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Porous Coordination Polymers Containing Pyridine 3,5 bis (5-azabenzimidazole): Exploration of Water Sorption, Selective Dye Adsorption and Luminescent Properties Avishek Dey, Satyanarayana K. Konavarapu, Himadri S Sasmal, and Kumar Biradha Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.6b01028 • Publication Date (Web): 23 Aug 2016 Downloaded from http://pubs.acs.org on August 29, 2016

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Crystal Growth & Design

Porous Coordination Polymers Containing Pyridine 3,5 bis (5azabenzimidazole): Exploration of Water Sorption, Selective Dye Adsorption and Luminescent Properties Avishek Dey, Satyanarayana K. Konavarapu, Himadri S. Sasmal and Kumar Biradha* Department of Chemistry, Indian Institute of Technology, Kharagpur-721302, India ABSTRACT: Six novel coordination polymers of Cd(II) and Zn(II) have been designed and synthesized using pyridine-3,5-bis(5azabenzimidazole), L, and various angular dicarboxylates as linkers. The dicaboxylates used are 4,4’-oxo bis benzoate (OBA), isophthalate (IPA) and 1,4-phenylene diacetate (PDA). All the six complexes are found to exhibit general formula of {[M(L)(dicarboxylate)]·xDMF·yH2O}n. The four complexes containing OBA and IPA exhibited two-dimensional layered structures with grid like cavities of dimensionalities 18x15 Å2 and 17×10 Å2 while those with PDA exhibited 3D-network consisting of CdSO4 topology. The coordination networks are propagated by M2(RCO2)2 SBUs and exhibit guest accessible volume of 23-33 %. The XRPD and gas sorption studies confirm their stability and porous nature. Further these materials exhibited a greater preference for the adsorption of water or alcohol vapours over nitrogen. The alcohol sorption found to depend on the size of the molecules that is they have shown greater ability to adsorb MeOH compared to isopropanol. The dye adsorption studies show that all these neutral network materials can selectively adsorb cationic dye such as crystal violet. Further, all the complexes exhibited solid state luminescence properties at room temperature.

Introduction In the recent years, significant attention has been paid in the exploration of water adsorption capability of porous coordination polymers (PCPs)/MOFs given their applications such as capture and release of water, electric dehumidifiers, adsorption-driven heat exchangers, adsorption based heat pumps and dehydration of organic solvents.1-8 The energy efficiency and working humidity range of these processes mainly depend on the water adsorption capabilities of the adsorbents. Traditionally, zeolites are known to have a good affinity of water adsorption at lower relative pressures and thus they are commonly used as water adsorbing materials.9-11 However, the use of PCPs or MOFs is of current interest as they exhibit great variety of materials in terms of metal-ligand compositions, metal-ligand clusters, pore structures and network topologies. 12-19 Further, the amenability of these materials by change of metal or by functionalization of ligands makes them ideal candidates for these studies. The water absorption process is driven by the hydrophilicity and micro-porosity of the absorbent.20-25 Several MOFs containing 3D-porous networks were shown to be capable of exhibiting water adsorption to date.26-33 The water stability of the MOFs is also one of the important factors for adsorption of water.30, 34-40 For example, Zn(II) containing MOF-5 and MOF-177 were shown to be inefficient for this purposes as they have low water stability. However, the Cu(II) containing HKUST-1 and MOF-505 were shown to be very efficient water adsorbers.41, 42 Further, the MOFs such as ZIF-8, DUT-4, MIL-100, and MIL-101 have been also shown to have affinity towards water sorption at relatively low pressures.30 More recently, Walton and co-workers have studied water adsorption properties for series of MOFs such as UiO66, Mg-MOF-74, DMOF-1 and UMCM-1 and established their micro-meso porous nature.32 Kitagawa and co-workers

have shown that increase in the hydrophilicity of the ligand significantly increases the water sorption ability of the MIL101. In particular, it was shown that the functionalization of terephthalate of MIL-101 with –NH2, –NO2 or –SO3H significantly enhances the water adsorption capability.26 Similar enhancement in water uptakes was also observed in the MOFs of MIL-53 (Al, Fe), MIL-88, and CID-5/6 by the functionalization of pillared dicarboxylates by hydrophilic functional groups.43-48 Although several 3D-MOFs were shown to exhibit water sorption, very few 2D-porous CPs were shown to exhibit this phenomenon. Recently, DUT-84 which is composed of 2Ddouble layers consisting of 6-connected SBUs was shown to exhibit water adsorption (150 cc g-1 at p/p0 = 0.95).49 Further, a two-dimensional CP containing pillared-bilayer structure had also been shown to exhibit water sorption up to 150 cc/g at p/p0 = 1.50 There are some more examples of 2D CPs which have shown the water adsorption capability below 100 cc/g at p/p0 = 1.51-57 Here we would like to present series of twodimensional CPs that contain the same ligand but differs in the di-carboxylate linkers in terms of their size and shape. All these CPs were found to have higher affinity for water adsorption ranging from 106 to 326 cc/g at P/P0 = 0.9. These CPs are designed by considering a longer and angular ligand such as pyridine 3,5-bis (5-azabenzimidazole) (L) which contains as many as five N-atoms to enhance hydrophilicity and there by water sorption. The angularity of the ligand is expected to create cavities in the networks for the inclusion of guest/H2O. Further, the resultant CPs of L are anticipated to exhibit good luminescence properties due to the presence of extended π-system. Further, the aromatic dicarboxylates such as IPA, OBA, and PDA (Scheme-1) are selected as co-ligands which also help in the increase in net-

ACS Paragon Plus Environment


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work dimensionality and hydrophilicity. The Cd(II) and Zn(II) metal salts are considered for complexation reactions with L and dicarboxylates. The resultant CPs are analyzed in terms of the structural changes and water sorption abilities with respect to change in the metal atoms and di-carboxylates.

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which the Zn(II) centers are double capped by carboxylates of two units of IPA. Within the SBU, the Zn(II) centers are separated by 4.098 Å. and the double chain exhibits perfect planarity.(Fig 1b) Scheme 2: Coordination modes displayed by OBA, IPA and PDA anion in complexes 1-6.

Scheme 1: Structural drawings for L, OBA, IPA and PDA

O

N

N

N

HN

O

O M

N H

M

N

O

M

N L

O

O M

O

M

O

O

IPA

PDA

O

O

O O

O O

O M

O

OBA

O

Results and Discussion: The solvothermal reactions of L and dicarboxylates with Cd(II) or Zn(II) metal salts in DMF-H2O solvent system resulted in six CPs with general formulae {[M(L)(IPA)]·DMF}n, 1 (M = Cd(II)) and 2 (M = Zn(II)); {[M(L)(OBA)]·2DMF}n, 3 (M= Cd(II)) and 4 (M= Zn(II)), {[M(L)(PDA)]·DMF 3H2O}n, 5 (M = Cd(II)) and 6 (M= Zn(II)). The complexes 2, 3 and 5 were obtained as single crystals suitable for X-ray diffraction analyses whereas the complexes 1, 4 and 6 were obtained as poly crystalline material. The crystal analyses of 2, 3 and 5 revealed that all of them exhibit a double layered structure containing rectangular cavities of different sizes. The X-ray powder diffraction (XRPD) patterns of polycrystalline materials of 1, 4 and 6 indicated that they are identical to XRPD patterns of 2, 3 and 5 respectively. Pertinent crystallographic details of 2, 3 and 5 are given in the table 1. Interestingly, all the three dicarboxylates found to exhibit similar coordination modes despite of several other possible coordination modes. Further all the complexes found to contain di-nuclear secondary building units (SBUs). The complex 2 crystallizes in P-1 space group and the asymmetric unit contains one unit each of Zn(II), ligand L, IPA and DMF molecule. The, Zn(II) centre adopts highly distorted octahedral geometry with the ZnO4N2 coordination environment. Each Zn(II) ligated to four O-atoms from carboxylates of IPA in the equatorial positions (Zn-O: 2.044 Å, 2.069 Å, 2.214 Å, 2.235 Å) and the axial positions are occupied by the N-atoms of ligand (Zn-N: 2.131 Å and 2.140 Å) (Fig 1a). In other words the IPA and Zn(II) forms a double chain that is constituted by secondary building unit (SBUs) in

O

O M

O

O

O

O

M

O

O M

Further these double chains are connected by the ligands to form a double two-dimensional network in which each edge is double lined in terms of ligand or IPA (Fig 1c). As a result the double chains of Zn(IPA) are separated from each other by a distance of 17.75 Å and the ligands within the layer overlap on each other about an inversion centre such that azabenzimidazole (ABIM) moieties have good π-π interactions with plane to separation of 4 Å (Fig1d). However the central pyridine units lie away from each other does not participate in the coordination. Further, it is interesting to note here that the imidazole N-atoms of ABIM also does not participate in the coordination. Therefore the uncoordinated N-atoms, N-H groups and carboxylate O-atoms make the cavities of the layer hydrophilic in nature. The N-H groups in the structure does perform two jobs: 1) helps in inclusion of DMF molecule via N-H···OHCNMe2 hydrogen bonding; 2) also governs the packing of the layers by hydrogen bonding to carboxylates of the neighbouring layers such that there exists continuous channels across the layers (Fig 1e). The DMF was found to occupy 26% of crystal volume by PLATON calculations. The calculated XRPD patterns of 2 are found to be in full agreement with those of experimental patterns of 1 and 2. This confirms that the Cd(II) also forms similar structure as Zn(II) with L and IPA and 1 is isostructural with 2 (Fig. S5). The complexes 3 and 4 are synthesized using longer but angular dicarboxylate such as OBA in anticipation of similar structures as 1 and 2 with bigger voids/channels. The crystal structure analysis of 3 reveals that it crystallizes in P-1 space group and the asymmetric unit contains one unit each of Cd(II), ligand L and OBA but two DMF molecules. The Cd(II) in 3 adopts similar geometry as that of 2 and also forms a double chain through Cd2(RCO2)2 SBU in which the Cd(II) centers are separated by 4.5 Å while the SBUs also separated from each other by a longer distance than in 2 given the bigger size of OBA.(15.0 Å in 3 vs 10.1 Å in 2) (Fig 2a and 2b). These 1D chains are linked by L units similar to the 2 to form 2D-layers containing larger cavities of dimension 18x15 Å2 (Fig 2c). The hydrogen bonding between N-H groups of L and carboxylates and other weak interactions governs the 3Dpacking of the layers such that there exists continuous channels which are occupied by DMF molecules (Fig 2d).


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(a)

(b)

(c)

(d)

3.855 Å

(e)

3.551 Å

(f)

Figure 1. Illustrations for the crystal structure of 2: (a) coordination environment around Zn(II) ion, (b) propagation of 1D-chain via M2(RCO2)2 SBUs, (c) 2D-double layered network containing rectangular grids that are occupied by DMF, (d) π-π interactions between two L units within the 2D-network, (e) channels across the 2D-double layers, (f) N-H···O hydrogen bonding interactions between the overlapped edges of the layers (DMF are shown in violet).

One of the two DMFs is hydrogen bonded with N-H group of the ligand while the other DMF could not be located as it is heavily disordered. The comparison of experimental XRPD patterns of 4 with those of 3 indicates that structure of complex 4 is identical with that of 3 (Fig. S6). The dianion PDA was used in complexation reactions of L with Cd(II) or Zn(II) in place of rigid angular IPA and OBA dicarboxylates. The PDA is flexible and can exhibit liner as well as angular geometry. These solvothermal reactions in DMF and H2O resulted in the single crystals of complex {[Cd(L)(PDA)]·DMF·3H2O}n, 5 and poly crystalline material

of complex 6. The crystal structure analysis reveals that complex 5 exhibits C2/c space group and the asymmetric unit contains one unit each of Cd(II), ligand L and PDA, half unit of DMF molecule and three uncoordinated water molecules. The Cd(II) exhibits similar coordination environment as the previous complexes and as a result it forms a double chain of PDA and Cd(II) via Cd2(RCO2)2 SBU (Fig 3a and 3b). However the geometry of the double chain differs significantly from previous structures: in 5 it has wavy geometry (Fig 3c) while in 1-4 it has nearly planar geometry.



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(a)

(b)

(c)

(d)

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Figure 2. Illustrations for the crystal structure of 3: (a) coordination environment around Cd(II) ion, (b) 1D-chain formed by the Cd(II) and OBA via Cd2(RCO2)2 SBU; (c) 2D double layers containing rectangular grids which are occupied by DMF, (d) rectangular channels across the packing of the double layers.

It may be noted that the two carboxylate groups of PDA exhibits dihedral angle of 83.64° which could be the probable cause of wavy geometry of the double chain. Due to such differences in geometry of 1D-chains the linking of these chains with L units also differed significantly. As described earlier for 1-4 each SBU is connected to four ligand units, two from each side. In 1-4, the arrangement of these ligands takes place via inversion centre such that the central pyridine rings face in opposite directions, while in 5, it takes place via plane of symmetry such that the entire length of the ligand has the overlap with the other ligand via π···π homo stacks between ABIM units, and central py units (Fig 3d). Due to such differences, it resulted in the formation of 3D-network containing channels that are occupied by free water and DMF molecules (Fig 3e). The reduction of SBU to a node and ligand and PDA to linear node connections reveals that the network contains CdSO4 topology (Fig3f). Platon calculation suggests that the 3D-network contains 23.5 % void space which is occupied by DMF and H2O. The comparison of XRPD pattern of complex 6 with that of 5 confirms their isostructurality (Fig. S7). Water vapour adsorption studies: All the materials were found to be stable up to 350 °C by thermo gravimetric analysis (TGA) (Fig. S15). Further, the XRPD patterns of apo-hosts confirm crystallinity and integrity

of the network (Fig. S23-S26). Therefore, the porous properties of theses materials were explored using gas and solvent sorption at 298 K. These materials found to show very low uptake of N2 at low pressure with type III sorption profile at high pressure indicating their lower preference for N2 (Fig. S32). The presence of polar/hydrophilic functional groups such as imidazole, pyridine and carboxylates prompted us to investigate sorption of water vapour, methanol and isopropanol. Interestingly all the materials 1-6 exhibited greater ability to adsorb water with some differences. The H2O adsorption profile for all complexes found to be type-II and the amount of H2O adsorbed in complexes 1-6 up to P/Po~0.9 are 107, 134, 326, 225, 117, and 106 cc/g respectively. The corresponding surface areas of 1-6 are 198, 252, 896, 778, 196 and 147 m2/g respectively. It is interesting to note that the water sorption abilities are in accordance with linker sizes and network geometries. The complexes 3 (326 cc/g) and 4 (225 cc/g) containing bigger linker such as OBA have shown higher water absorption than the other complexes which contain small angular linkers (IPA & PDA).


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(a)


(b)

(d)

3.644 Å

(c)

3.697 Å 3.947 Å

(f) (e)

Figure 3. Illustrations for the crystal structure of 5: (a) coordination environment around Cd(II) ion, (b) one-dimensional network of Cd(II) and PDA via Cd2(RCO2)2 SBU, (c) the angular nature of the ligand transpires into the wavy nature of the network, (d) π-π stacking interactions between two units of L within the layer, (e) 3D-network containing channels which are occupied by water and DMF (f) CdSO4 topology by the reduction of SBU to nodes and anions and L units to linear linkers.

Interestingly, the 3D-network containing complexes 5 (117 cc/g) & 6 (106 cc/g) have also shown the lower ability of water sorption than the 2D-network containing complexes of 1 & 2. In order to see the correlation of the cavity size vs adsorbent size, MeOH and isopropanol solvent sorptions were conducted with complexes 1-6 as they have shown the better ability to adsorb water (Fig 4a). It was found that complexes also exhibit MeOH (P/P0 up to 0.9) with characteristic type-II curve. The adsorbed amounts of MeOH by 1-6 are 85, 112, 185, 178, 84 and 69 cc/g respectively (Fig 4b). However, the tendency to adsorb isopropanol was shown only by complexes 3 (173 cc/g) and 4 (118 cc/g). These results indicate that the size of the solvent molecules play significant role in sorption properties of the materials which can be used for the separation of mole-

cules. For example, using 1, 2, 5 and 6, the MeOH can be easily separated from isopropanol. Dye adsorption studies: Dyes are very widely used in industries such as paper, textiles, cosmetics, printing etc. and the removal of dyes from waste water has been received much attention from an environmental point of view.58 Some CP-based materials have been explored for such dye absorption and removal from aqueous solutions. In those studies it was shown that the dyes show preferential adsorption depending on the nature of networks. The cationic networks prefer anionic dye sorption and vice-versa.59-71 To date CPs containing neutral networks were not shown to be effective for cationic dye removal applications, while there are few reports on the anionic dye removal by the neutral networks.66


Crystal Growth & Design (b)

300 250 200

1 2 3 4 5 6

150 100 50 0 0.0

0.2

0.4

0.6

0.8

(c)

300 250 200 150

Volume adsorbed (cc/g)

350



(a)

1 2 3 4 5 6

100 50 0 0.0

1.0

0.2

0.4

0.6

Relative pressure

Relative pressure (P/P0)

0.8 (P/P0)

1.0

200 3 4

150 100 50 0 0.0

0.2

0.4

0.6

0.8

Relative pressure (P/P0)

1.0

Figure 4. Adsorption-desorption isotherms for complexes1-6: (a) water vapour, (b) methanol vapour, (c) isopropanol vapour.

(a)

(b) 2.0

1.5

Absorbance

Absorbance

1.5 hr 2.5 hr

1.0

4 hr

1.0

10 hr 36 hr

0.5 0.0 400

2.0

CV(2) 30 min 1.5 hr 2.5 hr 4 hr 10 hr 36 hr

Absorbance

30 min

1.5

(c)

2.0

CV(1)

0.5

500

600

0.0 400

700

Wavelength (nm)

500

600

0.5 0.0 400

500

600

Wavelength (nm)

700

1.5 1.0 0.5 0.0 400

500

600

700

2.0


Absorbance

1.0

Absorbance

1.5

0.5

(f)

2.0


1.0

Wavelength (nm)

(e) 2.0

1.5


0.0 400

700

Wavelength (nm)

(d)

Absorbance

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

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500

600

700

Wavelength (nm)

1.5 1.0


0.5 0.0 400

500

600

700

Wavelength (nm)

Figure 5. UV−vis spectra for the uptake of crystal violet from aqueous solutions at various time intervals for complexes 1-6, (a)-(e) respectively.

The presence of large channels which are occupied by solvent molecules prompted us to study dye adsorption property of these complexes. The dye adsorption performances of all the six complexes have been studied using cationic (Crystal violet, CV) and anionic (Methyl Orange, MO) dyes. The aqueous dye (CV or MO) solutions are prepared with 10-5 molar concentrations and 25 mg of the CP (1-6) was immersed in the solution. These solutions are monitored by UV-vis spectrometry at different time intervals (Fig 5). With CV solution, the UV spectra suggest that the concentration of CV decreases with time for all the complexes. This indicates that all complexes have an ability to adsorb the cationic dye CV. However, the complexes 3 and 4 given their bigger cavities have shown greater ability to adsorb CV. In other wards, they

have shown to adsorb more amount of dye at faster rate when compared to the other complexes. In the first 30 minutes the complexes 3 and 4 adsorb 57 and 40% of the dye respectively. While the complexes 1, 2, 5 and 6 were found to adsorb only about ~25% in the same 30 minutes. The adsorption 88% and 71% of the CV was observed for complexes 3 and 4 respectively in 10 hrs. However, the complexes 1, 2, 5 and 6 found to adsorb much lesser percentages (50, 67, 61 and 48 respectively) than complexes 3 and 4 even after 36 hours. Similar experiments with MO indicate that all the complexes 1-6 have zero propensity to adsorb anionic dyes (Fig. S30). Further, when the dye absorbed material is heated with aqueous solution of sodium chloride or sodium nitrate, the dyes were found to be released into the solution. The selectivity of CPs towards


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cationic dye was also seen by considering another pair of dyes such as methylene blue (cationic, Fig. S33) and eosine (anionic, Fig. S34). The possible reason for the absorption of cationic dye over the anionic dye may be due to the presence of carboxylate struts in the CPs which favor to interact with cations than anions. The removal percentage (%) of dye was calculated using the following equation: Dye removal (%) =

Ci − Ce ×100 Ci

Where Ci and Ce are the initial and final concentration of the dye solution. Luminescence studies: Luminescent materials are of interest owing to their potential applications in photochemistry and also as chemo sensors.72-77 Therefore, the luminescence properties of the six CPs were studied given the presence of aza-benzimidazole moieties, d10 metal centers and aromatic carboxylates. The luminescence properties of the ligand (L) and complexes 1-6 were recorded at room temperature by solid state fluorometer. The free ligand molecule exhibited fluorescence emission at 472 nm (λex =370 nm), which may be attributed to intraligand π*-π transition. In solid state, benzene dicarboxylate ligand can also exhibit fluorescence emission at room temperature according to the previous literature where n-π* transition of these dicarboxylate may be responsible for the emission properties. However, due to strong π*-π transitions of the ligand the n-π* transition of the dicarboxylate are found to be negligible in these complexes. Therefore, in all the complexes the emission properties observed are exclusively due to the ligand L. The complexes exhibit fluorescence bands at 418 for 1, at 412 nm for 2, 435 nm for 3-5, 444 nm for 6 with excitation wavelength (λex) of 330 nm. All the complexes exhibited blue shift with respect to the ligand, which could have originated from the ligand to metal charge transfer. (a) (b) 4

8x10 4 7x10 4 6x10 4 5x10 4 4x10 4 3x10 4 2x10 4 1x10 0

7

1 4 6

Intensity (a.u.)

Intensity (a.u.)

1.0x10

3 2 5

6

8.0x10

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4.0x10

6

2.0x10

0.0

400

450

500

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Wavelength (nm)

Wavelength (nm) 7

1.4x10

(c) Intensity (a.u.)

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


L

7

1.2x10

7

1.0x10

6

8.0x10

6

6.0x10

6

4.0x10

6

2.0x10

0.0 450

500

550

600

650

Wavelength (nm)

Figure 6. Solid state emission spectra for the complexes (a) for 1, 4 and 6, (b) for 2, 3 and 5 (c) for L.

Conclusions: In summary, six porous and luminescent coordination polymers of Cd(II) and Zn(II) containing a rigid pyridine-3,5-bis-

(5-azabenzimidazole) (L) and dicarboxylate anions (IPA, OBA and PDA) have been studied and their crystal structures, sorption, dye adsorption and luminescence properties have been explored. All the complexes found to contain M2(RCO2)2 SBUs that leads to the formation of 1D-network of metal and di-carboxylates. In complexes 1-4, these 1D-networks are joined by L to form double layered structures containing cavities whereas in complexes 5 and 6, the linking of such 1Dnetworks resulted in the formation of 3D-network. Complexes 1-6 exhibited selective sorption of water vapours over the nitrogen gas. The presence of carboxylate O-atoms and pyridine N-atoms and N-H groups of the ligand are responsible for hydrophilicity of the pores and thereby the greater preferential adsorption of H2O. These materials have a potential to capture and release the water in the atmosphere like sponges. These results push the boundary of utility of CPs in the area of global molecular sponge. The complexes 1-6 were also found to exhibit selective absorption of cationic dye such as crystal violet over the other anionic dye such as methyl orange. We note here that these are the first examples of neutral CPs for selective adsorption of cationic dyes. The luminescence properties of the CPs confirm multi functional nature of the CPs presented here. Experimental section: All the chemicals, such as 3,4-diamino pyridine, pyridine3,5-dicarboxylic acid, polyphosphoric acid (PPA), isophalic acid, 4,4’-oxo bis benzoic acid, 1,4-phenylene diacetic acid, N,N’-dimethyl formamide and metal salts were purchased from local chemical suppliers and used without purification. NMR spectra were recorded on a Bruker DRX400 spectrometer and IR spectra were recorded on a Perkin Elmer Instrument Spectrum Rx Serial No. 73713. Melting points were taken using a Fisher Scientific melting point apparatus, cat. no. 12144-1. X-ray Powder diffraction (XRPD) data were recorded with a Bruker D8-advance diffractometer at room temperature. The solid state luminescence spectra were collected with a Spex Fluorolog-3 (model FL3-22) spectrofluorimeter. The gas sorption experiments were performed using a Quantacrome autosorb iQ automated gas sorption analyzer. The solution state absorbance spectra were recorded with the use of a Shimadzu (model no. UV-2450) UV−vis spectrophotometer. Synthesis of L: The compound L was synthesized using the following procedure.78 Pyridine-3,5-dicarboxylic acid (0.795 g, 4.76 mmol) and 3,4-diaminopyridine (1g, 9.52 mmol) were added to polyphosphoric acid (PPA) and mixed thoroughly to make a paste. The mixture was then heated slowly to 180–200 °C and stirred for 3-4 h; the mixture was allowed to cool to about 100 °C. The resultant grey colored viscous crude mixture was poured into a large volume of rapidly stirred cold water and it was neutralized with an aqueous ammonia solution to make the solution slightly basic. The insoluble residue was collected by filtration and washed with water until the residue part became base free. The product was dried under vacuum and the crystalline powder was isolated with good yield (70%). 1H NMR (400 MHz in DMSO-d6): δ = 13.79 (bs, 2H), 9.50 (s, 2H), 9.40 (s, 1H), 9.02 (s, 2H), 8.33 (s, 2H), 7.68 (s, 2H). FT-IR (KBr): 3887, 3732, 3397, 2361, 2066, 1626, 1589, 1438, 1292, 1224, 1150, 1111, 1027, 920, 864, 812, 716, 633, 584, 533, 455 cm1 . Synthesis of coordination polymers 1-6:



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A mixture of L (0.010 g, 0.0323 mmol), sodium salt of dicarboxylate (0.0323 mmol), Cd(NO3)2 or Zn(NO3)2 (0.0323 mmol), 3 mL DMF and 6 mL of water were taken in a sealed glass tube. The mixture was heated at 100 °C and then slowly cooled down to room temperature. After 3 days colourless complexes 1-6 were obtained, which were washed with water several times and dried in air. The yields of the complexes 1-6 were calculated to be 60, 42, 70, 68, 65 and 53%. Crystal structure determinations by Single crystal Xray: All of the single crystal data were collected on a BrukerAPEX-II CCD X-ray diffractometer that uses graphite monochromated Mo Kα radiation (λ = 0.71073 Å) at room temperature (293 K) by the hemisphere method. The structures were solved by direct methods and refined by least-squares methods on F2 using SHELX-2014.79 Non-hydrogen atoms were refined anisotropically, and hydrogen atoms were fixed at calculated positions and refined using a riding model. The H atoms attached to the O atom or N atoms are located wherever possible and refined using the riding model. One DMF molecule in CP3 is disordered, therefore the final refinement was carried out by using Platon squeeze option.80

ASSOCIATED CONTENT PXRD data, 1H NMR, FTIR data, TGA, UV spectra, sorption figure, hydrogen bonding parameter table. “This material is available free of charge via the Internet at http://pubs.acs.org”

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. Fax: +91-3222282252. Tel.: +91-3222-283346.

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT We acknowledge DST, New Delhi, India, for financial support, DST-FIST for the single crystal X-ray diffractometer and A. Dey acknowledges UGC for a research fellowship.

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Table 1. Crystallographic parameter for CPs 2, 3 and 5

2

3

5

Formula

C28 H22N8O5Zn

C37H33N9O7Cd

C57H57N15O15 Cd2

Mol.Wt.

615.90

828.12

1416.97

T (k)

293(2)

293(2)

293(2)

System

Triclinic

Triclinic

Monoclinic

Space group

P-1

P-1

C2/c

a (Å)

9.2346(2)

9.3678(2)

14.475(4)

b (Å)

10.087(2)

13.908(3)

16.613(4)

c (Å)

14.826(3)

15.026(3)

24.839(6)

α (°)

95.749(5)

110.881(6)

90

β (°)

92.112(5)

96.486(6)

95.062(7)

γ (°)

100.056(5)

100.673(6)

90

V (A3)

1350.9(5)

1762.9(6)

5950(3)

Z

2

2

4

D(mg/m3)

1.514

1.560

1.582

>

0.0837

0.0465

0.0406

wR2 (on F2, all data)

0.2673

0.1170

0.1451

R1 [I 2σ(I)]


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For Table of Contents Use Only

Porous Coordination Polymers Containing Pyridine 3,5 bis (5azabenzimidazole): Exploration of Water Sorption, Selective Dye Adsorption and Luminescent Properties Avishek Dey, Satyanarayana K. Konavarapu, Himadri S. Sasmal and Kumar Biradha*

The Cd(II) and Zn(II) coordination polymers of a new hydrophilic ligand and angular aromatic dicarboxylates have been synthesized. The analysis of crystal structures reveals the formation of double 2Dlayers and 3D-network of CdSO4 topology. Interestingly all the six materials have shown ability to water and methanol vapors and cationic dye sorptions.

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