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Coordination Polymers of Copper and Zinc ions with a Linear Linker Having Imidazole at Each End and an Azo Moiety in the Middle: Pedal Motion, Gas Adsorption and Emission Studies Ruchi Singh, Musheer Ahmad, and Parimal K. Bharadwaj Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/cg300988a • Publication Date (Web): 27 Aug 2012 Downloaded from http://pubs.acs.org on September 3, 2012

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Crystal Growth & Design

Revised Manuscript ID cg-2012-00988a

Coordination Polymers of Copper and Zinc ions with a Linear Linker Having Imidazole at Each End and an Azo Moiety in the Middle: Pedal Motion, Gas Adsorption and Emission Studies Ruchi Singh, Musheer Ahmad and Parimal K. Bharadwaj* *Department of Chemistry, Indian Institute of Technology Kanpur, 208016, India Email: [email protected]

Abstract. The imidazole donor ligand, bis-(4-imidazol-1-yl-phenyl)-diazene (azim) reacts readily with M(ClO4)2·6H2O [M(II) = Zn(II) and Cu(II)] salts at room temperature to afford {[Zn(azim)2]·(ClO4)2·3DMF}n (1) and {[Cu(azim)2(DMF)2]·(ClO4)2·2DMF}n (2) (DMF = N,N΄-dimethylformamide). With MCl2·6H2O [M(II) = Zn(II) and Cu(II)] salts under

solvothermal

conditions,

compounds

{[Zn(azim)(HCOO)2]}n

(3)

and

{[Cu(azim)(Cl)]}n (4) are obtained in moderate yields. Complexes 1 and 2 crystallize as 2D 4-connected 44 sql networks with rectangular and rhombus grids respectively. The frameworks are stabilized by an intricate array of hydrogen bonding interactions with guest molecules that also results in overall 3D frameworks. On the other hand, complexes 3 and 4 form 1D zigzag infinite chain structures. All compounds have been characterized by single-crystal X-ray diffraction, IR spectroscopy, thermogravimetric analysis (TGA) and powder X-ray diffraction (PXRD) measurements. The TGA and PXRD measurements reveal that integrity of the framework 1 and 2 are maintained upon guest removal. N2 and CO2 adsorption measurements are carried out for evacuated frameworks 1-2 and the adsorption studies show CO2 selectivity over N2 at low pressure in case of 2. Interestingly, heat and guest induced bicycle-pedal motion of the azo moiety can be observed in 1 and 4

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without losing crystallinity. Upon excitation at 304 nm, compounds 1-4 and 4′ exhibit solid-state luminescence at room temperature.

Introduction Porous coordination polymers (PCPs)1 are a new class of hybrid inorganic-organic materials with intriguing topologies. These compounds have been used as potential candidates in ion exchange,2 catalysis,3 gas storage,4 separation5, luminescent6 and other studies.7 More recently, frameworks whose structure and properties can be tuned by external factors such as guest molecules or physical stimuli such as heat, light are being explored.8 When the organic linker contains moieties that can undergo rotation9, dynamic motion may occur in the framework in the solid state. Such molecular motion serves to explain various dynamic aspects of molecules besides being potentially useful in fabricating molecular devices. We had earlier observed bicycle pedal motion with the ligand (Scheme 1) in the coordination polymer built with Cd(II) ion. We further show here that CPs built with other metal ions also shows such pedal-motion in response to external stimuli without losing crystallinity.10 Synthesis of PCPs with guest accessible functional sites on the pore surface is a very challenging task as the functional groups tend to coordinate metal ions as well making such compounds inaccessible for guest molecules. However, successful design of functional sites in the linker that can serve as Lewis acid/base sites, play an important role in selective gas adsorption.11 In recent year, selective CO2 adsorption has been one of the major areas of research12 due to the uncontrollable rise of the atmospheric CO2 concentration level which is one of the primary environmental concerns.


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Space for Scheme 1

Herein, we report four new coordination polymers with the ligand and zinc/copper ions, {[Zn(azim)2]·(ClO4)2·3DMF}n (1), {[Cu(azim)2(DMF)2]·(ClO4)2·2DMF}n (2) {[Zn(azim)(HCOO)2]}n (3) and {[Cu(azim)(Cl)]}n (4) for possible bicycle pedal motion and selective gas adsorption studies. Solid-state luminescence of 1-4 and 4′ at room temperature are also described.

Experimental Section Materials and methods Reagent grade 4-fluoronitrobenzene, imidazole, Zn(ClO4)2·6H2O, Cu(ClO4)2·6H2O, ZnCl2·6H2O and CuCl2·6H2O salts were procured from Aldrich and used as received. N,N'-dimethylformamide, methanol, K2CO3 and zinc dust were acquired from S. D. Fine Chemicals, India. All solvents were purified prior to use.

Physical measurements Infrared spectra were obtained (KBr disk, 400–4000 cm-1) on a Perkin-Elmer Model 1320 spectrometer. Thermogravimetric analyses (TGA) were recorded on Mettler Toledo Star System (heating rate of 5oC/min). Microanalyses for the compounds were obtained using a CE-440 elemental analyzer (Exeter Analytical Inc.). Solid-state photoexcitation and emission spectra were recorded on a Jobin Yvon Horiba Fluorolog-3 spectrofluorimeter at room temperature. Powder X-ray diffraction (Cu Kα radiation, scan



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rate 3o/min, 293 K) was performed on a Bruker D8 Advance Series 2 powder X-ray diffractometer. Gas adsorption measurements were performed using automatic volumetric Quantachrome Autosorb-1C adsorption equipment. Prior to adsorption measurements, the complexes 1-2 were immersed in dichloromethane (DCM) for 3 days at room temperature followed by heating at 120 °C for 12 h under vacuum. Single-crystal X-ray studies. Single crystal X-ray data on compounds 1-4, and 4′ were collected at 100 K on a Bruker SMART APEX CCD diffractometer using graphite monochromated MoKα radiation (λ = 0.71073 Å). The linear absorption coefficients, scattering factors for the atoms, and the anomalous dispersion corrections were taken from the International Tables for X-ray Crystallography.13 The data were processed as described earlier.14 In each case, the structure was solved by the direct methods and refined on F2 by full-matrix least-squares using the SHELXL-97 program15 package. All non-H atoms were refined anisotropically. The H atoms attached to carbon atoms were positioned geometrically and treated as riding atoms using SHELXL default parameters. For compound 1, squeeze refinement has been performed using PLATON that shows 2.25 N,N΄-dimethylformamide molecules per formula weight. The contributions of all the solvent atoms have been incorporated in both the empirical formula and formula weight. In case of 4′, the H atoms of lattice water molecule were located in difference Fourier maps and refined keeping the O–H bond distances constrained to ∼0.85 Å with the DFIX command. The crystal and refinement data are collected in Table 1 while selective bond distances and angles are given in Table S1.

Space for Table 1


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Synthesis of the ligand (azim). The ligand bis-(4-imidazol-1-yl-phenyl)-diazene was synthesized in two steps as described earlier.16 Synthesis of {[Zn(azim)2]·(ClO4)2·3DMF}n (1). A hot DMF solution (3mL) of the ligand (50 mg, 0.16 mmol) was added to 2mL of

mixed MeOH:H2O (1:1, v/v) solution

containing Zn(ClO4)2·6H2O (~60 mg, 0.16 mmol). On slow evaporation of the filtrate at RT, red crystals were obtained in ~43% Yield. Anal. calcd. for C45H49Cl2N15O11Zn: C, 48.59; H, 4.44; N, 18.88 %. Found: C, 48.68; H, 4.51; N, 18.96 %. IR (cm-1): 3119(m), 2927(w), 2854(w), 1669(s), 1602(m), 1526(s), 1435(w), 1407(m), 1335(m), 1308(s), 1092(s), 1008(s), 849(s), 773(m), 656(s). Synthesis of {[Cu(azim)2(DMF)2]·(ClO4)2·2DMF}n (2). A hot DMF solution (3mL) of the ligand (50 mg, 0.16 mmol) was added to 2mL of mixed MeOH:H2O (1:1, v/v) solution containing Cu(ClO4)2·6H2O (59 mg, 0.16 mmol). On slow evaporation of the filtrate at RT, brown crystals were obtained in ~42% Yield. Anal. calcd. for C48H56 N16O12Cl2Cu: C, 48.71; H, 4.77; N, 18.93 %. Found: C, 48.85; H, 4.70; N, 18.80 %. IR (cm-1): 3135(m), 2926(w), 1659(s), 1601(m), 1518(s), 1388(m), 1329(w), 1303(s), 1086(s), 962(m), 848(s), 739(m), 655(s), 621(s). Caution! Perchlorate salts are explosive (especially if they are dry) and should be handled with extreme caution. To minimize hazards associated with perchlorate complexes the following precautions should be taken: (i) keep reaction scales to 2σ(I)]

wR2 = 0.1858

wR2 = 0.2174

wR2 = 0.1286

wR2 = 0.0902

R indices

R1 = 0.0930

R1 = 0.0935

R1 = 0.0683

R1 = 0.0420

(all data)

wR2 = 0.2020

wR2 = 0.2314

wR2 = 0.1352

wR2 = 0.0960

Empirical formula


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Compound

1'

4'

Empirical

C42.75H43.75N14.25O10.25Cl2Zn

C18H16N6OClCu

Formula wt.

1057.45

431.36

Crystal system

Monoclinic

Triclinic

Space group

P21/n

P-1

a, Å

13.419(5)

8.253(3)

b, Å

20.811(2)

8.374(5)

c, Å

19.156(7)

12.733(4)

α (°)

90

85.951(5)

β (°)

108.284(5)

79.422(7)

γ (°)

90

77.990(5)

U, Å3

5079(3)

845.6(8)

Z

4

2

ρcalc g/cm3

1.168

1.694

µ, mm-1

0.641

1.472

F(000)

1824

440

Refl. collected

25587

4323

Independent

8917

2921

GOOF

1.146

1.048

Final R indices

R1= 0.1652

R1= 0.0643

[I>2σ(I)]

wR2 = 0.3910

wR2 = 0.1659

R indices

R1= 0.2265

R1= 0.0790

(all data)

wR2 = 0.4194

wR2 = 0.1905

formula

refl.



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N N

N

N Scheme 1

Scheme 2

(a)


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N

N

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(b)

Figure 1

Figure 2



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(a)

(b)

Figure 3


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Figure 4

(a)



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(b)

(c)

Figure 5


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(a)

(b)

Figure 6



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(a)

(b)

(c)


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(d)

Figure 7

(a)

(b)



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(c)

Figure 8 (a)


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(b)

Figure 9



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Figure 10

Figure 11


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Coordination Polymers of Copper and Zinc ions with a Linear Linker Having Imidazole at Each End and an Azo Moiety in the Middle: Pedal Motion, Gas Adsorption and Emission Studies Ruchi Singh, Musheer Ahmad and Parimal K. Bharadwaj* *Department of Chemistry, Indian Institute of Technology Kanpur, 208016, India Email: [email protected]. Captions for Figures and Schemes Scheme 1.

Representation of the ligand, bis-(4-imidazol-1-yl-phenyl)-diazene (azim).

Scheme 2.

Schematic Representation of Pedal-Motion.

Figure 1.

Crystal structure of 1 showing, (a) coordination environment around Zn(II) ion, and (b) perspective view of 2D grid (H atoms are omitted for clarity).

Figure 2.

Topological view of 4-connected net in 1. (H atoms are omitted for clarity).

Figure 3.

(a) 2D grid showing embedded DMF molecules in space-fill model in 1, and (b) ABAB stacking mode of grid layers of 1 (H atoms are omitted for clarity).

Figure 4.

3D packing of 1 along the crystallographic a axis (H atoms are omitted for clarity).

Figure 5.

Crystal structure of 2 showing, (a) coordination environment around Cu(II) ion, (b) perspective view of 2D rhombus grids (H atoms are omitted for clarity), and (c) topological representation of 4-connected sql net.

Figure 6.

(a) ABAB stacking mode of 2D rhombus grid layers of 2, and (b) 3D architecture showing embedded DMF molecules in space-fill model along b axis in 2. (H atoms are omitted for clarity).

Figure 7.

Crystal structure of 3 showing, (a) the distorted tetrahedral geometry and



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coordination environment around Zn(II) center, (b) 1D infinite chain structure, (c) depiction of π···π interactions between aromatic rings of parallel layers, and (d) 3D packing mode along the crystallographic bc plane. Figure 8.

(a) T-shaped geometry and coordination mode of Cu(I) center in 4, (b) 1D infinite chain of 4 along crystallographic a axis, and (c) 3D packing of 4 showing Hbonding interactions.

Figure 9.

Schematic representation (a) heat induced SC−SC pedal motion in 1, and (b) solvent and heat-induced reversible SC-SC pedal motion in 4.

Figure 10.

(a) N2 sorption isotherm of 1, (b) CO2 sorption isotherm of 1, and (c) CO2 and N2 sorption isotherms of 2.

Figure 11.

Solid-state emission spectra at room temperature.


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Coordination Polymers of Copper and Zinc ions with a Linear Linker Having Imidazole at Each End and an Azo Moiety in the Middle: Pedal Motion, Gas Adsorption and Emission Studies Ruchi Singh, Musheer Ahmad and Parimal K. Bharadwaj* *Department of Chemistry, Indian Institute of Technology Kanpur, 208016, India Email: [email protected]. For Table of Contents Four novel coordination polymers based on zinc and copper ions have been synthesized. The pore surfaces of all the frameworks are decorated with azo functional groups having the basic nitrogen sites. Interestingly, frameworks 1 and 4 exhibit bicycle pedal-motion when subjected to external stimuli. Gas adsorption measurements and luminescence properties have also been done.

Bicycle-Pedal Motion in Coordination Polymer


Coordination Polymers of Copper and Zinc Ions ... - ACS Publications

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