Isolation and Chemical Transformations Involving ... - ACS Publications

Subscriber access provided by University of Sussex Library

Article

Isolation and Chemical Transformations Involving a Reactive Intermediate of MOF-5 Juyeong Kim, Michelle R. Dolgos, and Benjamin J. Lear Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.5b00411 • Publication Date (Web): 28 Aug 2015 Downloaded from http://pubs.acs.org on September 5, 2015

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Crystal Growth & Design is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Crystal Growth & Design

Isolation and Chemical Transformations Involving a Reactive Intermediate of MOF-5 Juyeong Kim,† Michelle R. Dolgos,‡ and Benjamin J. Lear*,† †

Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania

16802, United States ‡

Department of Chemistry, Oregon State University, Corvallis, Oregon 97331-4003, United

States

ABSTRACT

We report the isolation of a nonporous plate-like intermediate species (MOF-i) obtained during the synthesis of MOF-5, and the testing of this intermediate’s reactivity towards three metal ions (ZnII, CuII, and MnII) in N,N-dimethylformamide (DMF) at 120 °C. We obtained interpenetrated MOF-5 crystals from the reaction between MOF-i and Zn(NO3)2·6H2O, accompanied by a change in morphology from a plate to a cube. Reaction with CuCl2·2H2O did not disrupt the plate-like morphology of MOF-i, but did result in the replacement of ZnII by CuII and formation of a novel porous copper MOF. MOF-i showed no reactivity towards MnCl2. Our results demonstrate that MOF-i imparts a selective reactivity that is different from the individual metal ions employed in conventional synthesis of MOFs and suggests that reactive intermediates may be useful in extending the diversity of metal-organic frameworks.

ACS Paragon Plus Environment

1


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 24

INTRODUCTION

Metal-organic frameworks (MOFs) are currently of interest in chemistry and materials science due to their superior surface area in comparison with other types of porous materials, and there is a large push for applications that exploit this porosity.1-3 While the focus of these applications was initially directed towards storage of gases, the MOF community has since explored other areas, including electronics, biomedicine, catalysis, and sensing.4-8 All of these applications bring with them a clear and persistent need for increasing control over the properties of MOFs, including crystal size,9,10 crystal morphology,11-13 and chemical composition and structure.14-17 At present, there are many techniques for realizing synthetic control over the properties of MOFs. Nano-sized MOFs can be synthesized by confining precursors in solvent droplets and heating the droplets subsequently through a spray-drying strategy.10 With respect to morphology, choice of surfactant and solvent molecules allows for anisotropic growth of MOFs and enables the synthesis of various shapes of MOFs.18-20 The chemical composition can, of course, be varied through choice of metal and ligand precursors. In addition to changes in starting materials, postsynthesis modification,21 solvent-assisted linker exchange,22,23 and transmetalation24-28 allow for control over functionalization of organic linkers as well as incorporation of different organic linkers or metal nodes while maintaining the original framework. The above approaches can be broadly classified as either modification of a stable final MOF structure or modification of synthetic starting conditions. However, recent work in the field of MOFs has demonstrated that stable MOFs do not always proceed directly from their precursors.29,30 Instead, the synthesis of MOFs can proceed through several metastable intermediate structures. Borrowing inspiration from more traditional chemical synthesis, we


2

Page 3 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


hypothesized that these metastable species might function as reactive intermediates, providing a synthetic branch point from which new MOF structures/morphologies could be accessed. Herein, we report the isolation and reactivity of such an intermediate, collected during the synthesis of the prototypical MOF-5.31,32 We term this species MOF-i, and demonstrate that the reactivity of this intermediate species is selective towards specific metals (Scheme 1), and allows access to new MOFs with unique sizes, shapes, chemical compositions, and molecular structures.

(A)

(B)

(C)

(D)

(E)

(F)

Scheme 1. (i) Synthesis of MOF-5 proceeds through the intermediate, MOF-i. (ii) The isolated MOF-i shows selective reactivity towards various synthetic conditions. Also shown is (iii) the product obtained via the reaction between CuCl2·2H2O, Zn(NO3)2·6H2O and TPA (TPA = terephthalic acid) in DMF.

EXPERIMENTAL SECTION Chemicals and materials. Zinc nitrate hexahydrate [98%, Zn(NO3)2·6H2O, Strem Chemicals], terephthalic acid [98+%, C8H6O4, Alfa Aesar], copper(II) chloride dihydrate [99.999%,


3


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 24

CuCl2·2H2O, Strem Chemicals], and manganese(II) chloride [97%, MnCl2, Acros Organics] were purchased and used without further purification. All solvents were ACS grade, and were used without further purification. Synthesis of MOF-5 and MOF-i. MOF-5 was synthesized by combining 0.9534 g (5.74 mmol) of TPA and 5.030 g (17.0 mmol) of Zn(NO3)2·6H2O with 100 mL of DMF in a 250 mL flask. After the precursors were stirred and dissolved in DMF, the solution was stirred at 350 rpm and refluxed at 120 oC for 16 h. Precipitation occurred after roughly 1.5 h of reaction. The solution was cooled to room temperature for 1 h before the work-up. The white precipitates were soaked in 50 mL of fresh DMF in a 100 mL flask without stirring and the solvent was decanted. This process was repeated six times to remove any remaining precursors. Then, the product was soaked in 30 mL of chloroform and the solvent was decanted six times to exchange DMF with chloroform. The product was stored in 50 mL of chloroform for 1 day. Afterwards the solvent was decanted and the product was dried under vacuum overnight. MOF-i was prepared by the above synthesis by allowing the reaction to proceed for only 3 hours. Reactivity of MOF-i. For each reaction condition (Scheme 1ii), the following solutions were prepared by combining the white precipitates in 20 mL of DMF in a 25 mL flask (left to right, Scheme 1ii): (A) no additional reactants, (B) 0.2515 g (0.850 mmol) of Zn(NO3)·6H2O, (C) 0.0477 g (0.288 mmol) of TPA, (D) 0.0477 g (0.288 mmol) of TPA and 0.2515 g (0.850 mmol) of Zn(NO3)·6H2O, (E) 0.1614 g (0.947 mmol) of CuCl2·2H2O, and (F) 0.1191 g (0.946 mmol) of MnCl2. For the reaction with MnCl2, the reaction was performed under argon with dry DMF. All reactions were stirred at 350 rpm and refluxed at 120 oC for 5 h. The solution was cooled to room temperature for 1 h before the work-up. Any solids collected were gently soaked in 20 mL of fresh DMF and the solvent was decanted. This process was repeated five times to remove any


4

Page 5 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


remaining precursors. Then, the product was soaked in 10 mL of chloroform and the solvent was decanted three times to exchange DMF with chloroform. The product was stored in 20 mL of chloroform for 1 day. Afterwards the solvent was decanted and the product was dried under vacuum overnight. Synthesis of Cu-Zn-MOF. Cu-Zn-MOF was synthesized by combining 0.1907 g (1.15 mmol) of TPA, 1.006 g (3.40 mmol) of Zn(NO3)2·6H2O, and 0.1614 g (0.947 mmol) of CuCl2·2H2O with 20 mL of DMF in a 25 mL flask. The solution was stirred at 350 rpm and refluxed at 120 oC for 5 h. Precipitation of blue solids occurred after roughly 1 h of reaction. The following work-up was performed identically as mentioned above. Materials characterization. Powder X-ray diffraction (XRD) patterns were collected using a Bruker-AXS D8 Advance diffractometer with Cu Kα radiation and a LynxEye 1-D detector. A FEI Quanta 200 environmental scanning electron microscopy (SEM) in low vacuum mode was used for SEM imaging, energy dispersive X-ray spectroscopy (EDS), and EDS mapping. The size distribution was obtained by measuring 40 - 50 particles from the SEM images of each sample. Thermal gravimetric analysis (TGA) was performed using a TGA 2050 with a ramping rate of 5 oC/min from 25 oC to 600 oC under air. Infrared (IR) spectra were acquired using a Perkin-Elmer Spectrum 400 FT-IR/FT-NIR spectrometer with an attenuated total reflectance (ATR) crystal. ASAP 2020 Automated Surface Area and Porosimetry System was used for measuring surface area and pore volume by using N2 at 77 K, and all samples were degassed for 16 hours at room temperature under vacuum at 100 µmHg before the measurements. CHN elemental analyses were carried out by Atlantic Microlab, Inc., Norcross, GA, and all samples were stored under argon in order to avoid any exposure to water before the analysis.


5


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 24

XRD simulation. The XRD patterns of MOF-i and Cu-MOF-i samples were indexed using Topas Academic.33 Goodness of fit (gof) values for MOF-i were very low due to the low crystallinity of the sample. A Pawley fit was performed (also using Topas Academic) using the best unit cells from indexing, but none of the units cells we tried provided an acceptable match, most likely due to the low crystallinity of the sample. However, high goodness of fit values were found for Cu-MOF-i diffraction pattern. The Pawley method was applied to test the unit cell parameters with the 5 highest gof values and only the reported unit cell was able to fit all of the peaks in the pattern.

RESULTS AND DISCUSSION Formation of MOF-i We isolated the intermediate of interest during a conventional synthesis of MOF-5,34,35 which involved a reaction between Zn(NO3)2·6H2O and terephthalic acid (TPA) in DMF at 120 °C. Allowing this reaction to run longer than 5 hours yielded a mixture of both interpenetrated and non-interpenetrated MOF-5 structures as testified by the relative intensity of the first two peaks at 2θ = 7.0° and 9.8° in the XRD (Figure 1e).36 However, we also observed the appearance of a different plate-like solid (MOF-i) prior to the emergence of MOF-5. The shape of the observed plates is rather irregular (Figure 1f) compared to the well-defined cubic shape of MOF-5 (Figure 1i) that we obtain at longer reaction times that pervades the literature of MOF-5.32 The XRD pattern of MOF-i (Figure 1a) is also different from that of MOF-5 (Figure 1e). We note that the appearance of MOF-5 in the XRD and SEM is concomitant with the loss of MOF-i. Based upon this observation, and the fact that we observe aggregations of MOF-i at late time points in the


6

Page 7 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


synthesis of MOF-5 (Figure 1g and 1h), leads us to suggest that MOF-5 is generated via the conversion of these aggregates of MOF-i. Though the XRD of MOF-i is different than that of MOF-5, we note that the XRD obtained for the samples that we lable as MOF-i can change from batch to batch (Figure S1). Thus, it is likely that the MOF-i is actually a mixture of products. As shown in Figure S1, the XRD of our obtained MOF-i species contain some features similar to those identified in the intermediates produced in the course of other reactions between zinc nitrate and TPA.37-42 However, due to the poor crystallinity as well as the likely mixture of species for our MOF-i, they could not be identified specifically those found in these previous reports. However, it seems likely that at least the peaks found near 2θ = 20.0° are due to a zinc hydroxide or zinc hydroxide-nitrate phase41 – though we were unable to confirm this for our samples. Furthermore, it is likely that these products have differential solubility, as washing the as-synthesized MOF-i with chloroform results in changes to the XRD pattern (Figure S2). Nevertheless, the reactivity of MOF-i discussed below did not appear to change upon washing with chloroform, and we retained this processing as a simple means by which to isolate and dry these samples.


7


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 24

Figure 1. (a)-(e) XRD patterns associated with solids obtained during the course of the formation of MOF-5. Also shown (f)-(i) are representative SEM images of the solids associated with each time point. All scale bars are in units of micrometers.

The kinetics of the transformation of MOF-i to MOF-5 was such that the largest plate-like solids of MOF-i (average dimensions of 34 ± 13 µm in width and 5 ± 2 µm in thickness, as shown in Figure S3) were obtained at 3 hours after the start of the reaction. If the reaction is allowed to proceed without isolation of MOF-i, the growth of the characteristic XRD peaks for


8

Page 9 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


MOF-5 is detected after 4 hours of the reaction (Figure 1c), and cubic species started to appear in the corresponding SEM image (Figure 1g). Though we were unable to determine the structure of MOF-i, we did obtain both elemental analysis, infrared spectra, and surface area for this species. The elemental analysis is presented in Table S1, and is consistent with solvated units of Zn(TPA), while the presence of solvent is consistent with the low temperature mass losses found in the TGA analysis (Figure S4). Futhermore, the asymmetric vibration mode of the TPA ligands (seen in the infrared spectrum, Figure S6) indicates that the TPA ligands are not coordinately saturated, which is consistent with reactivity of MOF-i toward ZnII (vide infra). The surface area analysis at 77 K (Figure 2 and Table 1) reveals that MOF-i does not appear porous under these conditions. It is possible that there is activated diffusion between pores, which is not observed at 77 K, however we were unable to either confirm or refute such a hypothesis and we hope to do so in future work. For now, we strongly suspect that MOF-i is composed of sheets of Zn-TPA coordination compounds. However, we note that the MOF-5 that we obtain via continuation of the reaction possesses a Langmuir surface area of 1053 m2/g, which is consistent with literature values for interpenetrated MOF-5 materials that are synthesized in DMF.34 Thus the formation of MOF-5 from MOF-i seems to result from large scale changes to the structure – yielding a porous material from a nonporous one (or at least one without activated diffusion from one with).


9


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 24

Figure 2. N2 isotherms of Zn-MOF-i, MOF-5, Cu-MOF-i, and MOF-i at 77 K.

Table 1. Langmuir surface area, microporous area, average pore width, and micropore volume of Zn-MOF-i, MOF-5, Cu-MOF-i, and MOF-i from N2 isotherms. Langmuir surface area

Microporous area

Average pore width

Micropore volume

Microporous area/Langmuir

(m2/g)

(m2/g)

(Å)

(cm3/g)

surface area (%)

Zn-MOF-i

1170

938

16

0.36

80

MOF-5

1053

910

16

0.35

86

Cu-MOF-i

191

115

71

0.05

60

6

-

69

-

-

MOF-i

Conversion of MOF-i to MOF-5: Reactivity towards ZnII In order to further demonstrate that MOF-i can be directly converted to MOF-5, we isolated MOF-i at the 3 hour time point and investigated its reactivity under four different conditions that had the possibility for conversion of MOF-i to MOF-5: (A) heat, (B) heat + Zn(NO3)2·6H2O, (C) heat + TPA, and (D) heat + TPA + Zn(NO3)2·6H2O (Scheme 1ii). Each of these conditions


10

Page 11 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


involved the use of DMF as a solvent and was held at a temperature of 120 °C for 5 hours – a time sufficient to generate MOF-5 starting from only ZnII and TPA. Of these four conditions investigated, we found that only the reaction of MOF-i with Zn(NO3)2·6H2O produced MOF-5, as observed via XRD (Figure 3c for reaction with ZnII and Figure S7 for all reactions). The MOF-5 obtained from this reaction (Zn-MOF-i) were cubic, and the dimensions of the cubes of MOF-5 (Figure 3j) were the same as the thickness of the plates of MOF-i (Figure 3i) from which they were obtained (5 ± 2 µm). This observation suggests that the MOF-5 generated by addition of ZnII ions is obtained directly via fragmentation of MOF-i to the final MOF-5 – a process distinct from the aggregative process observed when MOF-5 is generated starting from the zinc salt and TPA. Surface area analysis of Zn-MOF-i yields a surface area of 1170 m2/g (Figure 2 and Table 1), which is slightly larger than that of directly synthesized MOF-5. The ratio of microporous area to Langmuir surface area reveals that ZnMOF-i contains slightly lower portion of the microporous area than that in MOF-5, which might be attributed to the smaller size of the Zn-MOF-i crystals. The almost identical micropore volume between MOF-5 (0.35 cm3/g) and Zn-MOF-i (0.36 cm3/g) also supports the highly porous structure in Zn-MOF-i. Thus, very similar structures are being produced, even though we suspect they are being generated via different reaction mechanisms. Support for the hypothesis that MOF-5 is generated from MOF-i via a mechanism different than for the direct synthesis of MOF-5 is found in the fact that MOF-i produces MOF-5 only in the presence of ZnII ions and will not produce MOF-5 upon the addition of pure TPA. We would like to note that there are some changes to the XRD pattern upon exposure of MOF-i to TPA, and so it certainly undergoes some changes, however, this reaction condition does not result in formation of MOF-5.


11


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 24

Surprisingly, even exposure of MOF-i to both ZnII and TPA in the same proportions as used to directly produce MOF-5 (reaction (i) in Scheme 1) failed to produce MOF-5. In other words, MOF-i acts as both a reactive intermediate to MOF-5 and as an inhibitor for the generation of MOF-5, depending upon reaction conditions. This inhibition can be overcome through the use of excess zinc, and by doubling the amount of zinc nitrate added to MOF-i, while keeping the amount of TPA added the same, we obtained MOF-5. Recalling that the infrared spectrum of MOF-i indicates that the TPA ligands are unsaturated provides a rational for the reactivity towards excess ZnII ions, however, further work is needed to fully establish any reaction mechanism. To the best of our knowledge, this is the first demonstration of using an intermediate MOF to selectively access new sizes and mechanisms of subsequent MOF generation, as well as inhibition of MOF generation via an intermediate.


12

Page 13 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 3. (a)-(g) XRD patterns associated with solids obtained from the reaction of MOF-i with various conditions (see Scheme 1). Digitalized simulated XRD of (e) Zn-MOF-2-sim. and (f) Cu-MOF-2-sim. are obtained from the data presented in ref 45 and ref 48. Also shown (h)-(m) are representative SEM images of the solids associated with each reaction. For the reaction with


13


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 24

CuII we also show (l, inset) EDS scanning results for both copper and zinc. The atomic ratio of Cu to Zn is 9:1. All scale bars are in units of micrometers.

Reactivity of MOF-i with CuII The fact that MOF-i showed reactivity only towards ZnII ions led us to examine reactivity towards other first-row transition metal ions. We began with CuII, as consideration of the IrvingWilliams series43,44 suggested that the copper ions would be capable of displacing the zinc ions. For this reaction, we charged a flask with MOF-i, CuCl2·2H2O, and DMF, and then refluxed the contents of this flask at 120 °C for 5 hours. During the course of this reaction, the color of solids turned from white to blue. The blue product was isolated and found to possess the same platelike morphology as MOF-i (Figure 3k), and SEM EDS mapping on a single plate of Cu-MOF-i demonstrated that CuII ions have almost totally replaced the ZnII ions (Figure 3l), producing a new MOF: Cu-MOF-i. Perhaps the most striking result of the reaction between MOF-i and CuII ions is the fact that porosity of the crystals increases dramatically upon reaction with CuII (Figure 2 and Table 1) – even without a change in the overall morphology of the crystal. Indeed, the structure changes from a crystal without detectable porosity, to one with significant porosity – though this porosity is not as great as observed for MOF-5. The observed change in porosity also indicates that there should be a large change in crystal structure, upon reaction with CuII ions. The XRD of Cu-MOF-i (Figure 3d) confirms that a change in crystal structure occurs during the conversion to Cu-MOF-i. It was found that Cu-MOF-i has a monoclinic structure with a unit cell of a = 6.734(2) Å, b = 15.484(6) Å, c= 12.138(5) Å and β = 102.38(3)° with a possible space group of P21/n (Figure S8). A search of the literature reveals that the unit cell of Cu-MOF-i


14

Page 15 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


closely resembles that associated with the known framework, Zn-MOF-2.38,45 This MOF structure consists of a 2-D network of Zn-paddlewheel units, and we also show that the simulated XRD of Zn-MOF-2 (Figure 3e) closely resembles that of Cu-MOF-i (Figure 3d). Thus, we conclude that the structure of Cu-MOF-i is that of Zn-MOF-2, but with the ZnII centers replaced by CuII atoms. This could not be confirmed via rietveld refinement as Cu-MOF-i is not crystalline enough for such detailed analysis. However, the porous properties of Cu-MOF-i (191 m2/g in Langmuir surface area and 0.05 cm3/g in micropore volume) are comparable to those of Zn-MOF-2 (270 m2/g in Langmuir surface area and 0.09 cm3/g in micropore volume) observed in literature.45 The lowered porosity in Cu-MOF-i (compared to Zn-MOF-2) might be caused by some disorder in the framework as shown in the broadened XRD pattern. Interestingly, there is a separate known copper/TPA MOF (Cu-MOF-2) – also involving 2D arrays of the paddlewheel structure.46-49 However, the structure of Cu-MOF-i is not the same as Cu-MOF-2, as verified by comparison of their respective calculated XRD patterns (Figure 3e and 3f). The most notable differences between the assigned structures of Cu-MOF-i and Cu-MOF-2 lie in the orientation of the TPA ligands, the distance between the metal centers in adjacent stacks, and the fact that the proposed Cu-MOF-i structure contains two different sized pores, while the structure of Cu-MOF-2 contains a single type of pore (Figure 4). In addition, the Langmuir surface area analysis is consistent with the difference in porosity expected from the structural differences between Cu-MOF-i and Cu-MOF-2 (191 m2/g for Cu-MOF-i and 752 m2/g for Cu-MOF-248). Thus, we conclude that we were able to use MOF-i to realize a novel copper MOF structure, highlighting the unique reactivity imparted by MOF-i, in the role of a reactive intermediate – and the possible general utility of this idea.


15


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 24

Figure 4. The structure and packing of Zn-MOF-2, viewed (a) down the pores and (b) along the metal-metal axis. A similar structure is produced via reaction of CuII with MOF-i in DMF. The structure and packing of Cu-MOF-2, viewed (c) down the pores and (d) along the metal-metal axis. This structure is produced via the reaction of CuII, ZnII, and TPA in DMF. These packing diagrams are generated from the crystal structures from ref 45 and ref 48.

We confirmed the unique reactivity imparted by MOF-i by running a reaction with a mixture of copper and zinc metal salts with TPA in DMF (Scheme 1iii), yielding blue cubic solids of CuMOF-2 (Figure 3g and 3m). Thus, the Cu-MOF-2 structure appears to be the preferred product of the reaction of CuII ions, ZnII ions, and TPA. The fact that the presence of MOF-i allows for production of a novel copper MOF (Cu-MOF-i) than this otherwise preferred product highlights the power of using a reactive intermediate to obtain new MOFs with new structures and morphologies using synthetic conditions that are otherwise identical.


16

Page 17 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Reactivity of MOF-i towards MnII The reactivity of MOF-i towards CuII was anticipated from the Irving-Williams series, due to copper’s stronger interaction with ligands, when compared to ZnII. Following similar reasoning, we hypothesized that MnII would be incapable of replacing ZnII within MOF-i, owing to its weaker interaction with ligands. Indeed, refluxing of MOF-i in DMF at 120 °C for 5 hours in the presence of MnCl2 resulted in no significant changes to the MOF-i. The crystallinity remained the same as for MOF-i (Figure S9). This result indicates that conventional chemical reasoning can be used to predict the reactivity of reactive intermediates, such as MOF-i. This, in turn, suggests a number of future research direction, in which the full reactivity of these intermediates is characterized and rationalized using the known relative reactivity of metal ions.

CONCLUSIONS In summary, we have isolated an intermediate MOF species (MOF-i) during the synthesis of MOF-5. We have demonstrated that this intermediate (MOF-i) undergoes reaction with both ZnII and CuII ions – producing a 3D (MOF-5) and 2D (Cu-MOF-i) MOF, respectively. Interestingly, the presence of MOF-i allowed for production of a different size (MOF-5) as well as a different structure and morphology (Cu-MOF-i) than would be obtained starting from metal ions and ligands. All of this was done while displaying remarkable selectivity for the reaction conditions. For instance, MOF-i was found to be reactive only towards metal ions, rather than organic ligands. However, despite this unique reactivity, chemical reasoning (e.g. the Irving-Williams series) can be used to predict the behavior of these intermediates. Thus, the use of MOF-i opens


17


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 24

new and selective synthetic pathways for the rational production of MOFs, and serves as the first example of the utility of reactive MOF intermediates.

ASSOCIATED CONTENT Supporting Information XRD of MOF-i from different batches; XRD of MOF-i via different post-treatment; size distribution of MOF-i, Zn-MOF-i, and MOF-5; Elemental analysis; TGA of MOF-i, Zn-MOF-i, and MOF-5; IR of MOF-i, Zn-MOF-i, and MOF-5; XRD of MOF-i, Heat, Heat + TPA, Heat + ZnII, and Heat + TPA +ZnII; Simulated XRD of Cu-MOF-i; XRD of MOF-i and Mn-MOF-i. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT


18

Page 19 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


We thank Dr. Hemant P. Yennawar for helpful discussion about crystal structures and data. We would also like to thank Prof. Raymond E. Schaak for use of his powder X-ray diffractometer. We thank the Pennsylvania State University for financial support of this work and NSF funding (CHE-0131112) for the diffractometer purchase. Michelle R. Dolgos would like to thank Oregon State University for the financial support of this work.

REFERENCES (1) Eddaoudi, M.; Moler, D. B.; Li, H.; Chen, B.; Reineke, T. M.; O’Keeffe, M.; Yaghi, O. M. Acc. Chem. Res. 2001, 34, 319. (2) Rowsell, J. L. C.; Yaghi, O. M. Microporous Mesoporous Mater. 2004, 73, 3. (3) Czaja, A. U.; Trukhan, N.; Müller, U. Chem. Soc. Rev. 2009, 38, 1284. (4) Lee, J.; Farha, O. K.; Roberts, J.; Scheidt, K. A.; Nguyen, S. T.; Hupp, J. T. Chem. Soc. Rev. 2009, 38, 1450. (5) Allendorf, M. D.; Schwartzberg, A.; Stavila, V.; Talin, A. A. Chem. Eur. J. 2011, 17, 11372. (6) Shekhah, O.; Liu, J.; Fischer, R. A.; Wöll, Ch. Chem. Soc. Rev. 2011, 40, 1081. (7) Horcajada, P.; Gref, R.; Baati, T.; Allan, P. K.; Maurin, G.; Couvreur, P.; Férey, C.; Morris, R. E.; Serre, C. Chem. Rev. 2012, 112, 1232. (8) Cui, Y.; Yue, Y.; Qian, G.; Chen, B. Chem. Rev. 2012, 112, 1126. (9) Schoedel, A.; Scherb, C.; Bein, T. Angew. Chem. Int. Ed. 2010, 49, 7225.


19


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 24

(10) Carné-Sánchez, A.; Imaz, I.; Cano-Sarabia, M.; Maspoch, D. Nature Chem. 2013, 5, 203. (11) Win, K. Y.; Feng, S. Biomaterials 2005, 26, 2713. (12) Manzano, M.; Aina, V.; Areán, C. O.; Balas, F.; Cauda, V.; Colilla, M.; Delgado, M. R.; Vallet-Regí, M. Chem. Eng. J. 2008, 137, 30. (13) Rocca, J. D.; Liu, D.; Lin, W. Acc. Chem. Res. 2011, 44, 957. (14) Farrusseng, D.; Aguado, S.; Pinel, C. Angew. Chem. Int. Ed. 2009, 48, 7502. (15) Song, F.; Wang, C.; Falkowski, J. M.; Ma, L.; Lin, W. J. Am. Chem. Soc. 2010, 132, 15390. (16) Corma, A.; García, H.; Llabrés i Xamena, F. X. Chem. Rev. 2010, 110, 4606. (17) Ma, L.; Falkowski, J. M.; Abney, C.; Lin, W. Nat. Chem. 2010, 2, 838. (18) Umemura, A.; Diring, S.; Furukawa, S.; Uehara, H.; Tsuruoka, T.; Kitagawa, S. J. Am. Chem. Soc. 2011, 133, 15506. (19) Yuan, Y.; Wang, W.; Qiu, L.; Peng, F.; Jiang, X.; Xie, A.; Shen, Y.; Tian, X.; Zhang, L. Mater. Chem. Phys. 2011, 131, 358. (20) Liu, K.; Shen, Z.; Li, Y.; Han, S.; Hu, T.; Zhang, D.; Bu, X.; Ruan, W. Sci. Rep. 2014, 4, 1. (21) Wang, Z.; Cohen, S. M. Chem. Soc. Rev. 2009, 38, 1315. (22) Karagiaridi, O.; Bury, W.; Sarjeant, A. A.; Stern, C. L.; Farha, O. K.; Hupp, J. T. Chem. Sci. 2012, 3, 3256.


20

Page 21 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(23) Bury, W.; Fairen-Jimenez, D.; Lalonde, M. B.; Snurr, R. Q.; Farha, O. K.; Hupp, J. T. Chem. Mater. 2013, 25, 739. (24) Kim, Y.; Das, S.; Bhattacharya, S.; Hong, S.; Kim, M. G.; Yoon, M.; Natarajan, S.; Kim, K. Chem. Eur. J. 2012, 18, 16642. (25) Brozek, C. K.; Dincă, M. Chem. Sci. 2012, 3, 2110. (26) Lalonde, M.; Bury, W.; Karagiaridi, O.; Brown, Z.; Hupp, J. T.; Farha, O. K. J. Mater. Chem. A 2013, 1, 5453. (27) Brozek, C. K.; Dincă, M. J. Am. Chem. Soc. 2013, 135, 12886. (28) Brozek, C. K.; Bellarosa, L.; Soejima, T.; Clark, T. V.; López, N.; Dincă, M. Chem. Eur. J. 2014, 20, 1. (29) Carson, F.; Su, J.; Platero-Prats, A. E.; Wan, W.; Yun, Y.; Samain, L.; Zou, X. Cryst. Growth Des. 2013, 13, 5036. (30) McKinstry, C.; Cussen, E. J.; Fletcher, A. J.; Patwardhan, S. V.; Sefcik, J. Cryst. Growth Des. 2013, 13, 5481. (31) Li, H.; Eddaoudi, M.; O’Keeffe, M.; Yaghi, O. M. Nature 1999, 402, 276. (32) Panella, B.; Hirscher, M.; Pütter, H.; Müller, U. Adv. Funct. Mater. 2006, 16, 520. (33) Coelho, A. Topas Academic Version 4.1. Computer Software, Topas Academic, Coelho Software, Brisbane, 2007.


21


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 24

(34) Huang, L.; Wang, H.; Chen, J.; Wang, Z.; Sun, J.; Zhao, D.; Yan, Y. Microporous Mesoporous Mater. 2003, 58, 105. (35) Hafizovic, J.; Bjorgen, M.; Olsbye, U.; Dietzel, P. D. C.; Bordiga, S.; Prestipino, C.; Lamberti, C.; Lillerud, K. P. J. Am. Chem. Soc. 2007, 129, 3612. (36) Kim, H.; Das, S.; Kim, M. G.; Dybtsev, D. N.; Kim, Y.; Kim, K. Inorg. Chem. 2011, 50, 3691. (37) Rosi, N. L.; Kim, J.; Eddaoudi, M.; Chen, B.; O’Keeffe, M.; Yaghi, O. M. J. Am. Chem. Soc. 2005, 127, 1504. (38) Clausen, H. F.; Poulsen, R. D.; Bond, A. D.; Chevallier, M. S.; Iversen, B. B. J. Solid State Chem. 2005, 178, 3342. (39) Hausdorf, S.; Wagler, J.; Mossig, R.; Mertens, F. O. R. L. J. Phys. Chem. A 2008, 112, 7567. (40) Lu, H.; Zhu, S. Eur. J. Inorg. Chem. 2013, 1294. (41) Zheng, C.; Greer, H. F.; Chiang, C.; Zhou, W. Cryst. Eng. Comm. 2014, 16, 1064. (42) Li, M.; Dincă, M. Chem. Sci. 2014, 5, 107. (43) Yao, Q.; Sun, J.; Li, K.; Su, J.; Peskov, M. V.; Zhou, X. Dalton Trans. 2012, 41, 3953. (44) Deria, P.; Mondloch, J. E.; Karagiaridi, O.; Bury, W.; Hupp, J. T.; Farha, O. K. Chem. Soc. Rev. 2014, 43, 5896. (45) Li, H.; Eddaoudi, M.; Groy, T. L.; Yaghi, O. M. J. Am. Chem. Soc. 1998, 120, 8571.


22

Page 23 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(46) Mori, W.; Inoue, F.; Yoshida, K.; Nakayama, H.; Takamizawa, S.; Kishita, M. Chem. Lett. 1997, 26, 1219. (47) Mori, W.; Sato, T.; Kato, C. N.; Takei, T.; Ohmura, T. Chem. Rec. 2005, 5, 336. (48) Carson, C. G.; Hardcastle, K.; Schwartz, J.; Liu, X.; Hoffmann, C.; Gerhardt, R. A.; Tannenbaum, R. Eur. J. Inorg. Chem. 2009, 2338. (49) Carson, C. G.; Ward, J.; Liu, X. T.; Schwartz, J.; Gerhardt, R. A.; Tannenbaum, R. J. Phys. Chem. C 2012, 116, 15322.


23


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 24

For table of Contents Use Only Isolation and Chemical Transformations Involving a Reactive Intermediate of MOF-5 Juyeong Kim,† Michelle R. Dolgos,‡ and Benjamin J. Lear*,† †Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, United States ‡Department of Chemistry, Oregon State University, Corvallis, Oregon 97331-4003, United States

TOC graphic

Synopsis We isolated plate-like intermediate species during synthesis of MOF-5 and investigated reactivity of the intermediate species to metal ions. Its reaction with Zn(NO3)2·6H2O led to morphological change from a plate to a cube along with structural transformation from nonporous to MOF-5 structure. However, reaction with CuCl2·2H2O resulted in structural change to a novel copper-based MOF-2 while maintaining the plate-like shape.


24

Isolation and Chemical Transformations Involving ... - ACS Publications

Recommend Documents