Set of Multifunctional Azo Functionalized Semiconducting Cd(II)-MOFs

Article pubs.acs.org/IC

Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

Set of Multifunctional Azo Functionalized Semiconducting Cd(II)MOFs Showing Photoswitching Property and Selective CO2 Adsorption Dilip Kumar Maity,† Arka Dey,‡ Saheli Ghosh,† Arijit Halder,† Partha Pratim Ray,*,‡ and Debajyoti Ghoshal*,† †

Department of Chemistry, Jadavpur University, Jadavpur, Kolkata 700 032, India Department of Physics, Jadavpur University, Jadavpur, Kolkata 700 032, India

‡

S Supporting Information *

ABSTRACT: Syntheses, structural characterizations, photoluminescence, and adsorption properties of three new azo-functionalized Cd(II)-MOFs, namely, {[Cd(azbpy)(msuc)]· 2.5(H2O)}n (2), {[Cd(azbpy)(mglu)]·5(H2O)}n (3), and {[Cd1.5(azbpy)2(glu)]·(NO3)· MeOH}n (4) [where msuc2− = methylsuccinate; mglut2− = methylglutarate; glut2− = glutarate; azbpy = 4,4′-azobispyridine] have been reported. The compounds show different structures only with the variation of aliphatic dicarboxylates. The photoswitching behavior for the above-mentioned newly synthesized Cd(II)-MOFs along with one of our previously reported other azo-functionalized Cd(II)-MOF, namely, {[Cd(azbpy)(suc)]·2(H2O)}n (1), has been studied extensively. At photoilluminated condition, the conductivity values can draw a clear structure−property relationship among the structures of compounds 1−4. Single crystal structural analysis reveals that all the compounds exhibit a three-dimensional (3D) framework connected by azbpy linker and respective aliphatic dicarboxylate through their bis-chelating mono/bis oxo-bridging fashion. Compounds 1−3 exhibit an isostructural honeycomb like 3D framework showing the same coordination environments, where the metal-carboxylate 2D sheets of compounds 1−3 are pillared by N,N′-donor azbpy linkers. On the other hand, compound 4 exhibits a 2-fold interpenetrated 3D framework with a little difference in its coordination environment and the pillaring of 1D metal-carboxylate ladder by azbpy linkers. All the compounds significantly demonstrate their enhanced sensitivity under light rather than the dark condition. The gas and solvent vapor sorption studies have been performed for the synthesized compounds 2−4. Moreover, compound 2 exhibits an enhanced type IV selective CO2 adsorption isotherm over N2 along with the appearance of gate opening phenomena in that.

■

INTRODUCTION

There is a wide number of MOFs that have been extensively studied individually for properties such as gas storage/ separation, photophysical properties, electrical conductivity, etc. So far any single MOF showing the multifunctionalities such as selective gas sorption, photoresponsive electrical property as well as photoluminescence property is not very usual and also the correlation of such multifunctionalities in a MOF has not been very well explored. Therefore, to achieve the desired multifunctionalities in MOFs, a rational design through metal−ligand combination is extremely essential in order to produce smart materials. In the domain of all N,N′donor organic ligands, trans-4,4′-azobispyridine (azbpy) is very much popular15,20−22 and has been utilized as one of the most effective ligands in MOF synthesis. This is first because of the presence of an electron rich Lewis basic azo (−NN−) group in azbpy which is helpful for selective uptake of carbon dioxide gas.20,21 Second, the delocalized π-electrons of the pyridyl ring of the said ligand are also capable to promote the photo-

The metal−organic frameworks (MOFs) are exhilarating class of materials and their design has become an important area in interdisciplinary research. This is principally due to their endless potential applications in several important fields of chemistry as well as materials science such as gas storage and separation,1−3 photoluminescence,4,5 catalysis,6,7 magnetism,8−10 fuel cell,11−13 barrier diode,14,15 photoelectric material16,17 so on and so forth. In last few decades, the contemporary researchers have successfully synthesized numerous MOFs and implemented them for showing several significant properties. The gas storage and separation, particularly the selective trapping of carbon dioxide1−3 is very much important for minimizing sky-rocketing elevation of CO2 concentration; which may cause severe environmental disorder.18,19 On the other hand, a limited number of MOFs have been studied very recently showing fascinating electrical properties for their application in the design of Schottky barrier diode14,15 as well as for solar cell which is very important to the contemporary research for finding out an alternative energy. © XXXX American Chemical Society

Received: September 22, 2017

A

DOI: 10.1021/acs.inorgchem.7b02435 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

(TG) analysis. The photoluminescence properties of the solid compounds 2−4 along with free N,N′-donor azbpy ligand have also been investigated at room temperature.

luminescence as well as electrical conductivity in the resultant MOF.15,22 Notably, the multifunctionalities in MOFs can be tuned by not only the effect of functional group(s) and/or the size/shape of the organic ligand(s); but also it can be dramatically varied through the use of ligand(s) substituted by alkyl group(s) with the same size/shape.23,24 Thus, with the use of functional organic ligand(s) in MOF synthesis for availing desired multifunctionalities,1−17 researchers have focused their attention for the design and synthesis of MOFs, particularly three-dimensional (3D) MOFs.25−28 Hence, exploiting the aforesaid understanding, we have synthesized a set of azo functionalized three-dimensional (3D) Cd(II)-MOFs with an objective to achieve the multifunctionalities in a single MOF. Herein, we report the syntheses and structures of three new azo-functionalized Cd(II)-MOFs, namely, {[Cd(azbpy)(msuc)]·2.5(H2O)}n (2), {[Cd(azbpy)(mglu)]·5(H2O)}n (3), and {[Cd1.5(azbpy)2(glu)]·(NO3)·MeOH}n (4) through the variation of substituted/nonsubstituted aliphatic dicarboxylates by a slow diffusion technique at room temperature. We have studied the photoconduction behavior for the above-mentioned compounds along with our previously reported other similar type of azo-functionalized Cd(II)-MOF, {[Cd(azbpy)(suc)]· 2(H2O)}n (1) to correlate their photoconductivity with the variation of carboxylates used. It is worth mentioning that the descending order of conductivity values for the compounds 1− 4 is 1 > 2 > 4 > 3, which corroborates the effect of length and substituent on the dicarboxylate linkers.14,29,30 We have also performed CO2 adsorption selectivity31,32 study for the azofunctionalized Cd(II)-MOFs of 2−4, where the dehydrated framework of 2 exhibits a typical type-IV enhanced selective CO2 adsorption over N2. Thus, the compounds show two environmentally important properties together, such as photoconduction and selective carbon dioxide adsorption, where there is a visible role of substituted/nonsubstituted aliphatic dicarboxylate(s) to control both the functionalities. From the aforesaid order of photoconductivity for compounds 1−4, it is quite obvious that the traveling distance for π-electron delocalization between the two adjacent Cd(II) centers is comparatively shorter for succinate/methyl substituted succinate than the glutarate/methyl substituted glutarate. Besides, the methyl substitution in both the succinate and glutarate can hinder the easiness of electron delocalization, which can affect negatively for showing electrical conductivity for compounds 2 and 3 compared to 1 and 4. On the other hand, in terms of the CO2 uptake capacities for the newly synthesized compounds (i.e., 2, 3, and 4), the order is also the same, which is 2 > 4 > 3. The glutarate-/methyl-substituted glutarate contain larger chain length than the succinate/methyl substituted succinate, so it can form the interpenetrated or noninterpenetrated structure accompanying with small pore channel more easily due to its higher structural flexibility. Besides, the methyl substitution with the respective dicarboxylate can also encumber the incoming of the quadrupolar CO2 molecule into the azo functionalized polar pore channel. These two factors can affect individually and/or additively for showing the aforesaid order for CO2 uptake capacities for compounds 2−4. The materials, therefore, have possible importance for design of device for producing photocurrent and also for selective adsorption of CO2 from the environment, simultaneously. The compounds 2−4 have been characterized by single crystal X-ray crystallography, IR spectroscopy, powder X-ray diffraction (PXRD), elemental analysis, and thermogravimetric

■

EXPERIMENTAL SECTION

Materials. The 4,4′-azobispyridine (azbpy) ligand has been prepared according to literature procedures.33 The preparatory material for the desired ligand synthesis, i.e. 4-aminopyridine, was purchased from Sigma-Aldrich Chemical Co. Inc. and used as received. Besides, cadmium(II) nitrate tetrahydrate, methylsuccinic acid (H2msuc), glutaric acid (H2glu), and methylglutaric acid (H2mglu) were also purchased from Sigma-Aldrich Chemical Co. Inc. and used as received. Disodium salts of the aforesaid dicarboxylic acids have been synthesized by the continuing addition of Na2CO3 to the aqueous suspension of all dicarboxylic acids individually in 1:1 ratio; in the meantime neutralization was also checked by measuring the pH of the solution and then it was allowed to stand for 45 min. After that, the solvent was evaporated in water bath to dryness. All other chemicals and solvents were AR grade and were used as received. Physical Measurements. For all the compounds, elemental analyses (C, H, and N) were performed using a Heraeus CHNS analyzer. FT−IR spectra (4000−400 cm−1) were taken on KBr pellets, using the PerkinElmer Spectrum BX-II IR spectrometer. Thermogravimetric analysis (TGA) was carried out in the temperature range 30− 700 °C using a METTLER TOLEDO TGA 850 thermal analyzer under nitrogen atmosphere (flow rate: 10 cm3 min−1), with a heating rate of 10 °C min−1. Solid state X-ray powder diffraction (PXRD) patterns of the bulk sample were studied in Bruker D8 Discover instrument using Cu Kα radiation. Photoluminescence property was analyzed on a HORIBA Jobin Yvon (Fluoromax-3) fluorescence spectrophotometer. Conductivity and Photosensitivity Measurements. In this report, the electrical conductivity and photosensitivity studies have been performed on a thin film based solid state device. Prior to measuring the electrical parameters we had to fabricate synthesized materials (compounds 1−4) based metal−semiconductor (MS) devices. The devices were fabricated by depositing a thin film of synthesized compounds as it makes a highly stable dispersion in DMF and allowed uniform coating on a large area of ITO coated glass substrate. Prior to developing the thin film, ITO coated glass substrates were cleaned by acetone, ethanol, and distilled water with the help of an ultra-Sonicator repeatedly and sequentially. Then they were dried well by purging nitrogen (N2) gas. All the synthesized compounds were mixed individually with DMF in the right proportion and were sonicated for several minutes until production of a well dispersion. Then on the top of the cleaned ITO coated substrate, just prepared well dispersed compounds 1−4 were spun at 800 rpm for 5 min and, thereafter, at 1000 rpm for another 5 min. Before depositing the aluminum electrode as metal contact, the as-deposited thin film was dried in a vacuum oven at 80 °C for 6 h and then kept in vacuum desiccators overnight to evaporate the solvent part fully. For the characterization of the developed thin film, thickness was measured by surface profiler as 1 μm. The aluminum electrodes were deposited onto the film through a shadow mask by a Vacuum Coating Unit under a base pressure of 10−6 Torr, maintaining the effective area as 7.065 × 10−2 cm−2. For electrical characterization of the device, the current−voltage (I− V) characteristic was measured under both dark and illumination condition and recorded with the help of a Keithley 2400 source meter by a two-probe technique. All the measurements were performed at room temperature and under ambient conditions. Sorption Measurements. The adsorption isotherms of N2 (77 K) and CO2 (195 K) were measured for dehydrated 2−4 using a Quantachrome Autosorb-iQ adsorption instrument. High purity gases were used for the adsorption measurements (nitrogen, 99.999% and carbon dioxide, 99.95%). The nitrogen gas adsorption was carried out at 77 K taking the dehydrated samples of 2−4 individually, maintaining the temperature by a liquid-nitrogen bath, with pressure ranging from 0 to 1 bar, and also the carbon dioxide adsorption for the B


Article

Inorganic Chemistry dehydrated framework of said compounds were measured at 195 K (maintained by dry ice-acetone cold bath) in the same pressure range using the same instrument. For the aforesaid purposes, the as synthesized compounds of 2, 3, and 4 (∼50 mg) were placed in the sample tube and dehydrated at 423 K, under a 1 × 10−1 Pa vacuum for about 4 h prior to measurement of the isotherms. Helium gas (99.999% purity) at a certain pressure was utilized to calculate the dead volume. Different gases were introduced in the gas chamber and allowed to diffuse into the sample chamber by opening the valve. The amount of gas adsorbed was calculated from the pressure difference (Pcal − Pe), where Pcal is the calculated pressure with no gas adsorption and Pe is the observed pressure at equilibrium. All operations were computer-controlled and automatic. Using a similar procedure, adsorption isotherms for different solvents (i.e., H2O and dry EtOH) were measured at 298 K in the pressure range 0 to 21 Torr for H2O and 0 to 42 Torr for EtOH, respectively, in their vapor state by taking the dehydrated compounds of 2−4 using the same instrument. The samples of 2, 3, and 4 (∼50 mg) were activated under similar conditions as mentioned earlier. The different solvent molecules used to generate the vapor were degassed fully by repeated evacuation. Crystallographic Data Collection and Refinement. The single crystals of compounds 2−4 were mounted on the tip of thin glass fibers with commercially available super glue. X-ray single crystal data collection for three complexes was performed using a Bruker APEX II diffractometer at room temperature, equipped with a normal focus, sealed tube X-ray source with graphite monochromated Mo Kα radiation (λ= 0.71073 Å). The data were integrated using the SAINT34 program, and the absorption corrections were made with SADABS.35 The structures were solved by direct methods (SIR-92),36 and full-matrix least-squares refinements were carried out on F2 for all non-hydrogen atoms using SHELXL-2016/437 with anisotropic displacement parameters. The lattice water molecule (O3W) for complex 2 is in special position with 0.5 occupancy; but due to high thermal disorder, it was split into two fragments of 0.25 occupancy and refined isotropically without any hydrogen atom. Similarly, for complex 4, the oxygen atoms (i.e., O6 and O7) of lattice nitrate ion are very thermally disordered; so each of them are split into two fragments with 0.5 occupancy and isotropically refined. Besides, for complex 3 the lattice water molecule (O5W) also being highly thermal disordered, no hydrogen atom has been fixed with it. All other hydrogen atoms were fixed geometrically at their proper positions either by HFIX command or by using the OLEX238 program. All the calculations and molecular graphics were carried out using SHELXL2016/4,37 PLATON v1.15,39 WinGX system Ver-1.80,40 DIAMOND,41 MERCURY,42 and TOPOS43,44 program. The crystallographic data collection and structural refinement parameters for the compounds 2−4 are specified in Table 1. CCDC 1575852−1575854 contain the supplementary crystallographic data for this paper. Synthesis. {[Cd(azbpy)(suc)]·2(H2O)}n (1). The compound was reported earlier by our group.45 Here it has been taken into consideration to compare the photoswitchable electrical properties with the other compounds (2−4). It is needless to mention that the compound 1 was prepared as described in the reported procedure.45 {[Cd(azbpy)(msuc)]·2.5(H2O)}n (2). An aqueous solution (10 mL) of methylsuccinate (msuc2−) salt (1 mmol, 0.176 g) was added to the methanolic solution (10 mL) of 4,4′-azobispyridine (azbpy) (1 mmol, 0.184 g) and stirred for 30 min for making a homogeneous mixture. In a separate beaker Cd(NO3)2·4H2O (1 mmol, 0.308 g) was dissolved in 10 mL of water. After that, in a crystal tube 2 mL of Cd(II) solution was slowly and carefully layered with 4 mL of the above-mentioned mixed-ligand solution using a 5 mL of buffer solution (1:1 of H2O and MeOH) in the junction of the two solutions. The sealing tube was kept undisturbed at room temperature. After 4 weeks, red colored block shaped single crystals appeared, which is suitable for single crystal X-ray diffraction analysis. The crystals were separated and washed with a methanol−water (1:1) mixture and dried under air (Yield 55%). Anal. Calc. of C60H76 N16O26Cd4 (%): C, 38.19; H, 4.04; N, 11.88. Found: C, 38.25; H, 4.09; N, 11.86. IR spectra (in cm−1): ν(H2O), 3412; ν(CC, Ar), 1416 (stretch); ν(C−H, alkane), 2943

Table 1. Data Collection and Refinement Parameters for Single Crystal Analysis for Complexes 2−4 compound formula formula weight crystal system space group a/Å b/Å c/Å α/deg β/deg γ/deg V/Å3 Z Dc/g cm−3 μ /mm−1 F(000) θ range/deg reflections collected unique reflections reflections (I > 2σ(I)) Rint goodness-of-fit (F2) R1 (I > 2σ(I))a wR2 (I > 2σ(I))a Δρ min/max/e Å3 a

2

3

4

C60H76 N16O26Cd4 1886.96 monoclinic I2/a 14.304(5) 11.610(5) 24.471(5) 90 106.443(5) 90 3898(2) 2 1.604 1.160 1888 2.0−27.6 65093

C16H26 N4O9Cd 530.81 monoclinic C2/c 23.102(5) 14.275(5) 13.712(5) 90 104.738(5) 90 4373(2) 8 1.606 1.052 2144 1.7−27.6 34715

C52H52N18O16Cd3 1522.31 monoclinic P21/n 10.105(5) 20.995(5) 13.705(5) 90 90.678(5) 90 2907.4(19) 2 1.739 1.172 1524 1.8−27.5 48927

4512 3887

5060 3355

6616 6276

0.043 1.06

0.094 1.01

0.028 1.22

0.0372 0.0957 −0.47, 1.73

0.0499 0.1370 −0.92, 1.18

0.0558 0.1200 −1.99, 2.65

R1 = ∑||Fo| − |Fc||/∑|Fo|, wR2 = [∑(w (Fo 2 − Fc2) 2)/∑w(Fo2)2]1/2.

(stretch), 1417−1296 (bending); ν(C−O), 1300 (stretch); and ν(N = N), 1563 (Figure S1). {[Cd(azbpy)(mglu)]·5(H2O)}n (3). Complex 3 was synthesized by the same procedure as that of 2 using methylglutarate (mglu2−) salt (1 mmol, 0.190 g) instead of methylsuccinate (msuc2−) (1 mmol, 0.176 g). The orange colored block shaped crystals suitable for X-ray diffraction analysis were obtained after 3 weeks. The crystals were separated and washed with a methanol−water (1:1) mixture and dried under air (Yield 70%). Anal. Calc. for C16H26 N4O9Cd (%): C, 36.20; H, 4.94; N, 10.56. Found: C, 36.25; H, 4.96; N, 10.58. IR spectra (in cm−1): ν(H2O), 3403; ν(CC, Ar), 1413 (stretch); ν(C−H, alkane); 2950 (stretch); 1405 (bending); ν(C−O), 1228 (stretch); and ν(N = N), 1564 (Figure S2). {[Cd1.5(azbpy)2(glu)]·(NO3)·MeOH}n (4). Complex 4 was synthesized by the same procedure as that of 2 using glutarate (glu2−) salt (1 mmol, 0.176 g) instead of methylsuccinate (msuc2−) (1 mmol, 0.176 g). The red colored block shaped crystals suitable for X-ray diffraction analysis were obtained after 5 weeks. The crystals were separated and washed with a methanol−water (1:1) mixture and dried under air (Yield 45%). Anal. Calc. for C52H52N18O16Cd3 (%): C, 41.03; H, 3.44; N, 16.56. Found: C, 41.06; H, 3.40; N, 16.58. IR spectra (in cm−1): ν(H2O), 3402; ν(C = C, Ar), 1421 (stretch); ν(C−H, alkane), 2956 (stretch) 1383 (bending); ν(C−O), 1218 (stretch) and ν(N = N), 1565 (Figure S3). The purity of the complexes was investigated by measuring solid state PXRD at room temperature, which gives good correspondence with the simulated PXRD patterns. The purity of the bulk samples was further confirmed by the results of elemental analysis and IR spectra as well, which were also found in accordance with the data obtained for the single crystals. C


Article

Inorganic Chemistry

Figure 1. (a, b) Atom labeling scheme showing the coordination environment around the heptacoordinated Cd(II) ion in 2 and 3, respectively, where Cd (green for 2 and pink for 3), O (red), N (blue), and C (black) (some of N,N′-donor azbpy ligands and dicarboxylates are omitted for clarity).

Figure 2. (a,b,c) Metal-carboxylate 2D (4,4) layer showing the bis-chelated oxo-bridging fashion of methylsuccinate and methylglutarate in compounds 2 and 3, respectively, where both the metal and respective carboxylate behave as a 3-connected node. (d) Honeycomb like 3D structure through the pillaring of metal carboxylate 2D layer by the azbpy ligands in a criss-cross fashion in 2. (e) Honeycomb like 3D structure pillared by the azbpy ligands in a criss-crooss manner showing guest water filled 1D channel along crystallographic c-axis in 3.

■

RESULTS AND DISSCUSSION Structural Descriptions. {[Cd(azbpy)(suc)]·2(H2O)}n (1). The structural explanation of compound 1 was extensively discussed in our previously reported work.45 Compound 1 was crystallized in the monoclinic C2/c space group, and it exhibits a honeycomb-like three-dimensional (3D) porous framework with the guest water filled 1D channel showing a heptacoordinated CdO5N2 coordination environment. {[Cd(azbpy)(msuc)]·2.5(H2O)}n (2) and {[Cd(azbpy)(mglu)]· 5(H2O)}n (3). Compounds 2 and 3 are isostructural with compound 1 but incompatible only on the basis of the coligands used, viz. methylsuccinate (msuc2−) and methylglutarate (mglu2−) and lattice water molecules. Both compounds 2 and 3 belong in the monoclinic system but crystallized in the I2/a and C2/c space group, respectively. The structural analysis of compounds 2 and 3 reveals that the formation of a honeycomb like 3D structure constructed through the coordination of Cd(II) metal ion with both the N,N′-donor azbpy linker and respective dicarboxylate, e.g. msuc2− for 2 and mglu2− for 3. The asymmetric unit of both the

compounds contains one Cd(II) ion, one azbpy linker, one respective dicarboxylate, along with a different number of lattice water molecules viz. two and a half water molecules for 2 and five water molecules for 3, respectively. In both cases, the heptacoordinated Cd(II) centers form a distorted pentagonal bipyramidal geometry with a CdO5N2 coordination environment (Figures 1a for 2 and 1b for 3) surrounded by the five oxygen atoms (O1, O2, O3a, O4a, and O4b) from three different dicarboxylates in the basal plane and two nitrogen atoms (N1 and N4c for 2 and N1 and N4 for 3) from two different azbpy ligands in the axial positions, respectively. The Cd−O bond lengths vary from 2.327(3) to 2.451(3) Å for 2 and 2.327(4) to 2.505(4) Å for 3, whereas the axial Cd−N bond lengths are in the range of 2.322(3) to 2.328(3) Å for 2 and 2.326(4) to 2.332(4) Å for 3 (Tables S1 for 2 and S4 for 3), respectively. Here in both cases, each methylated dicarboxylate bridges with three adjacent Cd(II) centers through bis-chelated mono oxo-bridging fashion to form a 2D (4,4) layer (Figures 2a,b for 2 and 2b,c for 3). Moreover, the 2D (4,4) layer in both 2 and 3 is pillared by the N,N′-donor azbpy linkers in a criss-cross fashion, resulting in the formation D


Article

Inorganic Chemistry

Figure 3. (a) Atom labeling scheme showing the coordination environment around both heptacoordinated (green) and hexacoordinated (pink) Cd(II) center in 4: O (red), N (blue), and C (black). (b,c) One dimensional metal-carboxylate ladder showing bis-chelated bis oxo-bridging fashion from both the carboxylate groups of glutarate ions in 4. (d) Three-dimensional (3D) framework of 4 constructed through the bipillaring of metal carboxylate 1D ladders by azbpy ligands in 4, where Cd1 centers (green) are bipillared by azbpy ligands both horizontally and vertically (e,f) and Cd2 centers (pink) are monopillared by the azbpy lignd (e).

of honeycomb like 3D structures containing guest water filled 1D channels along the crystallographic c-axis (Figures 2d and S4a for 2 and 2e for 3). Compound 2 also exhibits a supramolecular 3D structure by means of intermolecular Hbonding and π···π interactions (Figure S4b and Tables S2 and S3). Though the total solvent accessible voids estimated by PLATON39 through removing the guest water molecules are 883.4 Å3 (22.7%) for 2 and 1272 Å3 (29.08%) for 3, the dimension of the guest water filled 1D channel for 2 is quite appreciable, and it is larger (i.e., 6 × 3 Å2) viewed along the caxis than the negligibly small pore channels of 3 (Figures S6 for 2 and S7 for 3). The TOPOS43,44 analysis of compounds 2 and 3 reveals that the structures of both can be represented as a 3,5c binodal net with stoichiometry (3-c)(5-c) and the corresponding Schläfli symbol for the net is {4·6·8}{4·65·83· 10}(Figure S4c). {[Cd1.5(azbpy)2(glu)]·(NO3)·MeOH}n (4). Single-crystal X-ray analysis reveals that compound 4 crystallizes in the monoclinic P21/n space group. The structural analysis reveals that the formation of a three-dimensional structure was constructed through the bridging of both glutarate and azbpy linker with the Cd(II) centers. The asymmetric unit of 4 contains one and a half Cd(II) centers, two azbpy ligands, one glutarate (glu2−) as a coligand, one lattice methanol, and one nitrate anion as a counterion. There were two types of coordination environments around two crystallographically independent Cd(II) centers (i.e., Cd1 and Cd2), where Cd1 and Cd2 metal centers exhibit a CdO4N3 and CdO4N2 coordination environment to generate a distorted pentagonal bipyramydal and octahedral geometry, respectively. The heptacoordinated coordination environment for the Cd1 center (i.e., CdO4N3) has been originated through the bis-chelation of two different glutarate ions along with ligation of three different azbpy ligands (Figure

3a). On the other hand, the hexacoordinated coordination environment for the Cd2 center (i.e., CdO4N2) has been made by the coordination of two different azbpy ligands along with four different oxo-bridged glutarate dianions with their symmetry related N/O-atoms. For Cd1 and Cd2 centers the Cd−O bond length varies from 2.104(2) to 2.1298(16) Å and 2.0671(19) to 2.129(2) Å, respectively, whereas the Cd−N bond lengths are 2.132(2) and 2.150(2), respectively (Table S5). Here each glut2− bridges with four adjacent Cd(II) centers including two of each Cd1 and Cd2 centers by an interesting bis-chelated bis-oxo bridging fashion. Through this bridging fashion two different glut2− coordinate with six Cd(II) centers (four Cd1 and two Cd2), resulting in the formation of a 1D ladder along the crystallographic a-axis followed by making a Cd6(CO2)4 SBU (Figure 3b,c). In these 1D metal-carboxylate ladders, the Cd1 centers are bipillared and Cd2 centers are monopillared by the N,N′-donor azbpy ligands, resulting in the formation of an overall three-dimensional (3D) framework followed by the formation of 2D layers (Figure 3d−f). Interpenetration analysis with TOPOS43,44 for compound 4 reveals a 2-fold interpenetrated 3D net showing a class IIa interpenetration with Zt = 1 and Zn = 2 (Figure S5). Due to forming an interpenetrated structure and also containing nitrate anions as a counterion, compound 4 basically does not show any pore channel to accommodate the lattice methanol molecules. The topological analysis of compound 4 corroborates a 4,5,6-c trinodal net with stoichiometry (4-c)2(5-c)2(6c), and the Schläfli symbol for the net is{43·63}2{43·67}2{42·610· 8}. Powder X-ray Diffraction (PXRD) Analysis. To confirm the phase purity for the bulk materials of compounds 2−4 with their respective simulated pattern, powder X-ray diffraction (PXRD) experiments were carried out at room temperature E


Article

Inorganic Chemistry

Figure 4. UV−vis absorption spectra (insets) and Tauc’s plots for compounds 1(a), 2(b), 3(c) and 4(d).

are stable up to 190 and 230 °C, respectively, without any weight loss. On the other hand, compound 4 exhibits the weight loss of 4.50% (calcd 4.20%) at ∼113 °C for the loss of one lattice methanol molecule (Figure S9) and the dehydrated framework is stable up to ∼226 °C without any weight loss. With further heating, the dehydrated frameworks of 2, 3, and 4 are collapsed into unidentified product, and finally, they are probably converted into CdO at ∼700 °C (Figure S9). Optical Study. The optical properties of the compounds 1−4 were studied by UV−vis absorption. The absorption spectra were recorded in the solid state by UV−visible spectrophotometer in the wavelength range of 200−1100 nm. The absorption spectra of all the compounds 1−4 are shown in the insets of Figure 4(a), (b), (c), and (d), respectively. The absorption spectra of our synthesized materials illustrate energy absorption in the visible region at about 620−650 nm. The optical band gap of the thin film has been determined from fundamental absorption. This is corresponding to the excitation of electron from valence band to conduction band. The optical band gap energies (Eg) of the as synthesized compounds have been evaluated using Tauc’s equation:46,47

using as-synthesized powder samples of compounds 2−4 individually (Figure S8). For all the compounds, good correspondence exists of the entire peak positions of the simulated patterns with their corresponding as-synthesized patterns, which suggests the phase purity of the as synthesized compounds. Moreover, to check the framework rigidity of the dehydrated frameworks of compounds 2, 3, and 4 (activated at 150 °C) with their respective as synthesized patterns, PXRD measurements (Figure S8) have been also performed, where in all cases dehydrated frameworks show almost identical peak position to their corresponding as synthesized pattern, indicating the framework rigidity after complete removal of all volatiles. We have also studied the PXRD patterns for compounds 2−4 to ensure their chemical stability after solvent (i.e., H2O and EtOH) adsorption. The PXRD patterns of 2−4 after solvent adsorption exhibit similar framework integrity through the identical emergence of most of the significant peak positions with their respective as-synthesized as well as simulated PXRD patterns (Figure S8), which signature the framework robustness for the respective compound. Thermogravimetric Analysis (TGA). Thermogravimetric analysis (TGA) of compounds 2−4 has been carried out in the temperature range 30−700 °C with a heating rate of 10 °C min−1 and depicted in Figure S9. Before starting the analysis, compound 2 lost the thermally disordered water molecule O3W (split into two fragments with 0.25 occupancy for each of O3Wa and O3Wb) and compound 3 lost two thermally disordered lattice water molecules at room temperature. Both compounds 2 and 3 show the starting of weight loss for releasing of water molecules at temperature ∼40 °C. Compound 2 shows the weight loss of 7.18% (calcd 7.77%) at 160 °C for the remaining two lattice water molecules (Figure S9), whereas compound 3 shows the weight loss of 10.71% (calcd, 10.91%) at 201 °C for the remaining three lattice water molecules (Figure S9). The dehydrated frameworks of 2 and 3

αhν = A (hν − Eg )n

(1)

where “α” is the absorption coefficient, “Eg” is the band gap, “h” is Planck’s constant, “ν” is the frequency of light, and “n” is a constant. The value of “n” depends upon the nature of the transitions. For direct transition, n = 1/2 and for indirect allowed transitions n = 2.46,47 “A” is a constant, and it is dependent on temperature, photoenergy, and phonon energy. In an ideal case the value of “A” is taken as 1. Here we have determined the direct band gap of our synthesized materials. Hence the value of “n” in the above equation has been considered as n = 1/2.46,47 By extrapolating the linear portion of the plot (αhν)2 vs hν to α = 0 absorption, the values of the F


Article

Inorganic Chemistry

Much to our delight, the I−V characteristic curves in Figure 5 show that the devices based on our synthesized compounds exhibit highly nonlinear behavior. The nonlinearity of the I−V characteristic indicates that the prevalent conduction mechanism is non-Ohmic in nature. This nonlinearity nature also presumed the formation of some sort of junction between aluminum (metal) and composites (semiconductor). The nature of the I−V curve represents the rectifying nature, which is the signature of the Schottky diode behavior. Also the I−V characteristics of all the thin film devices with synthesized compounds show highly influencing rectifying nature upon irradiance of light. Hence, we have calculated the photosensitivity as 4, 3.82, 2.76, and 3.09 for the compounds 1−4, respectively. The rectification ratios (i.e., On/Off ratio) of the devices in dark condition have been found to be 28.85, 22.96, 18.76, and 21.23 for the compounds 1−4, respectively, whereas the same was enhanced after light soaking and it was measured as 75.29, 44.62, 28.73, and 37.43 for the compounds 1−4, respectively. These significant improvements in the rectifying nature of the devices are quite appreciable for these kinds of metal−organic framework materials. To get better insight into the fundamental machinery of charge transport and also the effect of incident light on the transport mechanism, we have studied the I−V characteristics by employing thermionic emission theory. In this regard, we started I−V curves analyzing quantitatively by considering the following standard equations:48,49

optical indirect band gaps of synthesized compounds have been evaluated as 2.00, 1.90, 1.95, and 1.92 eV for 1−4, respectively. The synthesized compounds exhibit strong absorbance in the visible wavelength range with band gap energy in the semiconducting region. This phenomenon predicts some impact of incident radiation on the charge transport property. Hence to check the applicability of the said compounds in the semiconductor field and for better understanding of the charge transport phenomenon, electrical characterization has been carried out. Electrical Study. To observe the electric behavior of the synthesized materials (i.e., compounds 1−4), a sandwich structured thin film device of Al/Cd-MOF/ITO configuration has been fabricated. At first, the electrical conductivity of the fabricated thin film has been determined in dark condition and under AM 1.5G radiation. The conductivity of the thin film device was measured in dark as 3.2 × 10−3 S m−1, 2.64 × 10−3 S m−1, 1.29 × 10−3 S m−1, and 2.07 × 10−3 S m−1 for compounds 1−4, respectively. Maintaining all experimental conditions the same, the conductivities of those films were measured under illumination conditions as 1.65 × 10−2 S m−1, 9.76 × 10−3 S m−1, 3.61 × 10−3 S m−1, and 6.60 × 10−3 S m−1 for compounds 1−4, respectively. The obtained optical band gap and the estimated electrical conductivity lie well within the semiconductor limit. Motivated from these results, the current− voltage (I−V) measurements of Al/Cd-MOF/ITO structured devices were performed within the voltage range ±2.0 V. Figure 5 represents the current−voltage (I−V) characteristic curves for compounds 1−4 based thin film devices under dark and photoillumination conditions.

⎛ qV ⎞⎡ ⎛ −qV ⎞⎤ I = I0 exp⎜ ⎟⎢1 − exp⎜ ⎟⎥ ⎝ ηkT ⎠⎣ ⎝ ηkT ⎠⎦

(2)

where I0 is the saturation current derived from the straight line intercept of ln(I) at V = 0 and is given by ⎛ −q ⌀B ⎞ ⎟ I0 = AA*T 2 exp⎜ ⎝ kT ⎠

(3)

where q stands for the electronic charge, k is the Boltzmann constant, T is the temperature in Kelvin, V is the forward bias voltage, A is the effective diode area, η is the ideality factor, and A* is the effective Richardson constant, respectively. The effective Richardson constant has been considered as 32 AK−2 cm−2 for all the devices. At low bias, linearity in current is observed, which is consistent with eq 2, while the deviation from linearity at higher bias voltages occurred due to the change in diode series resistance. From Cheung,49 in terms of

Figure 5. Current−voltage (I−V) characteristics curve for Al/CdMOF/ITO, structured thin film devices in compounds 1−4.

Figure 6. dV/d(ln I) vs I curves under dark (a) and photoillumination conditions (b) for all the compounds 1−4 based thin film devices, respectively. G


Article

Inorganic Chemistry Table 2. Different Parameters of 1−4 Related to the Analysis of Electrical Properties compound 1 parameters

dark

photosensitivity on/off conductivity (Sm1−) Ideality factor barrier height (eV) Rs from dv/d ln I (Ohm) Rs from H (Ohm)

3.96−4 18.76 1.29 × 10−3 3.24 0.398 1135.42 1057.84

compound 2

light

dark

75.29 1.65 × 10−2 1.22 0.294 225.79 222.96

3.82 22.96 2.64 × 10−3 2.11 0.348 575 582

compound 3

light

dark

44.62 9.76 × 10−3 1.74 0.317 262 270

2.76 18.76 1.29 × 10−3 3.24 0.398 1135.42 1057.84

compound 4

light

dark

light

28.73 3.61 × 10−3 2.88 0.347 802.62 747.16

3.09 21.23 2.07 × 10−3 2.67 0.382 687.40 655.09

37.43 6.60 × 10−3 2.19 0.332 303.31 293.43

Figure 7. H vs I curves under dark (a) and photoillumination condition (b) for all the compounds 1−4 based thin film devices, respectively.

just obtained ideality factor (η) value. A plot of H(V) versus I will also lead to a straight line (Figure 7) with the y-axis intercept being equal to η⌀B. The measured potential height (⌀B), ideality factor (η), and series resistance (RS) under dark and photoillumination conditions for the metal (Al)−semiconductor (synthesized compounds) (MS) junctions are listed in Table 2. It is evident from Table 2 that both methods (eqs 5 and 6) using Cheung’s functions returned more or less the same result. Series resistance (RS) of all the compounds in both cases decreases after soaking light, which signifies its applicability in the field of optoelectronics devices. From Table 2, it can be seen that each and every parameter for compound 1 based thin film metal−semiconductor (MS) devices shows better performance than the other three compounds. Even the performance of compound 1 improves more after light soaking than the other three compounds. It shows a higher photosensitivity (∼4), which is quite appreciable for these kinds of compounds. After light soaking, the ideality factor of compound 1 approaches very close to 1, indicating a more ideal device, which is generally an indication of less interfacial charge recombination and better homogeneity of Schottky junctions;52 that is, it may be stated that our synthesized compound 1 possesses less carrier recombination at the junction, i.e. better barrier homogeneity. Also the higher rectification ratio under photoirradiance conditions for compound 1 is attributed to the lower barrier height. From the Table 2, it can be seen that the compound 1 based MS junction device possesses lower barrier height. In the presence of light irradiance, the series resistance of compound 1 is drastically reduced compared to the others attributed to the large increase of photocurrent. All the calculated parameters are the evidence of compound 1 being a better contender in the field of optoelectronics. It is quite obvious that the structures of all the compounds 1−4 exhibit either an iso-structural or closely comparable 3D

series resistance the forward bias I−V characteristics can be expressed as ⎡ q(V − IR S) ⎤ I = I0 exp⎢ ⎥ ⎦ ⎣ η kT

(4)

where the IRS term is the voltage drop across the series resistance of the device. In this context, the values of the series resistance can be determined from the following functions using eq 450 ⎛ ηkT ⎞ dV =⎜ ⎟ + IR S d ln(I ) ⎝ q ⎠

(5)

Equation 5 also can be expressed as a function of I as H(I ) = IR S + η ⌀B

(6)

and H(I) is given as follows: ⎛ ηkT ⎞ ⎛ I ⎞ ⎟ H (I ) = V − ⎜ ⎟ ln⎜ ⎝ q ⎠ ⎝ AA*T 2 ⎠

(7)

The series resistance (RS) and ideality factor (η) for all devices under dark conditions have been determined from the slope and intercept of the dV/d ln(I) vs I plot (Figure 6). The obtained values of ideality factors for all the four devices under both dark and photoillumination conditions are listed in Table 2. From Table 2 we have found that the formed MS junction is not exactly ideal. This indicates the presence of inhomogeneities of the Schottky barrier height and the existence of interface states and series resistance.51 Equation 5 exhibits a straight line region, where the series resistance dominates, for the data in the downward-curvature region of the forward bias I−V characteristics. Thus, the plot of dV/d(lnI) vs I will give RS as the slope and ηkT/q as the yintercept. The value of H can be calculated from eq 6 using the H


Article

Inorganic Chemistry frameworks, where the closely placed Cd(II) metal centers are connected through the N,N′-donor azbpy ligand and their respective substituted/nonsubstituted aliphatic dicarboxylates. However, compounds 1−4 exhibit their different extents of electrical conductivity as well as enhanced semiconducting properties under photoilluminated conditions through charge transportation, which might be due to many factors, such as (i) metal−metal direct interaction and short metal to metal distance,14,53 (ii) formation of intermolecular H-bonding between the framework and the guest water molecules occupying the interstitial holes in MOFs,54 (iii) mixed valence oxidation state in the metal ions,55−57 (iv) the presence of lattice inorganic/organic moieties,14,15,22 and (v) dimensionality of MOFs.14,15,58−60 However, here all the compounds contain the same metal ion and also form a similar or closely similar 3D framework. So, in these cases, the role of ligands is the key factor for controlling their differences in conductivity values. It is well-known that the extent of charge transport in MOFs unwaveringly depends on the interaction (effective overlap of frontier orbitals) between the d-orbital of metal ions and the p-orbital of organic ligands. So in this case, the effective overlap of the dπ-orbitals of Cd(II)-ion with the pπ-orbital of the azbpy ligand can easily delocalized the charge between adjacent metal centers through the ligand, resulting in the semiconducting behavior of the compounds. But interestingly, the conductivity values for compounds 1−4 are quite different from each other; which might be due to the variation of size and structural substitution in the respective dicarboxylates used. However, the conductivity values for 1−4 corroborate that the shorter chain length of dicarboxylate (i.e., succinate) precedes over the longer chain one (i.e., glutarate), because the metal-tometal direct interactions are a very important factor for showing conductivity. Thus, when the metals are very close enough to form a metal−metal bond through the use of organic ligand(s) having very short chain length, then it is quite expected to show high conductivity value. Nevertheless, when the metal−metal distance increases with the use of organic ligand(s) having comparatively larger chain length, then the conductivity values should be decreased. Besides, the alkyl substitution in a same ligand (linker) can also hinder the charge delocalization process, so that the nonsubstituted one can give a better result than the methyl substituted one. Moreover, in compounds 1− 4, the lattice water molecules are placed in the interstitial position and stabilized through the formation of intermolecular H-bonding with the respective framework, which may affect additively for showing electrical conductivity for compounds 1−4. Gas and Solvent Vapor Sorption Study. Possessing effective solvent accessible voids and showing high thermal stability in the dehydrated frameworks of compounds 2 and 3, we have performed the sorption study on their dehydrated frameworks for different gases (e.g., N2 at 77 K and CO2 at 195 K) along with solvent vapors (e.g., H2O and dry EtOH at 298 K). A similar gas and solvent sorption study has also been carried out for the nonporous interpenetrated framework of 4. All the compounds were found to be stable and retain their framework stability after different solvent (i.e., H2O and dry EtOH) sorption measurements (Figure S8). Compound 2 possessed one-dimensional water filled channels (Figure S6c) along the crystallographic c-axis. Hence, it shows a typical type-III surface adsorption for N2 up to 106 cc/g at 1 bar (Figure 8). This is quite obvious because of having a comparably larger kinetic diameter of the

Figure 8. Different gas sorption isotherms for the dehydrated framework of 2 (CO2 at 195 K and N2 at 77K), where the filled and open symbols indicate adsorption and desorption isotherms, respectively.

N2 gas molecule (3.6 Å) than the pore size in the dehydrated framework of 2. It exhibits a two step gate opening CO2 adsorption isotherm, which sharply rises at the beginning and then at 0.30 bar up to a value of 145 cc/g (i.e., 28.5 wt %) at 1 bar, which is basically a typical type-IV CO2 adsorption isotherm (Figure 8). The selective uptake of CO2 over N2 by the dehydrated framework of 2 might be due to the smaller size of CO2 (3.3 Å) than N2 (3.6 Å) and also having a quadrupolar moment of CO2 gas molecules. The dehydrated framework of 2 also produces a reversible desorption isotherm for CO2, showing a large hysteresis with the adsorption isotherm, which corroborates a very strong adsorbate−adsorbent interaction61−65 during CO2 gas adsorption (Figure 8). To understand the interactions between the polar framework and the polar solvent molecules, we have measured the H2O and EtOH adsorption for dehydrated 2. It shows type-IV H2O adsorption isotherms up to 170 cc/g at P/Po = 0.9 accompanied by a desorption isotherm with a large hysteresis and incomplete branch signifying the strong interaction of the H2O molecule with the polar framework (Figure 9).61−65 The EtOH adsorption isotherms show an uptake of 120 cc/g at P/ Po = 0.9, and therefore, it can be stated that compound 2 shows selective H2O sorption over EtOH (Figure 9). Though the dehydrated framework of compound 3 possesses effective

Figure 9. H2O sorption (violet hexagons) and EtOH sorption (pink stars) of 2 at 298 K, respectively, where, the filled and opened symbols signify the adsorption and desorption isotherms in each case. I


Article

Inorganic Chemistry solvent accessible void spaces but its space filling model (Figure S7) does not show any water filled channel with significant dimension along any of the crystallographic axes. So the dehydrated framework of 3 shows a typical type-II CO2 adsorption isotherm up to 12 cc/g at 1 bar along with a surface adsorption for N2 up to 87 cc/g at 0.99 bar (Figure S10). Reversely the adsorption isotherms generate the desorption isotherm with a large hysteresis in between them signifying the strong adsorbate−adsorbent interaction.61−65 On account of the solvent sorption, dehydrated 3 exhibits a two step gate opened type-IV adsorption isotherm for water vapor up to 332 cc/g at P/Po = 0.9, where the sharp rising occurs at the beginning and P/Po = 0.3, respectively (Figure 10). On the

molecules and detection of metal ions, non linear optical (NLO) diode fabrication, and electroluminescence display,66−68 etc. The photoluminescence study of complexes 2−4 with free azbpy ligand has been investigated at room temperature, which is shown in Figure S13. Each N,N′-donor azbpy ligand and compounds 2−4 exhibit two emission peaks with maxima at 567 and 760 nm (λex = 467 nm), 568 and 768 nm (λex = 480 nm), 570 and 765 (λex = 482 nm) nm, and 569 and 764 nm (λex = 471 nm), respectively. All the compounds 2−4 exhibit a similar type free azbpy ligand based emission spectra, which are slightly red-shifted compared to the emission spectra of free N,N′-donor azbpy ligand. For the aromatic N,N′-donor azbpy ligand the emission may be due to the π*−n or π*−π transition. Similarly for complexes 2−4 the emission may occur through the intraligand charge transfer (ILCT) process from π*−n or π*−π due to having no possibility of MLCT/LMCT charge transfer, since the d10 metal ions are difficult to be reduced or oxidized.69,70 The variation of enhancement of luminescent intensity through coordination of the azbpy ligand in the MOFs can be regulated through the variation of the coordination capability of Cd(II) ions with the O-donor dicarboxylates used.

■

CONCLUSION In the past few decades, the synthesis and characterization of low-dimensional crystalline conducting materials have been studied extensively for their potential applications in electronics and optoelectronic devices as well as in selective adsorption. But here we have reported different multifunctional threedimensional (3D) azo functionalized Cd(II)-MOFs with photoswitchable semiconductivity and interesting sorption properties. All of the four Cd(II)-MOFs have labile pyridyl πelecton clouds in the N,N′-donor azbpy ligand, which facilitate the transport of electrons between the adjacent metal centers. This transport of electrons through the −NN− group of the azbpy ligands may originate the electrical conductivity in the said compounds. Moreover, compounds 2−4 exhibit gas uptake capacities particularly selective for CO2 uptake for the dehydrated framework of 2 and 4 as well as fascinating solvent (e.g., H2O and EtOH) adsorption isotherms, corroborating the nature of the polar−polar interaction between the polar adsorbate and polar dehydrated framework of 2−4. It is worthy of note that an unambiguous correlation between the structures and properties regarding their conductivities for 1−4 and gas/solvent uptake capacity for newly synthesized compounds 2−4 has been clearly revealed. In brief, the design of such multifunctional Cd(II)-MOFs showing two different environmentally important functionalities such as generation of photocurrent as a green energy supplier through a solar cell device and suitable CO2 adsorbent through selective sorption is very important in scientific endeavors. Therefore, it can be concluded that the aforesaid multifunctional materials may open up a new avenue toward the generation of smart materials which can perform several functionalities simultaneously.

Figure 10. H2O sorption (violet hexagons) and EtOH sorption (pink stars) of 3 at 298 K, respectively, where the filled and opened symbols signify the adsorption and desorption isotherms in each case.

other hand, it shows a type-II EtOH adsorption up to 31.8 cc/g at P/Po = 0.9 with an incomplete desorption isotherm, which produces large hysteresis with the adsorption isotherm signifying very strong adsobate-adsorbent interaction (Figure 10).61−65 Finally, the interpenetrated nonporous framework of 4 exhibits a selective CO2 adsorption up to 19 cc/g at 195 K and 1 bar pressure with a hysteresis over a negligible amount of surface adsorption for N2 gas (Figure S11). The lower uptake of both CO2 and N2 for the dehydrated framework of 4 is quite logical, as the dehydrated framework of 4 does not contain appreciable void spaces (7% voids w.r.t. total crystal volume) and pore channels due to forming an interpenetrated structure. But the selective uptake of CO2 over N2 is due to having a quadrupole moment of CO2 and it also being smaller size than N2. Besides, the dehydrated framework also contains lattice NO3− ion and a polar −NN− group in the pore wall, which can easily interact with the quadrupolar CO2 molecule. On account of solvent sorption, the dehydrated 4 also exhibits a similar type of H2O and EtOH adsorption isotherms up to 24 cc/g and 23 cc/g, respectively, at P/Po = ∼0.9 and 298 K (Figure S12). Both the solvent adsorption isotherms for the dehydrated framework of 4 produce the desorption isotherm reversibly, showing a large hysteresis between the adsorption and desorption isotherms, which corroborates the stronger interaction of adsorbate molecules with the polar framework.61−65 Luminescent Properties. Recently, the MOFs with d10 metal system showing the photoluminescence properties at room temperature have become very important on account of their potential application in selective sensing of small

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b02435. IR, PXRD patterns, and TGA of compounds 2−4 along with different structural and application based figures J


Article

Inorganic Chemistry

Redox, Luminescence, and Electron Paramagnetic Resonance Activities. Cryst. Growth Des. 2015, 15, 5604−5613. (10) Mahata, P.; Natarajan, S.; Panissod, P.; Drillon, M. Quasi-2D XY Magnetic Properties and Slow Relaxation in a Body Centered Metal Organic Network of [Co4] Clusters. J. Am. Chem. Soc. 2009, 131, 10140−10150. (11) Panda, T.; Kundu, T.; Banerjee, R. Structural Isomerism Leading to Variable Proton Conductivity in Indium (III) Isophthalic Acid Based Frameworks. Chem. Commun. 2013, 49, 6197−6199. (12) Maity, D. K.; Otake, K.; Ghosh, S.; Kitagawa, H.; Ghoshal, D. Sulfonic Group Functionalized Mixed Ligand Coordination Polymers: Synthesis, Characterization, Water Sorption, and Proton Conduction Studies. Inorg. Chem. 2017, 56, 1581−1590. (13) Samanta, D.; Mukherjee, P. S. Structural Diversity in Multinuclear PdII Assemblies that Show Low-Humidity Proton Conduction. Chem. - Eur. J. 2014, 20, 5649−5656. (14) Givaja, G.; Amo-Ochoa, P.; Gómez-García, C. J.; Zamora, F. Electrical conductive coordination polymers. Chem. Soc. Rev. 2012, 41, 115−147. (15) Bhattacharya, B.; Layek, A.; Alam, Md. M.; Maity, D. K.; Chakrabarti, S.; Ray, P. P.; Ghoshal, D. Cd(II) Based Metal−Organic Framework Behaving as a Schottky Barrier Diode. Chem. Commun. 2014, 50, 7858−7861. (16) Meng, S.; Zhang, X.; Zhang, G.; Wang, Y.; Zhang, H.; Huang, F. Synthesis, Crystal Structure, and Photoelectric Properties of a New Layered Bismuth Oxysulfide. Inorg. Chem. 2015, 54, 5768−5773. (17) Zhan, W.-W.; Kuang, Q.; Zhou, J.-Z.; Kong, X.-J.; Xie, Z.-X.; Zheng, L.-S. Semiconductor@Metal−Organic Framework Core−Shell Heterostructures: A Case of ZnO@ZIF-8 Nanorods with Selective Photoelectrochemical Response. J. Am. Chem. Soc. 2013, 135, 1926− 1933. (18) Allen, M. R.; Frame, D. J.; Huntingford, C.; Jones, C. D.; Lowe, J. A.; Meinshausen, M.; Meinshausen, N. Warming caused by cumulative carbon emissions towards the trillionth tonne. Nature 2009, 458, 1163−1166. (19) Meinshausen, M.; Meinshausen, N.; Hare, W.; Raper, S. C. B.; Frieler, K.; Knutti, R.; Frame, D. J.; Allen, M. R. Greenhouse-gas emission targets for limiting global warming to 2 °C. Nature 2009, 458, 1158−1162. (20) Maity, D. K.; Halder, A.; Bhattacharya, B.; Das, A.; Ghoshal, D. Selective CO2 Adsorption by Nitro Functionalized Metal Organic Frameworks. Cryst. Growth Des. 2016, 16, 1162−1167. (21) Maity, D. K.; Halder, A.; Ghosh, S.; Ghoshal, D. Azo Functionalized 5-Nitro-1,3-benzenedicarboxylate Based Coordination Polymers with Different Dimensionality and Functionality. Cryst. Growth Des. 2016, 16, 4793−4804. (22) Bhattacharya, B.; Maity, D. K.; Layek, A.; Jahiruddin, Sk.; Halder, A.; Dey, A.; Ghosh, S.; Chowdhury, C.; Datta, A.; Ray, P. P.; Ghoshal, D. Multifunctional mixed ligand metal organic frameworks: X-ray structure, adsorption, luminescence and electrical conductivity with theoretical correlation. CrystEngComm 2016, 18, 5754−5763. (23) Lin, Z.-J.; Lü, J.; Hong, M.; Cao, R. Metal−organic frameworks based on flexible ligands (FL-MOFs): structures and applications. Chem. Soc. Rev. 2014, 43, 5867−5895. (24) Janiak, C. Engineering coordination polymers towards applications. Dalton Trans. 2003, 14, 2781−2804. (25) Hasegawa, S.; Horike, S.; Matsuda, R.; Furukawa, S.; Mochizuki, K.; Kinoshita, Y.; Kitagawa, S. Three-Dimensional Porous Coordination Polymer Functionalized with Amide Groups Based on Tridentate Ligand: Selective Sorption and Catalysis. J. Am. Chem. Soc. 2007, 129, 2607−2614. (26) D’Vries, R. F.; Iglesias, M.; Snejko, N.; Alvarez-Garcia, S.; Gutiérrez-Puebla, E.; Monge, M. A. Mixed lanthanide succinate− sulfate 3D MOFs: catalysts in nitroaromatic reduction reactions and emitting materials. J. Mater. Chem. 2012, 22, 1191−1198. (27) Eubank, J. F.; Wojtas, L.; Hight, M. R.; Bousquet, T.; Kravtsov, V. C.; Eddaoudi, M. The Next Chapter in MOF Pillaring Strategies: Trigonal Heterofunctional Ligands To Access Targeted High-

(i.e., Figures S1−S13) and tables related to the crystal structures (i.e., Tables S1−S5) reported in this paper. (PDF) Accession Codes

CCDC 1575852−1575854 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

■

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]; Fax: +91 3324146223. *E-mail: [email protected]; Fax: +91 3324138917. ORCID

Partha Pratim Ray: 0000-0003-4616-2577 Debajyoti Ghoshal: 0000-0001-8820-8209 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The authors gratefully acknowledge the financial assistance given by SERB [No. SB/S1/IC-06/2014, grant to D.G.]. D.K.M. acknowledges UGC for the research fellowship. The authors are grateful to Prof. K. K. Rajak for the photoluminescence study.

■

REFERENCES

(1) Nagaraju, D.; Bhagat, D. G.; Banerjee, R.; Kharul, U. K. Situ Growth of Metal-Organic Frameworks on a Porous Ultrafiltration Membrane for Gas Separation. J. Mater. Chem. A 2013, 1, 8828−8835. (2) Kanoo, P.; Mostafa, G.; Matsuda, R.; Kitagawa, S.; Maji, T. K. A Pillared-Bilayer Porous Coordination Polymer With a 1D Channel and a 2D Interlayer Space, Showing Unique Gas and Vapor Sorption. Chem. Commun. 2011, 47, 8106−8108. (3) Maity, D. K.; Halder, A.; Pahari, G.; Haque, F.; Ghoshal, D. Hydrogen Uptake by an Inclined Polycatenated Dynamic Metal− Organic Framework Based Material. Inorg. Chem. 2017, 56, 713−716. (4) Mukherjee, S.; Samanta, D.; Mukherjee, P. S. New Structural Topologies in a Series of 3d Metal Complexes with Isomeric Phenylenediacetates and 1,3,5-Tris(1-imidazolyl)benzene Ligand: Syntheses, Structures, and Magnetic and Luminescence Properties. Cryst. Growth Des. 2013, 13, 5335−5343. (5) Wang, M.-S.; Guo, S.-P.; Li, Y.; Cai, L.-Z.; Zou, J.-P.; Xu, G.; Zhou, W.-W.; Zheng, F.-K.; Guo, G.-C. A Direct White-Light-Emitting Metal−Organic Framework with Tunable Yellow-to-White Photoluminescence by Variation of Excitation Light. J. Am. Chem. Soc. 2009, 131, 13572−13573. (6) Gole, B.; Sanyal, U.; Mukherjee, P. S. A Smart Approach to Achieve an Exceptionally High Loading of Metal Nanoparticles Supported by Functionalized Extended Frameworks for Efficient Catalysis. Chem. Chem. Commun. 2015, 51, 4872−4875. (7) Haldar, R.; Reddy, S. K.; Suresh, V. M.; Mohapatra, S.; Balasubramanian, S.; Maji, T. K. Flexible and Rigid Amine-Functionalized Microporous Frameworks Based on Different Secondary Building Units: Supramolecular Isomerism, Selective CO2 Capture, and Catalysis. Chem. - Eur. J. 2014, 20, 4347−4356. (8) Manna, P.; Tripuramallu, B. K.; Das, S. K. Synthesis, Structural Characterization, and Magnetic Properties of a New Series of Coordination Polymers: Importance of Steric Hindrance at the Coordination Sphere. Cryst. Growth Des. 2012, 12, 4607−4623. (9) Banerjee, K.; Roy, S.; Kotal, M.; Biradha, K. Coordination Polymers Containing Tubular, Layered, and Diamondoid Networks: K


Article

Inorganic Chemistry Connected Three Dimensional Nets, Isoreticular Platforms. J. Am. Chem. Soc. 2011, 133, 17532−17535. (28) Mallick, A.; Schön, E.-M.; Panda, T.; Sreenivas, K.; Díaz, D. D.; Banerjee, R. Fine-Tuning the Balance between Crystallization and Gelation and Enhancement of CO2 Uptake on Functionalized Calcium Based MOFs and Metallogels. J. Mater. Chem. 2012, 22, 14951− 14963. (29) Suzuki, T.; Lutz, T.; Payer, D.; Lin, N.; Tait, S. L.; Costantini, G.; Kerna, K. Substrate effect on supramolecular self-assembly: from semiconductors to metals. Phys. Chem. Chem. Phys. 2009, 11, 6498− 6504. (30) Ikeuchi, S.; Yamamura, Y.; Mitsumi, M.; Toriumi, K.; Saitoh, H.; Atake, T.; Saito, K. Effects of Alkyl Length in Ligands in Mixed Valence MMX Complexes: Properties of Pt2(n-HexCS2)4I (n-Hex = nHexyl Group). Chem. Lett. 2009, 38, 1190−1191. (31) Rao, K. V.; Mohapatra, S.; Kulkarni, C.; Maji, T. K.; George, S. J. Extended Phenylene Based Microporous Organic Polymers with Selective Carbon Dioxide Adsorption. J. Mater. Chem. 2011, 21, 12958−12963. (32) Nagarkar, S. S.; Chaudhari, A. K.; Ghosh, S. K. Selective CO2 Adsorption in a Robust and Water-Stable Porous Coordination Polymer with New Network Topology. Inorg. Chem. 2012, 51, 572− 576. (33) Theilmann, O.; Saak, W.; Haase, D.; Beckhaus, R. Reactions of Low-Valent Titanocene(II) Fragments with trans-4,4′-Azobispyridine (RNNR, R = C5H4N): Formation of Tetranuclear Molecular Squares by trans-cis Isomerization. Organometallics 2009, 28, 2799− 2807. (34) SMART (V 5.628), SAINT (V 6.45a), XPREP, SHELXTL;Bruker AXS, Inc.: Madison, WI, 2004. (35) Sheldrick, G. M. SADABS (Version 2.03); University of Göttingen: Germany, 2002. (36) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A. Completion and refinement of crystal structures with SIR92. J. Appl. Crystallogr. 1993, 26, 343−350. (37) Sheldrick, G. M. Crystal structure refinement with SHELXL. Acta Crystallogr., Sect. C: Struct. Chem. 2015, C71, 3−8. (38) Dolomanov, O. V.; Bourhis, L. J.; Gildea, R. J.; Howard, J. A. K.; Puschmann, H. OLEX2: A complete structure solution, refinement and analysis program. J. Appl. Crystallogr. 2009, 42, 339−341. (39) Spek, A. L. Structure validation in chemical crystallography. Acta Crystallogr., Sect. D: Biol. Crystallogr. 2009, D65, 148−155. (40) Farrugia, L. J. WinGX suite for small-molecule single-crystal crystallography. J. Appl. Crystallogr. 1999, 32, 837−838. (41) Brandenburg, K. DIAMOND, version 3.1 e; Crystal Impact Gbr, Bonn, Germany, 2007. (42) Macrae, C. F.; Bruno, I. J.; Chisholm, J. A.; Edgington, P. R.; McCabe, P.; Pidcock, E.; Rodriguez-Monge, L.; Taylor, R.; Streek, J. V.; Wood, P. A. Mercury CSD 2.0 − new features for the visualization and investigation of crystal structures. J. Appl. Crystallogr. 2008, 41, 466−470. (43) Blatov, V. A.; Shevchenko, A. P.; Serezhkin, V. N. TOPOS3.2: a new version of the program package for multipurpose crystal-chemical analysis. J. Appl. Crystallogr. 2000, 33, 1193. (44) Blatov, V. A.; Carlucci, L.; Ciani, G.; Proserpio, D. M. Interpenetrating metal−organic and inorganic 3D networks: a computer-aided systematic investigation. Part I. Analysis of the Cambridge structural database. CrystEngComm 2004, 6, 377−395. (45) Bhattacharya, B.; Dey, R.; Pachfule, P.; Banerjee, R.; Ghoshal, D. Four 3D Cd(II)-Based Metal Organic Hybrids with Different N,N′Donor Spacers: Syntheses, Characterizations, and Selective Gas Adsorption Properties. Cryst. Growth Des. 2013, 13, 731−739. (46) Pandiyan, R.; Micheli, V.; Ristic, D.; Bartali, R.; Pepponi, G.; Barozzi, M.; Gottardi, G.; Ferrari, M.; Laidani, N. Structural and nearinfra red luminescence properties of Nd-doped TiO2 films deposited by RF sputtering. J. Mater. Chem. 2012, 22, 22424−22432. (47) Middya, S.; Layek, A.; Dey, A.; Datta, J.; Das, M.; Banerjee, C.; Ray, P. P. Role of Zinc Oxide Nanomorphology on Schottky Diode Properties. Chem. Phys. Lett. 2014, 610, 39−44.

(48) Rhoderick, E. H. Metal Semiconductors Contacts; Oxford University Press: Oxford, 1978. (49) Dey, A.; Middya, S.; Jana, R.; Das, M.; Datta, J.; Layek, A.; Ray, P. P. Light Induced Charge Transport Property Analysis of Nanostructured ZnS Based Schottky Diode. J. Mater. Sci.: Mater. Electron. 2016, 27, 6325−6335. (50) Dey, A.; Layek, A.; Roychowdhury, A.; Das, M.; Datta, J.; Middya, S.; Das, D.; Ray, P. P. Investigation of Charge Transport Properties in Less Defective Nanostructured ZnO Based Schottky Diode. RSC Adv. 2015, 5, 36560−36567. (51) Gupta, R. K.; Yakuphanoglu, F. Photoconductive Schottky Diode Based on Al/p-Si/SnS2/Ag for Optical Sensor Applications. Sol. Energy 2012, 86, 1539−1545. (52) Miao, X.; Tongay, S.; Petterson, M. K.; Berke, K.; Rinzler, A. G.; Appleton, B. R.; Hebard, A. F. High Efficiency Graphene Solar Cells by Chemical Doping. Nano Lett. 2012, 12, 2745−2750. (53) Sun, L.; Campbell, M. G.; Dincă, M. Electrically Conductive Porous Metal−Organic Frameworks. Angew. Chem., Int. Ed. 2016, 55, 3566−3579. (54) Fuma, Y.; Ebihara, M.; Kutsumizu, S.; Kawamura, T. J. Am. Chem. Soc. 2004, 126, 12238−12239. (55) Takazaki, Y.; Yang, Z.; Ebihara, M.; Inoue, K.; Kawamura, T. Chem. Lett. 2003, 32, 120−121. (56) Mitsumi, M.; Yoshida, Y.; Kohyama, A.; Kitagawa, Y.; Ozawa, Y.; Kobayashi, M.; Toriumi, K.; Tadokoro, M.; Ikeda, N.; Okumura, M.; Kurmoo, M. Inorg. Chem. 2009, 48, 6680−6691. (57) Sheberla, D.; Sun, L.; Blood-Forsythe, M. A.; Er, S.; Wade, C. R.; Brozek, C. K.; Aspuru-Guzik, A.; Dincă, M. High electrical conductivity in Ni3 (2, 3, 6, 7, 10, 11-exaiminotriphenylene) 2, a semiconducting metal−organic graphene analogue. J. Am. Chem. Soc. 2014, 136, 8859−8862. (58) Tadokoro, M.; Yasuzuka, S.; Nakamura, M.; Shinoda, T.; Tatenuma, T.; Mitsumi, M.; Ozawa, Y.; Toriumi, K.; Yoshino, H.; Shiomi, D.; Sato, K.; Takui, T.; Mori, T.; Murata, K. A HighConductivity Crystal Containing a Copper (I) Coordination Polymer Bridged by the Organic Acceptor TANC. Angew. Chem., Int. Ed. 2006, 45, 5144−5147. (59) Su, W. P.; Hong, M. C.; Weng, J. B.; Cao, R.; Lu, S. F. A Semiconducting Lamella Polymer [{Ag (C5H4NS)}n] with a GraphiteLike Array of Silver (I) Ions and Its Analogue with a Layered Structure. Angew. Chem., Int. Ed. 2000, 39, 2911−2914. (60) Low, K. H.; Roy, V. A. L. S.; Chui, S. Y.; Chan, S. L. F.; Che, C. M. Highly conducting two-dimensional copper (i) 4-hydroxythiophenolate network. Chem. Commun. 2010, 46, 7328−7330. (61) Henke, S.; Fischer, R. A. Gated Channels in a Honeycomb-like Zinc-Dicarboxylate-Bipyridine Framework with Flexible Alkyl Ether Side Chains. J. Am. Chem. Soc. 2011, 133, 2064−2067. (62) Ma, S.; Wang, X.-S.; Manis, E. S.; Collier, C. D.; Zhou, H.-C. Metal− Organic Framework Based on a Trinickel Secondary Building Unit Exhibiting Gas-Sorption Hysteresis. Inorg. Chem. 2007, 46, 3432−3434. (63) Hua, J.-A.; Zhao, Y.; Liu, Q.; Zhao, D.; Chen, K.; Sun, W.-Y. Zinc (II) coordination polymers with substituted benzenedicarboxylate and tripodal imidazole ligands: syntheses, structures and properties. CrystEngComm 2014, 16, 7536−7546. (64) Park, H. J.; Suh, M. P. Stepwise and hysteretic sorption of N2, O2, CO2, and H2 gases in a porous metal−organic framework [Zn2(BPnDC)2(bpy)]. Chem. Commun. 2010, 46, 610−612. (65) Panda, T.; Gupta, K. M.; Jiang, J.; Banerjee, R. Enhancement of CO2 Uptake in Iso-reticular Co Based Zeolitic Imidazolate Frameworks via Metal Replacement. CrystEngComm 2014, 16, 4677−4680. (66) Lin, W.; Evans, O. R.; Xiong, R.-G.; Wang, Z. Supramolecular engineering of chiral and acentric 2D networks. Synthesis, structures, and second-order nonlinear optical properties of bis (nicotinato) zinc and bis {3-[2-(4-pyridyl)ethenyl]benzoato}cadmium. J. Am. Chem. Soc. 1998, 120, 13272−13273. (67) Moulton, B.; Zaworotko, M. J. From molecules to crystal engineering: supramolecular isomerism and polymorphism in network solids. Chem. Rev. 2001, 101, 1629−1658. L


Article

Inorganic Chemistry (68) Bhattacharya, B.; Halder, A.; Paul, L.; Chakrabarti, S.; Ghoshal, D. Eye-Catching Dual-Fluorescent Dynamic Metal−Organic Framework Senses Traces of Water: Experimental Findings and Theoretical Correlation. Chem. - Eur. J. 2016, 22, 14998−15005. (69) Wen, L.; Lu, Z.; Lin, J.; Tian, Z.; Zhu, H.; Meng, Q. Syntheses, Structures, and Physical Properties of Three Novel Metal−Organic Frameworks Constructed from Aromatic Polycarboxylate Acids and Flexible Imidazole-Based Synthons. Cryst. Growth Des. 2007, 7, 93−99. (70) Zhang, L.-P.; Ma, J.-F.; Yang, J.; Pang, Y.-Y.; Ma, J.-C. Series of 2D and 3D Coordination Polymers Based on 1,2,3,4-Benzenetetracarboxylate and N-Donor Ligands: Synthesis, Topological Structures, and Photoluminescent Properties. Inorg. Chem. 2010, 49, 1535− 1550.

M


Set of Multifunctional Azo Functionalized Semiconducting Cd(II)-MOFs

Recommend Documents