Polar Molecule Confinement Effects on Dielectric Modulations of Sr

Subscriber access provided by UNIV OF SOUTHERN INDIANA

Article

Polar Molecule Confinement Effects on Dielectric Modulations of Sr-Based Metal–Organic Frameworks Muhammad Usman, Pei-Hsuan Feng, Kuan-Ru Chiou, JenqWei Chen, Li-Wei Lee, Yen-Hsiang Liu, and Kuang-Lieh Lu ACS Appl. Electron. Mater., Just Accepted Manuscript • DOI: 10.1021/acsaelm.9b00007 • Publication Date (Web): 10 May 2019 Downloaded from http://pubs.acs.org on May 10, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 29 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

ACS Applied Electronic Materials

Polar Molecule Confinement Effects on Dielectric Modulations of Sr-Based Metal–Organic Frameworks Muhammad Usman,† Pei-Hsuan Feng,‡ Kuan-Ru Chiou,§ Jenq-Wei Chen,§ Li-Wei Lee,† YenHsiang Liu,*‡ Kuang-Lieh Lu*† †

Institute of Chemistry, Academia Sinica, Taipei 115, Taiwan

‡

Department of Chemistry, Fu Jen Catholic University, Taipei 24205, Taiwan

§

Department of Physics, National Taiwan University, Taipei 106, Taiwan

KEYWORDS. Dielectric constant • Metal–organic frameworks • Microelectronics • Polarity • Strontium

ABSTRACT: The dielectric behavior of metal–organic frameworks is highly dependent on the polarity of molecules that are confined in their structure. Hence, it is of fundamental importance to examine the influence of polar molecules in a well-designed framework. Herein, we clearly distinguish the role of polar molecular confinement on dielectric modulations in three isostructural Sr-based MOFs [Sr2(1,3-bdc)2(H2O)(DMF)]n (1D), [Sr2(1,3-bdc)2(H2O)2∙H2O]n (1W) and their dehydrated analog [Sr2(1,3-bdc)2]n (1). Synthesis of Sr-based MOF [Sr2(1,3-bdc)2(H2O)(DMF)]n (1D) was carried out by the solvothermal reaction of SrCl2·6H2O and benzene-1,3-dicarboxylic 1 ACS Paragon Plus Environment

ACS Applied Electronic Materials 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

acid (1,3-bdc) at 110 °C. The effective dielectric constant (κeff) of DMF-containing compound (1D) was found to be 22.4 (κ = 39.3; where κ = intrinsic dielectric constant) at 1 MHz (295 K) which serves to highlight the significant function of the coordinated DMF, when compared with its isostructural MOF having coordinated and guest H2O molecules (1W; κeff = 7.9, κ = 13.0) and the dehydrated analog (1; κeff = 2.4, κ = 3.2). The presence of DMF molecules between the 2D layers of compound 1D instead of H2O molecules or a vacuum resulted in a high dielectric constant due to the large kinetic diameter and dipole moment of DMF molecules. The significance of this study is the design of an elegant model with a stable core structure, which can be used to clearly distinguish the role of polar molecules as well as the presence and absence of guest molecules on the dielectric behavior of electronic materials. This is of fundamental significance in chemistry, which will pave the way for the design of dielectric MOFs in the future for the microelectronic applications.

1. Introduction Dielectric materials with their energy storing capacity have a plethora of applications particularly in designing capacitors, transformers, resonators, transistors, photovoltaic devices and integrated circuits (ICs) etc.1-2 With the emerging advancements and innovations in the semiconductor industry, the synthesis of novel dielectric materials has become a topic of great interest, particularly with regards to their use in designing multilevel nanoscale flexible electronic technology.3-4 Due to the shrinkage in the size of electronic components, the efficiency of traditional dielectric materials is a serious concern. Traditional materials such as SiO2, AlO2 and other inorganic metal oxide materials have reached their functional limits.5-6 Hence, low dielectric 2

ACS Paragon Plus Environment

Page 2 of 29

Page 3 of 29 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


behaviour has been reported for mesoporous silica composites,7-9 fluorine containing carbon materials,10

porous

films,11-13

polybenzoxazole-based

poly(p-xylylene)

polymers

and

organometallic compounds14, while methacrylate polymers, styrenes, poly(4-vinylphenol) (PVP), poly(vinylidene fluoride) (PVDF) and POSS polymers have been used as high dielectric gate polymeric materials.15-16 However, these organic dielectric materials possesses some series issues regarding their thermal stability, mechanical strength, compatibility with other inorganic components of devices and the fact that they degrade over time.17-18 Very recently, hybrid inorganic–organic dielectric materials have emerged as an alternative to organic as well inorganic dielectrics with unique features of having both organic and inorganic molecules within a single material.19-24 Metal–organic frameworks (MOFs)25 which are constructed through the coordination of inorganic nodes and organic linkers have been considered as potentially possible stable low or high dielectric materials.19-24 In the past decades, MOFs have developed a reputation for use in gas absorption,26-30 sensing,31 chemical separation,32-33 catalysis,34-37 drug delivery, optical and biomedical imaging.38-39 However, less attention has been paid to their dielectric applications. Due to their high porosity, low charge density and insulating behavior, MOFs have been reported as low dielectrics particularly as interlayer dielectric (ILD) component in the past few years.19, 21, 24 ZIF-8 has been reported as a low dielectric material which is not only thermally stable but also mechanically robust.40 In addition, some Zn, Mg, Ni and Pb based frameworks have also been reported which show low dielectric behaviour.24, 41-42 The low polarization and charge density in these porous MOFs are key factors that contribute to their low dielectric behavior. A vacuum has the lowest dielectric constant (κ = 1) and as MOF structures have large pore volumes or a void 3



space on their interior, they exhibit low dielectric constants. However, these pores are not always empty but filled with guest molecules which are highly influential for tuning the physical and chemical properties of the parent frameworks. In addition to the intrinsic properties of guest molecules due to its free moment, they also play an important role in altering intermolecular interactions such hydrogen bonding and stacking interactions. Host–guest chemistry has been established to be intrinsically correlated with the dielectric behavior of MOFs. In some cases, the temperature-dependent motion of the dipolar guest molecules can lead to significant dielectric modulations at particular temperature.43 It has been reported that, when polar molecules are present in a porous organic–inorganic hybrid cage with a perovskite‐type structure, the MOF acquires switchable dielectric behavior in MOF.44 Polar solvents, particularly H2O and DMF can generate interfacial polarization effects that can result in very high dielectric constants at room temperature.45 Dielectric measurements of Ni-based supramolecular networks indicated a significant decrease in the dielectric constant value when their guest molecules having high polarity were exchanged by the molecules with low polarity.46 The low dielectric permittivity in a mixed solvent system can be attributed to the polarization of both solvents which cancel each other, thus resulting in a slight increase in dielectric permittivity.47 A few reports have also been appeared in which the effect of H2O molecules on the dielectric properties of MOFs have been investigated.24 However, a comparison has not been drawn to show the effect of the different polar molecules on the dielectric constant of MOFs. Herein, unambiguous dielectric modulations of two commonly used polar molecules (H2O and DMF) in MOFs is highlighted. A model with three isostructural frameworks [Sr2(1,3-bdc)2(H2O)(DMF)]n (1D), ([Sr2(1,3-bdc)2(H2O)2·H2O]n; 1W) and their dehydrated compound [Sr2(1,3-bdc)2]n (1) (1,34


Page 4 of 29

Page 5 of 29 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


bdc = benzene-1,3-dicarboxylic acid) adopting a highly thermal stable core structure was successfully designed (Scheme 1). The results of dielectric studies clearly revealed the role of polar solvents on the dielectric modulations in MOFs. This study is of fundamental importance and will pave the way for the design of future dielectric materials for microelectronic applications.

Scheme 1. Systematic diagram showing the increase in dielectric constant with the inclusion of polar molecules in the core framework.

2. Experimental Details 2.1 Materials and methods All the reagents were obtained from commercial sources and were used as received without additional treatment. Perkin-Elmer 2400 analyzer have been used to perform elemental analyses. Powder diffraction measurements for the bulk samples were recorded on a Bruker D2 PHASER powder X-ray diffractometer using Cu Kα (λ = 1.54056 Å) source in the step mode with a step size 5



of 0.02° in 2θ at 2 s/step speed. Thermogravimetric analyses (TGA) were carried out from 30 to 900 °C at a heating rate of 5 °C/min–1 under a nitrogen atmosphere (20 mL/min) with a PerkinElmer TGA thermogravimetric analyzer. Perkin-Elmer PARAGON 1000 FT-IR spectrometer was operated to perform Fourier transform infrared (FTIR) spectroscopy using KBr disk method. N2 adsorption/desorption isotherms were measured by a volumetric method using Micromeritics ASAP 2020 instrument at 77 K. 2.2 Synthesis of [Sr2(1,3-bdc)2(H2O)(DMF)]n (1D) A 40.1 mg of SrCl2·6H2O (0.15 mmol) was dissolved in 2.0 mL of ethanol solution, and the solution was treated by ultrasonic for 3 min. A 66.5 mg (0.4 mmol) of 1,3-benzenedicarboxylic acid (1,3-bdc) was first dissolved in 3.0 mL of N,N-dimethylformamide (DMF), and then was added to the ethanol solution of SrCl2. Another 2 mL of water was added to the mixture solution and the resulting solution was vacuum-packed in a Teflon-lined vessel (23 mL) which was placed in oven for two days at 110 °C. The colorless, thin plate-shaped crystals of 1D that were obtained and washed with 10 mL ethanol solution. Some of high quality crystals of 1D were chosen and used for the single-crystal X-ray analyses and other characterizations. Yield: 70.6%, (based on metal ions (Sr)). Elemental analysis data for 1D: Calcd. for C38H34N2O20Sr4: C, 38.38; H, 2.88; N, 2.36. Found: C, 38.33; H, 2.83; N, 2.08. 3.3 X-ray Crystallography Suitable single crystal of 1D was chosen for the X-ray crystallographic analysis at low temperature. A Nonius Kappa CCD diffractometer with built-in graphite monochromated Mo-Kα (λ = 0.71073 Å) X-rays source was operated to collect the single crystal crystallographic data at 6


Page 6 of 29

Page 7 of 29 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


200 K. The MULTI-SCAN method was applied using SADABS and SAINT for the absorption corrections.48,49 Crystal structural refinement data and the experimental parameters are listed in Table S1. The single crystal structure was resolved using direct methodologies as well as Fourier techniques, whereas SHELXL97 was used to refine structure via full-matrix least squares.50 All the non-hydrogen components were refined anisotropically, whereas the hydrogen (H) of the coordinated water molecule were located by difference Fourier mapping. The hydrogen atoms attached with oxygen atoms were refined using a riding model approximation (where Uiso(H) = 1.5Ueq(O)). Riding model approximations with Uiso(H) = 1.2Ueq(O) were applied for the refinement of the hydrogen atoms which were attached to carbon atoms and were positioned at the defined locations. Selected bond distances and their angles are given in Table S2. CIF data for 1D can be accessed at the Cambridge Crystallographic Data Center, under the deposition number of CCDC 1867216. 2.4 Electrical measurements All the electrical (dielectric constant and impedance) data have been measured using the HP 4284A Precision LCR Meter interfaced with a Lakeshore temperature controller with a basic accuracy of ±0.05% at all test frequencies with six digit resolution on every range. The standard calibration procedure for the instrument was adopted to ensure its basic accuracy (±0.05%). Measurements were conducted for the solid-state pellet samples of 1D in order to make a better comparison with previously reported pellet samples (1W, 1). In order to minimize the impact of potential voids in the pellet sample, crystals of 1D were finely ground to form uniform nano-scale particles and pressed to form high quality pellets of different thickness (t = 602‒730 µm); disk radius of 0.003 m and pellet area = 2.83 × 10‒5 m2 under a high mechanical pressure (30 Mpa). 7



Page 8 of 29

The obtained pellets have a density 70% that of the x-ray crystal density. Pellet samples of 1D were coated with silver paste to produce electrical contacts. All measurements were performed in the frequency range of 1 kHz to 1 MHz under a vacuum with the temperature range set as 300 to 80 K. Parallel plate capacitor (Cp) mode was adopted to collect and calculate the capacitance, dielectric loss, impedance and AC conductivity data using equations 1‒3. κ = Cpd/ ₀A

(1)

Ԑ = ₀tanδ

(2)

σ = ωCp d/A tanδ

(3)

Here, ε0 is the dielectric permittivity in a vacuum (8.85 × 1012 F/m); A is the area of the electrode (m2), and d is the thickness (m), σ is conductivity of the pellets. 3. Results and Discussion 3.1 Synthesis of Sr-based MOFs A Sr-based MOF [Sr2(1,3-bdc)2(H2O)(DMF)]n (1D) was synthesized under solvothermal conditions by the reaction of SrCl2·6H2O and benzene-1,3-dicarboxylic acid (1,3-bdc) in a mixed solvent system comprised of ethanol, DMF and H2O (Scheme 2). After 2 days, thin plate-like colorless crystals of 1D were collected in high yield (70.6%), which were suitable for a single crystal X-rays diffraction study. Compound 1W and 1 were synthesized and characterized following a previously reported procedure.23

8


Page 9 of 29 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


OH SrCl2 6H2O

O

+

H2O, DMF, EtOH 110 °C, 48 h

HO

[Sr2(1,3-bdc)2(H2O)DMF]n 1D

O

1,3-bdc Scheme 2. Synthesis procedure of compound 1D. 3.2 Crystal Structure of Sr-based MOFs The solid-state structure of 1D was determined by single crystal X-ray diffraction analysis, and the results revealed that 1D crystallizes in a monoclinic space group C2/c (Table S1). All of the powder X-ray diffraction (PXRD) peaks match well with the pattern obtained from the simulated data which confirmed the purity of as-synthesized crystals (Figure S4). The crystallographic asymmetric unit contains two crystallographically independent Sr2+ ions, two 1,3bdc, a coordinated DMF molecule as well as one coordinated water molecule. Functional groups (carboxylate) on the 1,3-bdc ligands were deprotonated, thus resulting in charge neutrality with the two Sr2+ cations. The bdc ligand serves as a 2-bridging unit that coordinated with five Sr2+ ions through the four oxygen atoms of the two carboxylate groups. In 1D, there are two crystallographically distinct Sr2+ cations (Figure 1(a)). One of the Sr(1) ion is coordinated with two chelating carboxylate linkers, three monodentate carboxylate groups from five different 1,3bdc ligands, and one coordinates DMF molecule (Figure S2(a)). On the other hand, the Sr(2) ion is also coordinated with two chelating carboxylate linkers and three monodentate carboxylate groups from five different 1,3-bdc linkers, but with one coordinated water molecule (Figure S2(b)). Both of the Sr ions are surrounded by eight coordinated oxygen atoms that are arranged in 9



a bisdispenoid fashion. It is noteworthy that the Sr(1) and Sr(2) centres are arranged in an alternate fashion and are bridged by two monodentate carboxylate groups between the Sr ions, and eight [SrO8] polyhedrons are edge-shared to form an eight membered ring unit (Figure S3). These [SrO8] eight-member rings are further linked to form a two-dimensional layered network expanded along the bc-plane. It is noteworthy that the distinct local coordination environment of the Sr(1) and Sr(2) ions by coordinating to different water or DMF molecules may play central role in regulating the layerto-layer interactions in the complex. Crystals of 1D were found to be isostructural to the previously reported ([Sr2(1,3-bdc)2(H2O)2·H2O]n; 1W) and its dehydrated analog [Sr2(1,3-bdc)2]n (1) (1,3-bdc = benzene-1,3-dicarboxylic acid). All of these compounds possess highly stable core, composed of bdc ligands and Sr metals, with thermal stability of more than 420 °C.23 Compound 1D contains no guest molecules between the two adjacent layers as compared with the previously reported compound 1W, which holds guest water molecules between the layers via hydrogen bonding. Compound 1 is a core structure without any coordinated or guest solvent molecule, obtained after the thermal treatment of either 1D or 1W at 140 °C under vacuum. With different guest molecules and no guests, layer-to-layer hydrogen-bonding interactions of all three compounds are completely different as shown in Figure 1(b). Thermogravimetric analyses (TGA) of 1D revealed a weight loss of 16.1% (calculated 15.3%) from 220 °C to 570 °C, which can be attributed to the loss of the coordinated water and DMF molecules (Figure S5). The dehydrated sample 1 is found to be highly thermal stable up to 450 °C (Figure S6). 3.3 Dielectric Investigations of Sr-based MOFs

10


Page 10 of 29

Page 11 of 29 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


To understand the effects of polar molecule confinement, temperature dependent dielectric measurements were carried out in the temperature range of 50˗300 K, as shown in Figures 2(a and b). To make a better comparison with previous studies, a similar dielectrics measurement method using a pelleted samples at 30 MPa was adopted for 1D. In order to minimize the impact of potential voids, crystals of 1D were finely ground to form uniform nano-scale particles and pressed to form high quality pellets of different thickness. PXRD, FTIR and BET were performed on the mechanical pressed samples to ensure that the MOF did not decompose by applying high mechanical pressure (30 MPa). The results of PXRD and FTIR clearly indicate that the MOF is crystalline even after applying a high pressure (Figures S4 and S7). Negligible variations in the BET surface area of as-synthesized and pressed samples of the compounds (1W and 1D) also confirm that MOFs retain its crystallinity (Figures S8). Furthermore, electrical measurements on different pellets samples indicated the dielectric properties of 1D do not display huge variations with standard deviation in the range of 1.47‒0.47 (Figure S11 and S12). The findings of dielectric study indicated that, when the compound 1D is cooled down from 300 to 50 K, the effective dielectric constant (κeff) decreases from 26.5 (1 kHz) to 22 (1 kHz), the decreasing behaviour of the dipole moment of thermally vibrant polar molecules (H2O and DMF) confined in the MOF was observed (Figure 3(a)).23, 40-44 The complex relative permittivity [ε'r(ω) + ε"r(ω)] (where ε'r(ω) is real part and ε"r(ω) is the imaginary part of permittivity) of compound 1D was also examined at various temperatures. Compound 1D indicated an effective dielectric constant of κ = 26.5 at lower frequency (~1 kHz) which rapidly reduced to κ = 22.4 at high frequency (~I MHz) (Figure S9). The relative permittivity (effective dielectric constant) curves displayed a decaying trend with frequencies. Incorporation of polar molecules (DMF) with high dipole moments between the layers 11



is responsible for such decay behavior of dielectric constant (26.5 to 22.4) from 1 kHz to 1 MHz. At higher frequencies, the mobility of the dipoles of DMF in 1D decreases, which result into a significant reduction in the dipole polarization. Hence, a decaying trend was observed in the dielectric behavior of 1D with respect to frequency (Figure S9). A similar trend was also observed for previously reported dielectric MOFs.23, 41-44 As the polar molecules are confined within a similar core structure, the dielectric constant is directly related to the dipole moment of those molecules inside the core under an applied field (Ea). The dipole moment of DMF is much higher (D = 3.82) than that for a water molecule (D = 1.85), hence, when the voltage is applied, the dielectric constant for the DMF containing compound (1D) is higher than that for the water containing compound 1W (Table 1).51-54 The delay in the reorientation of the dipole with respect to the applied voltage is measured in the form of dielectric loss. Dielectric loss (0.45 to 0.28) curves also display the decaying behavior with respect to increasing frequency for compound 1D as shown in Figure S10. Several polarization mechanisms as well as the impendence (capacitance and resistance) of the deposited electrodes are responsible for the dielectric loss in pellet samples.51, 52 This type of decreasing trend of dielectric curves with respect to frequency has also been reported for some ceramic, inorganic materials, composite compounds and other MOFs as well.40, 55-56 When the size of the molecules in the framework is increased, the vacuum will decrease. As a result, the dielectric constant will be enhanced (Figure 3). Pore or vacuum volume was confirmed using the Platon software which indicated that molecule volume per unit volume of compound 1D is 29.1% which is almost three times higher than that of H2O-containing compound 1W. A vacuum or an airgap have the lowest dielectric constant (κ = 1). It was also proposed by the international technology roadmap for 12


Page 12 of 29

Page 13 of 29 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


semiconductors that when the more pores or vacuum space are present in a solid-state material, the dielectric constant will be lower. In our case, the presence of DMF molecules in the empty space between the 2D layers of compound 1D, possess greater kinetic diameters (0.55 nm) than the water molecules (0.26 nm).51-53 Therefore, the diameter of the molecule in the core structure is very high while the vacuum or airgap in the core structure of 1D is lower than that of the H2O containing compound 1W. Hence, a high molecular volume or lower vacuum results in 1D having a higher dielectric constant when compared with the H2O-containing compound 1W whose vacuum is higher (Figure 3). Furthermore, thermogravimetric analyses (TGA) of both the MOFs (1W and 1D) also revealed a 16.1% weight loss for DMF in 1D, which is comparatively higher than the weight of solvent molecules lost (9.4%) in the water-containing compound (1W) due to the fact that molecular weight of DMF is higher than that for H2O (Figures S5 and S6). Heavier DMF molecules in between the core of MOF structure 1 results in a lower vacuum and, hence, a higher dielectric constant as compared with H2O containing MOF (1D) and 1. Pores size and their distribution in the core structure have significant roles in terms of understanding the effects of polar molecules in the pores of MOFs, particularly regarding their electrical properties.53,56-57 hence, the vacuum or porosity in the compounds (1W & 1D) were confirmed using gas sorption measurements at 77 K. The N2 adsorption-desorption isotherm indicated BET surface areas of 25.04 m²/g and 10.11 m²/g for 1W and 1D, respectively (Figure 4). The corresponding pore size distribution was calculated using the Horvath–Kawazoe (HK) method on the N2 desorption isotherms (insets of Figure 4). Pore size distribution of ~3 to 10 nm (maximum at 3.5 nm) was observed for both the compounds which indicated the presence of micro-sized pores in the core structure. The observed pore volume and surface area for 1D is 13



Page 14 of 29

comparatively lower than those found for 1W which is probably due to large molecular size of the coordinated DMF in 1D as compared with the smaller guest molecule of H2O in the core structure of 1W. Analogous gas isotherm behavior and lower surface area for 1D indicated that it has a lower porosity than 1W. Hence, with low porosity or vacuum, the dielectric constant of 1D is found to be higher when compared with relatively highly porous compound 1W. The relatively high dielectric constant due to low porosity of our compounds can be justified when compared ZIF-8 and IRMOFs which possess a high porosity and hence low dielectric constants.40, 58 Dielectric measurements have been performed on pellet samples of MOFs which contain substantial amount of voids. Hence, the measured dielectric constant has been denoted by effective dielectric constant (eff) of medium, composed of MOF as well as a small volume fraction of external voids with grain size distribution.59 In order to estimate the intrinsic dielectric constant () of MOF materials, effective medium approximations (EMA) has been applied using Bruggeman effective medium theory (Equation 4).59,60 The intrinsic dielectric constant for compound 1D, calculated using Bruggeman effective medium theory, is found to have similar tendency with respect to temperature and frequency with  value in the range of 46 to 25 (Figure S13). As the inclusion of porosity or vacuum usually decreases the dielectric constant of any material, hence, the relatively high intrinsic dielectric constant of 1D as compare with its effect dielectric constant is justified. Furthermore, intrinsic dielectric constant of 1W and 1 have also been estimated for 1W ( = 13.0 (1 MHz)) and 1 ( = 3.2 (1 MHz)) using Bruggeman effective medium approximation. ƒ

Ԑ Ԑ Ԑ Ԑ

1

ƒ

Ԑ Ԑ Ԑ Ԑ

0

14


(4)

Page 15 of 29 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


Where, ƒ is volume fraction of material, Ԑ is relative permittivity or intrinsic dielectric constant (κ) of material, Ԑ is permittivity of vacuum and Ԑ

is effective dielectric constant (κeff)

of pellet sample. A graph showing the increase in effective and intrinsic dielectric constants of Sr-based MOFs with respect to molecular volume in the core structure is shown in Figure 5. The dielectric constant of the Sr-based MOF is increasing with an increase in the polar molecule per unit volume of the compounds. In addition, polar molecules with a higher dipole moment will also assist in increasing the dielectric constant. A comparison of structural parameters and dielectric constants for all the three compounds is shown in Table 1. 3.4 Impendence and electrical conductivity measurements To understand the nature of the electrical behavior of compound 1D, we have studied measured the temperature dependent impedance spectroscopy (Z' Vs Z") for the mechanically pressed pellet samples (Figure 6). Due to presence of potential voids in the pellet, the measured value is the electrical conductivity of the pellet sample, composed of a MOF and small volume fraction of voids. Straight lines for all the frequencies in ln(κefff) vs ln(f) data also suggest that the dielectric behavior is associated with only one contribution which is due to the intrinsic pellet sample (Figure S14).23,

40

Dielectric materials require large energy gaps with low electrical

conductivity in order to control the leakage current that passes through the dielectric layer. Hence, insulating behavior would be highly desirable for any dielectric material. To further examine the conducting behavior in compound 1D, the AC conductivity was calculated on the pellet samples using the above mentioned equation 3. From the data shown in Figure 6, it can be seen that pellet sample of compound 1D exhibited a low electrical conductivity of the order of 10‒7 S/cm, even at 15



higher frequencies, which is comparable to previously reported conductivity values (~10‒7‒10‒9 S/cm) for dielectric MOFs.22-23, 40, 46,60 The reason for such a low AC conductivity of the MOF is poor overlapping between the d orbital of the metal to ligand which presents a hurdle to flow direct charge. There is no charge transfer path created within the framework, hence, a low conductivity is reported for compound 1D. A similar behaviour was reported for compound 1W after removing all of H2O molecules (compound 1). Given its relatively high dielectric constant and highly insulating nature, the reported compound 1D has the potential for use as a dielectric material in gate dielectrics, transistors and integrated circuits designs. The results presented promise to pave the way to the further design of dielectric MOFs in the future for various microelectronic applications. 4. Conclusions A model with three isostructural frameworks [Sr2(1,3-bdc)2(H2O)(DMF)]n (1D), ([Sr2(1,3bdc)2(H2O)2·H2O]n (1W) and the dehydrated sample [Sr2(1,3-bdc)2]n (1) (1,3-bdc = 1,3benzenedicarboxylic acid) with a highly thermal stable core structure was successfully designed. The results of a dielectric study clearly revealed the role of polar molecules on the dielectric modulations in MOFs. The findings indicate that the compound 1D possesses a relatively high dielectric constant (κeff = 22.4; κ = 39.2) at 1 MHz (300 K). The higher dynamic size and dipole moment of DMF molecules compared to H2O molecule result in the core frame having less voids and hence increases the dielectric constant of 1D compared to the H2O-containing MOF (1W) (κeff = 7.9; κ = 13.0) and solvent-free core framework (1) (κeff = 2.4; κ = 3.2). The dielectric properties of MOFs has been an emerging area of research and investigating the role of polar solvents is of fundamental importance in term of understanding the dielectric behavior of MOFs that contain 16


Page 16 of 29

Page 17 of 29 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


polar molecules in their structures. The foregoing results discussed in this work will lead the way for future research on dielectric MOFs and their applications in integrated circuit designing.

ASSOCIATED CONTENT Supporting Information. Crystal Data, crystal structures for 1D, bond lengths [Å] and angles [°], hydrogen bonding distances (Å) and angles (°), thermogravimetric analysis, powder X-ray diffraction studies, FTIR, Frequency dependent dielectric constant and electrical measurements. The following files are available free of charge. brief description (file type, i.e., PDF) brief description (file type, i.e., PDF) AUTHOR INFORMATION Corresponding Authors Kuang-Lieh Lu: [email protected] Yen-Hsiang Liu: [email protected] Author Contributions YHL and KLL supervised the overall project. MU conceived the project. PHF and YHL synthesized the crystal, performed the structural characterizations. LWL and YHL performed the crystallographic measurements. MU, KRC and JWC measured all the electrical properties. MU, YHL and KLL wrote the manuscript with the input from all of the authors.

17



Note: The authors declare no competing financial interest. Acknowledgment We gratefully acknowledge Academia Sinica, Fu Jen Catholic University and Ministry of Science and Technology, Taiwan for their financial support. References: 1. Li, Q.; Yao, F.-Z.; Liu, Y.; Zhang, G.; Wang, H.; Wang, Q., High-Temperature Dielectric Materials for Electrical Energy Storage. Annu. Rev. Mater. Res. 2018, 48, 219-243. 2. Wang, B.; Huang, W.; Chi, L.; Al-Hashimi, M.; Marks, T. J.; Facchetti, A., High-k Gate Dielectrics for Emerging Flexible and Stretchable Electronics. Chem. Rev. 2018, 118, 56905754. 3. Heremans, P.; Tripathi Ashutosh, K.; de Jamblinne de Meux, A.; Smits Edsger, C. P.; Hou, B.; Pourtois, G.; Gelinck Gerwin, H., Mechanical and Electronic Properties of Thin‐Film Transistors on Plastic, and Their Integration in Flexible Electronic Applications. Adv. Mater. 2015, 28, 4266-4282. 4. Javey, A.; Kim, H.; Brink, M.; Wang, Q.; Ural, A.; Guo, J.; McIntyre, P.; McEuen, P.; Lundstrom, M.; Dai, H., High-κ dielectrics for advanced carbon-nanotube transistors and logic gates. Nat. Mater. 2002, 1, 241. 5. Wallace, R. M.; Wilk, G., Alternative Gate Dielectrics for Microelectronics. MRS Bull. 2002, 27, 186-191. 6. Harrop, P. J.; Campbell, D. S., Selection of thin film capacitor dielectrics. Thin Solid Films. 1968, 2, 273-292. 7. Van Der Voort, P.; Esquivel, D.; De Canck, E.; Goethals, F.; Van Driessche, I.; RomeroSalguero, F. J., Periodic Mesoporous Organosilicas: from simple to complex bridges; a comprehensive overview of functions, morphologies and applications. Chem. Soc. Rev. 2012, 42, 3913-3955. 8. Li, S.; Li, Z.; Medina, D.; Lew, C.; Yan, Y. Organic-Functionalized Pure-Silica-Zeolite MFI Low-k Films. Chem. Mater. 2005, 17, 1851.

18


Page 18 of 29

Page 19 of 29 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


9. Goethals, F.; Ciofi, I.; Madia, O.; Vanstreels, K.; Baklanov, M. R.; Detavernier, C.; Van Der Voort, P.; Van Driessche, I., Ultra-low-k cyclic carbon-bridged PMO films with a high chemical resistance. J. Mater. Chem. 2012, 22, 8281. 10. Yanjun Ma, H. Y., J. Guo, C. Sathe, A. Agui, and J. Nordgren, Structural and electronic properties of low dielectric constant fluorinated amorphous carbon films. Appl. Phys. Lett. 1998, 72, 3353. 11. Vengatesan, M. R.; Devaraju, S.; Dinakaran, K.; Alagar, M., SBA-15 filled polybenzoxazine nanocomposites for low-k dielectric applications. J. Mater. Chem. 2012, 22, 7559. 12. Liu, H.-C.; Su, W.-C.; Liu, Y.-L., Self-assembled benzoxazine-bridged polysilsesquioxanes exhibiting ultralow-dielectric constants and yellow-light photoluminescent emission. J. Mater. Chem. 2011, 21, 7182. 13. Fukumaru, T.; Fujigaya, T.; Nakashima, N., Design and preparation of porous polybenzoxazole films using the tert-butoxycarbonyl group as a pore generator and their application for patternable low-k materials. Polym. Chem. 2012, 3, 369. 14. Sgarbossa, P.; Bertani, R.; Di Noto, V.; Piga, M.; Giffin, G. A.; Terraneo, G.; Pilati, T.; Metrangolo, P.; Resnati, G., Interplay between Structural and Dielectric Features of New Low k Hybrid Organic–Organometallic Supramolecular Ribbons. Cryst. Growth Des. 2012, 12, 297-305. 15. Kim, T. H.; Han, C. G.; Song, C. K., Instability of threshold voltage under constant bias stress in pentacene thin film transistors employing polyvinylphenol gate dielectric. Thin Solid Films. 2008, 516, 1232-1236. 16. Fan, C.-L.; Shang, M.-C.; Hsia, M.-Y.; Wang, S.-J.; Huang, B.-R.; Lee, W.-D., Poly(4vinylphenol) gate insulator with cross-linking using a rapid low-power microwave induction heating scheme for organic thin-film-transistors. APL Mater. 2016, 4, 036105. 17. Zschieschang, U.; Klauk, H.; Halik, M.; Schmid, G.; Dehm, C., Flexible Organic Circuits with Printed Gate Electrodes. Adv. Mater. 2003, 15, 1147-1151. 18. Lim, S. C.; Kim, S. H.; Koo, J. B.; Lee, J. H.; Ku, C. H.; Yang, Y. S.; Zyung, T., Hysteresis of pentacene thin-film transistors and inverters with cross-linked poly(4-vinylphenol) gate dielectrics. Appl. Phys. Lett. 2007, 90, 173512. 19. Usman, M.; Lu, K.-L., Metal–organic frameworks: The future of low-κ materials. Npg Asia Mater. 2016, 8, e333. 20. Mendiratta, S.; Lee, C.-H.; Usman, M.; Lu, K. L., Metal–organic frameworks for electronics: emerging second order nonlinear optical and dielectric materials. Sci. Technol. Adv. Mater. 2015, 16, 054204. 19



21. Usman, M.; Mendiratta, S.; Lu, K. L., Metal–Organic Frameworks: New Interlayer Dielectric Materials. ChemElectroChem 2015, 2, 786-788. 22. Han, S.; Zhang, J.; Teng, B.; Ji, C.; Zhang, W.; Sun, Z.; Luo, J., Inorganic-organic hybrid switchable dielectric materials with the coexistence of magnetic anomalies induced by reversible high-temperature phase transition. J. Mater. Chem. C 2017, 5, 8509-8515. 23. Usman, M.; Lee, C.-H.; Hung, D.-S.; Lee, S.-F.; Wang, C.-C.; Luo, T.-T.; Zhao, L.; Wu, M.K.; Lu, K.-L., Intrinsic low dielectric behaviour of a highly thermally stable Sr-based metalorganic framework for interlayer dielectric materials. J. Mater. Chem. C 2014, 2, 3762-3768. 24. Mendiratta, S.; Usman, M.; Lu, K.-L., Expanding the dimensions of metal–organic framework research towards dielectrics. Coord. Chem. Rev. 2018, 360, 77-91. 25. Furukawa, H.; Cordova, K. E.; O’Keeffe, M.; Yaghi, O. M., The Chemistry and Applications of Metal-Organic Frameworks. Science 2013, 341, 1230444 . 26. Han, S. S.; Mendoza-Cortes, J. L.; Goddard, W. A., 3rd, Recent advances on simulation and theory of hydrogen storage in metal-organic frameworks and covalent organic frameworks. Chem. Soc. Rev. 2009, 38, 1460-76. 27. Murray, L. J.; Dinca, M.; Long, J. R., Hydrogen storage in metal‒organic frameworks. Chem. Soc. Rev. 2009, 38, 1294-314. 28. Morris, R. E.; Wheatley, P. S., Gas storage in nanoporous materials. Angew. Chem. Int. Ed 2008, 47, 4966-81. 29. Babaei, H.; McGaughey, A. J. H.; Wilmer, C. E. Transient mass and thermal transport during methane adsorption into the metal–organic framework HKUST-1. ACS Appl. Mater. Interfaces, 2018, 10, 2400-06. 30. Budhathoki, S.; Ajayi, O.; Steckel, J. A.; Wilmer, C. E. High-throughput computational prediction of the cost of carbon capture using mixed matrix membranes. Energy Environ. Sci. 2019, 10.1039/C8EE02582G. 31. Kreno, L. E.; Leong, K.; Farha, O. K.; Allendorf, M.; Van Duyne, R. P.; Hupp, J. T., Metalorganic framework materials as chemical sensors. Chem. Rev. 2012, 112, 1105-25. 32. Li, J. R.; Kuppler, R. J.; Zhou, H. C., Selective gas adsorption and separation in metal-organic frameworks. Chem. Soc. Rev. 2009, 38, 1477-504. 33. Borjigin, T.; Sun, F.; Zhang, J.; Cai, K.; Ren, H.; Zhu, G., A microporous metal-organic framework with high stability for GC separation of alcohols from water. Chem. Commun. 2012, 48, 7613-5.

20


Page 20 of 29

Page 21 of 29 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


34. Lee, J.; Farha, O. K.; Roberts, J.; Scheidt, K. A.; Nguyen, S. T.; Hupp, J. T., Metal-organic framework materials as catalysts. Chem. Soc. Rev. 2009, 38, 1450-9. 35. Ma, L.; Abney, C.; Lin, W., Enantioselective catalysis with homochiral metal-organic frameworks. Chem. Soc. Rev. 2009, 38, 1248-56. 36. Farrusseng, D.; Aguado, S.; Pinel, C., Metal-organic frameworks: opportunities for catalysis. Angew. Chem. Int. Ed. 2009, 48, 7502-13. 37. Song, F.; Zhang, T.; Wang, C.; Lin, W., Chiral porous metal-organic frameworks with dual active sites for sequential asymmetric catalysis. P. Roy. Soc. A-Math. Phy. 2012, 468, 20352052. 38. Sun, C. Y.; Qin, C.; Wang, C. G.; Su, Z. M.; Wang, S.; Wang, X. L.; Yang, G. S.; Shao, K. Z.; Lan, Y. Q.; Wang, E. B., Chiral nanoporous metal-organic frameworks with high porosity as materials for drug delivery. Adv. Mater. 2011, 23, 5629-32. 39. Huxford, R. C.; Della Rocca, J.; Lin, W., Metal-organic frameworks as potential drug carriers. Curr. Opin. Chem. Biol. 2010, 14, 262-8. 40. Eslava, S.; Zhang, L.; Esconjauregui, S.; Yang, J.; Vanstreels, K.; Baklanov, M. R.; Saiz, E., Metal-Organic Framework ZIF-8 Films As Low-κ Dielectrics in Microelectronics. Chem. Mater. 2013, 25, 27-33. 41. Mendiratta, S.; Usman, M.; Chang, C.-C.; Lee, Y.-C.; Chen, J.-W.; Wu, M.-K.; Lin, Y.-C.; Hsu, C.-P.; Lu, K.-L., Zn(ii)-based metal-organic framework: an exceptionally thermally stable, guest-free low dielectric material. J. Mater. Chem. C 2017, 5, 1508-1513. 42. Wang, F.; Ni, C.-Y.; Liu, Q.; Li, F.-L.; Shi, J.; Li, H.-X.; Lang, J.-P., [Pb(Tab)2(4,4[prime or minute]-bipy)](PF6)2: two-step ambient temperature quantitative solid-state synthesis, structure and dielectric properties. Chem. Commun. 2013, 49, 9248-9250. 43. Ye, H.-Y.; Liao, W.-Q.; Zhou, Q.; Zhang, Y.; Wang, J.; You, Y.-M.; Wang, J.-Y.; Chen, Z.N.; Li, P.-F.; Fu, D.-W.; Huang, S. D.; Xiong, R.-G., Dielectric and ferroelectric sensing based on molecular recognition in Cu(1,10-phenlothroline)2SeO4·(diol) systems. Nat. Commun. 2017, 8, 14551. 44. Zhang, W.; Cai, Y.; Xiong, R. G.; Yoshikawa, H.; Awaga, K., Exceptional Dielectric Phase Transitions in a Perovskite‐Type Cage Compound. Angew. Chem. Int. Ed. 2010, 122, 67586760. 45. Bermudez-Garcia, J. M.; Vicent-Luna, J. M.; Yanez-Vilar, S.; Hamad, S.; Sanchez-Andujar, M.; Castro-Garcia, S.; Calero, S.; Senaris-Rodriguez, M. A., Liquid self-diffusion of H2O and DMF molecules in Co-MOF-74: molecular dynamics simulations and dielectric spectroscopy studies. Phys. Chem. Chem. Phys. 2016, 18, 19605-19612. 21



46. Mendiratta, S.; Usman, M.; Luo, T.-T.; Lee, S.-F.; Lin, Y.-C.; Lu, K.-L., Guest dependent dielectric properties of nickel(ii)-based supramolecular networks. CrystEngComm. 2014, 16, 6309-6315. 47. Yu, S.-S.; Yuan, G.-J.; Duan, H.-B., The low dielectric constant and relaxation dielectric behavior in hydrogen-bonding metal-organic frameworks. RSC Adv. 2015, 5, 45213-45216. 48. Bruker, SAINT. Bruker AXS Inc., Madison, Wisconsin, USA: 2003. 49. Bruker, SADABS. Bruker AXS Inc., Madison, Wisconsin, USA: 2002. 50. Sheldrick, G., A short history of SHELX. Acta Crystallogr. E 2008, 64, 112-122. 51. Ten Elshof, J. E.; Abadal, C. R.; Sekulić, J.; Chowdhury, S. R.; Blank, D. H. A., Transport mechanisms of water and organic solvents through microporous silica in the pervaporation of binary liquids. Micropor. Mesopor. Mater. 2003, 65, 197-208. 52. van Leeuwen, M. E., Derivation of Stockmayer potential parameters for polar fluids. Fluid Phase Equilib. 1994, 99, 1-18. 53. Van der Bruggen, B.; Schaep, J.; Wilms, D.; Vandecasteele, C., Influence of molecular size, polarity and charge on the retention of organic molecules by nanofiltration. J. Memb. Sci. 1999, 156, 29-41. 54. Shah, D.; Kissick, K.; Ghorpade, A.; Hannah, R.; Bhattacharyya, D., Pervaporation of alcohol– water and dimethylformamide–water mixtures using hydrophilic zeolite NaA membranes: mechanisms and experimental results. J. Memb. Sci. 2000, 179, 185-205. 55. Homes, C. C.; Vogt, T.; Shapiro, S. M.; Wakimoto, S.; Ramirez, A. P., Optical response of high-dielectric-constant perovskite-related oxide. Science 2001, 293, 673-6. 56. Cui, H. B.; Takahashi, K.; Okano, Y.; Kobayashi, H.; Wang, Z.; Kobayashi, A., Dielectric properties of porous molecular crystals that contain polar molecules. Angew. Chem. Int. Ed. 2005, 44, 6508-12. 57 Babaei, H.; McGaughey, A. J. H.; Wilmer, C. E. Effect of pore size and shape on the thermal conductivity of metal‒organic frameworks. Chem. Sci. 2017, 8, 583-89. 58 Zagorodniy, K.; Seifert, G.; Hermann, H. Metal-organic frameworks as promising candidates for future ultralow-κ dielectrics. Appl. Phys. Lett. 2010, 97, 251905. 59 Bergman, D. J.; Stroud, D. Physical properties of macroscopically inhomogeneous media. Solid State Physics, 1992, 46, 147-269. 60 Kaufman, J. L.; Tan, S. H.; Lau, K.; Shah, A.; Gambee, R. G.; Gage, C.; MacIntosh, L.; Dato, A.; Saeta, P. N.; Haskell, R. C.; Monson, T. C. Permittivity effects of particle agglomeration 22


Page 22 of 29

Page 23 of 29 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


in ferroelectric ceramic-epoxy composites using finite element modeling. AIP Adv. 2018, 8, 125020. 61 Stassen, I.; Burtch, N.; Talin, A.; Falcaro, P.; Allendorf, M.; Ameloot, R. An updated roadmap for the integration of metal–organic frameworks with electronic devices and chemical sensors. Chem. Soc. Rev. 2017, 46, 3185-3241.

23



Figures

Figure 1. (a) A two-dimensional layer network of 1D expanded by [SrO8] building subunits approximately along the bc plane. (b) A prospective view of the layer-to-layer coordination interactions of DMF in 1D. Color code: green: Sr(1); yellow : Sr(2), blue: N; red: O; grey: C.

24


Page 24 of 29

Page 25 of 29 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


Figure 2. (a) Effective dielectric constant (relative permittivity) as a function of temperature for 1D in the frequency range of 1 kHz to 1 MHz. (b) Dielectric loss (D) as a function of temperature for 1D in the frequency range of 1 kHz to 1 MHz.

25



Figure 3. The presence of polar molecule is shown for compound 1D, where two coordinated DMF molecules are present, compound 1W, where two guest H2O molecules exist, while the dehydrated compound 1 contains no molecules.

Figure 4. N2 adsorption–desorption isotherm and pore size distribution curve (inset) of compounds (a) 1D and (b) 1W.

26


Page 26 of 29

Page 27 of 29 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


Figure 5. Effective dielectric constants (κeff) and intrinsic dielectric constant (κ) of Sr-based MOFs (1, 1D, 1W) at 1 MHz versus the volume of polar molecules per unit volume of compounds (calculated by the PLATON software).

27



Page 28 of 29

Figure 6. (a) Temperature dependent impedance spectroscopy studies (Z' vs. Z ̎) for 1D. (b) AC conductivity vs. temperature for compound 1D.

Table 1. Comparison between dielectric properties of compounds based on the features of the polar molecules present/absent in their structures. S. No. Compounds 1

Molecule in MOF

[Sr2(1,3-bdc)2] [{Sr2(1,3-bdc)2(H2O)2}·H2O] [Sr2(1,3-bdc)2(H2O)(DMF)] (1) (1W) (1D) Molecule-free framework H2O-containing framework DMF-containing framework

2

Kinetic diameter51

N/A

0.26 nm (H2O)

0.55 nm (DMF)

3

Dipole moment (D)51

0

1.85 (H2O)

3.82 (DMF)

4

Molecular volumeb

0

10.5%

29.1%

5

Effective dielectric constant (κeff) Intrinsic dielectric constant (κ) (EMA)

2.4 @ 1 MHz (300 K)

7.9 @ 1 MHz (300 K)

22.4 @ 1 MHz (300 K)

3.2 @ 1 MHz (300 K)

13.0 @ 1 MHz (300 K)

39.3 @ 1 MHz (300 K)

6

*arefs. 23, 48, 49 & 51; bMolecule volume per unit volume of compounds was calculated from PLATON software

28


Page 29 of 29 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


Table of Contents

29


Polar Molecule Confinement Effects on Dielectric Modulations of Sr

Recommend Documents