKsp values used suggested to be occurring in which electrons are localised in at 20 °C: ‘Zn(OH)2’, 15.3; ZnS, 23.8; ‘Cd(OH)2’, 14; CdS, 28].individual crystallites of polycrystalline thin films.30 CdSe films Double-headed arrow shows typical region used for CdS deposition, have been grown where bandgap values were apparently up the path A to B to C is explained in the text. to 0.5 eV higher than in single-crystal samples.31 Similar observations relate to PbSe films32 which were found to contain bath containing zinc is unstable with respect to precipitation crystals of varying size depending on the deposition paramof the hydroxide at much lower values of pH>ca. 7.5.In the eters, in particular the nature of the complexing agent, the presence of modest amounts of a sulfiding agent, in the alkaline film thickness and the deposition temperature, and ZnS parregion, the cadmium bath deposits CdS while in the ticulate films (particle size 30–60 A° ).33 Although such eVects corresponding zinc bath ZnO/hydroxide is more easily formed.have been explained by quantum confinement, it is entirely The above calulations draw attention to a fact that we and possible that some of the films are chemically inhomogeneous others have commented on in several papers, i.e.the impor- with a significant quantity of oxide/hydroxide incorporation. tance of the supersaturation of cadmium solutions with respect to hydroxy species as a necessary condition for the growth of good quality films of CdS. It is possible to further develop Film composition. Many of the films reported as ZnS which have not been rigorously characterised are probably at best this approach in a comparative way by considering the solubility limits for metal hydroxy species as a function of pH.At heavily contaminated with zinc oxide or hydroxide. In an RBS study Mokili et al.22 showed that CBD deposits contained any value of pH there is a limiting value of pM (defined by KspOH2 /[OH]2) below which supersaturation will occur.These significant amounts of oxygen. EXAFS confirmed the presence of oxygen in the form of hydroxide and a high oxygen to limits are approximately linear on plots of pM vs. pH, Fig. 5. At pH 10–11, we know good quality CdS would be deposited sulfur ratio was found. The compositions of some films were even reported to be close to Zn(OH)2.In more basic solutions from such a solution. This condition is suYcient to define a minimum sulfide ion concentration at which metathesis to the containing hydrazine, deposits of material close in stoichiometry to ZnS were obtained, but even such samples were not sulfide becomes a preferred reaction (KspS/[M]). It is striking that CdS is much more stable than ZnS and this is again of the pure sulfide and were contaminated with either oxide (ZnO0.5S0.5) or hydroxide [Zn(OH)S0.5].graphically illustrated (Fig. 5). The actual supersaturation in a reactive chemical bath will depend on the sulfide ion concen- On the basis of these studies they proposed a deposition mechanism involving hydroxide intermediates and suggested tration, however the relative positions of the lines for cadmium and zinc will be unchanged. that if the transformation of hydroxide into sulfide is too slow, significant amounts of hydroxide would be present in the final If we assume that as CdS and ZnS are similar materials (structurally), a similar path is in principle possible for their film.A general conclusion is that the presence of a significant quantity of oxide or hydroxide in the ZnS films may be deposition as thin films. We can investigate this idea by defining equivalent conditions for ZnS and CdS in terms of explained by the proximity of the solubility lines of the sulfide and the hydroxide.supersaturation for the sulfide, which are found by following the line B–C on Fig. 5. Later EXAFS studies by Mokili et al.34 showed that thin films prepared by CBD in alkaline ammonia solutions contain- There are several important conclusions that we can draw from this simple calculation: (i) equivalent levels of supersat- ing a zinc salt, thiourea and diVerent amine additives were zinc hydroxosulfide, the oxygen content of which ranged uration for the sulfide are found at pH values ca. 2.5 lower for ZnS than CdS; (ii) if reactions are carried out in a high between 39 and 82%.FTIR studies supported the evidence suggesting that the films consisted mainly of Zn(OH)2 with pH regime more sulfiding agent (by ca. 4 orders of magnitude!) will be needed for the zinc system, even so the degree of little or no ZnO present. A clear absorption at 648 cm-1 was assigned to a ZnMOH stretching mode by KauVman et al.35 supersaturation for zinc with respect to the hydroxide will always be greater than for cadmium with respect to its The ZnMO bond peak position (at 430 cm-1 from a ZnO powder sample) was very weak in most spectra thus rejecting hydroxide (values of pM and pH being equal ); and (iii) at lower pH the rate of hydrolysis of the sulfide source is likely the hypothesis that significant amounts of ZnO were formed in the films.Such compositions were present even without to be lower so again even if a lower pH is used more sulfide source will be needed. post-annealing. A point worth stressing is the similarity of the conditions It is interesting to note that an intuitive attempt to develop this kind of approach has been reported.27 The chemical bath used in the Mokili study34 to those used in the majority of the other studies of ZnS by CBD, Table 1. All of the reported used contained zinc ions and urea, at modestly acid values of pH.The urea slowly hydrolysed in the bath to provide conditions for the deposition of ZnS as detailed in Table 1 are remarkably similar and suggest that there is the distinct hydroxide and thioacetamide hydrolysed as the hydroxide was 2312 J.Mater. Chem., 1998, 8(11), 2309–2314possibility of heavy oxide contamination or incorporation in many of the films reported as ZnS. The chemistry of sulfide delivery In essence, the chemistry involved in the CBD of ZnS is straightforward. Thiourea decomposition will occur in CBD baths essentially as described in the kinetics studies carried out by Marcotrigiano et al.36 into the desulfuration of thiourea in sodium hydroxide.They postulated that in alkaline solutions, thiourea first gives sodium sulfide and cyanamide which is then transformed into cyanamide, amidinourea, guanidine or, at pH 12, almost quantitatively into urea which isomerizes to ammonium cyanate and is finally hydrolysed to ammonium carbonate: (NH2)2CS+OH-ANCNH2+SH-+H2O (5) Fig. 6 Equivalent solutions. (A) An equivalent solution contour plot NCNH2+H2OAONC(NH2)2 (6) for pM=9 ([M]total vs. [en]total) for the cadmium ethylenediamine system at 50 °C (see ref. 8 for relevant constants); (B) [en]total/[M]total ONC(NH2)2ANH4CNO (7) for pM=9, (C) [en]/[M]total=3. (valid for pH&pKa2 of ethylenediamine). OCN-+2 H2OAHCO3-+NH3 (8) The cyanate and carbonate ion are thought to form very to predict for the CdS system the composition of baths which early in the reaction and may be responsible for the hydroxide will produce high quality films at diVerent concentrations or consumption being greater than that corresponding to reaction how the substitution of one ligand with another, e.g. ethylene- (2).It is assumed that the hydroxide consumption equals the diamine for ammonia, can be made in such a way as to SH- formation.It is known that thiourea behaves as a maintain good quality film deposition. A typical plot is shown zwitterion37 which may play a role in the thiourea desulfurin Fig. 6 for the ethylenediamine cadmium system. The contour ation. Recent observations in our laboratory may suggest that defining constant pM is a curve and much higher ratios of under typical CBD conditions, decomposition of thiourea ligand to metal are needed as the overall concentration proceeds only as far as urea. decreases.This idea is consistent with the tendency of complexes to dissociate on dilution. The third line shows the Strategies for growth contour for a constant ligand to metal ratio of 351 which The fact that the CBD of CdS produces highly crystalline, emphasises that this line is diVerent from that defining a conformal, adherent films relatively easily suggests that one constant pM.There will of course be a critical ratio if one of strategy for growing good films of ZnS would be to alter the the variables is held constant as can be seen from Fig. 6 and bath conditions to favour the same mechanism that governs the concept is useful at high concentration, but this idea does CdS deposition. Froment and Lincot18 suggested that by not allow for the method to be generalised. changing the composition of the reacting solutions competition In related work on PbSe Gorer et al.41 appear to support between the processes of homogeneous and heterogeneous the possibility of a mechanism crossover.Experimental connucleation could be altered to favour thin film growth. ditions were demonstrated where either one or both growth Subsequent experimental work by Mokili in conjunction with mechanisms could lead to fine control of the film properties. Froment and Lincot,22 however, has shown that no marked changes with regards to the growth curves occurred for ZnS Conclusions understanding ZnS deposition in when the conditions approached and/or crossed the precipirelation to physico-chemistry tation lines.This behaviour is quite unlike that of the cadmium sulfide systems for which a clear change in the growth habitat The use of a second ligand is observed when supersaturation is achieved.38 They have also suggested that there is little or no induction time associated Many workers report the use of a second ligand in the chemical bath when attempting the deposition of ZnS.Hydrazine is a with ZnS growth which may suggest that growth depends on colloidal material in this case. popular choice in the CBD of ZnS. A typical observation is that of Ortega-Borges et al.27 who reported that the use of Gorer and Hodes39 suggested for CdSe that the presence or absence of hydroxide particulate material in solution may ammonia and thiourea without hydrazine resulted in films which were not homogeneous or adherent.govern the transition between atom-by-atom and colloidal growth. The change in mechanism was apparently indicated In a related observation Dona and Herrero21 have suggested that the addition of hydrazine, ‘although not essential, by a sharp change in crystal size (observed by shifts from blue to red in optical spectra).They suggested a ‘critical ratio’ R(c) improves homogeneity, specularity and growth rate’. Ndukwe also used hydrazine.42 Dona and Herrero have suggested that (concentration of complexing agent, nitrilotriacetate, to cadmium salt) below which Cd(OH)2 was present and above the rate-determining step for the heterogeneous process may involve the dissociation of a Zn2+ML bond.This suggestion which it was not, despite a visible Cd(OH)2 suspension under any condition. This led them to propose that below R(c) the is unlikely as zinc is classically a labile metal ion. Another possibility is that the hydrazine complex ions have a lower co- mechanism is initiated on the Cd(OH)2 colloidal particles adsorbed on the substrate and above R(c), deposition occurs ordination number (and therefore less steric impediment for the approach of the sulfide ion).Hydrazine could potentially directly on the substrate by initial film formation without Cd(OH)2. act as a bridging ligand and perhaps facilitate surface binding.One thing which must be noted is that at a constant pH the However, it is hard to justify the importance of a critical ratio of metal to ligand. We have defined a useful concept of addition of a second ligand can only lead to a lowering of the free metal ion concentration. In the case of zinc this will lower equivalence in terms of a contour defining a constant value of pM on a plot of total metal ion concentration against total supersaturation with respect to either oxide/hydroxide phases or the sulfide.ligand concentration.40 The use of such plots has enabled us J. Mater. Chem., 1998, 8(11), 2309–2314 2313The most detailed investigation into the addition of amines Amersham International Research Fellow and the Sumitomo/STS Professor of Materials Chemistry.has been carried out by Mokili et al.22 They found that, in all cases, the addition of either hydrazine, triethanolamine or ethanolamine to ammonia increased thin film growth rates. References Using hydrazine, a maximum growth rate (increased by a 1 M. Yoshimura, J. Mater. Res., 1998, 13, 795. factor of four) could be achieved at 3 mol dm-3.However, 2 J. M. Dona and J. Herrero, 12th E.C. Photovoltaic Solar Energy they suggest that hydrazine accelerates the hydrolysis of thio- Conf., Harwood Academic Publishers, Amsterdam, 1994, 597. urea. Other amines tended to increase the growth rate but did 3 M. T. S. Nair, P. K. Nair and J. Campos, Thin Solid Films, 1988, not change significantly the speciation in the bath (precipi- 161, 21.tation line, pH, etc.). Hence for hydrazine and triethanolamine 4 D. Lincot and R. Ortega Borges, J. Electrochem. Soc., 1992, 139, 1880. they proposed that these molecules participated in the 5 P. C. Rieke and S. B. Bentjen, Chem. Mater., 1993, 5, 43. decomposition of thiourea. 6 H. Hu and P. K. Nair, J. Cryst. Growth, 1995, 152, 57. Dona and Herrero reached similar conclusions21 and have 7 Y.Hashimoto, N. Kohara, T. Negami, N. Nishitani and T.Wada, speculated that the relationship between complexing agents Sol. Energy Mater. Sol. Cells, 1998, 50, 71. and growth rates are typical of a system which has ‘two 8 P. O’Brien and T. Saeed, J. Cryst. Growth, 1996, 158, 497. competing processes’ namely heterogeneous and homogeneous 9 R. Mach and G. O.Muller, Phys. Status Solidi A, 1982, 69, 11. 10 S. Yamaga, Jpn. J. Appl. Phys., 1991, 30, 437. precipitation. They also consider the heterogeneous process to 11 J. M. Squeiros, R. Machorro and L. E. Regalado, Appl. Opt., be ‘limited by complex ion adsorbability’ and by ‘the adsorp- 1988, 27, 2549. tion points on the substrate’. In considering the possibility 12 T. Saitoh, T.Yokogawa and T. Narusawa, Jpn. J. Appl. Phys., that the eVect of additional amines is primarily on the sulfiding 1991, 30, 667. agent Ortega-Borges et al.27 have developed an essentially 13 G. A. Landis, J. J. Loferski, R. Beaulieu, P. A. Sekula-Moise, S. M. Vernon, B. Spitzer and C. J. Keavney, IEEE Trans. Electron. ligand free system, vide supra. Devices, 1990, 37, 372. 14 M.A. Kinch, Semicond. Semimet., 1981, 18, 312. 15 A. E. Nielsen, Kinetics of Precipitation, Pergamon Press, Oxford, Important factors 1964. CBD is potentially a method for the deposition of thin films 16 G. A. Kitaev, A. A. Uritskaya and S. G. Moksushin, Russ. J. Phys. Chem., 1965, 39, 1101. of ZnS. It is also a method free of the many inherent problems 17 I. Kaur, D. K. Pandya and K.L. Chopra, J. Electrochem. Soc., associated with high temperature techniques such as MOCVD 1980, 127, 943. including increased point defect concentration, evaporation of 18 M. Froment and D. Lincot, Electrochim. Acta, 1995, 40, 1293. ZnS leading to polysulfide and a limited choice of substrate. 19 G. D. Parfitt, Pure Appl. Chem., 1976, 48, 415. However to date only a small number of papers have reported 20 D.Lincot, R. Ortega-Borges and M. Froment, Appl. Phys. Lett., 1994, 64, 569. on the deposition of ZnS, by the CBD method, in any detail. 21 J. M. Dona and J. Herrero, J. Electrochem. Soc., 1994, 141, 205. At present progress may be limited by a poor appreciation of 22 B. Mokili, M. Froment and D. Lincot, J. Phys. III, 1995, 5, C3- the complexity of the system and a more thorough understand- 261.ing of the underlying mechanism involved is required for the 23 P. W. M. Jacobs and F. C. Tompkins, in Chemistry of The Solid design of better deposition systems. State, ed. W. Garner, Butterworth, London, 1955, p. 184. In conclusion there are a number of fundamental diVerences 24 A. A. Frost and R. G. Pearson, Kinetics and Mechanism, 2nd edn., John Wiley & Sons, Chichester, 1965, p. 19. between the CdS and ZnS systems which need to be appreci- 25 M. Avrami, J. Chem. Phys., 1941, 9, 177. ated: (i) CdS must, in some cases, be deposited by a mechanism 26 A. E. Martell and R. D. Smith, Critical Stability Constants, 1972, operating at close to the atomic level; epitaxy can be observed. vol. 2: L. D. Petit, IUPAC Stability Constants Data Base, The deposition of ZnS is often diVerent and involves clusters Academic Software, 1997.of ZnS. Part of the challenge in developing the deposition of 27 R. Ortega-Borges, D. Lincot and J. Vedel, in Proc. 11th E.C. Photovoltaic Solar Energy Conf., Harwood Academic Publishers, ZnS and related ternaries is to drive the process toward a Switzerland, 1992, p. 862. surface controlled ion-by-ion process. (ii) The eVect of pH in 28 O. Madelung, Semiconductors other than Group IV Elements and the CdS system is to form Cdx(OH)y species; those crucial for III-V Compounds, Springer, Berlin, 1992, pp. 26–27. film growth are bound to the surface of the substrate. These 29 M. Moskovitz, Chemical Physics of Atomic and Molecular metathesise to the sulfide.In the ZnS system high pH tends Clusters, ed. G. Soles, North Holland, Amsterdam, 1990, p. 397. 30 R. Rossetti, R. Hull, J. M. Gibson and L. E. Brus, J. Chem. Phys., to lead to the formation of Zn(OH)2/ZnO either on the 1985, 83, 1406. surface or as bulk material. At high values of pH metathesis 31 G. Hodes, A. Albu-Yaron, F. Decker and P. Motisuke, Phys. of these compounds to the sulfide is much less favourable than Rev., 1987, 36, 4215. for the cadmium species which can be rationalised by the 32 S. Gorer, A. Albu-Yaron and G. Hodes, J. Phys. Chem., 1995, relatively small diVerences in the solubility products for ZnS 44, 16442. (pKsp=24 at 25 °C) and ZnO/Zn(OH)2 (pKsp=17 at 25 °C). 33 X. Kang Zhao and J. H. Fendler, J. Phys. Chem., 1991, 95, 3716. 34 B. Mokili, Y. Charreire, R. Cortes and D. Lincot, Thin Solid (iii) The deposition of good quality ZnS appears to be optimal Films, 1996, 288, 21. in the presence of two complexants, typically ammonia and 35 J. W. KauVman, R. H. Hauge and J. L. Margrave, J. Phys. Chem., hydrazine. The dominant advantageous eVect of the second 1985, 89, 3541. ligand may be to enhance the rate of decomposition of thiourea 36 G. Marcotrigiano, G. Peyronel and R. Battistuzzi, J. Chem. Soc., increasing the rate of sulfidization of the growing film. (iv) In Perkin Trans. 2, 1972, 1539. 37 J. L. Walter, J. A. Ryan and T. J. Lane, J. Am. Chem. Soc., 1956, many cases there is the possibility that the literature does not 78, 5560. strictly report ZnS growth but more accurately a zinc 38 R. Ortega-Borges and D. Lincot, J. Electrochem. Soc., 1993, 140, hydroxysulfide material. 3464. We consider that a more closely controlled growth 39 S. Gorer and G. Hodes, J. Phys. Chem., 1994, 98, 5338. environment is a necessity if substantial advances in this field 40 P.O’Brien, unpublished results, 1996. are to be made. 41 S. Gorer, A. Albuyaron and G. Hodes, Chem. Mater., 1995, 7, 1243. 42 I. C. Ndukwe, Sol. Energy Mater. Sol. Cells, 1996, 40, 123. P.O’B. thanks the EPSRC for financial support and BP Solar Ltd. for gifts of substrates. P.O’B. is the Royal Society Paper 8/04692A 2314 J. Mater. Chem., 1998, 8(11), 2309–2314

ISSN:0959-9428    

DOI:10.1039/a804692a

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 Communication A new oxide precursor: the synthesis of a bimetallic alkoxy derivative of strontium(II ) and tantalum(V) Hywel O. Davies,a,b Anthony C. Jones,*b Timothy J. Leedham,b Paul O’Brien,*a Andrew J. P. Whitea and David J. Williamsa aDepartment of Chemistry, Imperial College of Science, Technology and Medicine, South Kensington, London, UK SW7 2AY.E-mail: p.obrien@ic.ac.uk bInorgtech Limited, 25 James Carter Road, Mildenhall, SuVolk, UK IP28 7DE. E-mail: tony@TJconsultancy.demon.co.uk Received 14th August 1998, Accepted 21st September 1998 The compound [SrTa2(OEt)6(m-OEt)4(m-O-bis-dmap)2] 1 The complex [SrTa2(OEt)6(m-OEt)4(m-O-bis-dmap)2] 1† was has been prepared from the reaction of the mixed metal synthesised from the reaction of [SrTa2(OEt)8(m-OEt)4] 2 with alkoxide [SrTa2(OEt)8(m-OEt)4] with the nitrogen con- two equivalents of bis-dmapH in refluxing n-hexane.Removal taining ligand bis-dmapH [bis-dmapH=1,3-bis(dimethyl- of the solvent in vacuo and subsequent vacuum distillation amino)propan-2-ol]; the bimetallic alkoxide is a poten- yielded a colourless to pale yellow solution that solidified to a tially useful precursor for technologically important waxy solid on standing. Crystals were obtained by recrystallismixed metal oxides, the X-ray single crystal structure of 1 ation from n-hexane and storing at -20 °C for two weeks. has been determined.The compound is more air stable than the parent ethoxide and can be handled in air for several minutes without notable decomposition. Introduction The complex was characterised by microanalysis, NMR Thin films of the layered perovskite oxide SrBi2Ta2O9 (SBT) spectroscopy and an X-ray structure determination.‡ In the have attracted much recent attention as non-volatile ferroelec- crystalline state the compound is composed of discrete tric computer memories.1,2 SBT thin films have been deposited [SrTa2(OEt)6(m-OEt)4(m-O-bis-dmap)2] molecules (Fig. 1). by a variety of techniques including: sol–gel, metal–organic The two dmap ligands are inserted in cis positions with respect decomposition and metal organic chemical vapour deposition to the strontium centre, coordinating binuclearly (to tantalum (MOCVD). The MOCVD of SBT has been severely restricted and strontium) via oxygen and mononuclearly from nitrogen by a lack of suitable metal–organic precursors.Conventional to strontium leaving in each case the remaining ligand nitrogen precursors include metal alkoxides and b-diketonates which non-coordinated, as in related complexes with this ligand.13 are generally not compatible, having widely diVering physical The geometry at strontium is very distorted square antiprisproperties and/or decomposition properties.matic, the ‘square’ faces comprising N(1), O(4), N(11), O(14) The most extensively studied heterometallic alkoxides and O(21), O(24), O(27), O(30) respectively. The Sr–O involve titanium or zirconium in combination with other metal distances fall into two groups, with those to the ethoxides ions.3 In an attempt to improve the range of available precur- [2.547(8)–2.613(7) A° ] being shorter than those to the dmap sors, and to deliver both metals in a single source, we have started to develop the chemistry of mixed Sr/Ta alkoxides.Although compounds such as [Sr{Ta(OPri)6}2] have been used in combination with [Bi(OBut)3] to grow SBT,4 there exists the possibility that strontium and tantalum alkoxide species will partition during the precursor evaporation and transport stages of the MOCVD process.The strategy of our research has been to incorporate strontium and tantalum into one molecule. The double alkoxide5 [SrTa2(OEt)12] 2, and its reaction with nitrogen containing ligands has been investigated. However, the parent alkoxide contains a coordinatively unsaturated strontium centre making them susceptible to attack by moisture and air.The use of donor functional ligands should stabilise such compounds.6 We have now isolated and characterised a novel bimetallic strontium–tantalum ethoxide from the reaction of the parent ethoxide 2 with the nitrogenous ligand, 1,3-bis(dimethylamino) propan-2-ol. The structure of the parent ethoxide [SrTa2(OEt)8(m-OEt)4] 2 will be reported elsewhere.Although some of the chemistry of bimetallic alkoxy deriva- Fig. 1 The molecular structure of 1. Selected bond lengths (A° ); tives of Ta(V) is well established notably compounds with Sr–O(27) 2.547(8), Sr–O(24) 2.565(8), Sr–O(14) 2.595(7), Sr–O(4) Cr(III),7 Fe(II )8 or Co(II),9 we find only one reference to any 2.613(7), Sr–O(21) 2.654(8), Sr–O(30) 2.669(8), Sr–N(1) 2.744(9), double alkoxides of strontium with tantalum in the literature, Sr–N(11) 2.762(10), Ta(1)–O(36) 1.870(11), Ta(1)–O(33) 1.884(9), and only for the parent alkoxides.10 Only three double alkox- Ta(1)–O(39) 1.898(10), Ta(1)–O(21) 1.989(9), Ta(1)–O(4) ides of strontium with other metal ions have been character- 2.006(7), Ta(1)–O(24) 2.032(9), Ta(2)–O(45) 1.880(10), ised structurally to date: [{[Cd(OPri)3]Sr[Hf2(OPri)9]}2],11 Ta(2)–O(48) 1.890(10), Ta(2)–O(42) 1.906(11), Ta(2)–O(30) 1.983(9), Ta(2)–O(14) 2.015(8), Ta(2)–O(27) 2.029(8).[SrTi4(OEt)18]12 and [{Sr2Ti(OPri)8(PriOH)3}·2PriOH].12 J. Mater. Chem., 1998, 8(11), 2315–2316 2315IR (Nujol mull, NaCl plates): 3400s (br), 2900s (br), 1660w (br), ligands [2.654(8) and 2.669(8) A° ]. Not surprisingly the coordi- 1440s, 1410w, 1380s, 1320m, 1265s, 1150–1050s (v br), 1000m, 910s, nation distances to nitrogen are significantly longer [at 2.744(9) 835m and 820m. 1H (C6 D6): d 1.29 (t, CH3, 30H), 2.18 (m, NCH3 and 2.762(10) A° ]. The geometry at each tantalum centre is and NCH2, 32H) and 4.51 [m, OCH2CH3, m-OCH2CH3 and m-OCH distorted octahedral with cis angles ranging between 82.1(4) (bis-dmap), 22H].Analysis: Calc. for C34H84N4O12SrTa2: C, 34.30; and 96.2(4)° at Ta(1) and 82.6(4) and 95.3(3)° at Ta(2). The H, 7.11; N, 4.71; Found C, 34.12; H, 7.05; N, 4.80%. ‡Crystal data for 1: C34H84N4O12SrTa2, M=1190.6, monoclinic, space terminal Ta–O(ethoxide) distances are, as expected, distinctly group P21/n (no. 14), a=20.894(3), b=9.780(2), c=25.458(3) A° , shorter [1.870(11)–1.906(11) A° ] than those to their bridging b=102.66(1)°, V=5078(1) A° 3, Z=4, Dc=1.558 g cm-3, m(Cu- counterparts [1.983(9)–2.032(9) A° ]. The Ta–O(dmap) dis- Ka)=95.3 cm-1, F (000)=2384, T=203 K; clear blocks, 0.87×0.83× tances are 2.006(7) [Ta(1)] and 2.015(8) A° [Ta(2)].The non- 0.33 mm, Siemens P4/RA diVractometer, v-scans, 7799 independent bonded Sr···Ta separations are 3.414(1) and 3.415(1) A° to reflections.The structure was solved by direct methods and the major occupancy non-hydrogen atoms were refined anisotropically Ta(1) and Ta(2) respectively. using full matrix least-squares based on F2 to give R1=0.072, The compound has successfully been used in preliminary wR2=0.195 for 6227 independent observed absorption corrected growth work14 of SrTa2O6. Strontium tantalate thin films reflections [|Fo|>4s(|Fo|), 2h128°] and 527 parameters.Full crystal- (amorphous) were deposited at 400 °C at a growth rate of lographic details, excluding structure factors, have been deposited at >0.2 mm h-1. The full evaluation of this compound as a single the Cambridge Crystallographic Data Centre (CCDC). See Information for Authors, Issue 1.Any request to the CCDC for this source oxide precursor is in hand. material should quote the full literature citation and the reference number 1145/123. 1 T. Ami, K. Hironaka, C. Isobe, N. Nagel, M. Sugiyama, Y. Ikeda, Acknowledgements K. Watanabe, A. Machida, K. Miura and M. Tanaka, Mater. We acknowledge Mr Jack Hodgson of University of Liverpool Res.Soc. Symp. Proc., 1996, 415, 195. 2 T. Li, Y. Zhu, S. B. Desu, C. H. Peng and M. Nagata, Appl. for running the NMR spectra and also the microanalytical Phys. Lett., 1996, 68, 616. department at University of Liverpool. We also acknowledge 3 K. G. Caulton and L. G. Hubert-Pfalzgraf, Chem. Rev., 1990, the support of the Teaching Company Directorate. P.O.B. is 90, 969. the Sumitomo/STS Professor of Materials Chemistry and the 4 Y.Kojima, H. Kodakura, Y. Okahara, M. Matsumoto and Royal Society Amersham International Research Fellow T. Mogi, Ferroelectrics, 1997, 18, 183. 5 S. Govil, P. N. Kapoor and R. C. Mehrotra, J. Inorg. Nucl. (1997/98). H.O.D. is a Teaching Company Scheme Fellow. Chem., 1976, 38, 172. 6 L. G. Hubert-Pfalzgraf, Chemical Vapor Deposition, Proc. 14th Int. Conf. EUROCVD-11, ed. M. D. Allendorf and C. Bernard, Notes and references Electrochem. Soc. Proc., 1997, vol. 97, p. 825. 7 S. K. Agarwal and R. C. Mehrotra, Inorg. Chim. Acta, 1986, †Experimental: All operations were carried out under a dry dinitrogen 112, 177. atmosphere with exclusion of dioxygen and moisture. 1,3- 8 A. Shah, A. Singh and R. C. Mehrotra, Indian J. Chem.Sect. A, Bis(dimethylamino)propan-2-ol (bis-dmapH) and d6-benzene were 1989, 28, 392. purchased from Aldrich and used without further purification. Ethanol 9 R. K. Dubey, A. Singh and R. C. Mehrotra, Bull. Chem. Soc. and n-hexane were dried over molecular sieves and distilled prior to Jpn., 1988, 61, 983. use to remove impurities. Strontium metal and tantalum pentaethoxide 10 D.C. Bradley, R. C. Mehrotra and D. P. Gaur, Metal Alkoxides, were supplied by Inorgtech Limited. The preparation of the parent Academic Press, London, 1978 and references cited therein. alkoxide [SrTa2(OEt)8(m-OEt)4] 2 was essentially as described in ref. 5 11 M. Veith, S. Mathur, C. Mathur and V. Huch, J. Chem. Soc., but modified by dissolving the Sr in ethanol and omitting the use of Dalton Trans., 1997, 2101.the HgCl2 catalyst. The mixture was refluxed for 1 hour and then 12 I. Baxter, S. R. Drake, M. B. Hursthouse, K. M. A. Malik, solvent removed in vacuo. The compound was used for the preparation D. M. P. Mingos, J. C. Plakatouras and D. J. Otway, Polyhedron, 1998, 17, 625. of 1 without further characterization. 13 A. C Jones, T. Leedham, P. J. Wright, M. J. Crosbie, D. J. [SrTa2(OEt)6(m-OEt)4(m-O-bis-dmap)2] 1: A sample of 2 (16.9 g, Williams amd P. O’Brien, Mater. Res. Soc. Symp. Proc., 1998, 17 mmol) was dissolved in n-hexane (500 ml, 99%) and bis-dmapH 495, 11. (5 g, 34 mmol) added with stirring. The mixture was set to reflux for 14 M. J. Crosbie, P. J. Wright, H. O. Davies, A. C. Jones, T. J. 3 h and the solvent removed in vacuo. The pale yellow oil obtained Leedham, P. O’Brien and G. W. Critchlow, Adv. Mater., Chem. was vacuum distilled at 185–190 °C (0.2 mmHg) to yield a colourless Vap. Deposit., 1998, in press. liquid which solidified on standing to a white waxy solid (yield 60%). Crystals were obtained by recrystallisation from n-hexane and storing at -20 °C for 2 weeks. Communication 8/06420B 2316 J. Mater. Chem., 1998, 8(11), 2315–2316

ISSN:0959-9428    

DOI:10.1039/a806420b

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 Communication Preparation of SrBi2Ta2O9 thin films with a single alkoxide sol–gel precursor Yongtae Kim,a Hee K. Chae,*a Kyu S. Leeb and Wan I. Lee*b aDepartment of Chemistry, Hankuk University of Foreign Studies, Yongin 449-791, Korea bDepartment of Chemistry and Center for Chemical Dynamics, Inha University, Inchon 402-751, Korea Received 10th August 1998, Accepted 15th September 1998 For the first time, a single alkoxide sol–gel precursor The sol–gel precursor solution was prepared as follows. solution for the ferroelectric strontium bismuth tantalate Bismuth 2-methoxyethoxide, Bi(OCH2CH2OCH3)3, was (SrBi2Ta2O9, SBT) was synthesized and utilized for the obtained by modifying the literature method from the reaction fabrication of its thin films.The precursor was prepared between BiCl3 and Na(OCH2CH2OCH3) in tetrahydrofuran. from a 2-methoxyethanol solution of Sr(OCH2CH2- The bismuth complex, Bi(OCH2CH2OCH3)3, was recrys- OCH3)2, Bi(OCH2CH2OCH3)3, and Ta(OCH2CH2OCH3)5. tallized in benzene–hexane. Yield was 78% based on Bi. The 1H and 13C NMR spectra of the precursor in benzene show 1H and 13C NMR spectra of the complex in benzene-d6 show only one set of alkoxy groups, indicating the same chemical only one set of peaks for 2-methoxyethoxide.10 Tantalum 2- environment in solution.This observation suggests that it methoxyethoxide, Ta(OCH2CH2OCH3)5, was synthesized is a single sol–gel precursor, which is ideal for the sol–gel quantitatively by the reaction of alcohol exchange from processing of SBT thin films.The SBT films derived from Ta(OCH2CH3)5 in HOCH2CH2OCH3, and characterized by this precursor present outstanding ferroelectric properties NMR spectroscopy.11 Yellow powders of strontium 2-methoxy- and surface morphology. ethoxide, Sr(OCH2CH2OCH3)2, were also obtained quantitatively from the direct reaction of Sr chips with The sol–gel process is a versatile method for producing cer- HOCH2CH2OCH3.12 We observed that a homogeneous 2- amics and glasses with a variety of applications which include methoxyethanol solution containing Sr(OCH2CH2OCH3)2, electronic, magnetic, optic and optoelectronic materials, as Bi(OCH2CH2OCH3)3, and Ta(OCH2CH2OCH3)5 in a 15252 well as hard and protective coatings.1,2 In recent years this ratio could be prepared by refluxing the mixtures for 2 hours.technique has been extended to the fabrication of thin films The solvent was removed in vacuo to give a colorless syrup- of SrBi2Ta2O9 (SBT), which has been attracting profound like complex. The complex [SrBi2Ta2(OCH2CH2OCH3)18] was interest as a fatigue-free ferroelectric material.3 A variety of characterized by 1H and 13C NMR spectroscopy which shows fabrication methods, such as magnetron sputtering,4 metalthree peaks at 4.65, 3.52 and 3.38 ppm and 76.00, 68.54 and organic chemical vapor deposition (MOCVD),5 pulsed laser 58.84 ppm, respectively, indicating that only one set of 2- deposition (PLD),6 sol–gel process,7 etc., have been applied methoxyethoxide exists in solution (see Fig. 1).13 The peaks for the Bi-based ferroelectric thin films including SBT.Among are quite diVerent from those of the starting materials. This is them, the sol–gel process is considered to be the most successful evidence for the formation of a single alkoxide precursor. The method in terms of composition control. However, the control of stoichiometry in the film has still been a knotty problem because of the relatively high volatility of bismuth components.Conventionally, mixed metal esters including 2-ethylhexanoate have been used for this sol–gel process,3,7 but they are not regarded as suitable precursors to obtain high quality SBT films. Recently, some papers have reported sol–gel processed SBT thin films derived from mixed alkoxide solutions prepared by mixing the individual metal alkoxides, but none of them have prepared any single alkoxide precursors.8,9 In the fabrication of multicomponent metal oxide films, precise control of stoichiometry, crystallographic phase and grain structure in the film is crucial and these properties could be tuned from the molecular level homogeneity, which is likely achieved from a single metal-organic precursor that evolves directly to a mixed-metal oxide, reproducibly. Prior to this study, however, little information was available regarding the preparation and characterization of single precursors for the Sr(OR)2–Bi(OR)3–Ta(OR)5 system.Here, we demonstrate a synthesized single alkoxide sol–gel precursor for the fabrication of SBT thin films. It has been found that only the stoichiometric amount of the Bi precursor, diVerently from other sol–gel solution systems, is necessary for the formation of a ferroelectric SBT phase.SBT thin films with this precursor present outstanding ferroelectric properties and the surface morphology of the film is considerably improved compared with that of films from conventional 2- Fig. 1 NMR spectra of complex isolated from SBT precursor solution in benzene-d6.(a) 1H NMR; (b) 13C NMR. ethylhexanoate sol–gel solution. J. Mater. Chem., 1998, 8(11), 2317–2319 2317complex contains strontium, bismuth and tantalum in a 15252 Fig. 4 shows the hysteresis loop of the Pt/SBT/Pt capacitor. Excellent ferroelectric properties were obtained for a 250 nm ratio as determined by elemental analysis and the complex does not undergo dissociation in alcohol solution.Mass spec- thick SBT film. Remanent polarization (Pr) is 9 mC cm-2 and the coercive field (Ec) is 33 kVcm-1 (or 0.8 V). In addition, trometry data obtained so far indicate that the complex does not exist in the monomeric form, but as a dimer. Hence, the its leakage current density (10-6–10-7 A cm-2) is very low. It has been reported that a pyrochlore phase can be incorpor- synthesized solution could be an ideal sol–gel precursor for the fabrication of SBT thin films.ated under Bi-deficient conditions and 20–30% more of the Bi component is necessary for the sol–gel solution in order to The precursor solutions used for the SBT films contain the stoichiometric amount of Bi (that is, the molar ratio of compensate for the loss of Bi during the heat-treatment.Moreover, several reports indicate that Bi-rich conditions Sr5Bi5Ta is 1.052.052.0) and the concentration was adjusted to 0.10 M. The solution is stable for more than one month and induce better crystallinity in the SBT film and a higher value of remanent polarization as a result.14,15 In this work, however, the aging eVect is negligible.Spin-coated films at 2500 rpm were baked at 120 °C and subsequently at 320 °C to remove we have found a diVerent result, that is, extra Bi is not necessary for the formation of a pure ferroelectric phase, organic solvents. The spin coating and baking cycles were repeated three times to obtain a film of final thickness about which is directly ascribed to the intrinsic role of the single 2- methoxyethoxide precursor.It is deduced that Bi loss is 250 nm. The baked samples were then heat-treated at 800 °C for 1 h in oxygen atmosphere to produce a ferroelectric phase. minimized during the heat-treatment, since the three metals are chemically bonded together. The thermal decomposition The substrates used for the SBT deposition were Pt/Ti/SiO2/Si. On the Si(100) substrate with 300 nm of SiO2 deposited, a behaviour of the prepared single alkoxide sol–gel precursor was analyzed by TGA and DSC.The precursor was dried at 20 nm layer of Ti and a 240 nm layer of Pt were sputterdeposited, respectively. 150 °C and then slowly heated in air with a ramp of 5 °Cmin-1. The weight change and heat exchange as a function of tempera- The glancing angle mode XRD patterns in Fig. 2 indicate that the SBT films consist of a pure ferroelectric phase. The ture were monitored, and are shown in Fig. 5. The dried single field emission SEM image of a fabricated SBT thin film shown in Fig. 3 indicates that the surfaces of prepared thin films are considerably homogeneous, grains are very dense and there seemed to be no secondary structures between the grains.Fig. 4 Hysteresis loop obtained for SBT thin films derived from single alkoxide solution. Fig. 2 XRD patterns of the SBT thin films (glancing angle: 3°). Fig. 5 TGA and DSC curves for the dried single alkoxide sol–gel Fig. 3 Field emission SEM image of SBT thin films (film thickness: ca. 250 nm). precursor. 2318 J. Mater. Chem., 1998, 8(11), 2317–23197 K.Amanuma, T. Hase and Y. Miyasaka, Appl. Phys. Lett., 1995, alkoxide precursor was decomposed slowly and monotonously 66, 221. with no abrupt heat release. This is another important factor 8 I. Koiwa, T. Kanehara, J. Mita, T. Iwabuchi, T. Osaka, S. Ono in retarding the loss of Bi component and in improving grain and M. Maeda, Jpn. J. Appl. Phys., 1996, 35, 4946. structure. 9 T.Hayashi, T. Hara and H. Takahashi, Jpn. J. Appl. Phys., 1997, 36, 5900. 10 IR (Nujol mull, cm-1): 1235 w, 1197 w, 1126 w, 1061 w, 1019 w, 964 w, 894 w, 834 w, 559 w. 1H NMR (C6D6): d 4.98 (t, 6 H, CH2, The financial support for this work from Korean Science and JH–H=4.5 Hz), 3.53 (t, 6 H, CH2, JH–H=4.6 Hz), 3.25 (s, 9 H, Engineering Foundation (KOSEF 97-05-01-03-01-3) is grate- CH3). 13C NMR (C6D6): d 77.75 (s, CH2), 62.45 (s, CH2), 58.17 fully acknowledged. (s, CH3). 11 1H NMR (C6D6): d 4.78 (br, 10 H, CH2), 3.61 (br, 10 H, CH2), 3.27 (s, 15 H, CH3). 13C NMR (C6D6): d 75.61 (s, CH2), 71.18 (s, CH2), 58.47 (s, CH3). 12 1H NMR (C6D6): d 4.27 (br, 4 H, CH2), 3.63 (br, 4 H, CH2), 3.39 Notes and references (s, 6 H, CH3). 13C NMR (C6D6): d 79.19 (s, CH2), 63.08 (s, CH2), 1 C.D. Chandler, C. Roger and M. J. Hampden-Smith, Chem. Rev., 58.66 (s, CH3). 1993, 93, 1205. 13 Anal calc. for C54H126O36SrBi2Ta2: C, 29.23; H, 5.72; Sr, 3.95; Bi, 2 R. C. Mehrotra, A. Singh and S. Sogiani, Chem. Rev., 1994, 94, 18.84; Ta, 16.30. Found: C, 28.95; H, 5.75; Sr, 3.71; Bi, 17.93; Ta, 15.45%. 1H NMR (C6D6): d 4.65 (t, 36 H, CH2), 3.52 (t, 36 H, 1643. CH2), 3.38 (s, 54 H, CH3). 13C NMR (C6D6): d 76.00 (s, CH2), 3 C. A. Araujo, J. D. Cuchiaro, L. D. McMillan, M. C. Scott and 68.54 (s, CH2), 58.84 (s, CH3). J. F. Scott, Nature, 1995, 374, 627. 14 T.-C. Chen, T. Li, X, Zhang and S. B. Desu, J. Mater. Res., 1997, 4 H.-M. Tsai, P. Lin and T.-Y. Tseng, Appl. Phys. Lett., 1998, 12, 1569. 72, 1787. 15 I. Koiwa, Y. Okada, J. Mita, A. Hashimoto and Y. Sawada, Jpn. 5 T. Li, Y. Zhu, S. B. Desu, C.-H. Peng and M. Nagata, Appl. Phys. J. Appl. Phys., 1997, 36, 5904. Lett., 1996, 68, 616. 6 H. Tabata, H. Tanaka and T. Kawai, Jpn. J. Appl. Phys., 1995, 34, 5146. Communication 8/06275G J. Mater. Chem., 1998, 8(11), 2317–2319 2319

ISSN:0959-9428    

DOI:10.1039/a806275g

出版商:RSC    

年代:1998

数据来源: RSC

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J O U R N A L O F C H E M I S T R Y Materials Communication Preparation and characterization of nanocrystalline Cu2-xSe by a novel solvothermal pathway Wenzhong Wang,a,b Ping Yan,b Fuyu Liu,b Yi Xie,b Yan Gengb and Yitai Qian*a,b aStructure Research Laboratory bDepartment of Chemistry, University of Science and Technology of China, Anhui, Hefei 230026, P. R. China, E-mail: wzwang@mail.ustc.edu.cn Received 5th August, 1998, Accepted 8th September 1998 A novel solvothermal method has been developed to obtain nanocrystalline Cu2-xSe at low temperature; CuI and Se were placed at 90 °C for 4 h in an autoclave with ethylenediamine as solvent and the product was characterized by XRD,TEM and XPS.The results revealed that as prepared Cu2-xSe grains were nearly homogeneously spherical and the average grain size was ca. 18 nm. Ethylenediamine coordinated to Cu+ probably plays an important role in the formation of nanocrystalline Cu2-xSe. It is reasonable to expect that this simple one-step solvothermal route can be extended to obtain other nanocrystalline materials. Extensive attention has been paid to the preparation and characterization of selenides, owing to their interesting proper- Fig. 1 XRD pattern of as prepared nanocrystalline Cu2-xSe. ties and potential applications. Copper selenide has been widely used in solar cells,1,2 as an optical filter3 and as a superionic material.4 Many methods have been utilized to the XRD pattern of as prepared nanocrystalline Cu2-xSe. All synthesize copper selenide, such as heating Cu and Se powder peaks in the pattern could be indexed to cubic Cu2-xSe.After mixtures to 400–470 °C in flowing Ar,5 using toxic H2Se as refinement, the cell constant was calculated to be a=57.4 nm, source,3 or mechanical alloying of Se and Cu with a high close to the reported value.11 The grain size of the sample, as energy ball mill.6 Parkin and coworkers reported a room calculated from the half-width of the diVraction peaks using temperature route to selenides by the reaction of selenium the Scherrer equation, was 20±5 nm.with elemental metals in liquid ammonia in thick walled glass The morphology and grain size were determined by transvessels. 7,8 In this method, many operations must be carried mission electron microscopy (TEM). The TEM image was out at -77 °C, and because reactions in liquid ammonia have taken with Hitachi H-800 transmission electron microscope. been known to explode,7,8 all operations should be conducted Fig. 2 shows a TEM microphotograph of a typical sample of with care and behind a safety screen. nanocrystalline Cu2-xSe. It was obvious that the nanocrystal- Obtaining materials under mild conditions has been a goal line Cu2-xSe grains were nearly homogeneously spherical.The of many scientists. Traditional methods usually need high grain sizes varied from 15 to 20 nm, and the average size was temperature, and/or high pressure, and/or inert atmosphere ca. 18 nm, close to the result from XRD. protection, and/or toxic organometallic precursors and it is The product purity and composition (to a sensitivity of diYcult to grow nanocrystalline materials under such con- <0.5 atom%) were detected by X-ray photoelectron spectra ditions.However, nanoscale materials are becoming important (XPS) recorded on an ESCALab MKII instrument with Mgfor studying the variation of a material’s property with size. Ka radiation as the exciting source. The binding energies The solvothermal pathway is a newly developed route, which obtained in the XPS analysis were corrected for specimen does not require organometallic or toxic precursors and is carried out at comparatively low temperature. The organic solvent plays an important role in the formation of nanocrystalline materials.Compared with other methods, this method is convenient, simple and mild and we have obtained many kinds of non-oxide nanocrystalline materials at low temperature in this way.9,10 In this paper we report a novel solvothermal method to form nanocrystalline Cu2-xSe at low temperature.Powdered CuI (11 mmol) and Se (5 mmol) were placed in a Teflon lined stainless steel autoclave, then the autoclave was filled with ethylenediamine up to 90% of its capacity. The autoclave was kept at 90 °C for 4 h, and then allowed to cool to room temperature. The precipitate was filtered, washed with distilled water and dried in vacuum at 50 °C for 4 h.The final black product was collected for characterization. X-Ray powder diVraction (XRD) patterns were collected on a Japan Rigaku D/max cA rotation anode X-ray Fig. 2 TEM image of a typical sample of nanocrystalline Cu2-xSe.diVractometer with Ni-filtered Cu-Ka radiation. Fig. 1 shows J. Mater. Chem., 1998, 8(11), 2321–2322 2321the resultant grains were much bigger at higher temperatures or longer times. When the reaction was carried out at 180 °C for 4 h, the grain size reached 100 nm (XRD). In general the grain size varied with the reaction temperature and time. In the solvothermal process, the solvent plays an important role in the formation of nanocrystalline Cu2-xSe.Ethylenediamine(en) was selected as solvent because it is a Nchelating ligand which dissolves CuI to form a complex. This was supported by the fact that CuI powder slowly dissolved after addition of ethylenediamine and the solution color changed from transparent to light then to dark blue. As Cu+ dispersed into the solution, the reaction surface area greatly increased, which promotes the reaction between CuI and Se.Thus nanocrystalline Cu2-xSe formed at relatively low temperature. There is a related report that [Cu(en)2]2+ reacts with thiourea to produce amorphous CuS.12 Furthermore, the solvent absorbed the heat produced during the reaction, so leading to smooth reaction. Ethylenediamine limits the product size and mediates the reaction.In the solvothermal process, CuI reduced Se to Se2-. To our knowledge, the reducibility of I- has been seldom utilized to prepare nanocrystalline materials at comparatively low temperatures. Although the reducibility of I- is low (EI2/I-G= 0.535 V (ESe/Se2-G=-0.78 V), the reaction goes to completion since the Cu2-xSe formed precipates out of solution.The byproduct I2 was removed from the product by washing and has no eVect on the product purity. It is reasonable to expect that iodides can be widely used as reductants to obtain other nanoscale materials at low temperatures in solvothermal processes. This work is supported by Chinese National Natural Science Foundation and Huo Yingdong Foundation for Young Teachers.References Fig. 3 XPS analysis of nanocrystalline Cu2-xSe. 1 U. Hiroto, Jpn. Kokai Tokkyo Koho, JP 01, 298, 010. 2 S. T. Lakshmikvmar, Sol. Energy. Mater. Sol. Cells, 1994, 32, 7. charging by referencing the C 1s to 284.60 kV. Results are 3 H. Toyoji and Y. Hiroshi, Jpn. Kokai Tokkyo Koho, JP 02, 173, shown in Fig. 3 and no obvious peaks for copper oxides, 622.iodides or selenium oxide were observed indicating high prod- 4 A. A. Korzhuev, Fiz. Khim. Obrab. Mater., 1991, 3, 131. uct purity. Quantification of peaks gave a ratio of Cu to Se 5 Oshitasi Akira, Jpn. Kokai Tokkyo Koho, JP 61, 222, 910. 6 T. Ohtani and M. Motoki, Mater. Res. Bull., 1995, 30, 1495. of 1.83:1. 7 G. Henshaw, I. P. Parkin and G. Shaw, Chem. Commun., 1996, In the experimental process, several factors aVected the 1095.product quality. The reaction occurring is as follows: 8 G. Henshaw, I. P. Parkin and G. Shaw, J. Chem. Soc., Dalton Trans., 1997, 231. (4-2x) CuI+2 Se CCCCCA H2NCH2CH2NH2 90 °C, 4 h 2 Cu2-xSe+(2-x) I2 9 W. Z. Wang, Y. Geng, Y. Qian, C. Wang, Y. Xie and G. Zhou, Mater. Res. Bull., in press. 10 W. Z. Wang, Y. Geng, Y. Qian, Y. Xie and L. Liu, Mater. Res. Optimum conditions for preparing nanocrystalline Cu2-xSe Bull., in press. were at 90 °C for 4 h in the autoclave. Lower temperatures or 11 JCPDS No. 6-680. shorter times led to incomplete reaction with decreased yield 12 H. Grijavala, M. Inoue, S. Buggavarapu and P. Calvert, J. Mater. and crystallinity with a large amount of unreacted Se and CuI Chem., 1996, 7, 1157. being present (XRD). When the temperature was lower than 50 °C, the reaction can not be initiated. On the other hand, Communication 8/06166A 2322 J. Mater. Chem., 1998, 8(11), 2321–2322

ISSN:0959-9428    

DOI:10.1039/a806166a

出版商:RSC    

年代:1998

数据来源: RSC

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J O U R N A L O F C H E M I S T R Y Materials Communication Double perovskites containing hexavalent molybdenum and tungsten: synthesis, structural investigation and proposal of a fitness factor to discriminate the crystal symmetry Yasutake Teraoka,*a Ming-Deng Weib and Shuichi Kagawaa aDepartment of Applied Chemistry, Faculty of Engineering, Nagasaki University, Nagasaki 852-8521, Japan. E-mail: yasu@net.nagasaki-u.ac.jp bDepartment of Marine Resources Research and Development, Graduate School of Marine Science and Engineering, Nagasaki University, Nagasaki 852-8521, Japan Received 17th August 1998, Accepted 16th September 1998 Double perovskites AII 2BIIBVIO6 (AII=Ba, Sr, Ca; BII= vigorous stirring.The obtained solid mixture was ground and Mg, Ni, Co, Cd, Ca; BVI=W, Mo, W0.5Mo0.5) have been heat-treated at 623 K for 1 h in order to decompose remaining synthesized and their crystal structures investigated by metal nitrates. After regrinding, the mixture was calcined in powder X-ray diffraction measurements. In order to dis- air for 5 or 10 h at temperatures varying between 1173 and criminate the crystal systems of the double perovskites, a 1523 K with an interval of 50 K, and the calcination was fitness factor is proposed which corresponds to the size repeated with regrinding at every interval.Crystal phases in matching between the A cation and the cubo-octahedral the products were identified by powder X-ray diVraction cavity formed by eight BO6 octahedrons. The fitness factor (XRD) using Cu-Ka radiation (Rigaku RINT-2200VL, 30 kV, can discriminate the crystal systems of obtained com- 16 mA).Lattice constants were calculated using the PIRUM pounds more exactly than the well known tolerance factor. program.3 In the syntheses of the double perovskites, AMoO4 and AWO4 (A=Ba, Sr) were the main and obstinate impurity It is known that hexavalent Mo and W are stabilized not in phases. Calcination for prolonged time or at higher tempera- the primitive ABO3 perovskites but in the ordered double tures was repeated until the XRD peak intensities of the perovskites, AII2BIIBVIO6,1,2 in which AII is an alkaline earth impurity phase disappeared or, if present, became as low as ion, BII a divalent metal ion such as Mg, Ca, Co, Ni and Cu, possible.The lowest temperature, though with longer calci- and BVI a hexavalent Mo or W ion.These compounds, in nation period, was adopted as the synthesis condition for each which the charge diVerence between BII and BVI is four, adopt oxide (Table 1). an ordered structure with the rock-salt arrangement of BII and Double perovskites containing Mo were not obtained for BVI cations as shown in Fig. 1.2 Systematic series of AII2BIIWO6 AII=Ca but were for AII=Ba and Sr.To the best of our compounds have been so far reported with AII=Ba, Sr and knowledge, the oxides in Table 1, except for Sr2BIIMoO6 (BII= Ca and BII=Mg, Ca, Co, Cu, Fe, Ni and Zn.1,2 In contrast, Co and Ni),4 are new compounds. Compounds with AII=Ba reports on Mo-containing double perovskites are limited. The crystallized in the cubic double perovskite structure with the first aim of the present communication is to report the synthesis lattice constant close to 2ap; ap is the lattice constant of cubic and structural investigation of Mo-containing double perovperovskite of the primitive ABO3 type (ap#4 A° ). XRD pat- skites of AII2BIIMoO6 and AII2BIIW0.5Mo0.5O6 (AII=Ba, Sr, terns of cubic Ba2CoMoO6 and Ba2CoW0.5Mo0.5O6 are Ca; BII=Mg, Ni, Co, Cd, Ca).The success in the synthesis of depicted in Fig. 2. The appearance of superlattice lines of 111, the Mo-containing double perovskites and the systematic 311 and 511 evidences the rock-salt ordering of Co2+ structural investigation of the Mo and W systems lead to the and Mo6+/W6+ ions.2 The fact that Ba2CoMoO6 and proposal of a new fitness factor which can discriminate the Ba2CoW0.5Mo0.5O6 gave almost the same XRD patterns crystal system of the AII2BIIBVIO6 double perovskites more implies that in the latter oxide W6+ and Mo6+ ions randomly exactly than the well known tolerance factor.occupy the smaller octahedra (BVIO6 in Fig. 1) and they form Polycrystalline powders of double perovskites were synthethe rock-salt sublattice with larger BIIO6 octahedra.As exem- sized from starting materials of MoO3, WO3 and nitrates of plified by the XRD pattern of Sr2CoMoO6 (Fig. 2), splitting other elements. Molybdenum and/or tungsten trioxide was of some diVraction peaks was observed for all the Sr com- added into a mixed aqueous solution of metal nitrates, and pounds, and their powder XRD patterns could be satisfactorily the suspended solution was evaporated to dryness under indexed with an orthorhombic (BII=Ca) or tetragonal (others) unit cell having a size close to Ó2ap×Ó2ap×2ap.It was reported2 that only cubic (2ap) and monoclinic (Ó2ap×Ó2ap×2ap) unit cells occur in double perovskites with the rock-salt sublattice. Accordingly, it is speculated that the monoclinic distortion of the Sr compounds synthesized in this study, if present, is too small to distinguish the monoclinic system from the orthorhombic and tetragonal systems by powder XRD measurements alone.It is noted here that, in accordance with a previous report,5 we could discern a monoclinic Ó2ap×Ó2ap×2ap unit cell of Ca2CaWO6 with a slight distortion (b=90.18°). Fig. 3 shows the relation between the primitive perovskite parameter (ap) and the ionic radius6 of divalent BII cations. Fig. 1 Crystal structure of AII2BIIBVIO6 double perovskites with the rock-salt ordering of larger BII and smaller BVI cations. Values of ap were calculated from (VUC/8)1/3 for cubic oxides J. Mater. Chem., 1998, 8(11), 2323–2325 2323Table 1 Lattice parameters and synthesis conditions of Mo-containing double perovskites Compound CSa Lattice parameter/A° Synthesis conditions Ba2BIIMoO6 1 BII=Ni C a=8.035(1) 1373 K, 30 h 2 BII=Co C a=8.076(1) 1273 K, 20 h 3 BII=Cd C a=8.3242(9) 1173 K, 20 h Sr2BIIMoO6 4 BII=Ni T a=5.5464(7), c=7.892(1) 1373 K, 40 h 5 BII=Mg T a=5.598(2), c=7.875(2) 1373 K, 60 h 6 BII=Co T a=5.562(2), c=7.941(5) 1423 K, 25 h 7 BII=Ca O a=5.753(2), b=5.841(1), c=8.186(3) 1373 K, 5 h Ba2BIIW0.5Mo0.5O6 8 BII=Ni C a=8.053(1) 1273 K, 70 h 9 BII=Co C a=8.0928(6) 1273 K, 60 h 10 BII=Cd C a=8.3360(8) 1173 K, 30 h Sr2BIIW0.5Mo0.5O6 11 BII=Ni T a=5.587(2), c=7.852(2) 1423 K, 40 h 12 BII=Mg T a=5.603(2), c=7.882(2) 1373 K, 20 h 13 BII=Co T a=5.611(3), c=7.872(4) 1473 K, 20 h 14 BII=Ca O a=5.766(1), b=5.847(1), c=8.183(3) 1323 K, 60 h aCrystal system: C; cubic, T; tetragonal, O; orthorhombic.and (VUC/4)1/3 for tetragonal and orthorhombic oxides, where VUC is the unit cell volume of the original double perovskite. As expected, the cell size increases with increasing the radius of BII cations in each series of oxides. The cell size diVerences of Ba2BIIBVIO6>Sr2BIIBVIO6 and A2BIIW0.5Mo0.5O6> A2BIIMoO6 are also consistent with ionic size diVerences6 of Ba>Sr and W>Mo.In parallel with the investigation of the Mo-containing double perovskites, the synthesis and structural investigation of the W analogues have been carried out. The following compounds were obtained, and their crystal systems were in accordance with the literature. (2ap)-type cubic phase; Ba2BIIWO6 (BII=Ni,7 Co,7 Cd,8 Ca7) (Ó2ap×Ó2ap×2ap)-type tetragonal phase; Sr2BIIWO6 (BII=Ni,7 Mg,8 Co,7 Cd) (Ó2ap×Ó2ap×2ap)-type orthorhombic phase; Sr2CaWO6,9 Ca2BIIWO6 (BII=Ni, Co)1 (Ó2ap×Ó2ap×2ap)-type monoclinic phase; Ca2CaWO65 The Goldschmidt tolerance factor (t)10 is often used to predict the formation of perovskites and the crystal symmetry for a given pair of A- and B-site cations.The tolerance factor is given by t=(rA+rO)/Ó2(rB+rO) (1) where rX is the ionic radius6 of X ion, and rB=(rBII+rBVI)/2 for A2BIIBVIO6 double perovskites.The relation between the t Fig. 2 Powder XRD patterns of AII2CoMoO6 (A=Ba, Sr) and value and the crystal symmetry is depicted in Fig. 4A. All of Ba2CoW0.5Mo0.5O6. V: BaWO4. the Ba compounds with t values >0.96 are cubic. In each series of the Sr and Ca compounds, oxides with the smallest t values (BII=Ca) have unit cells with lower symmetry than the others; orthorhombic vs. tetragonal for the Sr compounds, and monoclinic vs.orthorhombic for the Ca compounds. In this way, the t value can discriminate the crystal symmetry in the series of each AII cation. When all the compounds are taken into account, however, overlap regions exist.At t values between 0.95 and 1.0, both the cubic (Ba compounds) and tetragonal (Sr compounds) systems occur, and the t value of tetragonal Sr2CdWO6 is smaller than those of orthorhombic Ca2BIIWO6 (BII=Ni, Co). This suggests that a new parameter, which reflects more pronouncedly the size diVerence of A site cations, is necessary to exactly discriminate the crystal system of double perovskites.For this purpose, we propose a new fitness factor (W) defined by eqn. (2). Fig. 3 Primitive perovskite parameter (ap) of Mo-containing double perovskites as a function of ionic radius of divalent BII cation. See W=Ó2rA/(rB+rO) (2) text for the calculation of ap and Table 1 for the listing of compounds. For the ideal cubic unit cell of the primitive ABO3 type (t= 2: Ba2 BIIMoO6, %: Ba2 BIIW0.5Mo0.5O6, +: Sr2 BIIMoO6, #: Sr2BIIW0.5Mo0.5O6. 1.0, rA=rO), the B–O interionic distance, rB+rO, is equivalent 2324 J.Mater. Chem., 1998, 8(11), 2323–2325fitness factor, the borderline between the cubic Ba compounds and the tetragonal Sr compounds becomes clear. In addition, all of the orthorhombic Sr and Ca compounds have similar W values, giving a clear borderline at W=0.93 to distinguish from tetragonal systems. The cubic system occurs at 1.00<W, the tetragonal system at 0.93<W<1.00, the orthorhombic system at 0.90<W<0.93, and the monoclinic system at W<0.90; the borderline value of W=0.90 between orthorhombic and monoclinic systems is not definitive owing to lack of data.The reduction of crystal symmetry of perovskites usually results from the tilting of BO6 octahedrons.2,11 When an A cation is closely packed in the cubo-octahedral cavity (W1), tilting would be suppressed and the cubic system results.At W<1 with the loose packing of the A cation, tilting of BO6 octahedrons or distortion would be expected, and would become larger with decreasing W. It is well known that B site vacancies in perovskite-type oxides are rare, while those at A sites are commonly found in, for example, ReO3, NaxWO312 and La2/3TiO3.13 This indicates that the framework made of BO6 octahedra is of primary importance for the construction of the perovskite structure and that A site cations stabilize the structure by sitting in the cubo-octahedral cavities.The concept of the proposed fitness factor is in line with this.References 1 G. Blasse, J. Inorg. Nucl. Chem., 1965, 27, 993. 2 M. T. Anderson, K. B. Greenwood, G. A. Taylor and K. P. Poeppelmeier, Prog. Solid State Chem., 1993, 22, 197. 3 P-E. Werner, Ark. Kemi, 1969, 1, 513. 4 JCPDS 15-556 (B¾=Co) and 15-601 (B¾=Ni). 5 JCPDS 22-541. 6 R. D. Shannon, Acta Crystallogr., Sect. A, 1976, 32, 751. 7 E. J. Fresia, L. Katz and R. Ward, J. Am. Chem. Soc., 1959, 81, 4783. 8 G. Blasse and A. F. Corsmit, J. Solid State Chem., 1973, 6, 513. Fig. 4 Tolerance factor (A) and fitness factor (B) for discriminating 9 E. G. Steward and H. P. Rooksby, Acta Crystallogr., 1951, 4, 503. unit cell systems of AII2BIIBVIO6 double perovskites. 10 V. M. Goldschmidt, Skrifter Nordske Videnskaps-Akad. Oslo I, Mat-Naturvidensk Kl., 1926, 8, 2. to half of the cell edge and rA/(rB+rO) is equal to 1/Ó2 (W= 11 A. M. Glazer, Acta Crystallogr., Sect. B, 1972, 28, 3348. 1.0). This parameter corresponds to size matching between 12 A. Magneli, Acta Chem. Scand., 1953, 7, 315. the A cation and the cubo-octahedral cavity formed by eight 13 M. Abe and K. Uchino, Mater. Res. Bull., 1974, 9, 147. BO6 octahedrons. As shown in Fig. 4B, the W factor can exactly discriminate the crystal system. By introducing the Communication 8/06442C J. Mater. Chem., 1998, 8(11), 2323–2325 2325

ISSN:0959-9428    

DOI:10.1039/a806442c

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 Communication Novel honeycomb structure: a microporous ZSM-5 and macroporous mullite composite Sridhar Komarneni,a Hiroaki Katsukib and Sachiko Furutab aMaterials Research Laboratory and Department of Agronomy, The Pennsylvania State University, University Park, PA 16802, USA. E-mail: komarneni@psu.edu bSaga Ceramics Research Laboratory, 3037-7, Arita-machi, Saga 844, Japan Received 22nd July 1998, Accepted 25th August 1998 We have developed a novel honeycomb composite struc- hydroxyls to reduce the deformation during final sintering at ture consisting of microporous ZSM-5 and macroporous 1650 °C.The calcined clay was ball-milled, dried and then mullite by in-situ crystallization of ZSM-5 utilizing glass thoroughly mixed with 10 wt % methyl cellulose binder and from a sintered kaolin honeycomb.This in-situ crystalliz- 25 wt% water before extrusion forming of a honeycomb of ation of ZSM-5 leads to better adhesion and mechanical 15×15×100 mm (cell size, 1.4×1.4 mm; wall thickness, strength for the zeolite film and results in a graded structure 510 mm). This extruded honeycomb was heated initially at with three layers consisting of strongly adhered ZSM-5 300 °C for 2 h to remove the binder and heated to 1650 °C at film at the surface, a composite ZSM-5 and mullite layer the rate of 2.2 °Cmin-1 followed by sintering at 1650 °C for below the pure ZSM-5 layer and porous mullite at the 2 h.The sintered body was determined to be composed of core. These novel composite structures are expected to 58 wt% mullite and 42 wt% silica glass.The silica glass in this have major applications in the areas of automotive sintered body was transformed to ZSM-5 zeolite in-situ and other catalysts, pervaporation membranes, cation by hydrothermal treatment at 190 °C for 14–28 days in exchange separations, etc. Teflon-lined hydrothermal vessels at autogenous pressure.The molar ratios of the starting chemicals for hydrothermal synthesis were as follows: SiO2 in honeycomb5NaOH5tetra- A novel composite honeycomb consisting of microporous propylammonium bromide (TPAB)5H2O=100512.8 (or ZSM-5 and macroporous mullite is developed with many 25.5)5552800. potential applications. The automotive industry utilizes cordi- First, a sintered honeycomb body of mullite and silica glass erite ceramic honeycomb structures in catalytic converters of was produced.By hydrothermally treating this honeycomb in gasoline-powered cars to reduce carbon monoxide, nitrous alkaline solutions, one can convert it into a porous mullite oxide and hydrocarbon emissions. The macroporous honeyhoneycomb, 10,11 by dissolving silica into the solution. By comb structures are also used in diesel-powered cars to trap treating this honeycomb with NaOH in the presence of TPAB and burn particulate carbon from the exhaust gases.In gasotemplate at 190 °C for two weeks, we converted the silica in line-powered cars a significant amount of the total emissions that a vehicle emits in a single trip are emitted in the first few minutes of operation1 because the operating temperature of the catalytic converter is below 300 °C at the very beginning of the trip.Below a 300 °C, the catalytic converter is ineVective in decomposing the various emissions while it has a maximum eYciency in the range 400–800 °C. A great deal of eVort at present is being devoted to reduce the emissions in the first few minutes by using electrically-heated catalysts.An alternative approach is to trap the hydrocarbon emissions until the catalytic converter reaches an operating temperature of 300 °C by using microporous adsorbents such as zeolites. Here we report the fabrication of a novel ZSM-5 (microporous)–mullite (macroporous) composite honeycomb structure which can be located at the entrance of the three-way catalyst and is potentially useful to trap the emissions until the catalytic converter reaches its operating temperature.There is also a great deal of interest in the preparation of composite materials containing continuous zeolite films for other applications such as catalysis, pervaporation, adsorption, cation exchange, etc..2–9 However, most of these studies led to limited success because of the problems of zeolite adhesion to the ceramic substrate.Here we overcome the adhesion problems by in-situ crystallization of ZSM-5 zeolite. Monolithic honeycomb was prepared from a commercially available New Zealand kaolin clay. The kaolin (halloysite) powder supplied by New Zealand Clay Company has the Fig. 1 Cross-section of honeycomb body showing (A) four layers of following chemical composition: SiO2, 50.07; Al2O3, 35.76; ZSM-5, ZSM-5+mullite, porous mullite and mullite+glass upon Fe2O3, 0.26; TiO2, 0.07; CaO, trace; MgO, 0.08; Na2O, 0.07; hydrothermal treatment with 12.8 M NaOH at 190 °C, 14 days and K2O, 0.01 and ignition loss, 13.79 wt%.This powder was first (B) three layers of ZSM-5, ZSM-5+mullite and porous mullite upon hydrothermal treatment with 25.5 M NaOH at 190 °C, 14 days.calcined at 500 °C for 3 h to remove adsorbed water and J. Mater. Chem., 1998, 8(11), 2327–2329 2327Fig. 2 Cross-section at higher magnification showing ZSM-5 layer, ZSM-5 plus mullite layer and porous mullite after hydrothermal treatment at 190 °C, 21 days. Fig. 5 Morphology of porous mullite after hydrothermal leaching of glass at 190 °C, 21 days.Table 1 The eVect of time and concentration of NaOH on the surface area of zeolite–mullite composites Hydrothermal conditionsa Time/days Amount of NaOH/mol Surface area/m2 g-1 7 25.5 43.7 14 25.5 76.2 21 25.5 92.2 7 12.8 60.9 14 12.8 78.3 21 12.8 82.7 Fig. 3 Powder X-ray diVraction pattern of ZSM-5 and porous mullite 28 12.8 110.8 composite prepared at 190 °C for 14 days.aHydrothermal conditions: 190 °C; autogeneous pressure and molar ratios, SiO2 in kaolin5NaOH5TPABr5H2O=1005(12.8, 25.5)5 552800. the honeycomb to ZSM-5 zeolite. Fig. 1A shows the initial conversion of the honeycomb to four layers from the surface to the core as follows: ZSM-5 on the surface, ZSM-5+mullite below the surface, porous mullite and mullite+glass at the phology of the porous mullite with an average pore size of about 0.57 mm.10 The results presented here clearly show that core.By continuing the treatment for three weeks, we completely converted all the glass to ZSM-5 zeolite with a sequence a novel microporous–macroporous composite was prepared with a very high surface area (Table 1). The adhesion and of three layers as follows: ZSM-5 layer on the surface, ZSM- 5+mullite below the surface and porous mullite at the core compressive strengths of a zeolite film with a thickness of 200 mm on the surface of the porous mullite were found to be (Fig. 1B). A cross-section of this novel composite clearly shows ZSM-5 on the surface followed by ZSM-5 + mullite very good and are in the ranges of 9–17MPa and 319–483 MPa, respectively.complex and porous mullite (Fig. 2). Powder X-ray diVraction patterns of the composite showed mullite and ZSM-5 crystal- We heated this porous mullite with a zeolite film of 200 mm at 900 °C for 60 h to determine its thermal stability and found line phases only (Fig. 3). Scanning electron micrographs of ZSM-5 from the surface show that a continuous layer of this it to be very stable with no cracks or pinholes.The surface areas of several samples heated at 900 °C were determined to phase had formed (Fig. 4). The size of the ZSM-5 crystals ranged from 20 to 60 mm. Fig. 5 shows the needle-like mor- be in the range of 80–100 m2 g-1. Thus we have fabricated a Fig. 4 Morphology of continuous zeolite film on the surface of the honeycomb at two diVerent magnifications.This film was prepared at 190 °C, 14 days in 12.8 M NaOH solution. 2328 J. Mater. Chem., 1998, 8(11), 2327–23292 J. G. Tsikoyiannis and W. O. Haag, Zeolites, 1992, 12, 126. novel microporous ZSM-5 and macroporous mullite composite 3 E. R. Geus, H. V. Bekkum, W. J. W. Bakker and J. A. Moulijn, with excellent mechanical properties and very high surface Microporous Mater., 1993, 1, 131.areas. This combination of mechanical properties, micro- and 4 M-D. Jia, K-V. Peinemann and R-D. Behling, J. Membr. Sci., macro-porosities with a high surface area has never been 1993, 82, 15. achieved before and these composites are expected to find 5 S. Yamazaki and K. Tsutsumi, Microporous Mater., 1995, 4, 205. 6 V. Valtchev, S. Mintova, B. Schoeman, L. Spasov and applications as automotive catalysts, adsorbents, cation L.Konstantinov, in Zeolites: A Refined Tool for Designing exchangers, pervaporation membranes, etc. Such application Catalytic Sites, ed. L. Bonneviot and S. Kaliaguine, Elsevier studies are now in progress. Science, Amsterdam, 1995, pp. 527–532. 7 S. Morooka, S. Yan, K. Kusakabe and Y. Akiyama, J. Membr. Supported by Materials Research Laboratory Consortium on Sci., 1995, 101, 89. Chemically Bonded Ceramics and Saga Ceramics Research 8 Z. A. E. P. Vroon, K. Keizer, M. J. Gilde, H. Verweij and A. J. Burggraaf, J. Membr. Sci., 1996, 113, 293. Laboratory. 9 H. H. Funke, M. G. Kovalchick, J. Falconer and R. D. Noble, Ind. Eng. Chem. Res., 1996, 35, 1575. References 10 H. Katsuki, S. Furuta, A. Shiraishi and S. Komarneni, J. Porous Mater., 1996, 2, 299. 1 J. T. Woestman and E. M. Logothetis, The Industrial Physicist, 11 H. Katsuki, S. Furuta and S. Komarneni, J. Porous Mater., 1997, American Institute of Physics, College Park, MD, 1995, 3, 127. pp. 20–24. Communication 8/05724I J. Mater. Chem., 1998, 8(11), 2327–2329 2329

ISSN:0959-9428    

DOI:10.1039/a805724i

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 Communication Molecular tectonics: design, synthesis and structural analysis of a molecular network based on inclusion processes using a doubly fused p-isopropylcalix[4]arene Julien Martz,a Ernest Graf,a Mir Wais Hosseini,a* Andre� De Cianb and Jean Fischer aLaboratoire de Chimie de Coordination Organique and bLaboratoire de Cristallochimie et Chimie Structurale, Universite� Louis Pasteur, UMR CNRS 7513, F-67000 Strasbourg, France.E-mail: hosseini@chimie.u-strasbg.fr Received 31st July 1998, Accepted 1st September 1998 The synthesis of a hollow molecular module (koiland) possessing two divergent cavities was achieved by double fusion of two p-isopropylcalix[4]arenes in cone conformation by two silicon atoms. The formation of either a discrete binuclear inclusion complex in the presence of CH2Cl2 acting as stopper or of an infinite 1-D inclusion network (koilate) in the presence of hexadiyne acting as connector was demonstrated in the solid state by singlecrystal diffraction studies.The inclusion network was based on the interconnection of consecutive koilands by connector molecules. Over the last ten years much attention has been focused on molecular crystal engineering and the design of molecular networks in the solid state is still a subject of current interest.1 The majority of reported molecular networks are either based on hydrogen bonding2,3 or on coordination bonds.4,5 However, we have proposed that one may use inclusion processes based on van der Waals interactions as a construction principle to design molecular networks in the solid state.6 Thus, we demonstrated that 1-D molecular networks (koilates)7 may be generated under self-assembly conditions using hollow molecular receptors (koilands)8 possessing at least two divergent cavities Scheme 1 Structures of p-isopropylcalix[4]arene 1 and of hexadiyne 3 and connector molecules capable of bridging by double as welle as schematic representations of 1 in cone conformation and inclusion consecutive koilands (Fig. 1). of the koiland 2 obtained upon fusion of two units 1 by two Here we describe the synthesis of a new koiland as well as silicon atoms. its use in the formation of either a discrete exobinuclear inclusion complex or an infinite 1-D molecular network in the solid state. obtained in 9% yield by crystallisation from a 159 mixture of The design of the koiland 2 is based on the double fusion CH2Cl2–hexane.by two silicon atoms of two p-isopropylcalix[4]arenes 1 The synthesis of 2 (Scheme 1) was achieved in 39% yield (Scheme 1). The latter appeared to be an interesting backbone upon treatment of 1 in dry THF by NaH followed by addition since it has been shown that in the presence of p-xylene it of SiCl4.7 Compound 2 was obtained as colourless crystalline forms (151) and (251) inclusion complexes in the solid state.9 material after crystallisation from a CH2Cl2–MeOH mixture.Although the preparation of 1 based on Ni catalysed direct In addition to 1H and 13C NMR spectroscopy, mass specisopropylation of calix[4]arene using propene was recently trometry and elemental analysis, compound 2 was also reported,10 for the sake of experimental simplicity, we modified characterised by 29Si NMR in CDCl3 which revealed, as the reported Zinke–Conforth procedure11 by heating at 110 °C expected, a signal at -112.48 ppm.† for 2 h a 50575510 mixture of p-isopropylphenol, formal- In order to study the inclusion ability of 2, the latter was dehyde and sodium hydroxide.The pure compound 1 was crystallised from solvents capable of acting as stoppers. Thus, in the presence of CH2Cl2, 2, possessing two divergent cavities, formed indeed a discrete exobinuclear inclusion complex in the solid state. Single crystals (air stable rod-type morphology) were obtained upon slow diVusion of MeOH into a CH2Cl2 solution of 2.The X-ray analysis‡ (Fig. 2) revealed the following features: (i) 2 possessing a centre of symmetry was indeed composed of two p-isopropylcalix[4]arene units in cone conformation fused by two Si atoms adopting a tetrahedral coordination geometry with an average Si–C distance of ca. Fig. 1 Schematic representation of a discrete exobinuclear inclusion 1.61 A° and OSiO angle of ca. 109.4°; (ii) a discrete binuclear complex (a) and of an infinite inclusion network (b) formed between inclusion complex was formed between 2 and two CH2Cl2 an hollow molecular module and a stopper or connector units respectively. molecules; (iii) each cavity of the koiland was occupied by J. Mater. Chem., 1998, 8(11), 2331–2333 2331Fig. 2 Crystal structure of the exobinuclear inclusion complex formed between 2 and CH2Cl2 molecules acting as stoppers.For sake of clarity, H atoms are not presented. one solvent molecule with the shortest distance of ca. 3.68 A° between the carbon atom of the solvent and one of the carbon Fig. 3 A portion of the crystal structure showing the formation of an atoms of the koiland; (iv) whereas hydrogen atoms of the infinite inclusion network between koilands 2 and connectors 3.For sake of clarity, CHCl3 molecules present in the lattice and H atoms solvent were oriented towards the interior, the chlorine atoms are not presented. were facing the exterior of the cavity. The ability of 2 to form linear molecular networks based on inclusion processes was studied using as connector 3 possessing a cylindrical shape.Upon slow diVusion at 21 °C Notes and references of MeOH into a CHCl3 solution of 2 and 3 in large excess †1H NMR: (CDCl3, 300 MHz; 25 °C): d 1.07 (d, CH3, 12H, 6.8 Hz), (200-fold), suitable colourless single crystals (rhombic mor- 1.13 (d, CH3, 12H, 6.8 Hz), 1.22 (d, CH3, 24H, 6.8 Hz), 2.74 (m, isopr., phology) were obained after 8 h. The crystals, unstable outside 8H); 3.31 (d, CH2, 4H, 13.4 Hz), 3.39 (d, CH2, 4H, 13.9 Hz), 4.48 (d, the solution, thus obtained were studied by X-ray diVraction§ CH2, 4H, 13.6 Hz), 4.58 (d, CH2, 4H, 13.4 Hz), 6.79 (s, arom., 4H), 6.89 (s, arom., 4H), 6.91 (s, arom., 8H), 13C NMR: (CDCl3, which revealed the following features: (i) the crystals (mono- 50.32 MHz, 25 °C): d 23.67, 23.83, 24.12, 32.73, 33.15, 33.54, 34.44, clinic, P21/a space group) were compared of 2, 3 and CHCl3 126.04, 126.12, 127.19, 127.29, 129.14, 130.13, 132.66, 142.36, 145.02, molecules; (ii) as predicted, a 1-D network was formed between 148.44; 29Si NMR: (CDCl3, 59.63 MHz, 25 °C): d -112.48; 2 and 3 (Fig. 3), the solvent molecules were not participating FAB+ (meta-nitrobenzyl alcohol matrix) m/z 1232.7 (M·+, 100%), directly in the formation of the network; (iii) the observed 1217.6 (M·+ -CH3, 25%); Found: C 73.35, H 6.70; Calc.for network resulted from the interconnection, through inclusion C80H88O8Si2·CH2Cl2 (1232.60) C 73.78, H 6.88%. ‡Crystal data for 2·2CH2Cl2: (colorless, 173 K): C80H88O8Si2· processes, of 2 by 3; (iv) the assembling core leading to the 2CH2Cl2, M=1403.63, triclinic, a=11.6667(4), b=13.0829(5), formation of the 1-D network by translational symmetry could c=13.8915(5) A° , a=108.628(9), b=110.871(9), c=91.648(9)°, be identified as the inclusion of one of the methyl groups of 3 U=1852.9(5) A° 3, space group P19, Z=1, Dc=1.26 g cm-3, Nonius within a cavity of 2; (v) both the connector and the koiland CCD, Mo-Ka, m=0.244 mm-1, 4741 data with I>3s(I ), R=0.066, were centrosymmetric; (vi) the coordination geometry around Rw=0.081.§Crystal data for (2,3)n network (colorless, 173 K): C80H88O8Si2· the silicon atoms was tetrahedral with an average Si–O distance C6H6·2CHCl3, M=1550.63, monoclinic, a=13.6981(3), b= of 1.60 A° and an average OSiO angle of 109.4°; (vii) the 19.7336(6), c=15.3589(4) A° , b=95.721(9), U=4131.0(4) A° 3, space shortest C–C distance of 3.56 A° between the CH3 group of group P21/a, Z=2, Dc=1.25 g cm-3, Nonius CCD, Mo-Ka, m= connector and one of the carbon atoms bearing the phenolic 0.289 mm-1, 4567 data with I>3s(I ), R=0.065, Rw=0.081.Full crysgroup at the bottom of the cavity indicated a high degree of tgraphic details, excluding structure factors, have been deposited at inclusion.the Cambridge Crystallographic Data Centre (CCDC). See Information for Authors, Issue 1. Any request to the CCDC for this In conclusion, a molecular module possessing two divergent material should quote the full literature citation and the reference cavities was shown to form in the crystalline phase either a number 1145/116. discrete exobinuclear inclusion complex in the presence of solvent molecules acting as stoppers, or an infinite inclusion 1 M.C. Etter, Acc. Chem. Res., 1990, 23, 120; J. D. Dunitz, Pure molecular network in the presence of connector molecules. Appl. Chem., 1991, 63, 177; A. Gavezzotti, Acc. Chem. Res., 1994, 27, 309; G. R. Desiraju, Angew. Chem., Int. Ed. Engl., 1995, 34, Thus, one may use as a construction principle inclusion 2311; G.M. Whitesides, J. P. Mathias and T. Seto, Science, 1991, processes between hollow molecular modules and full connec- 254, 1312; M. Simard, D. Su and J. D. Wuest, J. Am. Chem. Soc., tor units to design molecular networks in the solid state. 1991, 113, 4696; F. W. Fowler and J. W. Lauher, J. Am. Chem. Further research dealing with the formation of inclusion Soc., 1993 115, 5991; X.Delaigue, E. Graf, F. Hajek, networks using chiral hollow molecular modules is currently M. W. Hosseini and J.-M. Planeix, in Crystallography of Supramolecular Compounds, ed. G. Tsoucaris, J. L. Atwood and under investigation. J. Lipkowski, NATO ASI Series C, Kluwer, Dordrecht, 1996, vol. 480, p. 159; G. Brand, M. W. Hosseini, O. Fe� lix, P. SchaeVer and R. Ruppert, in Magnetism a Supramolecular Function, We thank the CNRS and the Institut Universitaire de France ed.O. Kahn, NATO ASI Series C, Kluwer, Dordrecht, 1996, vol. 484, p. 129. (IUF) for financial support. 2332 J. Mater. Chem., 1998, 8(11), 2331–23332 C. B. Aakero�y and K. R. Seddon, Chem. Soc. Rev., 1993, 22, 397; E. Graf, M. W. Hosseini, A. De Cian, N. Kyritsakas and J. Fischer, Chem.Commun., submitted. D. Braga and F. Grepioni, Acc. Chem. Res., 1994, 27, 51; 6 M. W. Hosseini and A. De Cian, Chem. Commun., 1998, 727 and S. Subramanian and M. J. Zaworotko, Coord. Chem. Rev., 1994, references therein. 137, 357; D. S. Lawrence, T. Jiang and M. Levett, Chem. Rev., 7 X. Delaigue, M. W. Hosseini, A. De Cian, J. Fischer, E. Leize, 1995, 95, 2229; V. A. Russell and M.D. Ward, Chem. Mater., S. KieVer and A. Van Dorsselaer, Tetrahedron Lett., 1993, 34, 1996, 8, 1654; J. F. Stoddart and D. Philip, Angew. Chem., Int. Ed. 3285; F. Hajek, E. Graf and M. W. Hosseini, Tetrahedron Lett., Engl., 1996, 35, 1155. 1996, 37, 1409; F. Hajek, M. W. Hosseini, E. Graf, A. De Cian 3 M. W. Hosseini, R. Ruppert, P. SchaeVer, A. De Cian, and J. Fischer, Tetrahedron Lett., 1997, 38, 4555.N. Kyritsakas and J. Fischer, J. Chem. Soc. Chem. Commun., 8 F. Hajek, E. Graf, M. W. Hosseini, X. Delaigue, A. De Cian and 1994, 2135; M. W. Hosseini, G. Brand, P. SchaeVer, R. Ruppert, J. Fischer, Tetrahedron Lett., 1996, 37, 1401; F. Hajek, A. De Cian and J. Fischer, Tetrahedron Lett., 1996, 37, 1405; M. W. Hosseini, E. Graf, A. De Cian and J. Fischer, Angew.O. Fe� lix, M. W. Hosseini, A. De Cian and J. Fischer, Angew. Chem., Int. Ed. Engl., 1997, 37, 1760; F. Hajek, E. Graf, Chem., Int. Ed. Engl., 1997, 36, 102; O. Fe� lix, M. W. Hosseini, M. W. Hosseini, A. De Cian and J. Fischer, Cryst. Eng., 1998, A. De Cian and J. Fischer, Tetrahedron Lett., 1997, 38, 1755; 1, 79. O. Fe� lix, M. W. Hosseini, A. De Cian and J. Fischer, Tetrahedron 9 M. Perrin, F. Gharnati, D. Oehler, R. Perrin and S. Lecocq, Lett., 1997, 38, 1933; O. Fe� lix, M. W. Hosseini, A. De Cian and J. Inclusion Phenom., 1992, 14, 257. J. Fischer, New J. Chem., 1997, 21, 285. 10 B. Yao, J. Bassus and R. Lamartine, New J. Chem., 1996, 20, 913. 4 R. Robson in Comprehensive Supramolecular Chemistry, ed. 11 B. Dhawan, S. I. Chen and C. D. Gutsche, Makromol. Chem., D. D. Macnicol, F. Toda and R. Bishop, Pergamon, Oxford, 1996, 1987, 188, 921. vol. 6, p. 733. 5 C. Kaes, M. W. Hosseini, C. E. F. Rickard, B. W. Skelton and A. White, Angew. Chem., Int. Ed. Engl., 1998, 37, 920; G. Mislin, Communication 8/06006A J. Mater. Chem., 1998, 8(11), 2331&nda

ISSN:0959-9428    

DOI:10.1039/a806006a

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 Communication EVects of RuO2 on activity for water decomposition of a RuO2/Na2Ti3O7 photocatalyst with a zigzag layer structure Shuji Ogura, Mitsuru Kohno, Kazunori Sato and Yasunobu Inoue* Department of Chemistry, Nagaoka University of Technology, Nagaoka, 940-2188, Japan Received 6th July 1998, Accepted 26th August 1998 Sodium trititanate, Na2Ti3O7, with a zigzag layer structure photocatalyst when ruthenium oxide is dispersed as small particles on the titanate.produces a surface lattice O- radical upon UV irradiation and has the ability to decompose water to hydrogen and Na2Ti3O7 was prepared by calcining an equimolar ratio of TiO2 (high purity grade, Soekawa Chemical Co.) and Na2CO3 oxygen when ruthenium oxide is highly dispersed on the titanate.(high purity grade, Soekawa Chemical Co.) in air at 1073 K for 16 h. The formation of these titanates was confirmed by X-ray diVraction. For measurements of EPR signals, about Barium tetratitanate, BaTi4O9, with a pentagonal-prism tunnel structure and alkaline metal hexatitanates, M2Ti6O13 (M= 300 mg of the titanates were placed in a quartz cell and degassed at 573 K in high vacuum.The g values were calibrated Na, K, Rb), with a rectangular tunnel act as good photocatalysts to decompose water to oxygen and hydrogen in combi- by Mn2+ in MgO, the error of which was within ±0.001. For the preparation of a photocatalyst, Na2Ti3O7 was impregnated nation with ruthenium oxide.1–3 The common features of these titanates are that both have tunnel structures and give rise to with the two kinds of ruthenium compounds: one consisted of RuCl3 aqueous solutions which were the same as used in the surface lattice O- species in the presence of gases at 77 K upon UV irradiation.4–6 These results lead to a view that previous procedures,1–3 and the new other was dodecacarbonyltriruthenium, Ru3(CO)12, dissolved in tetrahydrofuran.photocatalysis by the titanates is closely related to the surface lattice O- radical generated by UV irradiation. The Ru metal loading was 0.7 wt%, unless otherwise specified. The impregnated titanate was dried at 353 K and then sub- In a series of titanates with the chemical formula Na2TinO2n+1 to which Na2Ti6O13 belongs, Na2Ti3O7 has a jected to reduction at 673 K in a H2 atmosphere for 4 h, followed by oxidation in air at 623 K.Ruthenium oxides zigzag layer structure.7 Fig. 1 shows a schematic structure of Na2Ti3O7, together with the rectangular tunnel structure of prepared using RuCl3 and Ru3(CO)12 are referred to as RuO2(CL) and RuO2(CB), respectively. A powdered photo- Na2Ti6O13. When RuO2 was supported on Na2Ti3O7 by the same conventional impregnation method using RuCl3 aqueous catalyst (250 mg) was dispersed in a quartz reaction cell filled with distilled and deionized pure water (20 cm3), stirred by solutions as employed for BaTi4O9 and M2Ti6O13 (M=Na, K, Rb), poor photocatalytic performance for water decompo- bubbling with Ar gas, and irradiated through a water filter with a Xe lamp operated at 400 W.Hydrogen and oxygen sition has been known to occur.It is of particular importance to clarify the reasons for the photocatalytic diVerences between produced were analyzed by a gas chromatograph directly connected to the reaction system. the tunnel and the layer titanate and to confirm whether or not a correlation between photocatalytic activity and the The HRTEM images of the RuO2-dispersed titanates were obtained with a JEOL 2010 transmission electron microscope surface lattice O- radical formation holds for the layer titanate, for better understanding of the photocatalysis mechanism.operated at 200 kV. The energy-dispersive X-ray (EDS) spectra were collected for nanometer-sized areas of the samples Since the photocatalytic processes in water decomposition on RuO2-deposited titanates are composed of photoexcited with a Voyager energy dispersive analyzer (Noran Instruments) installed on the microscope. charge formation in the titanates and charge transfer to the surface reactants through RuO2, each step has to be examined Fig. 2 shows the EPR signals of Na2Ti6O13 and Na2Ti3O7 obtained at 77 K in 4 kPa O2 under UV irradiation by a 500 W separately in order to shed light on the diVerences between the two types of titanates.In the present study, the ability of photoexcited charge formation was examined by an electron paramagnetic resonance (EPR) method, and that of charge transfer by changing the eVects of RuO2 deposited on the titanates and then by high resolution transmission electron microscopic (HRTEM) observation. We have discovered that a layered titanate of Na2Ti3O7 has a high ability for photoexcited charge formation and the eVects of RuO2 dispersion are important for photocatalysis: Na2Ti3O7 is a promising Fig. 2 Comparison of EPR signals of Na2Ti6O13 (a) and Na2Ti3O7 (b) with UV irradiation. The signals were recorded at 77 K in the Fig. 1 A schematic representation of Na2Ti3O7 with a zigzag layer (a) presence of 4 kPa oxygen.The signal of Na2Ti6O13 was the same as reported previously (cf. ref. 4). and Na2Ti6O13 with a rectangular tunnel structure (b). J. Mater. Chem., 1998, 8(11), 2335–2337 2335Fig. 3 Production of hydrogen and oxygen from water by a RuO2(CB) and RuO2(CL)/Na2Ti3O7 photocatalyst with a zigzag layer structure. $, H2; #, O2 for RuO2(CB)/Na2Ti3O7; &, H2; %, O2 for RuO2(CL)/Na2Ti3O7.high pressure mercury lamp. As reported previously, the tunnel structure Na2Ti6O13 provided a strong signal with g=2.020, g=2.018 and g=2.004, which is assigned to a surface lattice O- radical.4,6 For Na2Ti3O7, nearly the same signal with g= 2.021, g=2.018, and g=2.004 was observed. The close similarity clearly indicates that Na2Ti3O7 is able to produce the surface lattice O- radical.Since the formation of the radical is associated with highly eYcient photoexcited charge separation in BaTi4O9 and Na2Ti6O13,8 Na2Ti3O7 is concluded to have the ability of photoexcited charge formation. Fig. 3 shows water decomposition on a RuO2(CB)-deposited Na2Ti3O7 [referred to as RuO2(CB)/Na2Ti3O7] photocatalyst, together with a RuO2(CL)/Na2Ti3O7 photocatalyst.In addition to hydrogen, the evolution of oxygen occurred from Fig. 4 HRTEM images of RuO2(CL)/Na2Ti3O7 (a) and RuO2(CB)/ an initial stage and continued at a constant rate as long as the Na2Ti3O7 (b). sample was irradiated. Note that a RuO2(CL)/Na2Ti3O7 photocatalyst which underwent the same reduction and oxidation resulted in little evolution of oxygen, although a small amount of hydrogen was produced.Fig. 4 shows HRTEM images of RuO2 deposited Na2Ti3O7. For RuO2(CL)/Na2Ti3O7, large egg-shaped black spots, whose sizes were around 20–30 nm, were observed. On the other hand, for RuO2(CB)/Na2Ti3O7 spherical dark spots of 2–4 nm in diameter were mostly distributed uniformly on the regular lattice image of Na2Ti3O7. EDS analysis showed that the dark egg-like and spherical spots are composed of ruthenium.Note that RuO2(CB) produces smaller, better distributed RuO2 particles than does RuO2(CL). In order to compare the roles of RuO2(CL) and RuO2(CB) in photocatalysis, these Ru oxides were supported on Na2Ti6O13 with a rectangular tunnel structure. Fig. 5 shows the photocatalytic activities of RuO2(CL)/ and RuO2(CB)/Na2Ti6O13.RuO2 (CL)/Na2Ti6O13 produced Fig. 5 Photocatalytic activities of RuO2(CL)/ and RuO2(CB)/ hydrogen and oxygen in nearly the stoichiometric ratio. These Na2Ti6O13. Ru content: 1 wt%. results exclude the possibility that the poor performance of the RuO2(CL)/Na2Ti3O7 photocatalyst is due to a Cl residue which might remain on the surface. Interestingly, the photo- diVerences in RuO2 particle sizes and shapes between RuO2(CL) and RuO2(CB), as shown in Fig. 4. catalytic activity was higher by a factor of 2.2 for RuO2(CB)/Na2Ti6O13 than for RuO2(CL)/Na2Ti6O13. This It is likely that the larger RuO2 particles produce an oxygen-deficient state in the interior of the particles, because indicates that a larger number of active sites are produced in the former, thus suggesting that RuO2(CB) is superior to of the diYculty of complete oxidation, and/or weak interactions at interface between RuO2 and the titanate surface, RuO2(CL) in the formation of smaller RuO2 particles.The surface geometric eVect of a pentagonal-prism tunnel structure which has unfavorable influences on the photoexcited charge transfer in photocatalysis. These considerations lead to the of BaTi4O9 has been previously described as playing the role of a ‘nest’ in the accommodation of Ru oxides, which presents view that the good photocatalytic performance of H2 and O2 production observed for RuO2(CB)/Na2Ti3O7 is due to the a barrier for the aggregation and growth of RuO2 particles and keeps Ru oxide particles small.1 Thus, the diVerences in presence of smaller RuO2 particles.In conclusion, there is no intrinsic diVerence in photo- particle sizes between RuO2(CL) and RuO2(CB) are considered to be rather small in Na2Ti6O13 in view of the tunnel catalysis between the tunnel and layer structures: a Na2Ti3O7 titanate with a zigzag layer structure makes a good photocata- structure. For a layered titanate of Na2Ti3O7 which has no tunnel space, there is little geometric eVect to suppress the lyst which produces H2 and O2 when RuO2 is highly dispersed.The view that the ability to form O- surface radicals upon aggregation and growth of RuO2. This leads to significant 2336 J. Mater. Chem., 1998, 8(11), 2335–23373 Y. Inoue, T. Niiyama and K. Sato, Top. Catal., 1994, 1, 137. UV irradiation is correlated with the photocatalytic activity 4 S.Ogura, M. Kohno, K. Sato and Y. Inoue, Appl. Surf. Sci., 1997, may be also applicable to the layered titanate. For the design 121/122, 521. of eYcient photocatalysts, in addition to the choice of titanates 5 M. Kohno, S. Ogura, K. Sato and Y. Inoue, J. Chem. Soc., Faraday which permit the formation of O- radicals upon UV irradia- Trans., 1994, 93, 2433. tion, it is also important to have well dispersed small RuO2 6 M. Kohno, S. Ogura, K. Sato and Y. Inoue, Stud. Surf. Sci. Catal., particles. 1996, 101, 143. 7 S. Andersson and A. D. Wadsley, Acta Crystallogr., 1961, 14, 1245; 1962, 15, 194. Notes and references 8 M. Kohno, S. Ogura, K. Sato and Y. Inoue, Chem. Phys. Lett., 1997, 267, 72. 1 Y. Inoue, Y. Asai and K. Sato, J. Chem. Soc., Faraday Trans., 1994, 90, 797. 2 Y. Inoue, T. Kubokawa and K. Sato, J. Phys. Chem., 1991, 95, Communication 8/05172K 4059. J. Mater. Chem., 1998, 8(11), 2335–2337 2337

ISSN:0959-9428    

DOI:10.1039/a805172k

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 Crystal engineering using polyphenols. Host–guest behaviour of planar ribbons in C-methylcalix[4]resorcinarene–4,4¾-trimethylenedipyridine –methanol (1/2/0.5), and capture of 2,2¾-bipyridyl molecules by paired calixarene bowls in C-methylcalix[4]- resorcinarene-2,2¾-bipyridyl–methanol–water (1/1/1/1.16) George Ferguson,a Christopher Glidewell,b* Alan J.Lough,c Gordon D. McManusb and Paul R. Meehana aDepartment of Chemistry and Biochemistry, University of Guelph, Guelph, Ontario, Canada N1G 2W1 bSchool of Chemistry, University of St Andrews, St Andrews, Fife, UK KY16 9ST cLash Miller Chemical Laboratories, University of Toronto, Toronto, Ontario, Canada M5S 1A1 Received 4th June 1998, Accepted 13th August 1998 Co-crystallisation of the rccc isomer of C-methylcalix[4]resorcinarene 1 with 4,4¾-trimethylenedipyridine from methanol yields a solvated 152 adduct 2 in which the resorcinarene acts as a quadruple donor and the dipyridines both act as double acceptors, in O–H,N hydrogen bonds.The supramolecular structure consists of linear and nearly planar ribbons with the bowls of the resorcinarene units in one ribbon acting as hosts towards the -(CH2)3- spacer units of a neighbouring ribbon, acting as guests.Co-crystallisation of the same resorcinarene 1 with 2,2¾- bipyridyl yields a doubly solvated 151 adduct resorcinarene–2,2¾-bipyridyl–methanol–water (1/1/1/1.16) 3. The resorcinarene, methanol and water molecules combine by means of multiple O–H,O hydrogen bonds to form paired, essentially-planar two-dimensional nets in which centrosymmetric pairs of resorcinarene bowls act as selfassembled carcerands to form large cavities in which pairs of 2,2¾-bipyridyl molecules are held by a combination of O–H,N and C–H,O hydrogen bonds.The design and construction of self-assembled microporous NC5H4C5H4N to continuous {2, 2, 1} interweaving in molecular solids is an attractive target in crystal engineering.[Fe(C5H4COC6H4OH)2]. Such interweaving arises because One approach which has proved successful for the formation the reticulations in the nets are large compared with the of structures containing isolated linear channels formed by the eVective diameters of the molecular strands forming the nets. self-assembly of small molecular building blocks, via hydrogen- To prevent interweaving in supramolecular systems containing bond formation, is the construction of cyclic fragments which large rings, it is necessary to increase the thickness of the can then be induced to stack, in register, to form the channels.strands relative to the hole size; this principle has been demon- Thus 4,4¾-sulfonyldiphenol, O2S(C6H4OH)2, and piperazine strated in 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl) form such a channel structure when co-crystallised from butane/(CH2)6N4 (1/1), where the nets contain alternating either methanol or acetonitrile: pairs of phenolate anions R6 6(40) and R6 6(60) rings, but are not interwoven because of [HOC6H4SO2C6H4O]- form hydrogen-bonded R2 2(24) the presence of the tert-butyl groups in the tris-phenol.9 rings1,2† which are bound into parallel linear stacks by piperaz- Seeking to develop further the use of large and stericallyinium dications [C4H12N2]2+.Within each stack there is a demanding molecular building blocks, we have turned our channel of cross-sectional area ca. 14 A° 2, too small to accom- attention to polyhydroxylated calixarenes, specifically those modate methanol molecules but large enough to hold derived from resorcinol, 1.In general, two isomeric forms of acetonitrile molecules.3 The use of this approach for the for- C-alkylcalix[4]resorcinarenes can be obtained, a C4v (rccc or mation of wider channels requires the construction of larger crown10,11) isomer, 1a, and a C2h (rctt or chair) isomer, 1b, but rings, and we have reported the formation of nets of despite this structural versatility and the ease of synthesis, R4 4(32) rings in pure O2S(C6H4OH)2,4 of R4 4(40) rings rather little use of such compounds has hitherto been made in [Fe(C5H4COC6H4OH)2],5 and of R6 6(48) rings in in crystal engineering.C-Methylcalix[4]resorcinarene, 1a CH3C(C6H4OH)3/(CH2)6N4 (1/1),6 while nets of R12 12(126) with R=Me (2,8,14,20-tetramethylpentacyclo[19.3.1.13,7.19,13 rings are formed in CH3C(C6H4OH)3/NC5H4C5H4N (2/3).7 .115,19]octacosa-1(25),3,5,7(28),9,11,13(27),15,17,19(26),21,23- However, in all these examples the nets are interwoven, with dodecaen-4,6,10,12,16,18,22,24-octol, C32H32O8), has been the interweaving characterised by diVering degrees of shown12 to form a 152 hydrogen-bonded adduct with 4,4¾- complexity, ranging from pairwise {4, 2, 1}8 interweaving of bipyridyl which entraps acetonitrile, but the gross suprathe nets in O2S(C6H4OH)2 and CH3C(C6H4OH)3/ molecular structure in this product does not exploit the (CH2)6N4 via {10,10,9} interweaving in CH3C(C6H4OH)3/ hydrophobic nature of the calixarene bowl.We have now studied the solid-state adducts, 2 and 3 respectively, of this same C-methylcalix[4]resorcinarene with †Pattern designators1,2 for graph sets are of the general type Ga d(r); the descriptor G may be C (chain), D (dimer, or other finite set), R both an extended-reach bipyridyl, 4,4¾-trimethylenedipyridine (ring), or S (self ) (i.e. an intramolecular hydrogen bond).The degree and with 2,2¾-bipyridyl.We reasoned that addition of an r represents the total number of atoms in a ring or in the repeating aliphatic spacer group between the pyridine units in 4,4¾- unit of a chain, the superscript a indicates the number of hydrogenbipyridyl would lead to chain-formation in 2 of a type similar bond acceptors and the subscript d indicates the number of hydrogento that formed by 4,4¾-bipyridyl itself,12 but that additionally bond donors.Thus, for example, the hydrogen-bond pattern in the familiar carboxylic acid dimer is represented as R2 2(8). the C–H,p(arene) interactions between the trimethylene J. Mater. Chem., 1998, 8(11), 2339–2345 2339two half-occupied equivalent sites related by a two-fold rotation axis parallel to [010]. Within one of the molecules of the dipyridine, the heterocyclic ring containing atom N71 was found to be disordered.The diVraction data were most satisfactorily fitted by a model which assigned to this ring two equallypopulated sets of atom-sites, generated by rotation of the ring about the N71,C74 vector, such that the two ring-orientations are inclined at 35.7(4)o to one another. The orthorhombic space group Pbca was uniquely assigned for compound 3 from the systematic absences: 0kl absent when k=2n+1, h0l absent when l=2n+1, hk0 absent when h=2n+1.The asymmetric unit contains one molecule each of the resorcinarene, 2,2¾- bipyridyl and water, all in general positions and fully ordered, together with a disordered molecule of methanol. The water and the methanol molecules in 3 both participate in the spacer units in one chain and the calixarene bowls of neighhydrogen- bonding scheme: there is also a partially-occupied bouring chains could be suYcient to control the mutual water site, with s.o.f.of 0.159(7), which is not involved in any arrangement of the chains of 2 in the solid state. Similarly, close contacts with the rest of the structure. For both 2 and with 2,2¾-bipyridyl in compound 3, we reasoned that the 3, all the hydrogen atoms of the resorcinarene and the bipyri- location of the hydrogen-bond acceptor sites in the bipyridyl dine components, as well as those of the water molecule and would preclude the formation of a simple chain motif, possibly the hydroxy hydrogen in the methanol in 3, were located from leading to a two- or three-dimensional system instead, resulting diVerence maps.All hydrogen atoms located in this way were from some alternative mode of linkage of neighbouring included in the final refinements as riding atoms with O–H resorcinarene units by the bipyridyl molecules. 0.820 A° and C–H in the range 0.93–0.98 A° . Supramolecular analysis of the refined structures was made with the aid of Experimental PLATON;20 the figures were prepared with the aid of ORTEPII19 and PLATON.20 Details of the hydrogen-bonding schemes The C4v isomer of C-methylcalix[4]resorcinarene 1a was are in Table 2 and 3.Fig. 1 and 3 show the asymmetric units prepared by the literature method.13 Repeated attempts to of compounds 2 and 3 respectively, and Fig. 2, 4 and 5 recrystallise this compound from methanol or from aqueous illustrate aspects of the supramolecular architectures.methanol invariably provided microcrystalline or powdery Full crystallographic details, excluding structure factors, material for which microanalysis and 1H NMR consistently have been deposited at the Cambridge Crystallographic Data indicated 6–8 molecules of water per calixarene unit.Co- Centre (CCDC). See Information for Authors, J. Mater. crystallisation of this resorcinarene with either 4,4¾-trimethyl- Chem., 1998, Issue 1. Any request to the CCDC for this enedipyridine or 2,2¾-bipyridyl from methanol solutions yielded material should quote the full literature citation and the 2 and 3 respectively, regardless of the molar ratio of resorcinarreference number 1145/115.ene to dipyridine originally taken, within the range of 151 to 154. Analysis for 2, resorcinarene·4,4¾-trimethylenedipyridine ·MeOH (1/2/0.5): found C, 73.5; H, 6.6; N, 5.6%; C58.5H62N4O8.5 requires C, 73.4; H 6.5; N, 5.8%; for 3, Results and discussion resorcinarene·2,2¾-bipyridyl·MeOH·H2O (1/1/1/1.16): found Co-crystallisations C, 68.6; H, 6.3; N, 3.7%; C43H46.32N2O10.16 requires C, 68.5; H, 6.2; N, 3.7%.Crystallisation of the resorcinarene from neat The C4v isomer of C-methylcalix[4]resorcinarene, when copyridine at room temperature yielded the 154 adduct 4 (Found: crystallised with 4,4¾-trimethylenedipyridine from solutions in C, 72.0; H, 6.2; N, 6.4%; C52H52N4O8 requires C, 72.5; H, methanol, provided the expected 152 adduct 2, although 6.1; N, 6.5%), while co-crystallisation with 4,4¾-bipyridyl from solvated with one half a molecule of methanol per resorcinarsolutions in either methanol or ethanol, with input molar ene.The 152 stoichiometry was expected on the grounds that ratios of resorcinarene to bipyridyl in the range 151 to 154, this isomer of the resorcinarene generally exhibits four intraconsistently yielded a microcrystalline material 5 of composi- molecular O–H,O hydrogen bonds,12,21–23 and hence acts as tion resorcinarene5bipyridyl5water (1/2/3) (Found C, 68.3; H, a donor of only four intermolecular hydrogen bonds, while 5.8; N, 6.0%: C52H54N4O11 requires C, 68.5; H, 6.0; N, 6.2%).the 4,4¾-trimethylenedipyridine acts as a double acceptor. However, 2,2¾-bipyridyl was not expected to act as a simple X-Ray crystallography bridging unit between pairs of resorcinarene molecules in the manner of 4,4¾-bipyridyl12 or 4,4¾-trimethylenedipyridine, com- Crystals of compounds 2 and 3 suitable for single-crystal Xpound 2, because of the closeness of the two nitrogen atoms ray diVraction were selected directly from the analytical and the likely orientation of the resulting O–H,N hydrogen samples. Details of the X-ray experimental conditions, cell bonds, regardless of the twist about the central C–C bond of data, data collection and refinements, and the computer prothis bipyridyl.Accordingly the observed 151 ratio in 3 was grams employed14–20 are summarised in Table 1. For comnot unexpected. pound 3, a data set collected using a CAD-4 diVractometer at The degree of solvation and guest-inclusion in the calixarene room temperature provided the essential features of the struccavity is unpredictable and varies quite subtly with crystallis- ture, but the ratio of observations to parameters was very low.ation conditions. Thus when C-methylcalix[4]resorcinarene Accordingly a second data set was collected at low temperature was crystallised by dissolution in boiling pyridine, followed by using a Nonius Kappa-CCD diVractometer as described in cooling, a 156 adduct was produced in which four molecules Table 1.of pyridine are hydrogen bonded to the resorcinarene, a fifth For compound 2, the orthorhombic space group Pbcn was is included in the calixarene cavity and the sixth is outside the uniquely assigned from the systematic absences: 0kl absent calixarene·(pyridine)4 complex as solvent of crystallisation.12 when k=2n+1, h0l absent when l=2n+1, hk0 absent when By contrast, crystallisation of the same calixarene from pyri- (h+k)=2n+1.As well as the resorcinarene and two molecules dine wholly at room temperature yielded just a 154 complex of 4,4¾-trimethylenedipyridine in general positions, the structure analysis also revealed methanol molecules disordered over 4; while structure determination for 4 has so far been precluded 2340 J.Mater. Chem., 1998, 8(11), 2339–2345Table 1 Experimental details Compound 2 Compound 3 Crystal data Chemical formula C58.5H62N4O8.5 C43H46.32N2O10.16 Chemical formula weight 957.12 754.35 Cell setting Orthorhombic Orthorhombic Space group Pbcn Pbca a/A° 25.7972(4) 13.9906(4) b/A° 16.5089(3) 17.8679(5) c/A° 23.7612(4) 29.3316(7) V/A° 3 10119.5(3) 7332.4(3) Z 8 8 F (000) 4072 3199.2 Dx/Mg m-3 1.256 1.367 Dm/Mg m-3 not measured not measured Radiation type Molybdenum Ka Molybdenum Ka Wavelength/A° 0.71073 0.71073 No. of reflections for cell parameters 10286 7408 h range (°) 1.70–26.37 1.97–26.37 m/mm-1 0.084 0.098 Temperature/K 150(1) 150(1) Crystal form Block Plate Crystal size/mm 0.42×0.37×0.36 0.25×0.20×0.05 Crystal colour Brownish-yellow Brownish-yellow Data collection DiVractometer Kappa-CCD Kappa-CCD Data collection method 360×1° w scans 360×1° w scans Absorption correction none none No.of measured reflections 69128 42325 No. of independent reflections 10286 7408 No. of observed reflections 4980 4173 Criterion for observed reflections I>2s( I) I>2s(I ) Rint 0.031 0.031 hmax (°) 26.37 26.37 Range of h, k, l -32AhA32 -17AhA17 -19AkA20 -22AkA22 -29AlA29 -36AlA36 Intensity decay (%) no decay no decay Refinement Refinement on F 2 F 2 R[F 2>s(F 2)] 0.0465 0.0505 wR(F 2) 0.1312 0.1433 S 0.865 0.916 No.of reflections used in refinement 10286 7408 No.of parameters used 671 505 H-atom treatment constr constr k in w=1/[s2(Fo2)+(kP )2] 0.0712 0.0815 [P=(Fo2+2Fc2)/3] (D/s)max 0.001 0.000 Drmax/e A° -3 0.312 0.649 Drmin/e A° -3 -0.347 -0.368 Extinction method SHELXL None Extinction coeYcient 0.00073(12) — Source of atomic scattering factors International Tables for Crystallography (Vol. C) Computer programs Data collection Kappa-CCDa Cell refinement DENZOb Data reduction DENZO Structure solution SHELXS97c Structure refinement NRCVAX96d and SHELXL97e Molecular graphics NRCVAX96, ORTEPf and PLATONg Preparation of material for publication NRCVAX96 and SHELXL97 aRef. 14.bRef. 15. cRef. 16. dRef. 17. eRef. 18. fRef. 19. gRef. 20. by a lack of suitable crystals, the most plausible interpretation during crystallisation.The extreme sensitivity of structure in these systems to the solvent employed for crystallisation is of the 154 stoichiometry is in terms of the hydrogen-bonded adduct previously observed,12 but without the cavity-included further illustrated by the resorcinarene itself, for which both aquated cubic (space group I432, Z=12)24 and butanone- and the solvating pyridine units.Similarly, co-crystallisation of C-methylcalix[4]resorcinarene with 4,4¾-bipyridyl from solvated monoclinic (space group P21/m, Z=2)22 forms have been reported. acetonitrile solution yielded a 152 adduct, with acetonitrile trapped in the calixarene cavity;12 use of methanol or ethanol as solvent, as here, produced again the 152 adduct, but now The supramolecular structure of 2 solvated not by either alcohol, but by three molecules of water per calixarene, compound 5; the water in 5 has presumably In compound 2, the resorcinarene component forms four asymmetric intramolecular O–H,O hydrogen bonds (Fig. 1 been captured either from the solvent, or from the atmosphere J. Mater. Chem., 1998, 8(11), 2339–2345 2341Table 2 Hydrogen-bond dimensions in compound 2 and Table 2): the orientation of these hydrogen bonds is such as to reduce the overall symmetry of this component from C4v Bond D H A D,A/A° H,A/A° D–H,A (°) to C2v.There are thus four hydroxy groups available on each resorcinarene molecule in compound 2 for the formation of a O23 H23 O15 2.749(2) 1.94 171 intermolecular O–H,N hydrogen bonds to the 4,4¾-trimethyl- b O25 H25 O33 2.721(2) 1.92 165 c O43 H43 O35 2.753(2) 1.94 169 enedipyridine component: four of the eight oxygen atoms in d O45 H45 O13 2.838(2) 2.04 166 the resorcinarene component thus act as both donor and e O13 H13 N51 2.738(2) 1.93 169 acceptor of hard hydrogen bonds,25 and the other four as f O15 H15 N71 2.614(2) 1.82 162 donor only.The disordered methanol molecules, however, do g O33 H33 N81a 2.639(2) 1.85 160 not play any part in the hydrogen bonding in 2: the oxygen h O35 H35 N61a 2.734(2) 1.93 167 atom forms no non-bonded contacts significantly shorter than i C53 H53 O43b 3.397(3) 2.59 146 j C65 H65 O45b 3.399(3) 2.51 159 the sum of the van der Waals radii with any of the other atoms in the structure.Oxygen atoms O13 and O15 form Symmetry codes: ax, y, -1+z; b0.5-x, 1.5-y, 0.5+z.O–H,N hydrogen bonds with N51 and N71 respectively, within the asymmetric unit (Fig. 1 and Table 2), while atoms O33 and O35 at (x, y, z) form hydrogen bonds with N81 and N61 respectively in the neighbouring unit at (x, y, -1 +z). Table 3 Hydrogen-bond dimensions in compound 3 The basic supramolecular structure thus comprises a ribbon running parallel to the [001] direction and generated by Bond D H A D,A/A° H,A/A° D–H,A (°) translation: eight such ribbons run through the unit cell.This essentially flat ribbon propagated by translation may be com- a O13 H13 O45 2.741(2) 1.94 166 pared with the highly-puckered zig-zag ribbon in the analogous b O15 H15 O23 2.808(2) 2.04 155 c O25 H25 O33 2.749(2) 1.94 169 adduct formed by the same resorcinarene with 4,4¾-bipyridyl,12 da O35 H35 O43 3.191(3) 2.56 134 where the ribbon is propagated by the action of a two-fold e O43 H43 O8 2.705(3) 1.90 166 screw axis.f O45 H45 O7 2.759(3) 1.97 162 The eight identical ribbons in the structure of compound 2 g O7 H7 N51 2.727(3) 1.64 167 are connected together in pairs. The aliphatic spacer unit h O23 H23 O7b 2.685(3) 1.89 164 C57–C59 (Fig. 1 and 2) of the dipyridine at (x, y, z) fits across i O33 H33 N61c 2.680(2) 1.88 165 ja O35 H35 O25d 2.794(2) 2.22 128 the rim of the resorcinarene bowl in the neighbouring ribbon, k O8 H81 O35e 2.972(3) 2.05 144 at (0.5-x, 1.5-y, 0.5+z), while the aliphatic spacer C57–C59 l O8 H82 O33d 2.894(2) 1.94 138 of this latter unit fits across the bowl at (x, y, 1+z) in the first m C48 H48B O13f 3.127(3) 2.52 121 ribbon.Thus pairs of ribbons, in this case related by the action n C66 H66 O25c 3.310(3) 2.56 139 of the 21 screw axis at (0.25, 0.75, z), are held closely together: aHydrogen bonds d and j are part of a three-centre system with O43 aliphatic spacers in one ribbon are guests in the calixarene and O25d as the two acceptors: the angle O43,H35,O25c is 94° and bowls of the neighbouring ribbon.Additional stabilisation of the sum of the three hydrogen-bond angles around H35 is thus 360°. these inter-ribbon interactions arises from the precise align- Symmetry codes: b0.5-x, -0.5+y, z. c-x, -y, -z. d-0.5-x, 0.5+y, z. e0.5+x, 0.5-y, -z. f-0.5+x, y, 0.5-z. ment of a pair of aromatic C–H bonds in the dipyridine of one ribbon, acting as hydrogen-bond donors to a pair of oxygen atoms in the neighbouring ribbon.Thus atoms C53 and C65 in the dipyridine at (x, y, z), i.e. one carbon atom in each heteroaromatic ring of this dipyridine, act as hydrogen- Fig. 1 The asymmetric unit in compound 2, showing the atom- Fig. 2 View of part of the structure of 2, showing the aliphatic spacer unit C57–C59 of one ribbon fitting across the resorcinarene bowl in labelling scheme.Displacement ellipsoids are drawn at the 30% probability level. the neighbouring ribbon. 2342 J. Mater. Chem., 1998, 8(11), 2339–2345Fig. 4 Stereoview of part of the structure of 3, showing one of the two-dimensional nets generated solely by O–H,O hydrogen bonds with the centrosymmetric pairs of resorcinarene bowls.Fig. 3 The asymmetric unit of compound 3, showing the atomlabelling scheme. Displacement ellipsoids are drawn at the 30% probability level. bond donors to two atoms, O43 and O45 respectively, on the same aromatic ring of the resorcinarene at (0.5-x, 1.5-y, 0.5+z). These C–H,O hydrogen bonds to the rim of the resorcinarene represent a form of intermolecular bonding, soft hydrogen bonds with oxygen as acceptor, which has not hitherto been widely recognised or exploited in this area.Supramolecular structure of 3 The asymmetric unit of compound 3 contains one molecule each of the resorcinarene, 2,2¾-bipyridyl, water and methanol (Fig. 3): all four components participate in the formation of hard hydrogen bonds. The resorcinarene forms four intramolecular O–H,O hydrogen bonds, arranged not in the usual C2v configuration, but with only C1 symmetry (Fig. 3 and Table 3). The other four hydroxy groups, associated with O23, O33, O43 and O45, all form hydrogen bonds with other components of the structure: O23 and O45 form O–H,O bonds with methanol molecules, O33 with a bipyridyl molecule, and O43 with a water molecule; in addition, atom O35 by Fig. 5 View of part of the structure of 3, showing the placing of pairs forming a bifurcated (three-centre) hydrogen bond is linked of 2,2¾-bipyridyl molecules within the cavity formed by a pair of also to another resorcinarene molecule. Hence each resorcinarresorcinarene molecules. ene acts as a quintuple donor of hydrogen bonds to, and as a triple acceptor from, other molecules. The methanol molecule acts both as hydrogen-bond donor, to a bipyridyl, and as a pairs, there are no contacts which are significantly shorter double acceptor, from two diVerent resorcinarene molecules.than the sum of the van der Waals radii. The water molecule acts as a single acceptor from one resorcinarene and as donor to two others. Finally, the bipyridyl Hydrogen-bonding motifs molecule acts as a double acceptor in O–H,N hydrogen bonds, where the two donors are methanol and a resorcinarene All of the four independent intramolecular O–H,O hydrogen molecule.Within the asymmetric unit (Fig. 3) atoms O43 and bonds in compound 2, labelled a–d in Table 2, form cyclic O45 act as donors to water and methanol respectively; meth- motifs, whose graph set descriptor is S(8),1,2 while each of anol in turn acts as donor to atom N51 of the bipyridyl, while the O–H,N and C–H,O hydrogen bonds, e–h and i and j the other ring of the bipyridyl (N61 and C62–C66) lies over respectively in Table 2, is of type D.For the hard hydrogen the rim of the calixarene. The hydrogen bonding is thus much bonds, O–H,O and O–H,N, it is necessary to consider more complex in compound 3 than in compound 2.four-fold combinations of independent hydrogen bonds in The overall supramolecular structure of compound 3 order to describe the overall supramolecular structure (Fig. 1 consists of paired two-dimensional rhomboidal nets generated and 2). The combination of the four O–H,O hydrogen solely by intermolecular O–H,O hydrogen bonds. These nets bonds a–d gives N4=R4 4(24), while the combination of the are aligned so that pairs of calixarenes, which lie across centres four independent O–H,N hydrogen bonds e–h gives of inversion with their hydroxylic rims close to one another, N4=R4 4(36).There are also two independent combinations of generate large cavities in which pairs of 2,2¾-bipyridyl molecules O–H,O and O–H,N hydrogen bonds, defining the two are held (Fig. 4 and 5). Such a pair of nets utilises only half edges of the ribbon: each of (a+b+f+g) and (c+d+e+h) the contents of the unit cell and there are two such paired gives N4=C4 4(22). The inter-ribbon soft C–H,O hydrogen nets, one lying in the domain -0.27<z<+0.27 and the other bonds, i and j, combine to give a cyclic motif with N2=R2 2(14). in the domain +0.23<z<+0.77.Between the independent J. Mater. Chem., 1998, 8(11), 2339–2345 2343In compound 3, the water molecule at (x, y, z) acts as of the intra- and inter-molecular hydrogen bonds formed by the hydroxy groups around the rim, in particular those involv- hydrogen-bond donor, via H81 (Table 3), to atom O35 of the ing guest species within the calixarene bowl.The shape of the resorcinarene molecule at (0.5+x, 0.5-y, -z), while the calixarene bowl is most simply described in terms of the angles water molecule at (0.5+x, 0.5-y, -z) in turn acts as donor made by each of the aromatic rings Cnm (n=1–4; m=1–6) via H81 to atom O35 at (1+x, y, z). Propagation of this with a reference plane, conveniently chosen as the plane interaction thus produces a continuous chain running parallel defined by the atoms Cn7 (n=1–4).In both compounds 2 and to [100] and generated by the action of a two-fold screw axis: 3 these angles are alternately ca. 40° and ca. 65°, showing that this chain, built up from hydrogen bonds d, e and k in Table 3, the skeletal conformation is, in each case, much closer to C2v is thus a spiral and has graph-set descriptor N3=C3 3(6).The symmetry than to the idealised C4v. A complementary measure same water molecule at (x, y, z) also acts as hydrogen-bond of the deviation of the bowl from idealised symmetry is donor, this time via H82, to atom O33 of the resorcinarene at provided by the O,O distances in the intramolecular O–H,O (-0.5-x, 0.5+y, z), and the water at (-0.5-x, 0.5+y, z) in hydrogen bonds (Table 2 and 3).turn acts as donor to atom O33 at (x, 1+y, z). Propagation There are two independent molecules of 4,4¾-trimethylenedi- of this hydrogen-bond sequence (hydrogen bonds d, e and l pyridine in compound 2: in both, the central aliphatic spacer of Table 3) produces a zig-zag chain with N3=C3 3(10), generunit is in the fully-extended all-trans conformation. 4,4¾- ated by the glide plane and running parallel to [010]. The Trimethylenedipyridine itself does not appear in the Cambridge interaction of these two chain motifs generates a two-dimen- Structural Database,29 but the bond lengths and angles found sional, rhomboidal network parallel to the (001) plane. Each here in compound 2 are unexceptional. In compound 3, the chain utilises just one O–H bond of the water molecules, two pyridyl rings are inclined to one another at an angle of O–H81 in the [100] direction and O–H82 in the O–H82 40.4(1)°: the N,N bite distance, 2.806(3) A° , is thus rather direction, so that the intermediate water molecules in each larger than the 2.69 A° expected for a planar 2,2¾-bipyridyl chain still have hydrogen-bonding capacity to be accounted component.for. The intermediate water molecule in the [100] chain, at (0.5+x, 0.5-y, -z) acts as donor via H82 to atom O33 in the resorcinarene at (-x, -y, -z): similarly, an intermediate The Nonius Kappa-CCD diVractometer was purchased with water molecule in the [010] chain, at (0.5-x, -0.5+y, z) acts an equipment grant from NSERC (Canada). as donor via H81 to atom O35 in the same resorcinarene molecule at (-x, -y, -z).Hence the hydrogen-bonding role of the water molecules is two-fold: firstly, they generate the References two sets of chains parallel to [100] and [010] and hence the resulting two-dimensional network; secondly, they link 1 M. C. Etter, Acc. Chem. Res., 1990, 23, 120. 2 J. Bernstein, R. E. Davis, L. Shimoni and N.-L. Chang, Angew.together pairs of such parallel networks related by the action Chem., Int. Ed. Engl., 1995, 34, 1555. of centres of inversion. 3 P. I. Coupar, G. Ferguson and C. Glidewell, Acta Crystallogr., The arrangement of the two linked nets is such that pairs Sect. C, 1996, 52, 3052. of resorcinarenes lie across centres of inversion. The two 4 C. Glidewell and G. Ferguson, Acta Crystallogr., Sect C, 1996, calixarene bowls point towards each other but the local 52, 2528.(approximately four-fold) rotation axes of the resorcinarenes 5 A.C.Be� nyei, C. Glidewell, P. Lightfoot, B. J. L. Royles and D. M. Smith, J. Organomet. Chem., 1997, 539, 177. are oVset by ca. 2.9 A° . Together with the associated water and 6 P. I. Coupar, G. Ferguson, C. Glidewell and P. R.Meehan, Acta methanol molecules, these pairs of resorcinarenes produce a Crystallogr., Sect. C, 1997, 53, 1978. large cavity in which two molecules of 2,2¾-bipyridyl are held 7 A.C.Be� nyei, P. I. Coupar, G. Ferguson, C. Glidewell, A. J. Lough by a combination of O–H,N and C–H,O hydrogen bonds and P. R. Meehan, Acta Crystallogr., Sect. C, 1998, 54, in the (Fig. 5). The combination of the O–H,O hydrogen bonds a, press.b, c and f at the equator of the cavity and the O–H,N 8 G. Ferguson, C. Glidewell, R. M. Gregson and P. R. Meehan, Acta Crystallogr., Sect. B, 1998, 54, 330. hydrogen bonds g and i holding the bipyridyl molecules in the 9 P. R. Meehan, R. M. Gregson, C. Glidewell and G. Ferguson, cavity, generates a cyclic R12 12(46) motif. Acta Crystallogr., Sect. C, 1997, 53, 1637.In eVect, the supramolecular structure of 3 has formed by 10 V. Bo�hmer, Angew. Chem., Int. Ed. Engl., 1995, 34, 713. self-assembly of a network of hydrogen-bonded carcerands, 11 A. Shivanyuk, E. F. Paulus, V. Bo�hmer and W. Vogt, Angew. each cavity in which is constructed from two resorcinarenes, Chem., Int. Ed. Engl., 1997, 36, 1301. 12 L. R. MacGillivray and J.L. Atwood, J. Am. Chem. Soc., 1997, analogous to covalently-linked carcerands.13,26 Calixarene 119, 6931. dimers, having much more open structures with the two 13 L. M. Tunstad, J. A. Tucker, E. Dalcanale, J.Weiser, J. A. Bryant, components linked together by eight molecules of either J. C. Sherman, R. C. Helgeson, C. B. Knobler and D. J. Cram, propan-2-ol27 or water,28 have recently been reported, but in J.Org. Chem., 1989, 54, 1305. both cases the dimers were isolated rather than joined into a 14 Kappa-CCD data collection program, Enraf-Nonius, Delft, continuous connected network, as in compound 3. The forma- Holland, 1998. 15 DENZO data processing program, Enraf-Nonius, Delft, tion of isolated dimers can be associated, in the one case27 Holland, 1998.with external C60 fullerene units, one per dimer, which prevent 16 G. M. Sheldrick, SHELXS97, program for the solution of crystal any hydrogen-bonded connections between the dimers and, in structures, University of Go� ttingen, Germany, 1997. the other,28 with an interior [NEt4]+ cation assisting the 17 E. J. Gabe, Y. Le Page, J.-P. Charland, F. L. Lee and P. S. White, stability of the system by means of cation,p(arene) J. Appl. Crystallogr., 1989, 22, 384. 18 G. M. Sheldrick, SHELXL97, program for the refinement of interactions. crystal structures, University of Go� ttingen, Germany, 1997. 19 C. K. Johnson, ORTEP-II, Report ORNL-5138, Oak Ridge National Laboratory, Oak Ridge, TN, 1976. Molecular conformations and dimensions 20 A. L. Spek, PLATON, Molecular Geometry and Graphics Program, May 1998 version, University of Utrecht, Utrecht, The overall shape of the rccc isomer of a C-alkylcalix[4]resorcin- Holland, 1998. arene is largely controlled by the conformational require- 21 T. Lippmann, H. Wilde, M. Pink, A. Scha�fer, M. Hesse and ments of the 16-membered carbocycle forming the base of the G. Mann, Angew. Chem., Int. Ed. Engl., 1993, 32, 1195. calixarene, in which four distinct five-carbon fragments are 22 G. Zahn, J. Sieler, K. Mu� ller, L. Hennig and G. Mann, Z. constrained to be planar or nearly so, although these require- Kristallogr., 1994, 209, 468. 23 K. Murayama and K. Aoki, Chem. Commun., 1997, 119. ments are, of course, moderated by the strength and orientation 2344 J. Mater. Chem., 1998, 8(11), 2339–234524 L. R. MacGillivray and J. L. Atwood, Nature, 1997, 389, 469. 28 K. Murayama and K.mun., 1998, 607. 25 D. Braga, F. Grepioni, K. Biradha, V. R. Peddireddi and 29 F. H. Allen and O. Kennard, Chem. Des. Autom. News, 1993, G. R. Desiraju, J. Am. Chem. Soc., 1995, 117, 3156. 8, 31. 26 J. C. Sherman, C. B. Knobler and D. J. Cram, J. Am. Chem. Soc., 1991, 113, 2194. 27 K. N. Rose, L. J. Barbour, G. W. Orr and J. L. Atwood, Chem. Paper 8/04216K Commun., 1998, 407. J. Mater. Chem., 1998, 8(11), 2339–2345 2345

ISSN:0959-9428    

DOI:10.1039/a804216k

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 Electrically conductive graft copolymers of poly(methyl methacrylate) with varying polypyrrole and poly(3-alkylpyrroles) contents Siu-Choon Ng,a* Hardy S. O. Chana,b Jun-Feng Xiaa and Wanglin Yua aDepartment of Chemistry, National University of Singapore, Kent Ridge Crescent, Singapore 119260 bDepartment of Materials Science, National University of Singapore, Kent Ridge Crescent, Singapore 119260 Received 27th April 1998, Accepted 14th August 1998 Pyrrole and 3-alkylpyrroles were grafted via chemical oxidative polymerisation with FeCl3 to copolymers of methyl methacrylate and v-(N-pyrrolyl )alkyl methacrylates incorporating varying amounts of v-(N-pyrrolyl )alkyl methacrylates with varying alkyl chain lengths.The electrical conductivity of the resultant graft copolymers attained 10-4–10-3 S cm-1, with the length of the alkyl spacers in v-(N-pyrrolyl )alkyl methacrylates having little influence on the conductivity.A longer alkyl spacer, however, resulted in a lower glass transition temperature for the resulting graft copolymers. The graft copolymers from pyrrole were insoluble whilst those arising from 3-alkylpyrroles were completely soluble in common organic solvents even in their doped states.The past two and a half decades have witnessed intense Experimental interdisciplinary research attention on electrically conducting Synthesis of key monomers conjugated polymers such as polyacetylenes, polyanilines, polypyrroles and polythiophenes on account of their remarkable Pyrrole (Py), methacryloyl chloride and methyl methacrylate electronic, magnetic and optical properties as well as their (MMA) were distilled prior to use.a,a¾-Azobis(isobutyropotential in a wide range of technological applications.1–6 nitrile) (AIBN) (Koch-Light) was recrystallized from absolute However, the generally poor processability of these parent ethanol and dried at 40 °C in vacuo (0.2 mmHg).unfunctionalised systems has severely limited their appli- Triethylamine, dimethyl sulfoxide (DMSO) and nitromethane cations. Consequently, much research has been devoted to were distilled over CaH2. Other chemicals were used as improving the processability of the conductive polymers.7–12 received. Amongst these approaches, the combination of conducting The key monomers of v-(N-pyrrolyl )-n-alkyl methacrylate polymers, particularly polypyrroles, with conventional poly- (NPAM) were synthesized as shown in Scheme 1.mers has been the recent focus of several research groups. Tetrahydropyran (THP)-protected v-bromoalkanols used in Polypyrrole was first grafted onto polystyrene by electrochemi- this synthesis were prepared by bromination of a,v-diols13 cal polymerisation of pyrrole in the presence of a pyrrole followed by THP-protection of the terminal hydroxy groups.derivative of polystyrene.7 The graft copolymers had electrical 3-Alkylpyrroles (3APys) were synthesized according to literaconductivity of 0.05–5 S cm-1 depending on the pyrrole ture procedures14,15 except for the replacement of LiAlH4 for content.However, no information pertaining to the pro- NaAlH2(OCH2CH2OCH3)2 as the reducing agent. cessability of the graft copolymers was reported. Over the past several years, Stanke and co-workers have successfully grafted Polymerization polypyrrole to poly(methyl methacrylate) (PMMA) by The graft copolymers, poly[methyl methacrylate-co-v-(N-pyr- eVecting the chemical oxidative polymerisation of pyrrole in rolyl )alkyl methacrylate]s (PMMA-co-PNPAMs): PMMA-co- the presence of methyl methacrylate–2-(N-pyrrolyl )ethyl PNPHM, PMMA-co-PNPOM, PMMA-co-PNPDM, and methacrylate copolymer using FeCl3 as an oxidant.12 The film PMMA-co-PNPDDM corresponding to n-alkyl spacers of 6, conductivity of the graft copolymers attained a maximum of 8, 10 and 12 carbons, respectively, in NPAMs were obtained 2×10-2 S cm-1,12a,12c though only marginal solubility was by copolymerization of methyl methacrylate (MMA) with the achieved.12a Although soluble samples of the graft copolymers corresponding NPAMs in THF at 60 °C for 22 h using AIBN could be obtained at a very low polypyrrole content,12b no as an initiator.Thereafter, pyrrole and 3-alkylpyrrole moieties corresponding conductivity datum was reported.In addition, were grafted onto PMMA-co-PNPAMs by eVecting oxidative only an N-pyrrolylethyl spacer group on the pendant ester in polymerisation with 2.5 mole equivalents of anhydrous FeCl3 the precursor copolymer was studied. It is anticipated that in nitromethane at 0 °C for 6 h (Scheme 1). The resultant graft incorporation of longer alkyl spacers between pyrrole and the copolymers were precipitated by pouring into 5% HCl in PMMA backbone will have a significant impact on both the methanol at 0 °C.The precipitate was washed with methanol electrical conductivity and processability of the resultant graft until the solvent remained colorless (for the pyrrole grafted copolymers. Accordingly, with a view to investigating copolymers, the precipitate was stirred in THF overnight after structure–property relations, we have synthesized a series washing with methanol )12b,12e and dried under vacuum of graft copolymers of polypyrrole and poly(3-alkylpyrroles) (0.1 mmHg) at room temperature for 24 h.with the copolymers of methyl methacrylate (MMA) and v-(N-pyrrolyl )alkyl methacrylate of diVerent n-alkyl chain Measurements lengths.It was found that the attachment of long alkyl groups at the 3-position of pyrrole aVorded soluble, film-castable Elemental analyses from which the compositions of the graft copolymers in their doped states with electrical conduc- copolymers and the graft copolymers were calculated were performed at the National University of Singapore tivity in the semiconducting range.J. Mater. Chem., 1998, 8(11), 2347–2352 2347conducted from room temperature to 400 °C at a heating rate of 10 °Cmin-l with about 3 mg samples. Conductivity measurements were carried out on a four point probe connected to a Keithley constant-current source system. Gel permeation chromatographic analyses were carried out using a Waters 600E HPLC system with a Waters 410 diVerential refractometer.The molecular weights referred to the peak maxima of the elution curves were measured against polystyrene standards in THF at 30 °C using the following column combination: PhenogelTM MXL and MXM columns (300 mm×4.6 mm ID), with a separating range from 103 to 106 g mol-1. Results Precursor copolymers PMMA-co-PNPAMs The PMMA-co-PNPAM samples prepared in our experiments were soluble white powders with molecular weights (Mn) of ca. 50 000 g mol-1. Their chemical structures were confirmed by 1H NMR and FTIR spectroscopy. A representative 1H NMR spectrum for PMMA-co-PNPDDM containing 7.7 mol% of pyrrolyl moieties revealed resonances for the a-, b-ring protons at d 6.65 and 6.13 respectively.16a,16b The corresponding FT-IR spectra of the PMMA-co-PNPAMs depict characteristic vibrational bands at 1730 cm-1 (ascribable to ester carbonyl vibrations), 750 and 725 cm-1 ascribable respectively to pyrrole C–Hb and C–Ha bendings (Fig. 2a).12a,12c,12e TGA in air for PMMA-co-PNPAMs revealed an onset decomposition temperature at 180–240 °C, being completely degraded at ca. 450 °C leaving residues of <0.5%. Glass transition temperatures (Tg) of the copolymers were found to be lowered with increasing content of NPAMs.In addition, Tg at a given mole percentage of NPAM in the copolymer was also reduced with increasing length of the n-alkyl spacers in NPAMs (see Fig. 1) suggesting enhanced chain mobility of the copolymers with the longer spacers. Graft copolymers of PMMA with polypyrrole Black insoluble electrically conductive materials resulted from grafting of polypyrrole to PMMA-co-PNPAMs.However, those prepared from copolymers with a low content of NPAMs (<3 mol%) and of grafted polypyrrole (<20 mol%) showed some swelling in THF. Examination of the representative FTIR spectra (see Fig. 2) revealed that the absorption band at ca. 725 cm-1 attributed to C–Ha bending of the pyrrolyl Scheme 1 Reaction scheme for the syntheses of key monomers of v-(N-pyrrolyl )-n-alkyl methacrylate and graft copolymers with polypyrroles and poly(3-alkylpyrrole)s.Microanalytical Laboratory on a Perkin Elmer 240C elemental analyzer for C, H and N determinations. FT-IR spectra of polymers dispersed in KBr disks were recorded on a Bio-Rad TFS156 spectrometer. 1H NMR were recorded on a Bruker ACF 300 FT-NMR spectrophotometer operating at 300 MHz. CDCl3 was used as solvent and tetramethylsilane (TMS) as internal reference. Thermogravimetric analyses (TGAs) of polymer powders (about 5 mg) were conducted on a Du Pont Thermal Analyst 2100 system with a TGA 2950 thermogravimetric analyzer. A heating rate of 10 °Cmin-l with an air flow of 75 ml min-l was used, the runs being conducted from room temperature to 800 °C.DiVerential scanning calorimetry Fig. 1 Changes in Tg of the copolymers: (a) PMMA-co-PNPHM (2); (DSC) was conducted with a DSC 2910 module in conjunction (b) PMMA-co-PNPOM (&); (c) PMMA-co-PNPDM ($); (d) PMMA-co-PNPDDM (×). with the Du Pont Thermal Analyst system. The analyses were 2348 J. Mater. Chem., 1998, 8(11), 2347–2352Table 1 Shift in CNO stretching vibration of pyrroles grafted copolymers Contents of Py or nCNO/ Graft copolymersa 3APys/mol% cm-1 PMMA-co-PNPHM (6.7%) 20.4 1729 with pyrrole 28.9 1724 33.6 1721 PMMA-co-PNPDDM (1.6%) 12.7 1733 with pyrrole 33.1 1720 PMMA-co-PNPHM (2.6%) 12.4 1731 with 3-octylpyrrole 23.4 1731 31.1 1731 39.9 1729 aThe percentages in parentheses represent the content of NPAMs in PMMA-co-PNPAMs in mol%. moieties in PMMA-co-PNPAMs had disappeared subsequent to the grafting reaction due to the coupling of pyrrole rings.The intense absorption band due to the ester carbonyl functionality at 1730 cm-1 was observed to have shifted to lower wavenumber with increasing polypyrrole content (Table 1). This phenomenon could be ascribable to the formation of NH,ONC hydrogen bonding between the grafted polypyrrole and the ester groups of the PMMA copolymers.12c Table 2 summarises the electrical conductivity of the various polypyrrole grafted copolymers. The electrical conductivity Fig. 2 FTIR spectra of: (a) PMMA-co-PNPDDM with a NPDDM content of 4.2 mol% prior to grafting with pyrroles; (b) its polypyrrole grafted copolymer containing 28.2 mol% of pyrrole; (c) poly(3-octylpyrrole) grafted copolymer containing 21.4 mol% of 3-octylpyrrole.Fig. 4 Scanning electron microscopy (SEM) pictures of cast films of Fig. 3 1H NMR spectra of (a) copolymer of PMMA-co-PNPHM poly(3-alkylpyrrole) grafted onto PMMA-co-PNPHM containing 2.6 mol% of PNPHM: (a) poly(3-octylpyrrole) grafted copolymer containing 2.6 mol% of PNPHM and the poly(3-dodecylpyrrole) grafted copolymer containing 19.0 mol% of 3-dodecylpyrrole at (b) a containing 12.4 mol% of 3-octylpyrrole; (b) poly(3-decylpyrrole) grafted copolymer containing 24.7 mol% of 3-decylpyrrole. normal Relaxation Delay (RD) of 1 s; (c) when RD increased to 10 s. J.Mater. Chem., 1998, 8(11), 2347–2352 2349Table 2 Properties of polypyrrole grafter copolymers of PMMA Yield of Conductivitya/S cm-1 Copolymers Contents of NPAMs in Mn of PMMA- Feed ratio graft Contents of Py in (PMMA-co-PNPAMs) PMMA-co-PNPAMs/ co-PNPAMs/ CPNPAMs/ copolymers graft copolymers xpy/ Further used mol% g mol-1 Cpy (%) mol% Pristine doped with I2 PMMA-co-PNPHM 2.6 41400 1/10 43 26.7 — — 2.6 1/40 46 47.1 3.0×10-4 3.2×10-4 6.7 58600 1/5 57 20.4 — — 6.7 1/10 33 28.9 — 4.8×10-5 6.7 1/20 41 33.6 2.2×10-4 3.1×10-4 PMMA-co-PNPOM 0.2 44400 1/5 50 16.7 4.9×10-4 5.4×10-4 0.2 1/10 33 24.5 5.6×10-4 8.9×10-4 0.2 1/40 40 45.9 8.9×10-4 7.8×10-4 2.4 43300 1/10 46 18.4 — — 2.4 1/40 59 36.1 3.9×10-4 5.0×10-4 PMMA-co-PNPDM 0.9 49300 1/10 58 23.4 — — 0.9 1/20 47 26.3 3.4×10-4 3.2×10-4 0.9 1/40 43 44.2 6.0×10-4 7.7×10-4 3.6 47400 1/10 56 21.1 — — 3.6 1/20 58 27.6 — 1.8×10-5 3.6 1/40 38 30.4 5.5×10-4 8.3×10-4 PMMA-co-PNPDDM 1.6 41400 1/20 60 33.1 — — 1.6 1/40 38 44.7 6.5×10-3 7.8×10-3 4.2 52600 1/10 49 23.2 — — 4.2 1/40 52 29.7 1.2×10-4 5.8×10-4 a — means the conductivity is less than 1.0×10-5 S cm-1.was found to increase with increasing content of grafted chain have the eVect of reducing the chain mobility of the resultant graft copolymers to some degree which consequently polypyrrole attaining 10-4–10-3 S cm-1 when the pyrrole contents were less than 50 mol%.Higher contents of grafted results in higher Tg. polypyrrole did not result in any significant increase in the conductivity. In addition, further doping with iodine at room Graft copolymers of PMMA with poly(3-alkylpyrrole)s temperature did not result in any distinct rise in conductivity, indicating that the graft copolymers had already been fully The graft copolymers from 3-alkylpyrroles having octyl, decyl, and dodecyl pendants with PMMA-co-PNPAMs also aVorded doped in the grafting process. There were no obvious eVects arising from the use of diVerent alkyl spacers in NPAMs or black powders.Their key properties are summarised in Table 4.Their molecular weights (Mn) showed an apparently marginal of varying the content of NPAMs in PMMA-co-PNPAMs on the electrical conductivity of the resultant graft copolymers. increase in comparison to the precursor copolymers (PMMAco- PNPAMs). It was found that the graft copolymers prepared The Tg values of some polypyrrole-grafted copolymers are depicted in Table 3.On comparing Fig. 1 with Table 3, it is from PMMA-co-PNPAMs having low NPAM contents (<2.6 mol%) were completely soluble in common organic clearly evident that Tg of the polypyrrole-grafted copolymers are somewhat higher than the corresponding PMMA-co- solvents (THF, CHCl3, and acetone) even in their doped states irrespective of the grafted poly(3-alkylpyrrole) (P3APy) con- PNPAMs.In addition, Tg of the graft copolymers prepared from the same precursor copolymers PMMA-co-PNPAMs tent. Cast films of the P3APy grafted copolymers from their chloroform solutions on glass slides were examined using containing the same molar percentage of PNPAMs can be seen to increase with increasing grafted polypyrrole content. scanning electron microscopy (SEM) (see Fig. 4 for representative SEM pictures). At lower 3-alkylpyrrole contents, the graft This indicates that pyrrole units grafted onto the PMMA Table 3 Tg of polypyrrole grafter copolymers of PMMA Copolymers Contents of NPAMs in Mn of Contents of grafted Tg of graft (PMMA-co-PNPAMs) PMMA-co-PNPAMs/ PMMA-co-PNPAMs/ Py in copolymers xpy/ copolymers/ used mol% g mol-1 mol% °C PMMA-co-PNPHM 2.6 41400 0 124.1 2.6 26.7 130.0 6.7 58600 0 113.8 6.7 28.9 146.2 PMMA-co-PNPOM 2.4 43300 0 113.3 2.4 8.1 119.2 2.4 18.4 127.6 PMMA-co-PNPDM 0.9 49400 0 119.3 0.9 23.4 122.2 0.9 44.2 129.8 3.6 47400 0 110.0 3.6 13.1 113.5 3.6 27.6 124.9 PMMA-co-PNPDDM 1.6 41400 0 118.3 1.6 12.7 127.5 1.6 33.1 132.8 1.6 44.7 133.7 4.2 52600 0 95.3 4.2 16.4 122.8 2350 J.Mater.Chem., 1998, 8(11), 2347–2352Table 4 Properties of the poly(3-alkylpyrrole)s grafted copolymers of PMMA Content of Copolymers Yield of 3APy in (PMMA-co- Mn of PMMA-co- Feed ratio graft graft Mn of graft PNPAMs) PNPAMs/ CPNPAMs/ copolymers copolymers/ copolymers/ Conductivityb 3-Alkylpyrroles useda g mol-1 C3APy (%) mol% g mol-1 S cm-1 Solubilityc 3-Octylpyrrole PMMA-co- 41400 1/10 78 12.4 n.d.— + PNPHM (2.6%) 1/20 81 23.4 n.d. 4.8×10-4 + 1/30 89 31.1 42000 8.6×10-4 + PMMA-co-PNPOM 44400 1/10 88 12.4 n.d. — + (0.2%) 1/20 79 18.9 n.d. 8.8×10-5 + PMMA-co-PNPDM 49300 1/10 75 11.8 n.d. — + (0.9%) 1/20 80 25.5 50100 1.3×10-4 + PMMA-co-PNPDDM 41400 1/10 88 13.6 n.d. — + (1.6%) 1/20 90 20.2 n.d. 1.0×10-4 + PMMA-co-PNPDDM 52600 1/10 90 13.9 — — ± (4.2) 1/20 88 21.4 — 2.3×10-4 ± PMMA-co-PNPDDM 49800 1/10 89 19.4 — — – (7.7%) 1/20 86 24.0 — 1.2×10-4 – 3-Decylpyrrole PMMA-co- 41400 1/20 78 24.7 42300 3.0×10-4 + PNPHM (2.6%) PMMA-co-PNPOM 44400 1/20 81 21.4 n.d. 1.3×10-4 + (0.2%) PMMA-co-PNPDM 49300 1/20 79 18.3 n.d. 1.2×10-4 + (0.9%) PMMA-co-PNPDDM 41400 1/20 86 20.2 42100 2.3×10-4 + (1.6%) 3-Dodecylpyrrole PMMA-co- 41400 1/20 87 19.0 n.d. 2.5×10-4 + PNPHM (2.6%) PMMA-co-PNPOM 44400 1/20 84 19.4 44800 8.0×10-4 + (0.2%) PMMA-co-PNPDM 49300 1/20 85 20.2 n.d. 2.5×10-4 + (0.9%) PMMA-co-PNPDDM 41400 1/20 90 19.5 42100 3.9×10-4 + (1.6%) aThe percentages in parentheses represent the content of NPAMs in PMMA-co-PNPAMs in mol%. b — means the conductivity is less than 1.0×10-5 S cm-1. cRefers to solubility in CHCl3, THF, and acetone: ‘+’ completely soluble; ‘±’ partially soluble; ‘–’ insoluble.n.d. means not determined. copolymers appeared homogeneous suggesting the grafted prohibit crosslinking between pyrrole rings may also be the cause of the great improvement in the solubility of 3APy P3APy to have completely dissolved into the PMMA-co- PNPAM copolymers (Fig. 4a). However, at higher P3APy grafted copolymers.With increasing contents of NPAMs in PMMA-co-PNPAMs, the solubility of the resultant graft contents, the graft copolymers displayed a globular network structure (Fig. 4b) which could be attributed to phase copolymers decreased. Thus, the graft copolymers of 3-octylpyrrole with PMMA-co-PNPDDMs were completely soluble, separation/aggregation of the P3APy component in the graft copolymers.This observation is suggestive that at lower 3- partially soluble and insoluble when the content of NPDDM in PMMA-co-PNPDDMs was increased from 1.6 to 4.2 and alkylpyrrole contents, homogeneous grafted copolymers resulted whereas at higher contents, an apparently then 7.7 mol%, respectively (Table 4). This could be attributed to the crosslinking between NPAM units, which is more likely incompatible polymer blend between two polymers resulted.As with polypyrrole grafted copolymers the FTIR spectra with increasing content of NPAMs in PMMA-co-PNPDDMs. As with the polypyrrole grafted copolymers, the conductivity of P3APy (Fig. 2c) grafted materials revealed the disappearance of the C–Ha bending vibrational band indicative of a of the P3APy grafted copolymers increases with the content of P3APys attaining ca. 10-4 S cm-1 at about 20 mol%. successful grafting process via a–a couplings of P3Apy to the pyrrolyl moieties in PMMA-co-PNPAMs. Further corrobor- Thereafter, further increase in the content of 3APys did not result in any further increase of the conductivity of the ation for this was provided from the disappearance of the aproton signal in the 1H NMR spectra of the representative resultant graft copolymers as evident in Table 4 from the representative experimental results based on the graft copoly- poly(3-dodecylpyrrole) grafted copolymers (Fig. 3). However, the signal at ca. 6.15 ppm due to the b-protons of the pyrrolyl mer of 3-octylpyrrole and PMMA-co-PNPHM (containing 2.6 mol% NPHM). Further, from Table 2 and 4, the introduc- moiety also disappeared.This phenomenon was also previously observed by Stanke et al.12b,16b and was attributed to the tion of long alkyl groups onto the 3-position has only marginal influence on the conductivity of the resultant graft copolymers. formation of aggregates and slow relaxation of the said resonance.17, 18 In our samples, we have verified the existence of the pyrrolyl b-protons by conducting NMR experiments Conclusions with the relaxation delay increased to 10 seconds, whereupon the d 6.15 b-proton signal reappears (Fig. 3c and the inset). Pyrrole and 3-alkylpyrroles were grafted to the precursor copolymers of PMMA and NPAMs by eVecting an oxidative Unlike the graft copolymers from unsubstituted pyrrole, the carbonyl band in FTIR spectra of the soluble graft copolymers polymerisation with FeCl3 in nitromethane.The electrical conductivity of the graft copolymers increases with increasing did not show any significant shift to lower wavenumbers with increasing content of 3APy (Table 1). This could be ascribable pyrrole or 3-alkylpyrroles content attaining ca. 10-4–10-3 S cm-1. The carbon chain lengths of the n-alkyl spacers to the formation of NH,ONC hydrogen bonding being disfavoured by the steric eVects of the n-alkyl pendants between pyrrole and the methacrylate groups in NPAMs had little eVect on the conductivity of the resultant graft copoly- attached.Similarly, steric eVects of the pendant chains which J. Mater. Chem., 1998, 8(11), 2347–2352 23515 A. O. Patil, A. J. Heeger and F.Wudl, Chem. Rev., 1988, 29, 183. mers, though longer alkyl spacers have an eVect of lowering 6 N. Toshima and S. Hara, Prog. Polym. Sci., 1995, 20, 155. the glass transition temperatures of the polypyrrole grafted 7 A. I. Nazzal and G. B. Street, J. Chem. Soc., Chem. Commun., copolymers. The graft copolymers of polypyrrole were insol- 1985, 375. uble, whilst the graft copolymers of 3-alkylpyrroles prepared 8 J.H. Han, T. Motobe, Y. E. Whang and S. Miyata, Synth. Met., from low NPAM-containing PMMA-co-PNPHMs and low 3- 1991, 45, 261. 9 G. Ruggeri, E. Spila, G. Puncioni and F. Ciardelli, Macromol. alkylpyrroles contents were completely soluble in common Chem., Rapid Commun., 1994, 15, 537. organic solvents even in their doped states. The introduction 10 V.Castelvetro, A. Colligiani, F. Ciardelli, G. Ruggeri and of long alkyl pendants onto the 3-position of pyrrole was M. Giordano, New Polymeric Mater., 1990, 2, 93. shown to have little influence on the conductivity of the 11 M. R. Simmons, P. A. Chaloner and S. P. Armes, Langmuir, 1995, resultant graft copolymers. 11, 4222. 12 (a) D. Stanke and M. L. Hallensleben, Synth. Met., 1993, 55–57, 1108; (b) D. Stanke, M. L. Hellensleben and L. Toppare, Synth. We thank the National University of Singapore for financial Met., 1995, 72, 89; (c) ibid., 1995, 73, 1; (d) ibid., 1995, 72, 61; support through the research grant RP960613. W.-L. Yu is (e) D. Stanke, M. L. Hellensleben and L. Toppare, Macromol. grateful to NSTB for a postdoctoral research fellowship and Chem. Phys., 1995, 196, 1697. 13 S.-K. Kang, W.-S. Kim and B.-H. Moon, Synthesis, 1985, 1161. J. F. Xia to NUS for the award of a research studentship. 14 J. Ruhe, T. Ezquerra and G. Wegner, Makromol. Chem., Rapid Commun., 1989, 10, 103. 15 E. P. Papadopoulos and N. F. Haidar, Tetrahedron Lett., 1968, References 14, 1721. 16 (a) D. Stanke, M. L. Hallensleben and L. Toppare, Synth. Met., 1 G. Tourillon, Handbook Of Conducting Polymers, ed. T. A. 1995, 72, 167; (b) D. Stanke, M. L. Hallensleben and L. Toppare, Skotheim, Marcel Dekker, NY, 1986. Synth. Met., 1995, 73, 267. 2 A. G. MacDiarmid and A. J. Epstein, Faraday Discussions, 1989, 17 G. L. Baker and F. S. Bates, Macromolecules, 1984, 17, 2619. 88, 317. 18 B. Bidan and M. Guglielmi, Synth. Met., 1986, 15, 49. 3 E. M. Genies, A. Boyle, M. Lapkowski and C. Tsintavis, Synth. Met., 1990, 36,139. 4 M. G. Kanatzidis, Chem. Eng. News, 1990, Dec 3, 36. Paper 8/06438E 2352 J. Mater. Chem., 1998, 8(11), 2347–2352

ISSN:0959-9428    

DOI:10.1039/a806438e

出版商:RSC    

年代:1998

数据来源: RSC