Structural Diversity Observed in Two-dimensional Square Lattice

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Structural diversity observed in 2D square lattice metal-organic frameworks assembled from Zn(II) and 3-(4-pyridyl)benzoate Gift Mehlana, Chad Wilkinson, Christelle N. Dzesse T., Gaelle Ramon, and Susan A. Bourne Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.7b01101 • Publication Date (Web): 23 Oct 2017 Downloaded from http://pubs.acs.org on October 26, 2017

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Crystal Growth & Design

Structural diversity observed in 2D square lattice metal-organic

frameworks

assembled

from

Zn(II) and 3-(4-pyridyl)benzoate Gift Mehlana,ab* Chad Wilkinson,a Christelle N. Dzesse T.,a,c Gaëlle Ramona and Susan A. Bournea

a

Centre for Supramolecular Chemistry Research, Department of Chemistry, University of

Cape Town, Rondebosch 7701, South Africa. b

Department of Chemical Technology, Faculty of Science and Technology, Midlands State

University, Private Bag 9055 Senga Road, Gweru, Zimbabwe. c

Department of Chemistry, University of Buea, Cameroon, PO Box 63, Buea, Cameroon.

KEYWORDS: supramolecular isomers, coordination network, topology, xylene sorption

ABSTRACT

The reaction of 3-(4-pyridyl)benzoate (34pbz) under solvothermal and solvent evaporation conditions produced several 2D square lattice metal-organic frameworks compounds, {[Zn(34pbz)2] .·DMF}n (1),

{[Zn(34pbz)2.] .·DMF}n (2) and

{[Zn(34pbz)2] .·2 DMF

.·CH3OH·. ½ H2O}n (3). Although the frameworks of 1, 2 and 3 have identical elemental composition, these networks differ in the binding mode of the carboxylate moiety to the metal

ACS Paragon Plus Environment

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center. In compound 1 the carboxylate moiety assumes a monodentate binding mode while in 2 and 3 it assumes a chelating binding mode. Compound 1 and 3 crystallize in space group P21/c with different unit cell parameters while compound 2 crystallizes in the tetragonal crystal system. In all three crystal structures, networks are formed by connecting mononuclear Zn(II) units with 34pbz linkers forming a square grid network. The solvent accessible void volumes in 1 (21 %) and 2 (18 %) are comparable while compound 3 has a void volume of 42 %, which is extremely large for a 2D network. Crystals of 2 were activated by heat treatment to give [Zn(34pbz)2]n (2d) which has narrow pores. When exposed to the vapours of xylene isomers, the narrow pores in 2d expanded to accommodate the incoming guest molecules between the 2D layers. Thermogravimetric analysis established that when 2d is exposed to the isomers of xylene, the amount of the xylene adsorbed increases in the order meta- < para- < ortho-xylene, due to the different packing efficiency of the guest molecules in the cavities. Compound 2d shows no discrimination for one species from an equimolar mixture of all three xylenes.

Introduction The study of

metal-organic frameworks (MOFs) has attracted great attention due to their

promising applications in separation,1 sensing,2-4 catalysis, 5 luminescence,6 drug delivery7 and gas storage.8 Aromatic pyridylcarboxylate ligands can bind to metal centers to form frameworks which remain highly porous after evacuating the crystallization solvent molecules.9

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Despite

the great advances in reticular synthesis,15,16 the assembly of specific structures presents a huge challenge to solid state chemists. Generally the factors that influence the resultant frameworks can be grouped into two categories, that is, the reaction conditions and the nature of the reacting components.17 Thus, understanding how these factors influence crystal packing is of paramount


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importance in controlling coordination supramolecular arrays if we want to create materials with open frameworks. The existence of different crystal structures assembled from the same building blocks is termed supramolecular isomerism18-20 and is related to structural isomerism at molecular level. Supramolecular isomerism could be a result of the same molecular components generating different supramolecular synthons and is sometimes compared to polymorphism. These terms should not be used interchangeably however; polymorph is strictly used for a compound, or combination of compounds, which can crystallize in at least two different arrangements with identical connectivity and chemical composition. In the presence of guest molecules in the framework, the term isomerism may be controversial as it is usually used to refer to the framework only.21-23 The majority of the supramolecular isomers reported to date are influenced by the presence of different guest molecules.

24,25

This suggests that the inclusion of different

solvent molecules in the cavities may give rise to different networks. In this contribution, we report the synthesis, crystal structures and characterization of the 2D networks of {[Zn(34pbz)2] .·DMF}n (1), {[Zn(34pbz)2.] .·DMF}n (2) and {[Zn(34pbz)2] .·2 DMF .·CH3OH·. ½ H2O}n (3) which were prepared by solvothermal and solvent evaporation methods. Compound 1 and 2 were obtained concomitantly under the same reaction conditions. Compound 2 and 3 were isolated using the same reaction conditions but in different reaction vessels at room temperature. All three compounds have networks composed of the same building blocks but, while 1 and 2 have identical guest compositions, 3 includes a mixture of guests into a larger solvent-accessible void space. supramolecular isomers,

21

These compounds comprise a class of structural

whose different topologies can be ascribed to the influences of

solvent and temperature in their preparation. The sorption properties of the activated phase of 2


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towards xylenes were evaluated. Xylenes have similar boiling points which makes them difficult to separate by conventional methods. Experimental Section All materials were purchased from commercial sources and were used without further purification. All solvents used were dried over molecular sieves Preparation of compounds 1, 2, 3, 2d, 2d-ox, 2d-px and 2d-mx: The successful synthesis of compounds 1-3 is illustrated in scheme 1.

Scheme 1: Synthesis of 1-3. a.rtp refers to the first experiment carried out at room temperature while b.rtp refers to the repeat of the first experiment. 44bda is 4,4’-biphenyldicarboxylic acid.

Table S1 gives the experimental conditions that lead to the isolation of 1 and 2. In the first experiment carried out at room temperature , Zn(NO3)2.6H2O (290 mg, 1 mmol) was dissolved in 4 cm3 of DMF and 80 mg (0.4 mmol) of 3-(4-pyridyl)benzoic acid was dissolved in 4 cm3 of


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DMF. The two solutions were combined in a large vial. The solution was left to evaporate at room temperature. Colorless crystals were formed after two weeks. Two crystal forms were identified based on their morphology (Figure 1). The first reaction batch (a.rtp ) produced compound 1 as the dominant phase which was confirmed by PXRD studies, shown in Figure 2. Repeating the experiment (b.rtp) under the same conditions produced compound 2 as the dominant phase. Further experiments produced mixtures with 2 as the chief phase. Despite adjusting the reaction conditions, we were unable to produce 1 alone.

Figure 1: Left: crystals of 1; right: a single crystal of 2 In Figure 2, the PXRD of the first experiment (a.rtp) shows that compound 1 was the dominant phase as it matches well with the calculated pattern from its single crystal structure. The slight offset observed in the 2θ positions of the peaks is ascribed to the different temperatures at which the experiments (PXRD and single crystal X-ray data collection) were conducted. Repeating the first experiment (b.rtp) gave rise to the formation of compound 2 as the dominant phase. The PXRD of both a.rtp and b.rtp show diffraction peaks from both compound 1 and 2.


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Figure 2: PXRD patterns of experiments detailed in scheme 1. Quantitative Rietveld refinement was carried out on the PXRD outcome of experiment b.rtp (Details for this refinement are described later in the experimental section). Results obtained show that 13% of the mixture was compound 1, while the remaining phase compound 2 was 87%. The result for this analysis is given in Figure S1. Rietveld refinement was not performed on the PXRD outcome of experiment first (a.rtp) experiment because of the poor quality of the pattern. Compound 2 was formed as a pure product by carrying out the synthesis at 80 °C in an oven. The product of this reaction was formed within two days. A comparison of the experimental and calculated PXRD patterns (Figure 2) shows that the bulk material formed at 80°C is exclusively


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2. Hence, the solvothermal reaction was used for the preparation of 2 for further studies. Compound 2d was prepared by activating crystals of 2 at 200 °C under vacuum for 24 hrs. We have previously reported the structures of 2 and 2d.26 Their CSD refcodes are ROCYIT and ROCYOZ respectively. The activated crystals, 2d, were then exposed to vapours of o-xylene, mxylene, and p-xylene to give compound 2d-ox, 2d-mx and 2d-px respectively. While single crystal structures of 2d-ox and 2d-px could be obtained, crystals of 2d-mx diffracted poorly which prevented its full characterization by single crystal X-ray diffraction. In a different reaction setup, we used 4,4ʹ-biphenyldicarboxylic acid as a secondary ligand. We anticipated that the ligand would coordinate and give a mixed ligand MOF. Instead, crystals of compound 3 {[Zn(34pbz)2]·2DMF·CH3OH·0.5H2O}n were obtained. 3 was prepared by dissolving each of 3-(4-pyridyl)benzoic acid (80 mg, 0.40 mmol) and 4,4ʹ-biphenyldicarboxylic acid (20 mg, 0.083 mmol) in 3ml DMF. 30 mg (0.10 mmol) of zinc nitrate hexahydrate was dissolved in 3ml of methanol. The three solutions were combined and the solvents allowed to evaporate at room temperature. Colourless crystals were formed after one week. Unfortunately, insufficient material precluded PXRD studies to confirm the phase purity of the reaction outcome. Repeating the same experiment under the same conditions gave rise to the formation of 2. These results show how difficult it is to control the outcome of the products formed at room temperature. This may be attributed to the fluctuations of the laboratory temperatures as crystal formation is very sensitive to slight changes in the reaction conditions.17 Thermal analysis: Thermogravimetric analysis was carried out using a TA Instrument TA-Q500 instrument. In a typical experiment 1-5 mg of the sample was dried on filter paper, placed in an open aluminium pan and heated in a dry air atmosphere of nitrogen (50 ml.min-1) at a heating rate of 10 oC.min-1 over the temperature range of 25 - 600 oC.


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Powder X-ray Diffraction: Powder diffraction patterns were measured on a Bruker D8 Advance X-ray diffractometer operating in a DaVinci geometry equipped with a Lynxeye detector using a Cu Kα-radiation (λ = 1.5406 Å). X-rays were generated by an accelerating voltage of 30 kV and a current of 40 mA. A receiving slit of 0.6 mm and a primary and secondary slits of 2.5 mm were used. Samples were placed on a zero background sample holder and scanned over a range of 4° to 40° in 2θ with a step size of 0.01° per second. Pawley fitting: Pawley fitting was performed in TOPAS,27 the crystallographic data of the compound under study was inserted in the phase details section and allowed to refine. Profile fitting was done using the PV-TCHZ pseudo-Voigt function included in the peak picking routine in TOPAS. In order to account for significant profile shape distortion the absorption parameter was set to refine. The unit cell parameters were validated by profile matching using the hkl-phase refinement in TOPAS over a two theta range of 4 - 40°. The 4th order Chebychev function was used to model the background. Single crystal X-ray diffraction analysis: Structure determination was performed by single crystal X-ray diffraction using a Bruker KAPPA APEX II DUO diffractometer equipped with a graphite monochoromated Mo-Kα radiation. (λ =0.71073 Å). Data collections were performed at 173 K. The program SAINT28 was used for unit cell refinement and data reduction. Data were corrected for Lorentz-polarization effects and for absorption (program SADABS).29 Structure solutions were achieved by direct methods (program SHELXS)30 and refined by full-matrix least-squares on F2 using SHELXL30 within the X-SEED31 interface. The non-hydrogen atoms were located in the difference electron density maps and were refined anisotropically while all the hydrogen atoms were placed with geometric constraints and refined with isotropic temperature factors. The carbon atoms of the xylene molecules were refined isotropically due to


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their large thermal displacement parameters. The crystallographic data are given in Table 1. The material concerning the structures (CIF files) is available free of charge via the Internet at http://pubs.acs.org. The structures were deposited at the Cambridge Crystallographic Data Centre and allocated the numbers: CCDC 1474686-1474689. Topological analysis The network topology of compound 1, 2 and 3 were analysed using TOPOS32 and checked against the Reticular Chemistry Structural Resource (RSCR).33 The calculated point symbol and vertex

symbol

for

these

compounds

were

found

to

be

424.64

and

[4.4.4.4.4.4.4.4.4.4.4.4.43.43.43.*.*.*] respectively. The topological density value (TD 10) was found to be 221. Results and discussion Crystal structure and characterization of 1 Compound 1 is very similar to the related structure reported by Niu et al34 but differs in the guest type (water in that case) and β angle. 1 crystallizes in a monoclinic crystal system within the space group P21/c. The asymmetric unit comprises of one Zn(II) center, two deprotonated 34pbz ligands and one uncoordinated DMF molecule. The carboxylate moiety assumes the monodentate binding mode. The Zn(II) ion is coordinated to two nitrogen atoms of adjacent pyridyl rings and two carboxylate oxygen atoms to furnish a distorted tetrahedral geometry as displayed in Figure 3. Four 34pbz linkers bridge four Zn(II) ions to form a grid net. Linker A separates two zinc centers by 9.146 Å and linker B separates two metal centers by 11.652 Å. The difference in the distance of separation is attributed to the coordination modes assumed by the


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ligands. Linker A connects two Zn(II) ions via the near oxygen atom of the carboxylate group to the pyridyl nitrogen atom and B via the far oxygen atom.


10

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Table 1: Crystallographic data and refinement parameters 1

2d-ox

2d-px

{[Zn(34pba)2]·DMF}n

{[Zn(34pba)2]·0.4C8H10}n

{[Zn(34pba)2]·0.7C8H10}n

3

Molecular Mass

534.85

504.24

536.09

{[Zn(34pba)2]·2DMF·CH3O H·0.5H2O}n 649.02

Crystal Size (mm)3 Temp. Of collection /K Crystal symmetry

0.2 x 0.25 x 0.33

0.22 x 0.23 x 0.24

0.18 x 0.19 x 0.21

0.18 x 0.20 x 0.22

173(2)

173(2)

173(3)

173(2)

monoclinic

tetragonal

tetragonal

monoclinic

Empirical Formula

Space group

P21/c

P43212

P43212

P21/c

a (Å)

11.652(2)

11.6770(17)

11.6526(4)

15.1445(16)

b ( Å)

19.788(4)

11.6770(17)

11.6526(4)

15.0845(17)

c (Å)

10.715(2)

37.438(8)

37.559(3)

14.3663(14)

β (°)

90.03(3)

90

90

106.646(3)

Z

4

8

8

4

3

2470.7(8)

5104.8(18)

5099.8(5)

3144.40

-3

Dc / g cm

1.438

1.3212

1.396

1.3708

F(000)

1104

2074

2213

1352

2θ (°) range No. of reflections collected No. Unique reflections No. Reflections with I> 2σI Goodness of fit, S

2.03-27.49

2.39-27.12

1.83-28.40

1.95-28.34

9893

66329

69526

37716

5503

5578

6382

7821

2952

3702

5850

5500

1.016

1.033

1.147

1.059

R (I> 2σI)

0.0673

0.0642

0.0755

0.0675

Final wR2 (all data)

0.1722

0.1789

0.1976

0.2217

Volume Å

Min, Max e density / -0.59, 0.86 -0.44, 0.63 -0.97, 0.70 -0.67, 1.55 e 26 Compounds 2 and 2d were published previously and are in the CSD as refcodes ROCYIT and ROCYOZ. Both crystallize in the tetragonal crystal system and chiral space group P43212. For 2, a(Å) = 11.5631 and c(Å) = 37. 3168. For the activated phase of 2, 2d, the unit cell parameters were 11.5806 Å and 34. 904 Å for a and c respectively.

.


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Figure3: Coordination environment of the Zn(II) ion in compound 1. Symmetry Related: i-x, y-1/2, ½-z; iix+1, y, z; iiix-1, y, z; iv-x, ½+y, ½-z.

The Zn-O bond distances are 1.970(3) Å and 1.944(3) Å while the Zn–N bond distances are 2.024(4) Å and 2.068(4) Å. A comparison of the bond lengths of 1 and the structure by Niu are given in Table S2. The dihedral angles between the pyridyl and the phenyl ring are 13.6° and 28.0° for the two 34pbz linkers modelled in the asymmetric unit. In both cases, the monodentate carboxylate moiety is almost coplanar with the phenyl ring. The structure is stabilized by weak hydrogen bonds between the 2D layers (Table S3) and π···π interactions of the aromatic rings. A distance of 3.728 Å between the DMF molecules and the framework rings suggest the presence of C-H···π interactions. The packing diagram of 1 depicts 2D interdigited layers with guest molecules residing in the channels. Interestingly the overall structure is 3D with channels running along the c-axis. The change in dimensionality from 2D to 3D arises as a result of the type of interdigitation present in


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this network. A single 2D network interdigitates two adjacent 2D layers, one below and one above as shown in Figure 4a and b. This type of entanglement is rare for 2D networks. In reported cases, high dimensionality is observed as result of parallel or inclined interpenetration of 2D networks with square lattice (sql) topology.35

Figure 4: Packing diagram of compound 1. (a) Viewed along the b-axis and (b) along the c-axis, (c) and (d) intersecting channels depicted in grey. The solvent accessible void volume (i.e. the solvent-excluded or contact space) in 1 was estimated in the program Mercury36 using a probe radius of 1.2Å and grid spacing of 0.7 Å and was found to be 21% of the unit cell volume. This volume is occupied by the DMF molecules. Analysis of the cavities occupied by the DMF molecules using Mercury shows that they are intersecting as illustrated in Figure 4c and d.


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Thermal analysis of 1 could not be performed as the material could not be produced as a pure phase in bulk using our experimental conditions. Crystal structures and characterization of 2d-ox and 2d-px We previously reported compound 2, 2d and its cobalt analogue.26,37 Crystals of 2 and 2d were found to crystallize in the tetragonal crystal system and space group P43212. Both 2 and 2d have the same 2D networks. The geometry around the Zn(II) is distorted octahedral as a result of the chelating binding mode of two carboxylate groups and two nitrogen atoms from 34pbz linkers. Figure S2 illustrates the geometry around the Zn(II) ion in 2 and 2d. Compound 2 has four crystallographically independent channels, which together comprise 18% of the volume of the unit cell (calculated in Mercury36). Compound 2d-ox and 2d-px were obtained after exposing 2d to vapours of ortho- and para-xylene respectively. The crystals retain the characteristics of 2d and belong to the tetragonal crystal system and chiral space group P43212. In each of the asymmetric units of 2d-ox and 2d-px, two fully deprotonated 34pbz linkers and one Zn(II) ion were modeled. The guest ortho-xylene in 2d-ox was modeled with 80% site occupancy and the para-xylene in 2d-px with an occupancy of 70%. We noted that the carbon atoms of these guest molecules have high temperature factors which may be attributed to unresolved solvent disorder. In both 2d-ox and 2d-px , the adjacent carboxylate moieties are chelating and monodentately bound and the geometry around the metal centre in each of these compounds is trigonal bipyramidal (Figure 5a), indicating that there is a change in coordination mode in order to accommodate the solvent. The Zn - O bond distance in 2d-ox is within the range of 1.982(5) Å to 2.476(5) Å, while the two Zn - N bond distances are 2.079(6) Å and 2.081(7) Å. For 2d-px, the Zn-O bond distance are very similar to those of 2d-ox ranging from 1.985 (5) Å to 2.480(6) Å. The Zn-N bond distances are slightly shorter than those in 2d-ox (2.075(5) Å and 2.058(7) Å). In


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2d-px, the two linkers adopt the same conformation as those in 2d-ox as evidenced by similar torsional angles between the phenyl and pyridyl rings (comparable torsions are 8.9° and 36.2° in 2d-ox, and 10.9° and 33.1° in 2d-px). The overall structure in these two compounds is a 2D grid network in which the guest xylenes are sandwiched between the layers (Figure 5b).

Figure 5: (a) Coordination environment around the Zn(II) ion illustrated for 2d-ox. The metal ion is coordinated to three oxygen atoms and two nitrogen atoms. (b) The packing diagram displaying interdigited 2D layers in which the guest ortho-xylene molecules are trapped. The framework is shown in stick form while the guest is drawn with van der Waals radii. (c) and (d) packing diagram of the 2D network viewed along the b- and a- axis respectively.


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Figure 5b-d illustrates the packing observed in compound 2d-ox (that of 2d-px is similar). In both compounds the xylene molecules are involved in CH···π and face to face π···π interactions with the host framework. The guest molecules pack in a tail to tail fashion as illustrated in Figure 6. The crystal structure of 2d-mx could not be determined due to poor diffraction by the crystals.

Figure 6: Packing diagram of the guest xylene molecules in (a) 2d-px and (b) 2d-ox. Crystal structure and characterization of 3 Compound 3 crystallizes in the monoclinic crystal system and space group P21/c. In the asymmetric unit, we modeled two 34pbz linkers, one Zn(II) ion, two uncoordinated DMF molecules, one methanol molecule and a water molecule with 50% site occupancy. The metal ion is coordinated to four oxygen atoms and two nitrogen atoms of the linker to furnish a distorted octahedral geometry as displayed in Figure 7a. The Zn-O bond distances range from 1.991(3) to 2.507(3) Å while the Zn-N are 2.088(3) and 2.086(3) Å. The bond angles around the metal ion are within the range of 57.39(10)° to 155.88(11)°. Four 34pbz linkers bridges four Zn(II) ions to give a 2D network. The adjacent networks of 3 are involved in weak hydrogen bonding interactions with each other. These interactions are within the range of 3.113(5)-


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3.421(5) Å. Adjacent 2D networks are pairwise stacked and are involved in face to face π···π interactions with each other. The pairwise stacked nets are also interdigitated with another set of 2 networks. Figure 7b, c and d illustrates the packing diagrams of compound 3.

Figure 7: (a) Coordination environment around the Zn(II) ion in compound 3. The Zn1- O15B bond length (2.507 Å) is significantly longer than the other bonds; this has been observed in other zinc systems.38 (b) The packing diagram showing π···π interactions on pairwise stacked and interdigitated 2D networks. (c) and (d) packing diagrams viewed along the b and c- axes respectively. Hydrogen atoms and guest molecules omitted for clarity. The packing diagram of compound 3 shows the presence of intersecting channels occupied by the solvent molecules (Figure 8). These channels constitute 42% of the unit cell volume as estimated in Mercury36 which is remarkably high compared to other 2D systems that we have


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reported so far. 4,12, 26,37 Interestingly, the size of the windows of the channels perfectly match the size of the 4,4ʹ-biphenyldicarboxylic acid that was used in the synthesis. This may suggest that the organic compound may have played a role in templating the channels occupied by the solvent molecules (Figure 8.c). The DMF molecules in the channels are pairwise stacked with an interplanar distances of 3.558 Å. These DMF molecules are involved in weak hydrogen bonding with the framework through the C-H···O interactions with geometric parameters in the range of 3.265(8) to 3.469(7) Å. The guest methanol and DMF molecules are involved in hydrogen bonding interactions.

Figure 8: (a) Framework of compound 3. The guest DMF, methanol and water molecules have been omitted. (b) The hydrogen bonded guest network of DMF, methanol and water molecules drawn with the van der Waals radii found in the channels of 3. (c) The windows of the channels found in 3 as viewed along the a-axis (d) channels along the b-axis


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Compound 3 is not stable at room temperature as evidenced by the rapid loss of the guest methanol, water and DMF molecules over a temperature range of 20 to 93 °C (Figure S3 and Table S4). In the asymmetric unit of 3 we modeled a total of 28.85% guest content which is higher than the observed mass loss (25.9%). The difference between the observed and calculated values corresponds to ca. one water molecule or equivalent and could therefore arise from imperfect modelling of the electron density within the channels of 3. It is also possible that the presence of large intersecting channels in 3 would allow for the easy escape of the guest molecules, and that crystals from the same reaction vessel may have slightly different guest content, so that the crystal selected for single crystal X-ray diffraction has higher solvent content than the bulk.39 Different heating rates were used in an attempt to resolve the loss of different guest molecules in 3. However, there were no distinct mass losses for the three types of guest molecules in the TGA which may be attributed to the hydrogen bonding interactions between the guest molecules. Structural comparison of 1, 2 and 3 It is important to describe the relationships of the three main structures presented here in terms of widely accepted terminology. Compounds 1 and 2 crystallized concomitantly and have the same elemental composition in terms of the framework and guest content but differ in their coordination patterns. These can be regarded as structural supramolecular isomers. 2 and 3 have the same coordination patterns around the metal center and are appropriately called supramolecular isomers although they differ in the guest content found in the cavities. The networks of 2 and 3 can be considered to be supramolecular linkage isomers of 1. This is because in 1 the carboxylate moiety uses one oxygen atom to bind to the metal while in 2 and 3 both oxygen atoms binds in a chelating fashion.


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Compound 2 is the most stable compound of the three isomers. This notion is supported by energy profile of the 34pbz ligand which was calculated using Density Functional Theory by Zhou et al.11 In their paper, 34pbz ligand exhibits two stable conformation with torsion angles of +35.8°

and

-35.8° between the phenyl and pyridyl ring which are separated by an energy barrier of 6.3 kJ·mol-1. The torsion angles in compound 1 are 13.6° and 28.0° while for compound 2, these angles are 27.3° and 39.6°. The torsion angles in 2 may suggest a low potential energy profile as they are close to those reported for the stable conformation. In compound 3, the 34pbz torsional angles are 23.6° and 28.6° which may suggest that it has a higher potential energy than 2. The network connectivity in 2 and 3 is the same. However, the guest content in these two compounds is not identical. It would seem reasonable that the variable guest content in these two compounds gave rise to different crystal packing observed. One notable difference between these compounds is that the Zn-O bond distances in 3 are generally longer than those found in 2. This may suggest that bonding interactions in 2 are stronger than in 3 and thus there is greater stability for 2. Although factors such as the nature of interactions between the guest and host, bond angles as well as Zn- donor atom bond length contribute to the overall energy of a compound, based on the computational data provided by Zhou et al it would seem reasonable to say that compound 2 is the most stable of the three isomers. This concurs well with our experimental observations in which compound 2 crystallized out predominantly under different conditions, including at high temperatures, which further suggests that it may be the thermodynamic product. The differences in the binding mode of the carboxylate, the linker conformation and the position of the guest DMF molecules in the network gave rise to the different packing arrangements observed. During the crystallization process the guest location is influenced by the reaction


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temperature and the linker conformation (Figure 9). In compound 1, the guest DMF molecule is located far away from the phenyl ring of the framework with a distance of approximately 4.003 Å. The nitrogen atom of the DMF is not directly above the centre of the phenyl ring but it is in an offset position. This position minimizes possible charge interactions of the host and guest molecules. This is not the case with 2 in which the DMF molecule is positioned directly on top of the phenyl ring. The DMF is located at a distance of 3.621 Å from the phenyl ring with its nitrogen atom centered directly above the phenyl ring. This distance suggests some intermolecular charge interactions between these two groups which might give some stability in the compound.

Figure 9: Position of the DMF in (a) 1 and (b) 2 relative to the phenyl ring

Topological analysis All of compounds 1, 2, and 3 have a 4-connected net with an sql topology. The difference in the network packing was revealed by topological analysis. Although they have the same grid network (Figure S4), the nets differ in their packing as illustrated in Figure 10.


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Figure 10: Topological representation of the nets found in (a) compound 1, (b) compound 2 and its related structures, and (c) compound 3 Unlike the usual square grids assembled from linear bridging linkers and metal centers in the square planar coordination geometry, a zig-zag 2D single layered network parallel to the ab crystallographic plane is obtained for compound 1. For compound 3, the 2D nets are packed in an offset fashion with a distance of approximately 7.8 Å between the layers. Compound 2 and its related structures pack in an offset ABAB fashion. The different packing exhibited by these nets is attributed to the arrangement the guest molecules in the framework, linker conformation and the binding mode. Vapour sorption of xylenes by 2d Powdered samples of 2d were exposed to xylene vapours under controlled conditions. In a typical experiment 2d was placed in small open vials. The small vials containing the activated samples were then placed in large vials containing the respective dry solvents (xylenes). The large vials were capped and sealed tightly before being left at room temperature for 24 hours in a closed desiccator.


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PXRD traces of 2d-ox, 2d-mx, and 2d-px show subtle differences but are very similar to one another and to the traces of 2 and 2d (Figure S5). The thermal stability 2d, 2d-ox, 2d-mx, and 2d-px were investigated by TGA (Figure S3 and Table S4). Thermal analysis of 2d is featureless until decomposition which indicates that activation of compound 2 by heating successfully removes all solvent. TG of 2d-ox, 2d-mx and 2d-px indicates uptake of, respectively, 16.5, 9.9, and 13.6% of xylene. These values correspond to 0.8, 0.5 and 0.7 molecules of ortho, meta, or para-xylene per formula unit of [Zn(34pbz)2]. The uptake of the xylene molecules by the 2d was repeated several times and the TGA results were reproducible. These values were used to model the site occupancies of xylene molecules in the crystal structures of 2d-ox and 2d-px. The trend in occupation of the void space in 2d is mx < px < ox. The same trend was observed for adsorption of xylenes by a Werner clathrate.40 Those authors suggested that differences in packing efficiency of the guest molecules within cavities could account for this trend. That argument is supported by the densities of the two single crystal structures we have obtained in our series, viz. 1.423 and 1.396 g cm-3 for 2d-ox and 2d-px respectively. We noted in our previous studies that crystals of 2 shrink upon evacuation of DMF in the cavities to give a form with narrow pores (2d). We have now shown that 2d adsorbs all isomers of xylene when subjected to their vapours. In the cases of ortho- and para-xylenes, the process appears to be a single crystal to single crystal inclusion yielding compounds 2d-ox and 2d-px. Single crystal X-ray diffraction studies showed that sorption of o-xylene or p-xylene results in concomitant cleavage of the Zn-O bond and change in the linker conformation. Torsion angle analysis revealed the dynamic motion of the linkers (Table 2) upon uptake of the xylenes. Linker A (C3A-C4A-C7A-C8A) modeled in the asymmetric unit rotates by ca. 33° about the C-C bond


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while linker B (C3B-C4B-C7B-8B) rotates by ca. 12° upon inclusion of o-xylene. The degree the linker rotation upon sorption of p-xylene in the 2d network is also comparable to those observed on uptake of o-xylene (Table 2). Table 2: Parameters for the linker motion upon the uptake of xylenes by 2d

Compound 2d 2d-ox 2d-px

Linker A C3A-C4AC7A-C8A (°) 42.2 8.9 10.9

Degree of rotation relative to 2d (°) 33.3 31.3

Linker B C3B-C4BC7B-8B(°) 48.2 36.2 33.1

Degree of rotation relative to 2d(°) 12.0 15.1

Interestingly, linker B which exhibits the lower degree of rotation switches its binding mode from chelating to monodentate. Although the rotation of the linker induces some strain in the network, which can be relieved through breaking one of the Zn-O bond, this is clearly not the only factor involved in the change of coordination about the Zinc ion. The adsorption of mxylene resulted in poor diffraction by the crystals which thwarted the full study of this compound by single crystal X-ray diffraction. However, we were able to determine the unit cell parameters of 2d-mx using Pawley refinement of the PXRD pattern. Table 3 lists the crystallographic parameters of the 2, 2d, 2d-ox, 2d-mx and 2d-px, all determined from PXRD data to allow direct comparison (Figures S6-S8).

Table 3: Unit Cell parameters from Pawley fitting 2 2d 2d-px a (Å) 11.58 (9) 11.565(3) 11.6051(36) c (Å) 37.786(3) 35.632(7) 37.352(11) 3 V (Å) 5066.7(9) 4765.4(2) 5030(35) ∆V (relative to 2d) (%) 5.6

2d-mx 11.6343(33) 36.977(10) 5005(32)

2d-ox 11.6257(15) 37.2717 (49) 5037.5(15)

5.0

5.7


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The unit cell parameters of the xylene inclusion compounds are very similar although the TGA studies showed different amount of guest uptake. Adsorption of the para- and ortho-xylene in the 2D network is accompanied by an increase in the unit cell volume by 5.6% relative to the activated phase for both compounds. A similar effect was also observed when the same system was exposed to primary alcohols.26 The most interesting feature of this compound is that it is able to respond to guest molecules although it does not have enough space (in its contracted form) to accommodate the incoming molecules. There is an increase in the size of the cavities from the closed form to the open form upon uptake of the xylenes (Figure 11). This phenomenon has been observed in other systems.

41,42,43

Each cavity depicted in grey is occupied by two

xylene molecules which pack in an tail to tail fashion.

Figure 11: An illustration (for 2d-ox) on how the cavities change size upon absorption of the ortho-xylene by the activated phase. An attempt was made to evaluate the selectivity of 2d with respect to xylenes, by exposing an activated sample of 2d to a 1:1:1 (by volume) mixture of o-, m-, and p-xylene for 24 hours at room temperature. TGA and PXRD of the resulting material (2d-omp) indicated that 0.6 xylene molecules had been absorbed (per [Zn(34pbz)2] formula unit), and that the phase obtained is similar to those of the individual xylene structures (see Figures S5 and S9). 2d-omp was soaked in d6-DMSO and stirred for 24 hours after which the milky phase obtained was filtered and


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analysed by proton NMR spectrometry (Figure S10). The ratio of isomers was found to be o:m:p = 31.5 : 36.9 : 31.5. Thus 2d is unselective toward the xylene isomers. Conclusions Three supramolecular isomers based 3-(4-pyridyl)benzoate and Zn(II) were obtained and characterized. All three compounds form polymeric two-dimensional structures, but the Zn(II) cation is 4-coordinate in 1 and 6-coordinate in 2 and 3. Crystal structure analysis of 1 and 2 suggests that the different packing arrangements observed can be attributed to the location of the guest DMF molecules in the cavities. The guest location may influence the linker conformation via weak interactions, which in turn affects the binding mode of the carboxylate moiety. Hence, compound 1 and 2 have been referred to as structural supramolecular isomers. The role played by the guest location in inducing these different structures is a feature which has not previously been reported to our knowledge. For compounds 2 and 3 the isomerism is driven by the nature of the guest molecules in the cavities as has often been observed. Using DFT data published by Zhou et al,11 we have rationalised that the higher energetic synthesis conditions used for compound 2 favour the formation of this stable phase, which is reflected both in the linker conformations as well as in the Zn-donor atom bond lengths. We have also demonstrated experimentally that the activated phase of compound 2 readily absorbed xylene vapors which is accompanied by concomitant cleavage of the metal to oxygen bond. Its behavior towards the xylene and alcohol26 molecules makes compound 2 a suitable material for the sorption of volatile organic compounds.


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ASSOCIATED CONTENT Supporting Information. Crystallographic data, thermal analysis, PXRD and Rietveld refinement, and NMR data is available free of charge via the Internet at http://pubs.acs.org. (see separate document) AUTHOR INFORMATION Corresponding Author Email: [email protected] Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. ‡These authors contributed equally. GM, CW and CD carried out the experimental work while SAB and GR advised and guided on the aspects of the project. GM wrote the first draft of the manuscript which was then reviewed by SAB and GR. Funding Sources The authors would like to thank the South African National Research Foundation (grant 90495) for funding. Gift Mehlana would like to thank the University of Cape Town and the International Center for Diffraction Data for the financial support he received in 2014. ABBREVIATIONS 34pbz: 3-(4-pyridyl)benzoate, DMF: dimethylformamide, DSC: Differential Scanning Calorimetry, TGA: Thermogravimetric analyses, HSM: Hot Stage Microscopy, PXRD: Power X-ray Diffraction, MOF: metal-organic frameworks


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REFERENCES (1)

Saint Remi, J. C.; Rémy, T.; Van Hunskerken, V.; van de Perre, S.; Duerinck, T.; Maes, M.; De Vos, D.; Gobechiya, E.; Kirschhock, C. E. A; Baron, G. V; Denayer, J. F. M. ChemSusChem 2011, 4, 1074.

(2)

Wen, T.; Zhang, D.-X.; Liu, J.; Lin, R.; Zhang, J. Chem. Commun. 2013, 49, 5660.

(3)

Mehlana, G.; Wilkinson, C.; Ramon, G.; Bourne, S.A. Polyhedron 2015, 98, 224.

(4)

Mehlana, G.; Chitsa, V.; Mugadza, T. RSC Adv. 2015, 5, 88218.

(5)

Llabresixamena, F.; Casanova, O.; Galiassotailleur, R.; Garcia, H.; Corma, A. J. Catal. 2008, 255, 220.

(6)

Dias, H. V. R.; Diyabalanage, H. V. K.; Rawashdeh-Omary, M. a; Franzman, M. A; Omary, M. A. J. Am. Chem. Soc. 2003, 125, 12072.

(7)

Shekhah, O.; Wang, H.; Paradinas, M.; Ocal, C.; Schüpbach, B.; Terfort, A.; Zacher, D.; Fischer, R. A.; Wöll, C. Nature materials. 2009, 481.

(8)

Xue, M.; Ma, S.; Jin, Z.; Schaffino, R. M.; Zhu, G.-S.; Lobkovsky, E. B.; Qiu, S.-L.; Chen, B. Inorg. Chem. 2008, 47, 6825.

(9)

Zhou, H.; Li, M.; Li, D.; Zhang, J.; Chen, X. Sci. China Chem. 2014, 57, 1.

(10)

Zeng, M.-H.; Tan, Y.; He, Y.; Yin, Z.; Chen, Q.; Kurmoo, M. Inorg. Chem. 2013, 52, 2353.

(11)

Zhou, H.-L.; Lin, R.-B.; He, C.-T.; Zhang, Y.-B.; Feng, N.; Wang, Q.; Deng, F.; Zhang, J.-P.; Chen, X.-M. Nat. Commun. 2013, 4, 2534.

(12)

Mehlana, G.; Ramon, G.; Bourne, S. A. Zeitschrift für Krist. - Cryst. Mater. 2013, 228, 318.

(13)

Mehlana, G.; Ramon, G.; Bourne, S. A. CrystEngComm 2013, 15, 9521.

(14)

Mehlana, G.; Ramon, G.; Bourne, S. A. Microporous Mesoporous Mater. 2016, 231, 21.

(15)

Ockwig, N. W.; Delgado-Friedrichs, O.; O’Keeffe, M.; Yaghi, O. M. Acc. Chem. Res. 2005, 38, 176.

(16)

Garibay, S. J.; Cohen, S. M. Chem. Commun.. 2010, 46, 7700.

(17)

Bernini, M. C.; De La PeñO’Shea, V. A.; Iglesias, M.; Snejko, N.; Gutierrez-Puebla, E.; Brusau, E. V.; Narda, G. E.; Illas, F.; Monge, M. Á. Inorg. Chem. 2010, 49, 5063.

(18)

Moulton, B.; Zaworotko, M. J. Chem. Rev 2001, 101, 1629.

(19)

Braga, D.; Grepioni, F.; Maini, L. Chem. Commun. 2010, 46, 6232.

(20)

Bourne, S. A. In Supramolecular Chemistry: From Molecules to Nanomaterials; Gale, P. A., Steed, J. W., Eds.; John Wiley & Sons, Ltd, U.K, 2012; Vol. 6, pp 3121−3132.

(21)

Zhang, J.-P.; Huang, X.-C.; Chen, X.-M. Chem. Soc. Rev. 2009, 38, 2385.

(22)

Liang, J.; Wu, B.; Jia, C.; Yang, X.-J. CrystEngComm 2009, 11, 975.

(23)

Makal, T. A.; Yakovenko, A. A.; Zhou, H. J. Phys. Chem. Lett. 2011, 2, 1682.

(24)

du Plessis, M.; Barbour, L. J. Dalton Trans. 2012, 41, 3895.


28

Page 29 of 30

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


(25)

Dong, W.; Li, D.; Zhao, J.; Wu, Y.; Duan, P. CrystEngComm 2013,15, 5412.

(26)

Mehlana, G.; Bourne, S. A.; Ramon, G.; Bourne, S. A. CrystEngComm 2014, 16, 8160.

(27)

Coelho,A.A. TOPAS-Academic, version 4.1 (Computer software),Coelho Software, Brisbane, 2007.

(28)

SAINT, Version 7.60a; Bruker AXS Inc: Madison, WI, USA, 2006.

(29)

Sheldrick, G. M. SADABS, Version 2.05; 2007

(30)

Sheldrick, G. M. Acta Crystallogr. A. 2008, 64, 112–122.

(31)

Barbour, L. J. J. Supramol. Chem. 2003, 1, 189–191.

(32)

Blatov, V. A.; Peaskov, V. Acta Crystallogr. Sect. B Struct. Sci. 2006, 62, 457.

(33)

Keeffe, M. O.; Peskov, M. A.; Ramsden, S. J.; Yaghi, O. M. Acc. Chem. Res. 2008, 41, 1782.

(34)

Niu, C.-Y.; Zheng, X.-F.; He, Y.; Feng, Z.-Q.; Kou, C.-H. CrystEngComm 2010, 12, 2847.

(35)

Wang, S.; Wang, D.; Dou, J.; Li, D. Acta Crystallogr. Sect. C Cryst. Struct. Commun. 2010, 66, m141.

(36)

Macrae, C. F.; Bruno, I. J.; Chisholm, J. A.; Edgington, P. R.; Mccabe, P.; Pidcock, E.; Rodriguez-monge, L.; Taylor, R.; Streek, J. Van De; Wood, P. A. J. Appl. Crystallogr. 2008, 41, 466.

(37)

Mehlana, G.; Bourne, S. A.; Ramon, G.; Öhrström, L. Cryst. Growth Des. 2013, 13, 633.

(38)

Lee, C.; Mellot-Draznieks, C.; Slater, B.; Wu, G.; Harrison, W. T.; Rao, C. N. R.; Cheetham, A. K. Chem. Commun. 2006, 2687.

(39)

Mehlana, G.; Bourne, S. A; Ramon, G. Dalton Trans. 2012, 41, 4224.

(40)

Lusi, M.; Barbour, L. J. Angew. Chemie. 2012, 51, 3928.

(41)

Millange, F.; Serre, C.; Guillou, N.; Férey, G.; Walton, R. I. Angew. Chem. 2008, 47, 4100.

(42)

Millange, F.; Guillou, N.; Walton, R. I.; Grenèche, J.-M.; Margiolaki, I.; Férey, G. Chem. Commun. 2008, 39, 4732.

(43)

Yot, P. G.; Ma, Q.; Haines, J.; Yang, Q.; Ghoufi, A.; Devic, T.; Serre, C.; Dmitriev, V.; Férey, G.; Zhong, C.; Maurin, G. Chem. Sci. 2012, 3, 1100.


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Structural diversity observed in 2D square lattice metal-organic frameworks assembled from Zn(II) and 3-(4-pyridyl)benzoate Gift Mehlana,ab* Chad Wilkinson,a Christelle N. Dzesse T.,a,c Gaëlle Ramona and Susan A. Bournea

The reaction of 3-(4-pyridyl)benzoate with Zn(II) under different conditions afforded a variety of 4-connected supramolecular isomers.

Their formation has been attributed to inclusion of

different guest molecules and guest location in the cavities.


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Structural Diversity Observed in Two-dimensional Square Lattice

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