SEARCH

SEARCH BY CITATION

Keywords:

  • amines;
  • catalysis;
  • Heck reactions;
  • metal–organic frameworks;
  • nanoparticles;
  • palladium

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Results and Discussion
  5. Conclusion
  6. Experimental Section
  7. Acknowledgements
  8. Supporting Information

Well-dispersed palladium nanoparticles (Pd NPs) supported on amine-functionalized, mixed-linker metal–organic frameworks (MIXMOFs) based on MIL-53(Al) were prepared by using the ion-exchange method. Pd NPs were characterized by powder X-ray diffraction (XRD), N2 adsorption, transmission electron microscopy (TEM), inductively coupled plasma atomic emission spectroscopy (ICP-AES), and X-ray photoelectron spectroscopy (XPS). The mean diameter of Pd NPs is approximately 3.2 nm. It was found that the Pd NPs supported on amine-functionalized MIXMOFs are stable at high temperature. The Pd NPs exhibit efficient catalytic activity for Heck reaction and can be easily recovered and reused.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Results and Discussion
  5. Conclusion
  6. Experimental Section
  7. Acknowledgements
  8. Supporting Information

The palladium-catalyzed Heck reaction between aryl halides and olefins is one of the most important reactions for the formation of carbon–carbon bond in synthetic organic chemistry.1 In traditional Heck reactions, with palladium salts or organometallic complexes with special ligands (such as phosphines) that are sensitive to moisture and air, are generally used,1 and the homogeneous systems often suffer difficulty in separation and recycling of expensive Pd catalyst.2 Therefore, it is desirable to develop heterogeneous catalysts for Heck reactions to overcome such problems.3 Heterogeneous catalysts are distinguished from homogeneous catalysts in the industrial application for their advantages of easy of separation of product and the recovery of expensive catalyst. However, Pd NPs—an important kind of heterogeneous catalysts—are prone to aggregate and lose their catalytic activity without the use of a stabilizer.4 Therefore, they need to be supported on solid materials (such as carbon frameworks, zeolites, silica, polymers, Al2O3) to be useful as catalyst for Heck reactions.114 In addition, in many cases, the catalytic active sites may be lost due to the leaching of palladium in supported systems which makes the catalyst difficult to recovered and reused.3 Therefore, a suitable supports for Pd NP catalysts are important for heterogeneous catalysis.

Metal–organic frameworks (MOFs) have emerged as very promising functional materials for gas storage, separation, heterogeneous catalysis, sensing, and drug delivery because of their high surface area, porosity, and chemical tunability.1525 Although there are several approaches that are used to load Pd NPs onto porous MOFs by solution infiltration and surface grafting methods,2529 developing a general and facile method to incorporate active Pd NPs on MOFs remains a challenge owing to the easy agglomeration and leaching into solution without the need for protecting groups.25 Thus, there are a limited number of Pd NPs supported on MOFs and even fewer of them can act as catalysts for heterogeneous catalysis.15, 17, 25, 3033

Recently, mixed-linker metal–organic frameworks (MIXMOFs), which incorporate different functionalities on linking groups by the mixing linkers, have attracted substantial attention.3442 The MIXMOFs would constitute new materials that contain a tunable number of functional sites and would inevitably lead to a complex chemical environment.34 Therefore, they may provide opportunities for the preparation of materials with unusual properties, such as thermal stability, gas adsorption, and catalysis.3442 MIL-53(Al) (Al(OH)[O2C–C6H4–CO2]) is one of the most outstanding materials that has been extensively used in gas storage and separation science.4346 Amine-functionalized MIL-53(Al)-NH2 (Al(OH)[H2N-BDC], where H2N-BDC=2-aminoterephthalic acid), is an MIL-53(Al) analogue that contains free amine group.25, 4751 It not only drastically enhances the affinity for CO2 and basic catalysis, but can also be used for postmodification of amine groups with a set of cyclic anhydrides.49 Recently, Kleist, Baiker, and co-workers reported that amine-functionalized, mix-linker MIL-53(Al) materials exhibit higher thermostability than MIL-53(Al)-NH2.4041 As an extension of our previous work on the preparation of Pd NPs supported on amine-functionalized MIL-53(Al)-NH2 and their application in Suzuki–Miyaura cross-coupling reactions,52 herein we will report the facile preparation of highly active and stable Pd NPs supported on amine-functionalized, mix-linker MIL-53(Al) materials and their application in Heck reactions.

Results and Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Results and Discussion
  5. Conclusion
  6. Experimental Section
  7. Acknowledgements
  8. Supporting Information

Preparation and characterization of Pd NPs supported on MIXMOFs

Compared with MIL-53(Al)-NH2, MIXMOFs 1, 2, and 3 (Scheme 1) are more stable and economical to synthesize owing to the use of cheap terephthalic acid.41 Powder X-ray diffraction (XRD) studies indicate that all three compounds are highly crystalline and of the same structures as in MIL-53(Al) and MIL-53(Al)-NH2 (Figure 1).41, 44, 49 Nitrogen sorption studies show that the Brunauer–Emmett–Teller (BET) surface area of MIL-53(Al) (928 m2 g−1) and MIL-53(Al)-NH2 (654 m2 g−1) are lower than that of 2 (997 m2 g−1; Figure 2). The results demonstrate that the properties of MIXMOFs are not simple linear sums of those of the pure components, and thus support the notion that the sequence of functionalities within MIXMOFs can enhance a specific property.34

thumbnail image

Scheme 1. Synthesis of MIXMOFs 1 (x=0.1), 2 (x=0.5), and 3 (x=0.9) based on MIL-53(Al). BDC=benzene-1,4-dicarboxylate, ABDC=2-aminobenzene-1,4-dicarboxylate.

Download figure to PowerPoint

thumbnail image

Figure 1. Powder XRD patterns of the MIL-53(Al), 1, 2, 3, and MIL-53(Al)-NH2.

Download figure to PowerPoint

thumbnail image

Figure 2. Nitrogen sorption isotherms of MIL-53(Al), MIXMOFs 2, Pd/2, and MIL-53(Al)-NH2.

Download figure to PowerPoint

The high surface area, porous structure, and stability in water and common organic solvent make the amine-functionalized MIXMOFs attractive catalyst supports. Recently, Férey and co-workers reported an anion-exchange method for the encapsulation of noble metals over the ethylenediaminegrafted MIL-101(Cr) (Cr3(F,OH)(H2O)2O[(O2C)-C6H4-(CO2)]3nH2O (n≈25)).29 However, it is difficult to control the concentration of the strong base ethylenediamine; an excess amount of strong base may destroy the frameworks. Meanwhile the amine-functionalized MIXMOFs based on MIL-53(Al) can be obtained directly by replacing terephthalic acid with aminoterephthalic acid, and thus avoids introducing the strong base ethylenediamine to the MOFs. Herein, we use the ion-exchange approach for preparation of Pd NPs supported on amine-functionalized MIXMOFs based on MIL-53(Al). The surface amine groups of 1, 2, and 3 (see the Experimental Section for details) were first neutralized by aqueous HCl, followed by ionic reactions of the positively charged ammonium groups on the surface with anionic noble metal salts [PdCl4]2−.25b, 29, 52 Finally, the obtained material containing palladium salts were reduced with NaBH4 at low temperature.

After the loading of palladium, there is no apparent loss of crystallinity according to X-ray diffraction patterns, thus indicating that the framework of 2 is well maintained (Figure 3).52 The characteristic peak of Pd (111) at 2θ=40.1 ° is indistinguishable owing to the low Pd loading and small diameter Pd NPs.15 The Pd/2 exhibits a diminished BET surface area of 982 m2 g−1, whereas that of MIXMOFs 2 is 997 m2 g−1 (Figure 2). The decrease of surface area indicates that the cavities of 2 may be occupied and/or blocked by the palladium NPs located at the surface.15 The TEM images of Pd/2 (Figure 4) show that the Pd NPs are well dispersed on the outer surface of the support and no aggregation is observed, which are similar to the Pd NPs supported on MIL-53(Al)-NH252 and MOF-5.15 The mean diameter of Pd NPs is approximately 3.2 nm (Figure 4), meanwhile the palladium nanoparticles supported on the amino-free MIL-53(Al) aggregate immediately.52 The presence of amino group on the functionalized linker has been proven to be beneficial for the stabilization of Pd species.39 It may not be precluded that there exists coordination interactions between palladium nanoparticles and amino groups. X-ray energy-dispersive spectroscopy (EDS) further confirm the presence of the Pd in the Pd/2 samples (Figure 4). In the X-ray photoelectron spectroscopy (XPS) trace (Figure 5), the 3d5/2 and 3d3/2 peaks of Pd0 appear at 336.0 and 341.3 eV, respectively, and no obvious peak of Pd2+ is observed, thus indicating that palladium is in the reduced form.30

thumbnail image

Figure 3. Powder XRD patterns of the MIXMOF 2 containing 50 % of ABDC, Pd/2, and Pd/2 after 5th cycle.

Download figure to PowerPoint

thumbnail image

Figure 4. TEM and HRTEM images of a) and b) Pd/2 (0.96 wt % of Pd) before the reaction, c) and after five cycles. d) Size distribution of Pd NPs; mean size 3.2 nm, standard deviation 0.69. Inset in (a) is the EDS pattern of Pd/2.

Download figure to PowerPoint

thumbnail image

Figure 5. XPS measurement of Pd/2 (0.96 wt % of Pd).

Download figure to PowerPoint

Heck reactions catalyzed by Pd NPs

The Heck reactions were first performed using a low amount of palladium (a molar ratio: aryl halide/Pd=2000) and an excess of olefin with respect to aryl halide (molar ratio=1.5) to avoid of the formation of homocoupling by-products.3 Pure coupling products were obtained by column chromatography and characterized by NMR spectroscopy. The compounds were selectively obtained with trans configuration.

Initially, we used Pd/MIL-53(Al)-NH252 to investigate the effects of base and solvent for the Heck reaction of brombenzene and styrene at 120 °C (Table 1). The results showed that organic base triethylamine gave higher yields than that of inorganic bases such as Na2CO3, K3PO4, and NaOAc (Table 1, entries 1–4). No product was obtained in the absence of the base (Table 1, entry 5). The solvent also had a significant influence on the catalyst activity. Compared with NMP and o-xylene (Table 1, entries 6 and 7), higher TOF ((mol of prod) per (mol of Pd per hour)) was obtained in DMF (Table 1, entry 4). It was noted that no Pd black was observed under such rigorous conditions during the reaction. Therefore, the amino-stabilized Pd NPs are air-stable up to 120 °C and their catalytic activity is virtually independent of the presence of air. The amount of catalyst is also very important for the reaction. The reaction could not happen in the presence of only MIL-53(Al)-NH2. Although the use of 0.005 mol % and 0.01 mol % of Pd catalyst gave higher TOF, it gave only 28 % (Table 1, entry 10) and 59 % (Table 1, entry 9) yield of the desired products, respectively. It is very interesting that the bromobenzene can be activated effectively by only 0.05 mol % of Pd catalyst and very high yield was obtained (81 %; Table 1, entry 4). The product yield was only 83 % upon increasing the Pd catalyst to 0.1 mol % (Table 1, entry 11).

Table 1. Influences of the base and solvent on the Heck reaction of brombenzene (1 mmol) with styrene (1.5 mmol).[a]
Thumbnail image of
EntryBaseSolventYield [%][b]TOF [h−1]
  1. [a] Reaction conditions: Pd/MIL-53(Al)-NH2 (0.05 mol % of Pd), base (1.5 mmol), solvent (3 ml), 6 h. [b] Yield of isolated product. The products have trans configuration based on NMR spectroscopy. [c] Without base. [d] Only MIL-53(Al)-NH2 (0 mol % of Pd). [e] 0.01 mol % of Pd. [f] 0.005 mol % of Pd. [g] 0.1 mol % of Pd. DMF=N,N-dimethylformamide, NMP=N-methylpyrrolidone.

1Na2CO3DMF65217
2K3PO4DMF73244
3NaOAcDMF42140
4NEt3DMF81270
5[c]DMFtrace
6NEt3NMP77257
7NEt3o-xylene69230
8[d]NEt3DMFtrace
9[e]NEt3DMF59983
10[f]NEt3DMF28933
11[g]NEt3DMF83138

Because the type of support is important for Pd NPs catalysis, Pd NPs supported on different supports (MIL-53(Al), 1, 2, and 3) as well as commercially available Pd/C were used in Heck reactions (Table 2). Notably, no product was obtained without the use of Pd catalyst (Table 2, entry 7). The Pd NPs supported on amine-functionalized MOFs (1, 2, 3, and MIL-53(Al)-NH2) showed significantly higher reactivity (up to 76 % yield for the brombenzene substrates) than that of Pd/MIL-53(Al) and Pd/C. These results might be attributed to the Pd NPs agglomeration (Figure S1).29 Interestingly, the different amount of amines in the supports also affected the activity of the Pd catalyst. By increasing of the amount of the amine groups, the activity of the catalyst increases first (up to 93 % yield with Pd/2, 50 % NH2; Table 2, entry 3), and then declines (81 % yield with MIL-53(Al)-NH2; Table 2, entry 5). It may not preclude that there exists coordination interactions between palladium and amino groups.39, 52 A certain number of amino groups on the functionalized linker proved to be beneficial for the immobilization of Pd species, which prevent the agglomeration of Pd NPs. However, the strong interaction between the excess amine groups and Pd species may lead to weakening of the palladium activation for the substrate.53, 54 It may be that the presence of distinct sequences of functionalities in the MIXMOFs leads to a complex chemical environment for catalysis.34

Table 2. Influence of the supports on the Heck reaction of brombenzene (1 mmol) with styrene (1.5 mmol).[a]
Thumbnail image of
EntryCatalyst[b]Yield [%][c]TOF [h−1]
  1. [a] Reaction conditions: NEt3 (1.5 mmol), DMF (3 mL), 6 h. [b] Used 0.05 mol % of Pd. [c] Yield of isolated product. The products have trans configuration based on NMR spectroscopy. [d] Without Pd catalyst.

1Pd/MIL-53(Al)2687
21, Pd/MIL-53(Al) and 10 % NH276254
32, Pd/MIL-53(Al) and 50 % NH293310
43, Pd/MIL-53(Al) and 90 % NH286287
5Pd/MIL-53(Al)-NH281270
6Pd/C49164
7[d]trace

Next, Pd/2 as the most efficient catalyst was applied to examine the scope of different substrates in the Heck reaction. A variety of aryl halides were coupled with different olefins in the presence of Pd at low loading (0.05 mol % of Pd)6 under the optimized reaction conditions (Table 3). The Heck reaction of styrene with iodobenzene proceeded easily at 120 °C resulting in trans-stilbene in excellent yields after 30 minutes. Owing to the higher bond energy of the C[BOND]Br and C[BOND]Cl bonds, aryl bromide and chlorobenzene compounds are difficult to activate. Therefore, the reactions of aryl bromides (or chlorobenzene) with different olefins required harsh conditions and extended reaction times. Interestingly, as seen from Table 3, the Heck reactions of a variety of aryl bromide derivatives with styrene could also proceeded smoothly at 120 °C and gave the corresponding products in high yields after 6 h (Table 3, entries 2, 7–13). The electron-withdrawing groups (-NO2, -CN, -CF3, and -COCH3) in the para position relative to bromine can weaken the C[BOND]Br bond,3 so these substituted bromobenzene compounds reacted more rapidly than bromobenzene (Table 3, entries 7–10). Reactions between styrene and a variety of electron-rich substrates such as 4-methy- and 4-methoxyl-substituted aryl bromides, also proceeded smoothly and gave the coupling products in good yields (Table 3, entries 11 and 12). Notably, the electron-donating and sterically hindered 2-methoxyl-substituted bromobenzene also gave good yields (Table 3, entry 13). However, the most challenging, yet readily accessible, chlorobenzene had much lower reactivity even after 24 hours (Table 3, entry 3). In addition, various olefin derivatives with different ester substituents were applied to this reaction (Table 3, entries 4–6). It was found that the cross-coupling of bromobenzene with these ester-substituted olefins afforded the corresponding trans-configured products in excellent yields. Interestingly, the efficiency of the tert-butyl acetate-substituted olefin was not affected by its steric hindrance and gave high yield (Table 3, entry 6).

Table 3. Results for the Heck reaction catalyzed by Pd/2.[a]
Thumbnail image of
EntryR1XR2Yield [%][b]TOF [h−1]
  1. [a] Reaction conditions: aryl halide (1 mmol), olefin (1.5 mmol), Pd/MIX-MIL-53(Al) and 50 % of NH2 (0.05 mol % of Pd), NEt3 (1.5 mmol), DMF (3 mL), 6 h. [b] Yield of isolated product. [c] 30 min. [d] 24 h, yield base on GC analysis. [e] The catalyst was removed after 3 h. [f] The filtrate was kept stirring for 24 h. [g] After being stored in air for three months.

1[c]HIPh973880
2HBrPh93310
3[d]HClPh119
4HBrCO2CH395317
5HBrCO2nBu94313
6HBrCO2tBu91303
74-NO2BrPh98327
84-CNBrPh97323
94-CF3BrPh95317
104-COCH3BrPh96320
114-MeBrPh86287
124-OMeBrPh81270
132-OMeBrPh66220
14[e]HBrPh65 (67)[f]216
15[g]HBrPh92306

Notably, one of the disadvantages related to the use of supported Pd catalysts in the Heck reaction is leaching of the palladium into the solution, and results in contamination of the product with metal that is difficult to remove along with loss of the expensive Pd catalyst.35, 55 Therefore, the leaching of the metal from Pd/2 catalyst was examined. After the workup, inductively coupled plasma (ICP) analysis showed that the amount of Pd leached into the reaction mixture was very low (0.1 ppm). Pleasingly, the low amount of Pd satisfies specifications required by the pharmaceutical industry regarding the final purity of the products (Pd <2 ppm).3 A hot-filtration experiment clearly indicated that the reaction stopped when the filtrate was further subjected to the same reaction (Table 3, entry 14).

Advantages of the Pd/2 material were that the catalytic reactions could be conveniently carried out in air, and the separation of this heterogeneous catalyst could be achieved easily by filtration. Less active 4-methoxy-1-bromobenzene and styrene were used for reusability experiments. The results indicate that after being recycled for five runs, the Pd catalyst still showed a remarkable activity (a reduction from 81 % to 76 % yield; Table 4). The TEM image of the reused catalyst (Figure 5) reveals that the mean diameter of the nanoparticles is 3.4 nm, which is very similar to that before the catalysis reaction. The results illustrate that the loss of palladium active sites is negligible, thus resulting in the preservation of catalytic activity.30 Moreover, the Pd catalysts supported on amine-functionalized MOFs was comparably active after being stored in air for three months (Table 3, entry 15). These features are obvious improvements from existing air- and moisture-sensitive homogeneous palladium-phosphine catalysts.10

Table 4. Reusability of the Pd/2 catalyst in the Heck reaction of 1-bromo-4-methoxyenzene and styrene[a].
Thumbnail image of
CycleYield [%][b]CycleYield [%][b]
  1. [a] Reaction conditions: 1-bromo-4-methoxyenzene (1 mmol), styrene (1.5 mmol), Pd/2 (0.05 mol % of Pd), NEt3 (1.5 mmol), DMF (3 mL), 6 h. [b] Yield of isolated product.

1st814th78
2nd805th76
3rd82  

Conclusion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Results and Discussion
  5. Conclusion
  6. Experimental Section
  7. Acknowledgements
  8. Supporting Information

In conclusion, amine-functionalized MIXMOFs based on MIL-53(Al) drastically enhance N2 adsorption, thus suggesting that the properties of MIXMOFs are not simple linear sums of those of the pure components. Moreover, we have developed a facile approach for the preparation of Pd NPs catalysts supported on amine-functionalized MIXMOFs based on MIL-53(Al). These well-dispersed Pd NPs show high activity and selectivity for Heck reactions. The Pd NPs catalysts exhibit high stability which can be recycled and reused easily.

Experimental Section

  1. Top of page
  2. Abstract
  3. Introduction
  4. Results and Discussion
  5. Conclusion
  6. Experimental Section
  7. Acknowledgements
  8. Supporting Information

MIL-53(Al),44 MIL-53(Al)-NH2,49, 50 and amine-functionalized MIXMOFs Al(OH)(BDC)1−x(ABDC)x based on MIL-53(Al) (BDC=benzene-1,4-dicarboxylate, ABDC=2-aminobenzene-1,4-dicarboxylate, x=0.1; 0.5; 0.9, denoted 1, 2, 3, respectively; Scheme 1) were synthesized according to literature procedures.40 The as-synthesized MIL-53(Al) was treated at 330 °C for 12 h to remove unreacted terephthalic acid. The obtained MIXMOFs and MIL-53(Al)-NH2 were washed with DMF, and subsequently soaked in methanol at 70 °C for 24 h. The solid was finally dried overnight at 130 °C under vacuum. All other reagents were commercial available and used as received.

The activated MOFs MIL-53(Al)-NH2, 1, 2, and 3 (0.50 g) in H2O (40 mL) were treated with hydrochloric acid to give a pH value of 4. Then the solution of H2PdCl4 (containing 1.0 wt % of Pd) was added drop-wise to the above acidulated solution under vigorous stirring for 10 min and then stirring for 8 h. The resulting solid was centrifuged and washed with deionized water and ethanol. The samples were reduced by NaBH4 (0.04 g) at 273 K for 3 h to obtain Pd NPs (denoted Pd/MIL-53(Al)-NH2, Pd/1, Pd/2, and Pd/3). For comparison, a solution of H2PdCl4 (containing ca. 1.0 wt % of Pd) was added to the activated MIL-53(Al) (0.50 g) which was suspended in H2O (40 mL) under vigorous agitation for 10 min and the mixture was then stirred for 24 h. The solid was centrifuged and washed with deionized water and ethanol. The resulting MIL-53(Al) samples containing palladium salts were then reduced with NaBH4 (0.04 g) at 273 K for 3 h to obtain Pd/MIL-53(Al) (0.19 wt % of Pd based on ICP-AES).

Powder XRD patterns were recorded on a Rigaku-Dmax2500 diffractometer equipped with CuKα radiation (λ=0.154 nm). Analysis of the noble metal content was performed by inductively coupled plasma atomic emission spectroscopy (ICP-AES) on an Ultima 2 analyzer (Jobin Yvon). The morphologies of the catalysts were studied using a JEOL-2010 transmission electron microscope (TEM) working at 200 KV. The samples were prepared by placing a drop of product in ethanol onto a continuous carbon-coated copper TEM grid. The BET surface area measurements were performed on a Micromeritics ASAP 2010 instrument. X-ray photoelectron spectroscopy (XPS) measurements were performed on a Kratos Axis Ultra DLD system with a base pressure of 10–9 Torr. The NMR spectra were measured on an AVANCE III Bruker Biospin Corporation Spectrometer. The GC-MS measurements were performed on a Varian 450-GC/240-MS.

Typically, aryl halide (1 mmol), vinyl substrate (1.5 mmol), NEt3 (1.5 mmol), and palladium catalyst (0.05 mol % of Pd) were added to DMF (3 mL). The reaction mixture was stirred at 120 °C for 0.5–24 h. After the reaction was complete, the solution was centrifuged and washed with ethyl acetate three times. The organic phase was subsequently washed with water, brine, dried over Na2SO4, and concentrated in vacuo. The crude residue was quantified by GC-MS analysis. The product was purified by column chromatography on silica gel (mixture of light petroleum and ethyl acetate as the eluent). The identification of the products was conducted by 1H NMR and 13C NMR measurement.

For the measurement of the Pd leaching during the reaction, the mixture was hot-filtrated under vacuum. The solid was washed with water (5 mL) and ethanol (5 mL), and the liquid phase was analyzed by ICP-AES. Moreover, a hot-filtration experiment was also run to investigate if the reaction proceeded in a heterogeneous or homogeneous fashion. After 3 h, the catalyst was separated by hot-filtration and the filtrate was further subjected to the same reaction conditions for 24 h. For the recyclability test, the catalyst was recovered from the mixture after each reaction, washed with water and ethanol, and then dried for the next run.

Acknowledgements

  1. Top of page
  2. Abstract
  3. Introduction
  4. Results and Discussion
  5. Conclusion
  6. Experimental Section
  7. Acknowledgements
  8. Supporting Information

We acknowledge financial support from the 973 Program (2011CB932504, 2012CB821705), the NSFC (21003128, 20901078, and 91022007), the Fujian Key Laboratory of Nanomaterials (2006L2005), and the Key Project from CAS.

Supporting Information

  1. Top of page
  2. Abstract
  3. Introduction
  4. Results and Discussion
  5. Conclusion
  6. Experimental Section
  7. Acknowledgements
  8. Supporting Information

Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors.

FilenameFormatSizeDescription
cplu_201100021_sm_miscellaneous_information.pdf1121Kmiscellaneous_information

Please note: Wiley Blackwell is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.