Diverse MetalâOrganic Materials (MOMs) Based on 9,9â²-Bianthryl

Subscriber access provided by GAZI UNIV

Article

Diverse Metal-Organic Materials (MOMs) Based on 9,9'-BianthrylDicarboxylic Acid Linker: Luminescence Properties and CO2 Capture Saona Seth, Govardhan Savitha, Samik Jhulki, and Jarugu Narasimha Moorthy Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.5b01617 • Publication Date (Web): 23 Feb 2016 Downloaded from http://pubs.acs.org on March 4, 2016

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 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

Crystal Growth & Design

Diverse Metal-Organic Materials (MOMs) Based on 9,9'-BianthrylDicarboxylic Acid Linker: Luminescence Properties and CO2 Capture Saona Seth, Govardhan Savitha, Samik Jhulki and Jarugu Narasimha Moorthy* Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, INDIA E-mail: [email protected]

ABSTRACT A fluorescent organic linker, namely, 10,10'-bis(4-carboxyphenyl)-9,9'-bianthryl (H2L), was rationally designed and synthesized to access luminescent metal-organic materials (MOMs). A series of structurally diverse MOMs was synthesized with the diacid linker H2L by reacting it with main group, transition and lanthanide metal ions under different conditions. Amongst them, Zn-L MOM is a 1D polymeric chain, while Cd-L is a 2D structure in which 4,4'-bipyridyls mediate the formation of 2D networks by linking up the 1D metal-carboxylate chains. The Pb-L MOM is found to be a 2D polymeric net, while Sr-L–obtained under similar reaction conditions–is a non-interpenetrated 3D polymeric structure; the extension from 2D to 3D framework occurs by mediation of Cl- ions. Notably, the reaction of H2L with the lanthanide ions yielded isostructural 3D MOFs, i.e., Tb-L, Eu-L, Sm-L, Nd-L, La-L, Pr-L, Gd-L and YbL, which are non-interpenetrated and porous. The Ln-MOFs are highly robust and stable to solvent exclusion. The representative Ln-MOFS, viz., Tb-L, Eu-L and Sm-L, are shown to exhibit gas adsorption at ambient temperatures; the CO2 uptake capacities are found to be in the range of highest values observed for Ln-MOFs to date. All the MOMs, including lanthanide MOFs, exhibit linker-based luminescence in the solid state.

ACS Paragon Plus Environment


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

INTRODUCTION The research on metal-organic materials (MOMs), metal-organic frameworks (MOFs, which are MOMs with 3D network structures) in particular, has advanced significantly in recent years due to the promise of these organic-inorganic hybrid crystalline polymers as functional materials. Their applications are quite diverse in areas that range from synthetic chemistry to material science to biomedicine.1-11 It has been sufficiently established that the properties of MOFs are highly dependent on structural attributes as well as chemical nature of the organic linkers employed.12,13 Thus, the design of novel linkers in pursuit of MOFs with unique structural features and properties is a continuing quest. We have been interested in developing MOMs based on de novo design of organic linkers that are characterized by twisted aromatic planes, and exploring their functional utility.14-19 In continuation of our investigations, we designed and synthesized a dicarboxylic acid linker, i.e., 10,10'-bis(4-carboxyphenyl)-9,9'-bianthryl (H2L), which is luminescent in nature. The rationale for design of this organic spacer was based on following considerations: i) the high aromatic expanse inherent to the twisted anthracene rings may preclude interpenetration of the derived coordination polymers, ii) anthracene-based systems can be brilliantly fluorescent, when quenching pathways are suppressed, to enable access to luminescent MOFs,20 and iii) the linker can be readily synthesized without much difficulty. Herein, we report that a series of MOMs with a variety of transition, main group and lanthanide metal ions can be accessed with the linker H2L. Depending on the nature of the metal ion and the reaction conditions employed, distinct 1D, 2D and 3D hybrid metal-organic polymeric materials−referred to as M-L (M = metal ion)−are obtained. In addition to 1D and 2D MOMs, a 2


Page 2 of 23

Page 3 of 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


series of porous and chemically robust isostructural 3D MOFs, referred to collectively as Ln-L (Ln = Tb, Eu, Sm, La, Pr, Nd, Gd and Yb), is accessed when the linker H2L is reacted with the lanthanide ions. All Ln-L MOMs are shown to exhibit solid state linker-based luminescence and chemical robustness for gas adsorption. Indeed, the CO2 uptake capacities determined for LnMOFs at rt and atmospheric pressure are amongst highest values reported for Ln-MOFs in general.21-27

RESULTS AND DISCUSSION Synthesis of 10,10'-Bis(4-carboxyphenyl)-9,9'-bianthryl, H2L. The diacid acid linker H2L was synthesized starting from 10,10'-dibromo-9,9'-bianthryl, which was readily prepared by following the literature-reported procedure.20 Suzuki coupling of the dibromo compound with 4carbomethoxyphenylboronic acid under Pd(0)-catalyzed conditions led to 10,10'-bis(4carbomethoxyphenyl)-9,9'-bianthryl. The latter was heated at reflux with excess KOH and subsequently acidified with conc. HCl to furnish the diacid linker H2L in a very good isolated yield, Scheme 1.

Scheme 1. Synthetic Route for the Dicarboxylic Acid Linker H2L.

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 23

Synthesis of MOMs with H2L and Single Crystal X-Ray Structural Determinations. A series of M-L MOMs was obtained upon treatment of the diacid H2L with different metal salts under solvothermal conditions. Single crystal X-ray structure determinations revealed that the MOMs are 1D, 2D and 3D depending on the nature of the salt and reaction conditions employed. The compositions of the polymeric MOMs, polymer type, i.e., 1D or 2D or 3D, contents of the asymmetric unit and solvent-accessible void volume in each case are given in Table 1; the solvent-accessible void volume was calculated using PLATON with a probe radius of 1.2 Å.28 In the following are discussed structural aspects of each case. Table 1. Reaction Conditions, Codes and Other Details of MOMs Obtained with H2L by Solvothermal Synthesis Using Different Main Group, Transition and Lanthanide Metal Salts. reaction conditions

asymmetric unit

polymer void type vol. (%)

code

H2L/ZnCl2 DMF, 100 °C

[Zn(L)(DMF)2] (DMF)2

1D

56.1

Zn-L

H2L/Cd(NO3)2.6H2O/bipy [Cd(L)(DMF)(4,4'-bipy)0.5] DMF, 110 °C

2D

25.7

Cd-L

H2L/Pb(NO3)2 DMF, 110 °C

[Pb2(L)2(DMF)2]

2D

34.8

Pb-L

H2L/SrCl2 DMF, 110 °C

[Sr2(L)2(DMF)4Cl] (DMF)2

2D

35.6

Sr-L

H2L/Tb(NO3)2.6H2O DMF/H2O/HNO3,110 °C

[Tb2(L)2(H2O)4]

3D

34.2

Tb-La

a

Refers to the series of isostructural Ln-L MOMs formed with H2L, where Ln = Sm, Eu, Gd, La, Nd, Pr and Yb. Isostructurality was established based on PXRDs, which were similar to that of Tb-L, cf. text. Zn-L. Block-shaped orange crystals of Zn-L were obtained when the diacid H2L was reacted with ZnCl2 in DMF at 100 °C for 2 d. Single crystal X-ray intensity data collection followed by 4


Page 5 of 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


structure determination showed that the asymmetric unit contains one metal ion, one linker L and four molecules of DMF. Crystal structure analysis of Zn-L reveals that each Zn(II) ion is pentacoordinated by two carboxylate groups (one chelated and one monocoordinated) ion and two molecules of DMF, which coordinate through their oxygen atoms, cf. Figure 1b. As shown in the Figure 1a, one observes 1D Zn-carboxylate chains that are arranged in a zigzag manner along the crystallographic b-axis.

a)

b)

Figure 1. (a) Crystal packing of Zn-L down a-axis; the metal-carboxylate 1D chains are seen to propagate down the crystallographic b-axis in a zigzag manner. (b) The octahedral coordination mode of Zn(II) ions in Zn-L. Hydrogen atoms have been omitted in each case for clarity. Cd-L. Brown-colored crystals of Cd-L were obtained when H2L was reacted with Cd(NO3)2 in the presence of 4,4'-bipyridine under solvothermal conditions at 110 °C in DMF. Single crystal X-ray diffraction analysis revealed that the asymmetric unit of Cd-L consists of an octahedral Cd(II) metal ion that is chelated by two carboxylate groups of the linker L and further coordinated by one DMF molecule and one pyridyl group of the 4,4'-bipyridine ligand. The MOM is found to contain 1D metal-carboxylate chains that propagate in a zigzag manner and are connected further by 4,4'-bipyridine to form the 2D network, cf. Figure 2a. Analysis of the topology of the 2D network of Cd-L shows that it corresponds to hcb net, Figures 2a,d.17, 29-31 A 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

careful analysis of the structure reveals that two hcb nets are interwoven to account for less solvent-accessible void volume of 25.7%, Figures 2b,c.

a)

b)

c)

d)

Figure 2. (a) 2D network of Cd-L. (b) Interwoven 2D nets. (c) Crystal packing of Cd-L down the crystallographic b-axis. Hydrogen atoms and solvent molecules have been omitted in each case for clarity. (d) Honeycomb network of Cd-L by reducing the Cd(II) ions to 3-connecting nodes and the dicarboxylate as well as bipyridyl linkers to ditopic spacers. Pb-L. Metal-assisted self-assembly of H2L with Pb(NO3)2 in DMF at 110 °C for 2 d yielded brown crystals of Pb-L. X-ray crystal structure analyses revealed that there are two crystallographically independent Pb(II) ions, i.e., Pb1 and Pb2, with an occupancy of one each. While the Pb1 ions are found to exhibit distorted octahedral coordination geometry, Pb2 ions are found to be pentacoordinated with a distorted square pyramidal geometry. Pb1 ions are found to form dimers through bridging by two carboxylate groups of the linker L, Figure 3a. The distance 6


Page 6 of 23

Page 7 of 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


between the metal ions in the dimers is 4.49 Å. Overall, metal-ligand coordination in the MOM Pb-L leads to 2D networks, cf. Figure 3b. The solvent-accessible volume is calculated to be 34.8%. Simplification of the network structure by TOPOS program reveals that the 2D metalorganic polymeric nets correspond to FeS topology, Figure 3d.17,32,33

a)

b)

c)

d)

b c

Figure 3. (a) Dinuclear Pb-carboxylate unit. (b) 2D polymeric layer of Pb-L. (c) Overall crystal packing of Pb-L down b-axis. Hydrogen atoms and solvent molecules have been omitted in each case for clarity. (d) Arrangement of 2D layers of FeS topology, as revealed by TOPOS analysis. Sr-L. The reaction of H2L with SrCl2 in DMF yielded yellow crystals of Sr-L. X-ray crystal structure determination revealed that the asymmetric unit of the MOM contains two Sr(II) ions, i.e., Sr1 and Sr2, two units of L, six DMF molecules and one chloride ion; the two Sr ions are linked by carboxylate bridging. The distance between the metal ions in the dimer is 3.93 Å. Both metal ions in the asymmetric unit are found to be heptacoordinated, cf. Figure 4a. Sr1 is found to be coordinated by two monocoordinated carboxylate groups, one chelated carboxylate group, 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

one chloride ion, one DMF molecule, and bridged by another carboxylate group that is chelated to Sr2. The second metal ion, i.e., Sr2, is found to be coordinated by three DMF molecules, one chloride ion and bridged by the carboxylate group that is chelated to Sr1. A closer inspection of the crystal packing of Sr-L reveals 2D metal-carboxylate networks, cf. Figure 4b, that are further connected through the Sr(II) centers via chloride bridging, leading to 3D polymeric framework, Figure 4c. The Cl- ions bridge Sr1 and Sr2 ions of adjacent metal-carboxylate layers to generate the 3D framework structure. The Sr–Cl bond distances are 2.86 and 2.89 Å. Analysis of the

a)

b)

c)

d)

Figure 4. (a) Coordination environment of the dimeric [Sr2(COO)4(DMF)4Cl2] unit, which can be considered as 4-connecting when the Cl- ions are omitted. (b) 2D metal-carboxylate layer of Sr-L. (c) Overall crystal packing of Sr-L down b-axis. The 2D metal-carboxylate layers are connected to each other through chloride ions, which bridge metal ions of neighboring layers into an overall 3D framework structure. Observe the 1D zigzag chains of metal ions along c-axis, formed by chloride bridging. Hydrogen atoms have been omitted for clarity. (d) Crystal packing diagram of Sr-L as simplified by TOPOS, which reveals that the topology of the 3D network of Sr-L is of ′rod′ type. 8


Page 8 of 23

Page 9 of 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


topology of the structure reveals that the MOF consists of 1D 'rod'-shaped SBUs that are formed via chloride bridging between the metal centers, which lead to a non-interpenetrated network of ′rod′-type topology, cf. Figure 4d.34-39 The solvent-accessible void volume in the MOM is found to be 35.6%.

Tb-L. Fibrous yellow crystals of Tb-L were obtained by solvothermal reaction of H2L with Tb(NO3)3. Single crystal X-ray structural analysis revealed that the asymmetric unit consists of two crystallographically independent metal ions, two units of the linker L and four molecules of water. The Tb–Tb distance is found to be ca. 4.88 Å. While Tb1 is octacoordinated, Tb2 is found to be heptacoordinated. As shown in Figures 5a and 5b, the metal ions are organized in a zigzag manner, leading to 1D chains down b-axis; the metal-mediated polymerization of the diacid a)

b)

a

c)

Figure 5. (a) Crystal packing diagram of Tb-L; note that the channels run down the crystallographic b-axis. Hydrogen atoms have been omitted for clarity. (b) Tb-carboxylate chain in Tb-L. Note that the water molecules that are coordinated to the Tb metal ions are specifically shown in orange color. (c) The simplified network structure of Tb-L, which corresponds to ‘rod’ topology.

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 23

linker leads to the formation of a 3D framework structure with 1D channels down b-axis. The solvent-accessible volume was calculated to be 34.2%. Simplification of the framework structure using TOPOS reveals that the topology of the MOF is also of 'rod' type, Figure 5c.34-39

Ln-L MOMs. A series of lanthanide MOMs, viz., Sm-L, Eu-L, Gd-L, La-L, Nd-L, Pr-L and Yb-L, were obtained under the similar reaction conditions as those employed for Tb-L. Indeed,

the crystals were found to be similar in morphology to those of the MOF Tb-L, but were found to diffract very poorly. Thus, single crystal structure determinations of these MOFs were not possible. The fact that all of these MOFs are isostructural to that of Tb-L was established based on the PXRD profiles, Figure 6a. Thus, a series of Ln-MOFs that are 3D with a considerable solvent-accessible volume was readily accessed. The bulk purity of all the MOMs was established by PXRD analysis. The PXRD profiles of all as-synthesized MOMs were found to nicely match with that simulated for the X-ray single crystal structure of Tb-L, Figure 6a.

Although the structures of Zn-L, Cd-L, Pb-L and Sr-L were found to collapse upon solvent removal, the lanthanide MOMs were found to be stable. In particular, Tb-L, Eu-L and Sm-L were found to exhibit very good stabilities in different organic solvents such as DCM, MeOH, acetone, etc., Figures 6b-d. Remarkably, these three MOFs were found to be stable even in water and acidic buffer solutions of pH 3, which attests to their exceptional chemical stabilities. Furthermore, the lanthanide MOFs were found to be stable even after solvent evacuation. This is very important given that the structures often collapse upon removal of the ancillary ligands, namely, water and DMF in most cases.34-39 Based on the remarkable stabilities and structural robustness of the lanthanide MOFs in different polar and nonpolar common organic solvents,

10


Page 11 of 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


aqueous and acidic media and also under completely solvent excluded conditions, their functional property as applied to gas adsorption was explored.

a)

b)

2θ (degrees)

2θ (degrees)

c)

d)

2θ (degrees)

2θ (degrees)

Figure 6. (a) PXRDs of as-synthesized Ln-MOMs, namely, Tb-L, Sm-L, Eu-L, Gd-L, La-L, Nd-L, Pr-L, and Yb-L. Note that the PXRD profiles of all the lanthanide MOMs are very similar, which suggests that they all are isostructural to Tb-L. PXRDs of Tb-L (b), Eu-L (c) and Sm-L (d) in different solvents and after desolvation. The PXRD in each case was found to match with that of the as-synthesized material.

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 23

Gas Adsorption Properties of Ln-L MOFs. As mentioned earlier, MOFs have been

investigated immensely for gas storage, selective gas adsorption and separation, etc.6-8,24,25 Lanthanide MOFs have rarely been explored for gas adsorption.21-23,26,27 One of the reasons appears to

be the instability of the lanthanide-carboxylate frameworks to removal of the

ancillary ligands, e.g., water, DMF, etc.40 Clearly, accessibility of Ln-MOFs that sustain desolvation is difficult. Therefore, the stable Ln-L MOFs are excellent cases to explore gas adsorption. Three of the eight isostructural Ln-L MOFs, i.e., Tb-L, Eu-L and Sm-L, were chosen for gas adsorption studies due to their ready synthesis in respectable yields and high purity.

To begin with, the activated samples of the MOFs were examined for N2 adsorption at 77 K in the pressure range of 0 to 1 bar as shown in the Figures 7a,c,e. Surprisingly, the BET surface areas of the MOFs−calculated based on the nitrogen adsorption isotherms at 77 K−were found to vary from 415 m2 g-1 for Tb-L to 578 m2 g-1 for Eu-L and to 309 m2 g-1 for Sm-L. However, the MOFs were found to display comparable capacity for CO2 adsorption at 195 K as well as at ambient temperatures, Figure 7 and Table 2. The gas uptake capacities were measured from 0 to 1 bar in each case. The MOFs Tb-L, Eu-L and Sm-L were found to exhibit CO2 uptake of 165, 148 and 138 cc g-1, respectively, at 1 bar at 195 K, cf. Table 2. Similarly, the CO2 uptake capacities were found to be 67.1, 61.3 and 69.6 cc g-1, respectively, at 1 bar at 273 K and 41.2, 34.1 and 36.5 cc g-1, respectively, at 1 bar at 298 K. The selectivity for the adsorption of CO2 over N2 was also calculated at 0 °C.6 Maximum selectivity for adsorption of CO2 over N2 was observed for the Tb-L MOF. The selectivity factor was determined to be 15.2. In a similar

12


Page 13 of 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


a)

b)

c)

d)

e)

f)

Figure 7. N2 adsorption isotherms at 77 K (red) and CO2 adsorption isotherms at 195 K (blue) for MOFs Tb-L (a), Eu-L (c) and Sm-L (e) from low to atmospheric pressure range. CO2 adsorption isotherms at 273 K (blue) and at 298 K (black) and N2 adsorption isotherm at 273 K (red) for Tb-L (b), Eu-L (d) and Sm-L (f) up to atmospheric pressure.

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 23

manner, the CO2/N2 selectivities for Eu-L and Sm-L MOFs at 0 °C were found to be 14 and 12.3, respectively. One of the early reports on selective CO2 adsorption by a lanthanide MOF, i.e., [Er2(PDA)3] (H2PDA = 1,4-phenylendiacetic acid), showed an uptake of less than 25 cc g-1 of CO2 at atmospheric pressure and 273 K.41 The two isostructural Y-MOF and Sm-MOF based on tris(carboxyphenyl)phosphine oxide, i.e., [Ln2(TPO)2(HCOO)]·(Me2NH2)·(DMF)4·(H2O)6] (H3TPO = tris-(4-carboxylphenyl)phosphineoxide and Ln= Y, Sm), reported by Cao et al.42 were shown to exhibit CO2 uptake of 66.90 and 53.62 cc g-1 at 273 K and 43.44 and 31.76 cc g-1 at 298 K, respectively. Recently, Nayek et al. showed that the Ln-MOF constructed from triazine, i.e., {[La(TATAB)(H2O)]·6H2O} (TATAB = 4,4’,4’’-s-triazine-1,3,5-triyltri-p-aminobenzoate), shows CO2 adsorption capacity of 76.8 and 34.6 cc g−1 at 293 and 298 K respectively.26 The CO2 uptake capacities of Tb-L, Eu-L and Sm-L MOFs at ambient conditions are in the range of the highest uptake values reported for lanthanide MOFs to date.26,27,42 Table 2. Selective CO2 Uptake Capacities of Tb-L, Eu-L and Sm-L at Atmospheric Pressure.

MOF

a

CO2 uptakea at 195 K

CO2 uptakea at 273 K

CO2 vs N2 selectivity CO2 uptakea at 273 K at 298 K

Tb-L

165

67.1

15.2

41.2

Eu-L

148

61.3

14

34.1

Sm-L

138

69.6

12.3

36.5

All the gas uptake values are expressed in cc g-1 at STP.

Luminescence Properties of the MOMs. The diacid H2L was designed, as mentioned at the

outset, to access porous and luminescent MOMs. The luminescence properties of all MOMs and that of the parent acid H2L were evaluated in the solid state. As can be seen from the emission profiles shown in the Figure 8, all MOMs with main group and transition metal ions, i.e., Zn-L, 14


Page 15 of 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


Cd-L, Pb-L and Sr-L, exhibit photoluminescence properties that are similar to the solid-state

emission of the linker H2L. Solid-state emission properties of the lanthanide MOFs were also investigated for excitation at different wavelengths; linker-based emission was observed in all cases, cf. Figures 8e and 9. The emission maxima for all the MOMs were found to be almost superimposable and lie in a narrow range of 422-424 nm. These are blue-shifted relative to that

a)

b)

c)

d)

e)

f)

Figure 8. (a) Solid-state excitation (λem = 500 nm) and emission (λex = 350 nm) spectra of H2L. Similar solid-state excitation (λem = 450 nm) and emission (λex = 340 nm) spectra of Zn-L (b), Cd-L (c), Pb-L (d), and Tb-L (e). (f) Solid-state excitation (λem = 570 nm) and emission (λex = 380 nm) spectra of Sr-L.

of the solid acid H2L for which the emission maximum is observed at 452 nm, cf. Figure 9. Intriguingly, the emission profile of Sr-L is an outlier, which displays a red-shifted emission with respect to the acid H2L. Sr-L exhibits the emission maximum at 465 nm. The reason for observed differences in the emission spectra should be reconciled from subtle changes in 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 23

conformations of the linker in different MOMs and their rigidity. The fact that energy transfer to the lanthanide ions does not occur at all, as is evident from the lack of luminescence from Ln(III) ions, suggests that the metal ions are insulated from bianthryl moieties, which radiatively decay predominantly from their singlet-excited states. Evidently, sensitization from the bianthryl core to Tb does not occur to permit luminescence from the latter.

Figure 9. Solid-state emission spectra of MOMs, viz., Zn-L, Cd-L, Sr-L, Pb-L and Tb-L and the diacid H2L (λex = 350 nm), for comparison. Observe the red shift of emission for Sr-L with respect to H2L, while the emission maxima are blue-shifted in all other cases. CONCLUSIONS

A novel fluorescent diacid linker H2L based on twisted-bianthryl core was designed and its utility was explored for the synthesis of luminescent MOMs. Overall, 12 structurally diverse MOMs were accessed depending on the nature of the metal ions used and reaction conditions employed for the synthesis. The resulting MOMs are polymers of 1D, 2D and 3D types. For example, Zn-L is a 1D polymer, while Cd-L is a 2D structure; in the latter, 4,4'-bipyridine is found to mediate formation of 2D networks by linking 1D metal-carboxylate chains. In contrast to the 2D structure of Pb-L, Sr-L is found to be non-interpenetrated 3D structure of ′rod′ type 16


Page 17 of 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


topology, which is sustained by chloride bridging between the metal centers. The reactions of H2L with the lanthanide ions affords eight isostructural non-interpenetrated 3D MOFs with

crystallographic void volume of ca. 34.0 %. The Ln-MOFs are found to be porous with a high chemical stability to permit gas uptake studies. For Tb-L, Eu-L and Sm-L as the representative MOMs, the CO2 uptake capacities determined fall in the range of the highest uptake values reported for lanthanide MOFs. Additionally, all the MOMs exhibit linker-based luminescence in the solid state. The luminescence and chemical robustness of the Ln-L MOFs should permit opportunities for their exploration as functional materials, e.g., for sensing and heterogeneous catalysis. EXPERIMENTAL SECTION Synthesis of 10,10'-Bis(4-carbomethoxyphenyl)-9,9'-bianthryl. A mixture of toluene (15 mL),

EtOH (10 mL) and water (5 mL) contained in a two-necked round bottom flask was degassed by bubbling N2 for 20 min. Subsequently, the flask was charged with 10,10'-dibromo-9,9'-bianthryl (2.0 g, 3.90 mmol), 4-carbomethoxyphenylboronic acid (2.81 g, 15.6 mmol), K2CO3 (1.6 g, 11.7 mmol) and Pd(PPh3)4 (0.68 g, 0.59 mmol), and the resultant mixture was heated at reflux for 2 d. At the end of this period, toluene and ethanol were removed in vacuo and the reaction mixture was extracted two times with chloroform. The combined organic extract was dried over anhyd Na2SO4 and the solvent was removed in vacuo to obtain the crude product, which was purified by column chromatography to furnish the target compound as a pale yellow solid, yield 1.75 g (72%); mp > 300 °C; IR (solid) cm-1 3060, 2989, 1726, 1606, 1518, 1433, 1360; 1H NMR (CDCl3, 500 MHz) δ 4.07 (s, 6H), 7.17-7.38 (m, 12H), 7.78 (t, J = 5.1 Hz, 8H), 8.39 (d, J = 9.7 Hz, 4H);

13

C NMR (CDCl3, 125 MHz) δ 52.3, 125.6, 125.7, 126.8, 127.1, 129.6, 129.7, 129.8, 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 23

131.2, 131.6, 133.8, 136.6, 144.2, 167.1; ESI-MS+ m/z [M+H]+ Calcd for C44H31O4 623.2222, found 623.2224.

Synthesis of 10,10'-Bis(4-carboxyphenyl)-9,9'-bianthryl. A round-bottom flask was charged

with 10,10'-bis(4-carbomethoxyphenyl)-9,9'-bianthryl (2.23 g, 3.58 mmol), KOH (0.50 g, 8.95 mmol) and 20 mL of 1:1 mixture of THF and water. The contents were heated at reflux for 36 h. At the end of this period, THF was evaporated in vacuo and the reaction mixture was acidified with conc. HCl. The precipitate was filtered, washed thoroughly with water and dried to afford the pure product as a pale yellow solid, yield 1.92 g (90%); mp > 300 °C; IR (solid) cm-1 3449, 3063, 1690, 1607, 1411; 1H NMR (DMSO-d6, 500 MHz) δ 7.09 (d, J = 8.55 Hz, 4H), 7.27-7.30 (m, 4H), 7.43-7.46 (m, 4H), 7.69 (d, J = 8.6 Hz, 4H), 7.79 (d, J = 8.0 Hz, 4H), 8.29 (d, J = 8.55 Hz, 4H);

13

C NMR (DMSO-d6, 125 MHz) δ 126.1, 126.3, 126.4, 126.6, 129.2, 129.7, 130.4,

130.6, 131.5, 132.9, 136.6, 143.0, 167.3. ESI-MS- m/z [M-H]- Calcd for C42H25O4 593.1753, found 593.1759.

Activation of Tb-L, Eu-L and Sm-L MOFs for Gas Adsorption Studies. The lanthanide

MOFs, viz. Tb-L, Eu-L and Sm-L, were activated prior to the gas adsorption studies. For this purpose, the samples were soaked in methanol for two days, subsequently in acetone for another two days and finally in dichloromethane for three days. In each case, the supernatant solvent was replaced with a fresh solvent every day. After seven days, the MOFs were filtered and subjected to solvent evacuation overnight under vacuum at rt. The samples were thermally activated at 70 °C for 2 h under ultrahigh vacuum prior to the gas adsorption studies.

18


Page 19 of 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


Supporting Information Available. Details of synthesis of MOMs and X-ray crystal structure

determinations, crystallographic data in cif format (deposited at the CCDC with the following deposition numbers: 1429333-1429337), solid-state excitation and emission spectra, and 1H, 13C NMR and ESI-MS spectral reproductions of intermediates and the diacid H2L. This material is available free of charge via the Internet at http://pubs.acs.org. The cif files of the X-ray crystal structures can be obtained free of charge from The Cambridge Crystallographic Data Centre via http://www.ccdc.cam.ac.uk/data_request/cif. Acknowledgments. JNM is thankful to SERB, New Delhi for generous funding. SS and SJ are

grateful to CSIR, New Delhi for SPM and senior research fellowship. GS is immensely thankful to IITK for an institute research fellowship. The support from DORD, IITK for gas adsorption setup through CARE funding is gratefully acknowledged.

REFERENCES

1.

Uemura, T.; Yanai, N.; Kitagawa, S. Chem. Soc. Rev. 2009, 38, 1228.

2.

Ma, L.; Abney, C.; Lin, W. Chem. Soc. Rev. 2009, 38, 1248.

3.

Kurmoo, M. Chem. Soc. Rev. 2009, 38, 1353.

4.

Lee, J. Y.; Farha, O. K.; Roberts, J.; Scheidt, K. A.; Nguyen, S. B. T.; Hupp, J. T. Chem. Soc. Rev. 2009, 38, 1450.

5.

Getman, R. B.; Bae, Y.-S.; Wilmer, C. E.; Snurr, R. Q. Chem. Rev. 2012, 112, 703.

6.

Sumida, K.; Rogow, D. L.; Mason, J. A.; McDonald, T. M.; Bloch, E. D.; Herm, Z. R.; Bae, T.-H.; Long, J. R. Chem. Rev. 2012, 112, 724.

7.

Suh, M. P.; Park, H. J.; Prasad, T. K.; Lim, D.-W. Chem. Rev. 2012, 112, 782.

8.

Li, J.-R.; Sculley, J.; Zhou, H.-C. Chem. Rev. 2012, 112, 869. 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

9.

Page 20 of 23

Kreno, L. E.; Leong, K.; Farha, O. K.; Allendorf, M.; Duyne, R. P. V.; Hupp, J. T. Chem. Rev. 2012, 112, 1105.

10.

Yoon, M.; Srirambalaji, R.; Kim, K. Chem. Rev. 2012, 112, 1196.

11.

Liu, D.; Lu, K.; Poon, C.; Lin, W. Inorg. Chem. 2014, 53, 1916.

12.

Lu, W.; Wei, Z.; Gu, Z.-Y.; Liu, T.-F.; Park, J.; Park, J.; Tian, J.; Zhang, M.; Zhang, Q.; Gentle III, T.; Bosch, M.; Zhou, H.-C. Chem. Soc. Rev. 2014, 43, 5561.

13.

Lin, Z.-J.; Lü, J.; Hong, M.; Cao, R. Chem. Soc. Rev. 2014, 43, 5867.

14.

Natarajan, R.; Savitha, G.; Dominiak, P.; Wozniak, K.; Moorthy, J. N. Angew. Chem., Int. Ed. 2005, 44, 2415.

15.

Natarajan, R.; Savitha, G.; Moorthy, J. N. Cryst. Growth Des. 2005, 5, 69.

16.

Moorthy, J. N.; Natarajan, R.; Savitha, G.; Suchpar, A.; Richards, R. M. J. Mol. Struct. 2006, 796, 216.

17.

Seth, S.; Venugopalan, P.; Moorthy, J. N. Chem. -Eur. J. 2015, 21, 2241.

18.

Bajpai, A.; Chandrasekhar, P.; Savitha, G.; Banerjee, R.; Moorthy, J. N. Chem. -Eur. J. 2015, 21, 2759.

19.

Seth, S.; Savitha, G.; Moorthy, J. N. Inorg. Chem. 2015, 54, 6829.

20.

Natarajan, P.; Schmittel, M. J. Org. Chem. 2013, 78, 10383.

21.

Luo, J.; Xu, H.; Liu, Y.; Zhao, Y.; Daemen, L. L.; Brown, C.; Timofeeva, T. V.; Ma, S.; Zhou, H.-C. J. Am. Chem. Soc. 2008, 130, 9626.

22.

Ma, S.; Yuan, D.; Wang, X.-S.; Zhou, H.-C. Inorg. Chem. 2009, 48, 2072.

23.

Roy, S.; Chakraborty, A.; Maji, T. K. Coord. Chem. Rev. 2014, 273-274, 139, and references therein.

20


Page 21 of 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


24.

Eddaoudi, M.; Kim, J.; Rosi, N. L.; Vodak, D.; Wachter, J.; O'Keefe, M.; Yaghi, O. M. Science 2002, 295, 469.

25.

Rosi, N. L.; Eckert, J.; Eddaoudi, M.; Vodak, D. T.; Kim, J.; O'Keeffe, M.; Yaghi, O. M. Science 2003, 300, 1127.

26.

Pal, S.; Bhunia, A.; Jana, P. P.; Dey, S.; Möllmer, J.; Janiak, C.; Nayek, H. P. Chem. Eur. J. 2015, 21, 2789.

27.

Park, Y. K.; Choi, S. B.; Kim, H.; Kim, K.; Won, B.-H.; Choi, K.; Choi, J.-S.; Ahn, W.S.; Won, N.; Kim, S.; Jung, D. H.; Choi, S.-H.; Kim, G.-H.; Cha, S.-S.; Jhon, Y. H.; Yang, J. K.; Kim, J. Angew. Chem., Int. Ed. 2007, 46, 8230.

28.

Spek. A. L. Acta Cryst. 2009, D65, 148.

29.

Meng, M.; Zhong, D.-C.; Lu, T.-B. CrystEngComm 2011, 13, 6794.

30.

Guo, X.-G.; Yang, W.-B.; Wu, X.-Y.; Zhang, Q.-K.; Lin, L.; Yu, R.; Chen, H.-F.; Lu, C.Z. Dalton Trans. 2013, 42, 15106.

31.

Fan, L.; Zhang, X.; Zhang, W.; Ding, Y.; Fan, W.; Sun, L.; Pang, Y.; Zhao, X. Dalton Trans. 2014, 43, 6701.

32.

Li, D.-S.; Zhang, P.; Zhao, J.; Fang, Z.-F.; Du, M.; Zou, K.; Mu, Y.-Q. Cryst. Growth Des. 2012, 12, 1697.

33.

Xu, G.; Lv, J.; Guo, P.; Zhou, Z.; Du, Z.; Xie, Y. CrystEngComm 2013, 15, 4473.

34.

Rosi, N. L.; Kim, J.; Eddaoudi, M.; Chen, B.; O’Keeffe, M.; Yaghi, O. M. J. Am. Chem. Soc. 2005, 127, 1504.

35.

Devic, T.; David, O.; Valls, M.; Marrot, J.; Couty, F.; Férey, G. J. Am. Chem. Soc. 2007, 129, 12614.

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

36.

Page 22 of 23

Bernini, M. C.; Platero-Prats, A. E.; Snejko, N.; Gutiérrez-Puebla, E.; Labrador, A.; SáezPuche, R.; Paz, J. R.; Monge, M. A. CrystEngComm 2012, 14, 5493.

37.

Tang, K.; Yun, R.; Lu, Z.; Du, L.; Zhang, M.; Wang, Q.; Liu, H. Cryst. Growth Des. 2013, 13, 1382.

38.

Li, R.-J.; Li, M.; Zhou, X.-P.; Li, D.; O’Keeffe, M. Chem. Commun. 2014, 50, 4047.

39.

Santra A.; Bharadwaj, P. K. Cryst. Growth Des. 2014, 14, 1476.

40.

Kiritsis, V.; Michaelides, A.; Skoulika, S.; Golhen, S.; Ouahab, L. Inorg. Chem. 1998, 37, 3407.

41.

Pan, L.; Adams, K. M.; Hernandez, H. E.; Wang, X.; Zheng, C.; Hattori, Y.; Kaneko K. J. Am. Chem. Soc. 2003, 125, 3062.

42.

Lin, Z.-J.; Yang, Z.; Liu, T.-F.; Huang, Y.-B.; Cao, R. Inorg. Chem. 2012, 51, 1813.

22


Page 23 of 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


FOR TABLE OF CONTENTS USE ONLY

Diverse Metal-Organic Materials (MOMs) Based on 9,9'-Bianthryl-Dicarboxylic Acid Linker: Luminescence Properties and CO2 Capture

Saona Seth, Govardhan Savitha, Samik Jhulki and Jarugu Narasimha Moorthy*

A fluorescent diacid linker, i.e., 10,10'-bis(4-carboxyphenyl)-9,9'-bianthryl, has been exploited to access a series of structurally diverse luminescent MOMs with different metal ions. Highly robust and porous Ln-MOFs are shown to exhibit CO2 capture properties at ambient conditions with the uptake values comparable to the highest reported.

23


Diverse MetalâOrganic Materials (MOMs) Based on 9,9â²-Bianthryl

Recommend Documents

Diverse MetalâOrganic Materials (MOMs) Based on 9,9â²-Bianthryl