Luminescent Coordination Polymers of Naphthalene Based Diamide

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Luminescent Coordination Polymers of Naphthalene Based Diamide with Rigid and Flexible Dicarboxylates: Sensing of Nitro Explosives, Fe(III) Ion and Dyes Debarati Das, and Kumar Biradha Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.8b00498 • Publication Date (Web): 14 May 2018 Downloaded from http://pubs.acs.org on May 15, 2018

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Crystal Growth & Design

Luminescent Coordination Polymers of Naphthalene Based Diamide with Rigid and Flexible Dicarboxylates: Sensing of Nitro Explosives, Fe(III) Ion and Dyes Debarati Das and Kumar Biradha* Department of Chemistry, Indian Institute of Technology, Kharagpur-721302, India.

ABSTRACT.

An

naphthalene

based

diamide,

3-Pyridin-3-yl-N-[5-(3-pyridin-3-yl-

acryloylamino)-naphthalen-1-yl]-acrylamide ligand (L) with four dicarboxylates were shown to form Cd/Zn(II) coordination polymers under solvothermal conditions. Three of these CPs found to have 2D-networks while one of them contains 3D-network. The Cd(II) centers exhibited bimetallic and trimetallic SBUs to link the dicarboxylates and ligands. The CPs displayed high luminescence given the presence of electron rich moiety in the ligand.

This luminescent

property of CPs has been exploited for the detection of nitro aromatics and Fe(III) ions from aqueous solutions of 0.69 µM (0.16 ppm) and 1.29 µM (0.52 ppm) of picric acid and ferric ion respectively. Further, all the CPs have shown propensity to adsorb dyes such as methylene blue (MB), while eosin-Y (EY) is adsorbed by only one of the four CPs. The dye sorption found to influence the emission profiles in terms of absorption maxima.

ACS Paragon Plus Environment

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INTRODUCTION Coordination polymers (CPs) continue to fascinate the chemists with alluring architectures and intricate topologies1 as well as with their extensive applications in several contemporary areas of materials research such as luminescent sensing,2 catalysis,3 adsorption/separation,4 magnetic properties,5 and so on.6 Judicial choice of co-ligand with diverse functionalities and metal-ion templation may lead to well-defined coordination polymers.7 Although many examples of interesting coordination polymers have been reported, the control of structural diversity remains a challenge in the field of crystal engineering and the influential factors are less ascertained.6 With the rapid industrial progress, the water pollution is becoming severe around the world. Thus, access to clean water is becoming more challenging, and efficient technologies that can purify this contaminated water have become essential. One of the most common pollutants of water is organic dye molecules, which are toxic, and may cause severe problems to the aquatic environment and affect human health.8 Adsorption/separation of dye molecules by porous CPs (PCPs) are a promising technique to obtain clean water as it is eco-friendly and economical, since the adsorbed dyes can be released and materials recycled.9 Alternatively, luminescence-based approaches are becoming increasingly attractive for sensing of toxic environmental pollutants such as nitro-aromatic compounds (NACs) as these approaches have advantages in terms of high sensitivity, fast response, facile and low-cost operation.10 As the popularity of global terrorism has increased, the ability to quickly detect the presence of explosive compounds and precursors has become even more crucial.

Recently, some

luminescent PCPs based chemical sensors have been synthesized for detecting nitroaromatic explosives in vapor phase.11,12 Due to moderate vapor pressure and limited chemical reactivity, detection of NACs is not easy. Among all organic nitro-explosives 2,4,6-trinitrophenol (TNP) is


2

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highly dangerous for human health (Toxicology based drinking water value: 0.2 µg/L) and is extensively used for manufacturing explosive materials.13 On the other hand, Fe3+ ions are one of the most essential elements for humans and other living organisms for biochemical processes, such as the storage and transport of oxygen, muscle and brain function, immune and enzyme systems.14 Its deficiency or overload will result anemia, skin ailments, insomnia and even cancer.15 Therefore, the identification and quantification of Fe3+ is of great importance. The emergence of various applicative aspects of CPs has great relevance to their structural diversities.16 Rational selection of the organic ligands is one of the most significant factors to build the targetable CPs. The bis(amido-pyridine) based ligands containing various spacers have been shown to form CPs possessing both attractive architectures and functional properties.17 For example, these CPs were shown to have applications in templation of solid state [2+2] photopolymerization reactions,18 as water oxidation catalyst19 and guest inclusion properties.20 In this manuscript, a bis(amidopyridine)-based ligand containing electron rich spacer such as naphthalene core in conjugation with –C=C– was synthesized and its CPs with rigid dicarboxylates such as isophthalic acid (H2BDC) and 5-amino isophthalic acid (H2AIP) and flexible dicarboxylates such as

1,4-phenylene diacetic acid (H2PDA) and 1,4-cyclohexane

dicarboxylic acid (H2CHD) (Scheme 1) were explored in terms of their structures and their sensing abilities of nitro aromatics via luminescence quenching. RESULTS AND DISCUSSION The single crystals of four CPs [Cd(L)(BDC)] (CP-1), {[Zn2(L)(5-AIP)2].3H2O}n (CP-2) and {Cd(L)(PDA)(H2O)2}n (CP-3) and {[(Cd3(L)(CHD)3(DMF)2]·2DMF}n, (CP-4) are obtained by the solvothermal reactions of L with corresponding metal salts and carboxylic acids (Scheme-1) in DMA+H2O. The single crystal X-ray diffraction analyses of these CPs reveal that CP-1 and


3


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CP-3 are crystallized in P-1 space group while CP-2 and CP-4 are crystallized in P21/c and P2/c space groups respectively. The pertinent crystallographic details for CPs 1−4 were given in Table 1. O

HN N N NH

L

O

3-Pyridin-3-yl-N-[5-(3-pyridin-3-yl-acryloylamino)-naphthalen-1-yl]-acrylamide COOH NH2 HOOC

HOOC

COOH COOH

HOOC

COOH

H2AIP

H2BDC

HOOC

H2PDA

H2CHD

Scheme 1. Structural drawing for L and coligands The asymmetric unit of CP-1 comprises of one unit each of Cd(II), L and BDC. The Cd(II) center adopts a distorted octahedral geometry with the CdO4N2 coordination environment where four O atoms from carboxylates of BDC are occupied in the equatorial positions (Cd−O:2.258(4), 2.335(5), 2.427(4), 2.396(5) Å) and the two N atoms of ligand (Cd−N: 2.318(6) and 2.329(6) Å; Figure 1a) are occupied in the axial positions. The Cd(II) with BDC forms a one-dimensional network via bi-nuclear SBU (Figure 1b) and within the SBU, the Cd(II) centers are separated by 3.908 Å. Further, these 1D-networks are doubly connected by the ligands to


4

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(a)

(b)

O

O

M M

O

O

M

(c)

(d)

Figure 1. Illustrations for the crystal structure of 1: (a) depiction of coordination environment of Cd(II) to form SBU; (b) linking of 1D-chains of Cd(II)-isophthalates by L to form 2D-layer, notice intra-layer hydrogen bonding between amides (N···O: 2.280 Å); (c) interdigitation of 2Dlayers via N-H···O and C-H···O and π-π stacking interactions (centroid to centroid 3.748 and 3.939 Å); (d) a side view of the packing of the layers.


5


(a)

(c)

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(b)

(d)

Figure 2. Illustrations for the crystal structure of 2: (a) tetrahedral coordination environment around Zn(II); (b) 2D-layer of Zn(II)-AIP with (6,3) topology; (c) hydrogen bonding interactions between neighboring Zn(II)-AIP layers; (d) linking of the 2D-layers by the L units to form a bilayer. form a two-dimensional network such that Cd(BDC) chains are separated from each other by 23.795 Å. Within the network, the ligands interact via π-π interactions (3.800 Å face to face naphyl rings and 3.724 Å edge to face for pyridyl rings) and N-H···O hydrogen bonds (N- H···O: 2.28 Å, N···O: 3.125(8) Å, 167°). The layers further interdigitated via N-H···O and C-H···O (between −C=C−H and –NH of L with BDC) hydrogen bonding (Figure 1c,d) and π-π interaction between naphthalene ring and −C=C− (centroid to centroid 3.748 and 3.939 Å).


6

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The asymmetric unit of CP-2 contains one unit each of Zn(II), AIP and half unit of L and three uncoordinated water molecules. The Zn(II) exhibits distorted tetrahedral geometry as it coordinates with two N-atoms, one from (Zn−N: 2.046(4) Å) pyridyl group of L and one from amino group of AIP (Zn−N: 2.069(4) Å), and two O-atoms of the carboxylates (Zn−O: 1.949(3), 2.002(2) Å) in monodentate fashion (Figure 2a). The AIP acts as three connected triangular node to form a 2D-layer of (6,3) topology (Figure 2b). These 2D-layers are pillared by the ligands to form a bilayer structure with the separation of Zn(AIP) layers by 12.2 Å (Figure 2d). We note here similar type of 2D-networks by Zn(II) and AIP with pillaring ligands such as 4,4bipyridine (BPY), 1,2-di-4-pyridylethylene (DPE), 1,2-di-4-pyridylethane (DPA), and 1,3-di-4pyridylpropane with 1D-channels along b-axis was reported earlier.21 These 2D-layers are packed via N-H···O hydrogen bonding interactions (N-H···O: 2.32 Å, N···O: 3.1439 Å, 152°; 2.21 Å, 3.0888 Å, 166°) and π-π stacking (centroid to centroid 3.754 Å) (Figure 2c) with interlayer separation of 4.119 Å. The amide groups of the L participate in N-H···O hydrogen bonding interaction (N···O: 2.682(12) Å) (Figure S1b). The uncoordinated water trimers occupy the free spaces in the framework and interact with the carboxylates (O···O: 2.959(7), 2.859(6), 2.969(12) Å), ligands (O···N: 1.98(2) Å) and with each other (O···O: 3.01(2), 1.89(2), 2.703(13) Å) by plethora of hydrogen bonding interactions. The crystal structure analysis of CP-3 reveals that the asymmetric unit contains one unit each of Cd(II), ligand L and the dianion PDA and two coordinated water molecules (Figure 3b). The Cd(II) adopts slightly distorted octahedral geometry (Figure 3a) as it coordinates to two pyridyl N-atoms (Cd-N: 2.360(4) Å) and two carboxylates of PDA in monodentate fashion (CdO: 2.239(3) Å) in equatorial positions and two H2O molecules (Cd-O: 2.338(3) Å) in axial positions. This type of coordination resulted in the formation of 2D-layer with (4,4) topology


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with dimension 34.6 Å X 15.7 Å) (Figure 3b). The packing of the layers governed through plethora of C-H···O hydrogen bonding (Table S5) and C-H···π (2.943 and 3.754 Å) interactions between PDA and L (Figure 3c). (a)

(b)

(c)

Figure 3. Illustrations for the crystal structure of 3: (a) Octahedral coordination environment around Cd(II); (b) 2D-layer with (4,4) topology; (c) N-H···O, C-H···O and C-H···π interactions (2.943 and 3.754 Å) between the layers. In case of 4, the asymmetric unit is composed of one fully occupied and one half occupied metal centres, one unit of cis-CHD, half unit of trans-CHD, half unit of L, one coordinated DMF and one uncoordinated disordered DMF molecules (Scheme 2). Interestingly, both the Cd(II) atoms are joined together by six carboxylates to form a trimetalic linear cluster as a secondary building unit (SBU) (Figure 4a). In trimetallic SBU, all the Cd(II) centers adopt distorted octahedral geometry: the middle Cd(II) coordinates to six caboxylates in mono-dentate fashion (Cd−O: 2.156(5), 2.253(3), 2.247(3) Å) while the terminal one coordinates to three carboxylates(Cd-O: 2.326(3), 2.442(3) Å), bridging acids (Cd−O: 2.260(3), 2.273(3) Å ), one ligand (Cd−N:


8

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(a)

(b)

(d)

(c)

Figure 4. Illustrations for the crystal structure of 4: (a) a three centered SBU formed by two crystallographically independent Cd(II) centres; (b) six connected node that connects six neighboring SBUs; (c) a 2D-layer formed by the connections of Cd3-SBU and CHD units; (d) a 3D-network formed by the linking of metal-carboxylate 2D-layers by the L units, SBU was shown as a single node that is by considering the middle Cd(II). 2.360(3) Å) and one DMF molecule (Cd−O: 2.302(3) Å). Such coordination of carboxylates of CHD to Cd(II) centers resulted in a six connected corrugated 2D-layer (Figure 4c) which is further connected by the ligand to form a three-dimensional network (Figure 4d).

The

consideration of ligands and anions as spacers and Cd3 unit as six connected node resulted in a


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3D-network (Figure 4b). It was shown earlier, the mixture of cis and trans-CHD involved in the formation similar type of trinuclar Cd3 SBU to form a corrugated 2D-networks which are not linked by the exo-bidentate ligands.22 In the lattice, the coordinated and uncoordinated DMF molecules bound to ligand via hydrogen bonding (Figure S2). Notably, the DMF molecules coordinates to Cd2 with C=O coordination and thus the –NMe2 groups occupy the channels of the network. The PLATON23 calculation suggests solvent accessible void is 19% which also makes it a suitable candidate for dye adsorption. Coordination polymers containing Zn/Cd metal ions and electron rich organic chromophores such as naphthalene are known to exhibit luminescent properties with potential applications in various fields.2,10, 24-26 In this regard, the solid state luminescence properties of CPs 1-4 have been explored at room temperature and compared with emission profile of L (Figure S6a). The free ligand L, displayed intense luminescence emission maximum at ̴ 500 nm (λex = 320 nm) which can be attributed to π*→n or π*→π transitions. When the CPs are excited at 320 nm, CP1 emits at 525 nm, red shifted by 25 nm with respect to L, whereas CP-3 and CP-4 emits at 486 nm and 467 nm respectively, blue shifted by 33 nm and by 14 nm with respect to L due to the ligation to carboxylates and coordination environment of the SBUs/metal centers. The CP-2 exhibited an emission similar to L which probably caused by LLCT along with the synergistic effect between co-ligands and metal unit.27,28 The luminescence property of free ligand is also investigated in solution state. The ligand is found to be non emissive in solution state (DMSO) and weakly luminescent in aq. phase with λem 414 nm (Figure S15). The luminescent behavior of CPs in various solvents such as N,N′-dimethyl formamide (DMF), methanol (MeOH), acetonitrile (MeCN), benzene, nitromethane (NM), and nitrobenzene (NB) were recorded. Interestingly, the emission of the CPs found to be quenched to zero in the presence NM/NB


10

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(Figure S6c,d). This observation revealed the ability of CPs for the detection of toxic nitroexplosives. Herein, quenching behavior of CP-2 by the nitro-analytes has been thoroughly (a)

(b)

Luminescence 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


40000

blank 25 µL mM TNP 50 µL mM TNP 75 µL mM TNP 100 µL mM TNP 200 µL mM TNP 300 µL mM TNP 400 µL mM TNP 500 µL mM TNP

30000

20000

10000

0 350

400

450

500

550

Wavelength nm

(c)

Figure 5: (a) Titration plot of aq. suspension of CP-2 with 1 mM aq. TNP solution; (b) SternVolmer plot of CP-2 with incremental addition of all analytes (Inset: SV plot of CP-2 with TNP at low conc.); (c) quenching efficiency of CP-2 for all analytes.


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studied as it exhibited highly intense luminescence in aq. medium. Notably, after sonication CP2 is found to be stable in water as confirmed by XRPD patterns (Figure S5). Luminescent titrations were performed with several nitro derivatives such as 2,6-dinitro toluene (2,6-DNT), 2,4-dinitro toluene (2,4-DNT), 1,3-dinitrobenzene (DNB), 2-nitro phenol (2-NP), 4-nitrophenol (4-NP), 2,4,6-trinitrophenol (TNP), 4-nitro toluene (4-NT), phenol (PH), NM and NB (Figure. S8). The quenching efficiency is calculated by using the equation (I0−I)/I0×100%, where I0 and I are the luminescence intensities of CP-2 without and with addition of the analytes, respectively. Among all the analytes, the quenching efficiency is found to be more for phenolic nitro analytes. The order of quenching efficiency for CP-2 with various analytes found to be TNP> 4-NP > 4NT> 2-NP >NB>2,4-DNT>2,6-DNT > DNB > NM> PH (Figure 5c). These observations clearly indicate that the hydrogen bonding of –OH group of phenolic analytes with framework carboxylates, -NH2 and -CONH together with aromatic interactions might be resulting in the better quenching abilities. In case of TNP, the high acidity of –OH and highly electron deficient nature of TNP resulted in the high quenching efficiency over other NP or NB analytes. The CPs have shown the lowest sensing ability towards phenol confirming the affinity of CPs towards the analytes containing electron deficient functional groups such as nitro. Such diverse quenching efficiencies are analyzed further by using the Stern−Volmer (SV) equation (I0/I)=KSV[A] + 1, where, I0 represents the initial intensity of the CP-2 in absence of analyte, I is the luminescence intensity in the presence of analyte with molar concentration [A] and KSV is the quenching constant (M−1). The SV plots for TNP and 4-NP deviates from linearity at 0.1 mM concentration and bends upward upon incremental addition of those analytes (Figure 5b), while other analytes give linear variation with concentration in their corresponding SV plots. This nonlinear nature in the SV plot supports dynamic quenching processes or energy transfer between analytes and the


12

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host. The KSV value for TNP is 4.19 X 104 M-1 which is a moderate value and is comparable with reported values of other CPs such as {[Zn2(TPOM)(NH2–BDC)2]·4H2O}(Ksv 4.6 X 104 M1 29

) (Table S3). It has been well-established that the overlap of absorption band of analyte with

the emission band of the fluorophore results in resonance energy transfer (RET).24,27,30-34 The extent of RET depends on the area of their overlap (Figure S7). A red shift in the emission maximum (50 nm) at higher concentration upon the incremental addition of TNP indicates the existence of electrostatic interaction between TNP and CP-2.31 Thus the dual effect of electron and energy transfer processes may be responsible for selective and sensitive luminescence quenching response of CP-2 towards TNP compared with other nitro analytes in water. The lower limit of detection (LOD) for TNP by CP-2 is found to be 0.69 µM (0.16

ppm) which

is

better than

some

recently reported

related

CPs

such

as

{[Zn2(AIP)2(azobpe)2]·(DMF)·(H2O)}n [1.52 ppm]35 and {Zn(2,6-NDC)(H2O)}n [0.92 ppm]36 (Table S3). The selective sensing of TNP by CP-2 in the presence of other analytes is also explored (Figure S9b). The emissions are recorded at first with all the analytes (2 mL stock and 0.5 mL of analytes) then same amount of (0.5 mL) freshly prepared TNP solution is added to those vials. After 40 minutes of addition of TNP, the luminescence emissions of these solutions are recorded and found that the luminescence intensities are quenched further. This observation clearly indicates that the CP-2 has more propensity to detect TNP even in the presence of other nitro analytes in aqueous media. Similar to CP-2, other CPs (CP-1, CP-3 and CP-4) also found to have sensing ability towards nitro-explosives by luminescence quenching (Figure S13). The detailed quenching studies of CPs 1, 3 and 4 with four analytes namely 4-NP, 2,4-DNT, NB and PH were performed and efficiencies are compared with CP-2. All the CPs showed more affinity towards 4-NP (Table S1) compared with 2,4-DNT, PH and NB. The Ksv values indicate that the


13


CP-4 (3.11 X 104 M-1 for 4-NP) is as efficient as CP-2 (2.93 X 104 M-1) whereas the CP-1 (1.86 X104 M-1) and CP-3 (1.89 X104 M-1) have shown moderate abilities. Given the sensing abilities of nitro compounds by blue emmitive CP-2, its ability to sense metal ions is also examined. The luminescent responses of CP-2 towards aqueous solutions of various metal cations are shown in Figure 6a. The metal cations, including those abundant in cells (Na+, Mg2+, and Cu2+), present in trace quantities in living organisms (Zn2+, Co2+, Ni2+, and Fe2+/3+), as well as toxic metals prevalent in the environment (Cd2+ and Cr3+) were studied as analytes; however, only Fe3+ shows a significant quenching effect on the luminescence intensity (a)

(b)

50000

40000

+

40000

2

NH4

2+

2+

2+

Co

Ni

Mn

2+

Cu 30000

3+

Al 20000

3+

10000

Fe



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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blank 3+ 25 µL mM Fe 3+ 50 µL mM Fe 3+ 100 µL mM Fe 3+ 200 µL mM Fe 3+ 300 µL mM Fe 3+ 400 µL mM Fe 3+ 500 µL mM Fe 3+ 600 µL mM Fe

35000 30000 25000 20000 15000 10000 5000 0

2+

Zn

Mg

2+

+

Na

2+

Cd

3+

Cr

2+

360

Fe

380

400

420

440

460

480

500

Wavelength nm

Figure 6: (a) luminescence response of CP-2 in presence of metal ion solutions; (b) titration plot of aq. suspension of CP-2 with aq. 1mM Fe3+ solution. of CP-2 (Figure 6a). To better understand the response towards Fe3+, titration is carried out with incremental addition of aq. Fe3+ solution (Figure 6b). The Stern-Volmer constant KSV(Fe) is calculated as 4.475 X103 M-1 (Figure S10a). The lower limit of detection (LOD) is found to be 1.29 µM (0.52 ppm) which is comparable to the recently reported CP containing naphthalene core [LOD: 2 µM]37 (Table S2). The XRPD patterns indicate the retention of the framework


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throughout the sensing process. Furthermore, the d-d transition band of Fe3+ found to overlap with emission band of CP-2 which results in quenching by RET mechanism as well as the interactions of Lewis acidic metal cation with the framework further facilitated the process of quenching.38,39 The CP-2 also found to have the selective sensing ability of Fe3+ from the mixture containing Fe3+ and other metals (Figure S10b). However, CP-2 can be recycled upto two cycles (for TNP) and threes cycles (for Fe3+) for the detection process without loosing its structural integrity as confirmed by XRPD patterns (Figure S14). The recyclability is checked by reusing the samples that were regenerated by centrifugation of dispersed aq. solution and washing several times with water. (a)

(b) Normalized luminescence 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


1.0

574 nm 588 nm

642 nm

Pure EY dye -3 10 (M) EY + CP-4 -5 10 (M) EY + CP-4

0.8

0.6

0.4

0.2

0.0 550

600

650

700

750

Wavelength nm

Figure 7: Dye adsorption experiments: (a) UV−vis spectrum for the uptake of eosin-Y (EY) from aq. solutions at various time intervals by CP-4; (b) solid state luminescence emission (λex=400 nm) profile of the dye adsorbed CP-4 at different concentrations and pure EY. Organic dyes that are widely used in textile, paint, leather, and paper industries are toxic and affect human health. The CPs were shown as a solution for the removal of such pollutants from waste waters. The dye adsorption studies for all the CPs were carried out with aqueous solution


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containing methylene blue (MB), methyl orange (MO) or eosin-Y (EY). All the CPs have shown capability to adsorb MB but not MO. Further only CP-4 has shown the capability to adsorb EY (Figure 7a). The adsorption capacity is calculated as 6.38 mg/gm. In a typical reaction, 10 mg of CPs were immersed into the 10 mL of 10-5 M dye solutions. The solutions were monitored by UV-vis at various time intervals. With time the solutions found to become colorless due to the adsorption of the dye by the CPs. All the CP-frameworks being electron rich, they are found to adsorb MB upto 1.40 mg/gm (CP-2), 1.17 mg/gm (CP-4), 0.73 mg/gm (CP-1) and 0.86 mg/gm (CP-3) in 24 hrs. (Figure S17, Table-S4).

The emission profile of CP-4 is found to be

significantly influenced by the adsorption amounts of EY. With increase in adsorption of EY by CP-4 the emission peak of the material found to be red shifted with respect to CP-4 (467 nm, blue region). The emission maxima of the dye sorbed materials of CP-4 are observed at 588 and 574 nm (yellow region) for the CP-4 materials soaked in 10-3 and 10-5 solutions, respectively, with λex of 400 nm (Figure 7b). CONCLUSIONS Four new Cd(II)/Zn(II) coordination polymers with a naphthalene based diamide ligand along with rigid and flexible dicarboxylates have been synthesized and analyzed in terms of their structures and various sensing and sorption properties. Among four CPs, three contain 2Dcoordination networks while one contains a 3D-network. In CP-1, bimetallic SBUs of Cd(II) centres form 1D-linear chains which are connected further by L to result a 2D-network. In CP-2, the AIP with Zn(II) forms a 2D-layer of (6,3) topology and the L acts as pillars to form a bilayer structure. A 2D-layer of (4,4) topology is formed in CP-3 and the overall packing of the layers is driven by the plethora of C-H···O hydrogen bonding and C-H···π interactions between L and PDA. Interestingly, in CP-4 the coordination of flexible carboxylate CHD to Cd(II) centers


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results in a corrugated 2D-layer containing trimetallic SBUs which are further connected by the ligand to form a three-dimensional network. CP-4 is found to have 19% void space (PLATON) which is occupied by disordered DMF molecules.

All the CPs are found to detect nitro

explosives by luminescence quenching in aq. phase. The studies show that phenolic nitro aromatics are more efficiently quenched by the CPs due to hydrogen bonding interactions with the frameworks. Moreover, CP-2 is also shown to act as chemosensor for aq. Fe3+ in ppm level. In both the cases the material CP-2 can be recycled as confirmed by XRPD patterns. All the CPs are found to be capable of removing MB dye from water. Whereas, only CP-4 removes EY dye from water with the capacity of 6.38 mg/gm within 24 hrs. The adsorption of EY is further shown to influence the emission profile of CP-4. Moreover, the studies presented here highlight design and synthesis of CPs for sensing and removal of lethal environmental pollutants in aqueous medium. EXPERIMENTAL DETAILS All the reagents and solvents like N,N′-dimethylformamide, N,N′-dimethylacetamide, benzene, nitromethane, nitrobenzene and metal nitrate/acetates salts were purchased from local chemical suppliers and used as supplied without further purification. The solvents like methanol and acetonitrile were used HPLC grades. 5-amino isophthalic acid (H2AIP) is obtained from AlfaAesar.

1,5-naphthalene diammine, 1,4-cyclohexane dicaboxylic acid (H2CHD), 1,4-

phenylenediacetic acid (H2PDA) and all solid nitro explosives were purchased from SigmaAldrich. FTIR spectra were recorded with a PerkinElmer Instrument spectrum Rx Serial No. 73713.

The XRPD patterns were recorded with a BRUKER-AXS-D8-ADVANCE

diffractometer (Cu target).

Thermogravimetric analysis (TGA) data were recorded under

Nitrogen atmosphere at a heating rate of 5 ºC/min with a Perkin-Elmer instrument, Pyris


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Diamond TG/DTA. Melting point was taken using a Fisher Scientific melting point apparatus, cat. no. 12- 144-1. The solid state luminescence spectra were collected with a Spex Fluorolog-3 (model FL3-22) spectrofluorimeter. The solution state luminescence spectra were collected with a Shimadzu RF-6000 spectrofluorophotometer.

The solution state absorbance spectra were

recorded with the use of a Shimadzu (model no. UV2450) UV−vis spectrophotometer. The nitro compounds are explosive and should be handled with care. Dynamic light scattering (DLS) studies are performed to measure the particle size of the dispersed aq. solutions using Malvern Nano ZS instrument employing a 4 mW He−Ne laser (λ = 632.8 nm) and equipped with a thermostated sample chamber (Figure S16). Synthesis of Ligand (L). The ligand (L) was prepared by earlier reported procedures.17-20, 40 3pyridineacrylic acid (1.21 g, 0.008 mol) was added to pyridine (15 mL) solution of 1,5naphthalene diammine (0.63 g, 0.004 mol) and the reaction mixture was stirred for about 15-20 minutes. To this solution triphenyl phosphite (2.25 mL, 0.0086 mol) was added and was refluxed for 8-9 hours. It was allowed to cool to room temperature and pyridine was distilled out to reduce the volume up to 5 ml. The solid was washed with acetone several times. The brown solid product was recrystallized from DMF. Yield: 65%, melting point >300 °C. Synthesis of CP 1. The L (0.010 g, 0.025 mmol), Cd(NO3)2·4H2O (0.007 g, 0.025 mmol) and H2BDC (0.004 g, 0.025 mmol) were taken in DMA-H2O (3 mL:1 mL) solvent system in solvothermal tube and kept in preheated oven for 3 days at 100° C. Brown coloured single crystals were obtained with ∼42% yield. IR υmax/cm−1: 3460.90(m), 3397.66(m), 3053.49(w), 2930.04(w), 2374.48(w), 1699.98(s), 1607.70(w), 1597.54(s), 1541.83(s), 1223.91(m), 1169.60(s), 774.12(s), 756.01(s), 714.87(s), 406.14(m).


18

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Synthesis of CP-2. Similarly, the mixture of L (0.010 g, 0.025 mmol), Zn(NO3)2·6H2O (0.0077 g, 0.025 mmol) along with 5-amino isophthalic acid (H2AIP) (0.0043 g, 0.025 mmol) in DMA-H2O (3 mL/1 mL) solvent system were heated for 3 days. Brown colored crystals of CP-2 were obtained in 3 days with ∼40% yield. IR υmax/cm−1: 3422.02(b), 3265.87(w), 3134.47(s), 2358.02(b), 1618.43(s), 1569.40(b), 1426.95(w), 1341.18(s), 1231.83(w), 1192.81(w), 1129.13(w), 1095.05(s), 1034.65(vw), 960.71(w), 931.96(w), 898.99(w), 777.03(s), 731.18(s), 678.11 (w), 451.34(w), 424.64(w). Synthesis of CP-3. Same procedure was adopted for the synthesis of CP-3 taking H2PDA (0.0048 g, 0.025 mmol) as co-ligand. Light brown colored crystals of CP-3 were obtained after 2−3 days in ∼44% yield.

IR υmax/cm−1: 3392.05(b), 3215.68(w), 2953.35(w), 2363.79(m),

1660.40(s), 1627.68(s), 1559.91(s), 1415.83(s), 1388.81(s), 1347.39(s), 1273.72(m), 1225.98(m), 1203.85(m), 969.34(s), 861.00(w), 777.63(s), 689.93(s), 608.14(s). Synthesis of CP-4. In case of CP-4, the ligand L (0.010 g, 0.025 mmol), H2CHD (0.0043 g, 0.025 mmol) and Cd(NO3)2·4H2O (0.007 g, 0.025 mmol) in 4 mL DMF were heated at 100 °C. Light brown colored crystals of CP-4 were obtained after 7 days with ∼35% yield. IR υmax/cm−1: 3431.43(b), 2932.84(s), 2857.14(w), 2365.75(m), 2336.13(w), 1654.26(m), 1560.01(w), 1544.05(s), 1412.25(s), 1346.24(s), 1303.51(m), 1201.83(w), 1108.02(b), 981.81(w), 847.55(w), 791.66(w), 668.77(w). Single crystal X-ray analysis: The single crystal data for all the CPs were collected on a Bruker-APEX-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-2014.41 Non-hydrogen atoms were refined anisotropically, and hydrogen atoms were fixed at calculated


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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. The ligand L in CP-2 and uncoordinated DMF molecule in CP-4 were disordered which are modeled and refined (scheme 2).

(a)

(b) N

O

H N O

H N

N H

N

O

O

HN N

Scheme 2: Illustation for (a) disordered ligand L in CP-2, and (b) disordered DMF molecule in CP-4. General procedure for the preparation of stock solutions for luminescence measurements: For all the cases finely ground CPs were dispersed in millipore water to make 1.069 mM solution by sonication for 1 hr. The 1 mM analyte solutions were prepared freshly dissolving them in water. The solutions were excited at 320 nm (as λmax observed at 320 nm in UV) with 5/3 slit.


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Table-1: Crystallographic parameters for CPs 1, 2, 3 and 4 Structural formula

C34H24CdN4O6

C42H36N6O14Zn2

C36H30CdN4O8

C62H76Cd3N8O18

Formula wt.

696.97

979.51

759.04

1558.50

Temperature(K)

293(2)

293(2)

293(2)

293(2)

λ (Å)

0.71073

0.71073

0.71073

0.71073

Crystal System

Triclinic

Monoclinic

Triclinic

Monoclinic

Space Group

P -1

P 21/c

P -1

P 2/c

a(Å)

9.878(2)

17.051(5)

9.587(2)

20.268(3)

b(Å)

10.338(2)

7.763(2)

9.826(2)

8.740(1)

c(Å)

14.260(3)

16.210(4)

10.395(4)

20.325(3)

α(º)

86.414(5)

90

102.934(9)

90

β(º)

80.816(5)

108.837(8)

110.891(10)

114.019(3)

γ(º)

81.154(5)

90

107.855(6)

90

V(Å3)

1419.2(4)

2030.8(10)

807.4(4)

3288.5(7)

Z

2

2

1

2

ρcalcd (g cm-3)

1.6310(6)

1.5821(7)

1.5570(8)

1.5435(4)

R1(I>2σ(I))

0.0663

0.0608

0.0502

0.0497

all 0.1589

0.1574

0.0855

0.1661

wR2(onF2, data)

ASSOCIATED CONTENT Supporting Information: TGA profile of CPs, XRPD analysis of bulk samples, luminescence and UV-vis studies and calculation of LOD with related literature in tabular form.


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AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. Fax: +91-3222- 282252. Tel.: +91-3222-283346. ORCID Kumar Biradha: 0000-0001-5464-1952 Notes. The authors declare no competing financial interest. ACKNOWLEDGMENT We acknowledge SERB, DST, New Delhi, India, for financial support, DST-FIST for the single crystal X-ray diffractometer. D. D. acknowledges UGC for a research fellowship. D. D thanks Puja Poddar for DLS measurements. REFERENCES 1)

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For Table of Contents Use Only Luminescent Coordination Polymers of Naphthalene Based Diamide with Rigid and Flexible Dicarboxylates: Sensing of Nitro Explosives, Fe(III) Ion and Dyes Debarati Das and Kumar Biradha* Department of Chemistry, Indian Institute of Technology, Kharagpur-721302, India.

A naphthalene based diamide has been shown to form four luminescent CPs with rigid and flexible dicarboxylates with Cd/Zn metal ions. The dinuclear and trinuclear SBUs with Cd(II) resulted 2D and 3D-networks respectively. The CPs were shown to detect nitro explosives by luminescence quenching. Further, one of the CPs acted as a dual chemosensor and had detected TNP and Fe3+ in ppm level. The CP with 3D-network found to adsorb highly luminescent dye eosin-Y efficiently compared to others. Moreover, amount of dye adsorption has been observed to influence the emission maxima of the parent CP.


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Luminescent Coordination Polymers of Naphthalene Based Diamide

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