Anion-Controlled Dielectric Behavior of Homochiral Tryptophan-Based

Feb 20, 2014 - Cryst. Growth Des. , 2014, 14 (4), pp 1572–1579 ... All of the compounds crystallize in the monoclinic space group P21 and form homoc...
0 downloads 0 Views 3MB Size
Download PDF
Article pubs.acs.org/crystal

Anion-Controlled Dielectric Behavior of Homochiral TryptophanBased Metal−Organic Frameworks Shruti Mendiratta,†,‡,§ Muhammad Usman,† Tzuoo-Tsair Luo,† Bor-Chen Chang,⊥ Shang-Fan Lee,# Ying-Chih Lin,*,‡ and Kuang-Lieh Lu*,† †

Institute of Chemistry, Academia Sinica, Taipei 115, Taiwan Department of Chemistry, National Taiwan University, Taipei 106, Taiwan § Nano-Science and Technology Program, Taiwan International Graduate Program, Institute of Physics, Academia Sinica, Taipei 115, Taiwan ⊥ Department of Chemistry, National Central University, Taoyuan 320, Taiwan # Institute of Physics, Academia Sinica, Taipei 115, Taiwan ‡

S Supporting Information *

ABSTRACT: Three homochiral metal-tryptophanate frameworks, {[Zn2(L-trp)2(bpe)2(H2O)2]·2H2O·2NO3}n (1a, LHtrp = L-tryptophan, bpe = 1,2-bis(4-pyridyl)ethylene), {[Co(L-trp)(bpe)(H2O)]·H2O·NO3}n (1b), and {[Co(L-trp)(bpa)(H2O)]·H2O·NO3}n (2, bpa = 1,2-bis(4-pyridyl)ethane), were constructed from Zn2+ or Co2+ ions, bipyridyl ligands, and the amino acid L-tryptophan (L-Htrp), respectively. Compounds 1a, 1b, and 2 were characterized by single-crystal X-ray diffraction analysis. All of the compounds crystallize in the monoclinic space group P21 and form homochiral twodimensional (2D) layers with rectangle-like (4,4) topologies. Anion-controlled dielectric, luminescence, and nonlinear-optic (NLO) properties were measured for these chiral metal− organic frameworks (MOFs) in the solid state. Emission spectra confirmed that compound 1a exhibited a green emission at 546 nm. Dielectric studies of 1a revealed that it had very low dielectric constant (κ = 2.53 at 1 MHz), thus verifying that it is a promising candidate for interlayer dielectrics. The anion-controlled dielectric properties of 1a were observed after treatment with solutions of different anions. The results revealed a significant change in κ value in the case of the phosphate anion. Secondary harmonic generation (SHG) studies revealed that 1a had a good SHG intensity response that was about twice that of SiO2.

■

INTRODUCTION In recent years, significant efforts have been dedicated to the production of various types of materials with high or low dielectric constants, as they open great application prospects, especially in the fields of dielectric resonators and filters, multilayer ceramic capacitors, magnetic field dependent capacitive sensors, and ultralarge scale integration.1 Materials with extremely low dielectric constants (κ) are suitable for use as interlayer dielectrics for semiconducting devices and help overcome some of the resulting problems such as cross-talk noise and propagation delay. With the miniaturization of most devices, the introduction of low-κ dielectrics as an insulating material becomes inevitable. As per the 2011 International Roadmap for Semiconductors (ITRS), by 2020 dielectric materials with an effective κ value between 2−2.46 will be required for microprocessors with design features of 1.5 pitch.2 Many inorganic materials such as fluorine and carbon doped oxides have κ toward the higher side, while many organic materials such as spin-on polyimides and aromatic polymers which are potential candidates that could fulfill this requirement © 2014 American Chemical Society

suffer from low thermal stability, low modulus, poor interlayer adhesion, or poor mechanical strength.3 In the past few years, metal−organic frameworks (MOFs) have received considerable attention because they have advantageous properties of functioning as both inorganic and organic compounds. Their tunable structures, rich coordination chemistry, and fascinating topologies provide a suitable platform to a wide array of potential applications in gas storage,4 catalysis,5 luminescence,6 and magnetism.7 Furthermore, chiral MOFs belong to a distinct class of hybrid materials which are anticipated to be promising tools for various solid state applications such as nonlinear optical (NLO)8 and ferroelectric9 properties because of their non-centrosymmetric nature. Compared with a focus on developing electro-optical MOFs, it is surprising that significantly less effort has been directed toward studying dielectric properties of chiral MOFs.10 Received: October 4, 2013 Revised: February 18, 2014 Published: February 20, 2014 1572

dx.doi.org/10.1021/cg401472k | Cryst. Growth Des. 2014, 14, 1572−1579

Crystal Growth & Design

Article

Scheme 1. Preparation of the Chiral Metal-Tryptophanate Frameworks of 1 and 2

mg, 0.075 mmol) in a test tube. The mixture was heated at 50 °C in a water bath for 5 days. The obtained yellow crystals were washed with water and dried with acetone. Crystals were obtained in 33.3% (13.8 mg, 0.012 mmol) yield by filtration and were found to be suitable for single-crystal X-ray diffraction analysis. Anal. Calcd (%) for Zn2C46H50N10O14 (1a): C 50.33, H 4.59, N 12.75; found: C 50.23, H 4.20, N 12.68. IR (KBr pellet): ν = 3342 (m), 1947 (vw), 1681 (w), 1610 (vs), 1587 (m), 1567 (m), 1424 (s), 1385 (s), 1343 (s), 1322 (s), 1221 (m), 1164 (w), 1101 (m), 1069 (s), 1039 (w), 1019 (m), 967 (m), 954 (m), 931 (w), 828 (s), 751 (s), 702 (w), 667 (m), 592 (w), 552 (s) cm−1. Synthesis of {[Co(L-trp)(bpe)(H2O)]·H2O·NO3}n (1b). Compound 1b was prepared in the same way as compound 1a using Co(NO3)2·6H2O (21.7 mg, 0.075 mmol). The obtained orange crystals were washed with water and acetone dried. Crystals were obtained in 38% (15.5 mg, 0.014 mmol) yield by filtration and were found to be suitable for single-crystal X-ray diffraction analysis. Anal. Calcd (%) for CoC23H25N5O7 (1b): C 50.93, H 4.64, N 12.91; found: C 50.88, H 4.80, N 13.06. IR (KBr pellet): ν = 3340 (m), 1946 (w), 1688 (w), 1609 (vs), 1587 (m), 1561 (m), 1423 (s), 1385 (s), 1344 (s), 1320 (s), 1221 (m), 1164 (w), 1101 (m), 1068 (s), 1039 (w), 1018 (m), 967 (m), 954 (m), 932 (w), 828 (s), 751 (s), 701 (w), 673 (m), 591 (m), 553 (s) cm−1. Synthesis of {[Co(L-trp)(bpa)(H2O)]·H2O·NO3}n (2). An ethanol− water solution (5 mL/1 mL) of L-Htrp (20.4 mg, 0.1 mmol) and bpa (18.8 mg, 0.1 mmol) was layered over an aqueous solution (1.5 mL) of Co(NO3)2·6H2O (29.1 mg, 0.1 mmol) in a test tube. The mixture was placed in a water bath at 50 °C for a week. The obtained transparent orange crystals were washed with water and acetone dried. Crystals were obtained in 13.4% (7.3 mg, 0.013 mmol) yield by filtration and were found to be suitable for single-crystal X-ray diffraction analysis. Anal. Calcd (%) for CoC23H27N5O7 (2): C 50.74, H 4.99, N 12.86; found: C 50.79, H 5.04, N 13.23. IR (KBr pellet): ν = 3341 (s), 2922 (w), 2851 (w), 1943 (w), 1751 (w), 1685 (m), 1615 (vs), 1613 (vs), 1602 (vs), 1586 (vs), 1505 (m), 1494 (m), 1422 (vs), 1385 (s), 1325 (s), 1223 (s), 1163 (m), 1151 (m), 1100 (s), 1068 (vs), 1040 (m), 1023 (m), 1007 (w), 930 (m), 880 (w), 866 (m), 850 (m), 829 (vs), 761 (s), 751 (s), 720 (m), 701 (m), 674 (m), 592 (m), 553 (m), 509 (w) cm−1. Single-Crystal X-ray Crystallographic Analyses. Single-crystal X-ray diffraction was performed by using a Bruker P4 diffractometer equipped with graphite monochromatic Mo Kα radiation (λ = 0.71073 Å). Starting models for structure refinement were found using direct methods (SHELXS-97) for 1a, 1b, and 2. The structural data were refined by fullmatrix least-squares methods on F2 using the WINGX11 and SHELX-9712 program packages. Luminesence Measurements. Solid state emission measurements were performed on F-4500 FL spectrophotometer using 5.0 nm slit width, scan speed of 1200 nm/min, and PMT voltage of 700 V. Dielectric Measurements. Complex dielectric properties of powder samples were measured at room temperature using an Agilent 4294A impedance analyzer with dielectric measuring feature probe 16451B over the frequency range from 40 Hz to 1 MHz with an applied electric voltage of 0.5 V.

In addition, anion tuning of the dielectric properties of chiral MOFs still remains an area to be explored. Motivated by Yang et al.10a with respect to the design and construction of homochiral coordination polymer as dielectric and piezoelectric materials, we successfully demonstrate here the formation of three chiral MOFs based upon enantiopure Ltryptophan (L-Htrp) as a ligand, which is a particularly effective building block because (1) it has many potential coordination modes which allow for the construction of a structurally diverse family of functional materials; (2) the chiral center which would be effective in constructing a chiral framework; (3) the amino group which acts as an auxochromic and bathochromic group may confer emission properties due to charge transfer interactions in the framework. In addition, the presence of charge-balancing anions, which occupy the framework voids, provides a pathway for construction of anion receptors based on anion-exchange strategy. Three homochiral metal-tryptophanate frameworks, {[Zn2(Ltrp)2(bpe)2(H2O)2]·2H2O·2NO3}n (1a), {[Co(L-trp)(bpe)(H2O)]·H2O·NO3}n (1b), and {[Co(L-trp)(bpa)(H2O)]· H2O·NO3}n (2), were synthesized under mild conditions (Scheme 1) by reacting L-Htrp with rodlike and bridging ligands, such as bpe (1,2-di(4-pyridyl)ethylene) and bpa (1,2bi(4-pyridyl)ethane) in the presence of divalent metal ions (Co2+ and Zn2+). These crystalline materials feature a chiral two-dimensional framework and exhibit good luminescent, low-κ dielectric, and anion-controlled dielectric properties. The specially designed interior microenvironment serves as an excellent host receptor that can recognize and sense small guest molecules based on their size, geometry, binding ability, and lewis basicity under ambient conditions. In addition, the molecular size and the flexibility of the dipyridyl-type ligands used are crucial to determining the structures of the coordination architectures.

■

EXPERIMENTAL SECTION

General Information. L-Tryptophan and other chemical reagents were purchased commercially and were used as received without further purification. Elemental analyses were conducted on a PerkinElmer 2400 CHN elemental analyzer. The infrared spectra were recorded on a Perkin-Elmer Paragon 100 FT-IR spectrometer in the range of 4000−400 cm−1 using the KBr disc technique. Thermogravimetric analyses (TGA) was performed on a Perkin-Elmer TGA-7 TG analyzer. Single-phased powder samples were loaded into alumina pans and heated with a ramp rate of 10 °C/min from room temperature to 900 °C under nitrogen flux. Powder X-ray diffraction (PXRD) data were recorded on a Phillips X’Pert Pro diffractometer operated at a voltage of 40 kV and a current of 30 mA with Cu Kα radiation (λ = 1.5406 A). Synthesis of {[Zn2(L-trp)2(bpe)2(H2O)2]·2H2O·2NO3}n (1a). A methanolic solution (3 mL) of L-Htrp (15.3 mg, 0.075 mmol) and bpe (13.6 mg, 0.075 mmol) with a few drops of distilled water was layered over an aqueous solution (1.0 mL) of Zn(NO3)2·6H2O (22.4 1573

dx.doi.org/10.1021/cg401472k | Cryst. Growth Des. 2014, 14, 1572−1579

Crystal Growth & Design

■

Article

RESULTS AND DISCUSSION Synthesis. In comparison with the room temperature selfassembly of modular building units through layering, in this case we utilized a slightly elevated temperature in a water bath. Herein, as shown in Scheme 1, the reaction of M(NO3)2·6H2O (M = Zn and Co), L-Htrp with bipyridyl ligands, such as bpe (1,2-di(4-pyridyl)ethylene) and bpa (1,2-bi(4-pyridyl)ethane), resulted in the formation of transition-metal tryptophanate coordination frameworks {[Zn2(L-trp)2(bpe)2(H2O)2]·2H2O· 2NO3}n (1a), {[Co(L-trp)(bpe)(H2O)]·H2O·NO3}n (1b), and {[Co(L-trp)(bpa)(H2O)]·H2O·NO3}n (2). The three compounds are isostructural as can be seen from powder X-ray diffraction pattern (Figure S2, Supporting Information) and crystallize in the same monoclinic crystal system with the chiral space group P21. Therefore, only the structure of compound 1a is discussed in detail. Possible coordination modes of the L-trp ligand are shown in Scheme 2, and further structural details are described below.

(Figure 3a). In between these layers, there is significant interlayer hydrogen bonding interactions between the coordinated water molecules and the guest molecules (nitrate and water molecules). In addition, the guest molecules are positioned sequentially between the two stacked layers, displaying alternately arranged nitrate and water molecules (Figure 3b). The hydrogen bonding between them aids in stabilizing the structure. The ZnII···ZnII separation distances across the syn−anti-COO− and the μ2-bpe bridges are 5.53 Å and 13.68 Å, respectively. Modest-to-strong π-stacking is operating between the tryptophan-benzyl moiety and the bipyridyl ligand with a ring centroid contact of 4.97 Å. In compound 1b, the CoII···CoII separation distances across the syn−anti-COO− and the μ2-bpe bridges are 5.53 Å and 13.67 Å, respectively. The values are comparable for the former and slightly longer for the latter compared to the previously reported values for CoII compounds linked by two mixed heterobridges (syn−anti-COO− and μ2-bipyridine).6e,13 The crystallographic data and structural refinements of 1a, 1b, and 2 are summarized in Table 1, and their corresponding bond lengths and bond angles are listed in Tables S2−S4 (Supporting Information). Thermogravimetric Analysis (TGA) and Powder X-ray Diffraction (PXRD) Analysis. To assess the thermal stability and its structural variation as a function of the temperature, TGA for the single phase polycrystalline sample was performed. During the heating process, TGA (Figure S1, Supporting Information) revealed that compounds 1a, 1b, and 2 underwent a one-step weight loss and were thermally stable at temperatures up to 223, 291, and 242 °C, respectively. In compound 1a, a weight loss of 6.52% (Calc. 6.57%) corresponding to the loss of coordinated and solvated water molecules was observed, whereas in compound 1b, a weight loss of 6.66% (Calc. 6.64%) and in compound 2, a weight loss of 6.25% (Calc. 6.61%) was found. Individual PXRD patterns of compounds 1a and 1b are shown in the Supporting Information (Figures S3−S5). Luminescence and Nonlinear Optical Studies. The solid-state photoluminescent properties of 1a, 1b, and 2 were investigated at room temperature. Emission spectra of these compounds revealed that compound 1b, when excited with a wavelength of 237 nm, gave two peaks in the emission spectrum around 300 nm and a strong blue emission at 400 nm which corresponds to a ligand based emission (396 nm) due to π−π* transition (Figure 4a). It is noteworthy that when compound 1a was excited at a wavelength of 300 nm, a green emission occurred at 546 nm (Figure 4b). Compared with the free ligand bpe, the emission peak for 1a is red-shifted by 150 nm. The emission of compound 1a can be attributed to either intraligand transitions or a ligand-to-metal charge transfer transition (LMCT) or a combination of both.14 Metal−organic coordination polymers with d7 and d10 configuration (such as Co2+ and Zn2+) have been reported to exhibit photoluminescent properties.15 Compound 2 gave an emission spectrum similar to compound 1b where peaks appear basically due to π−π* transitions. Compounds 1a and 1b crystallized in the chiral space group P21. To detect the nonlinear optical properties, as per the methods suggested by Kurtz and Perry,16 the second harmonic generation (SHG) efficiency of 1a was measured (Figure S6, Supporting Information), and it was found to have SHG intensity ∼2.2 times that of silica. These studies demonstrate

Scheme 2. Possible Coordination Modes of the L-trp Ligand

Structural Description of {[Zn2(L-trp)2(bpe)2(H2O)2]·2H2O· 2NO3}n (1a). Single-crystal X-ray diffraction analysis revealed that compound 1a crystallized in the monoclinic space group P21. The asymmetric unit contained a Zn2+ center connected to the L-trp ligand, bpe ligand, and a coordinated water molecule together with guest water and a nitrate anion for charge balance (Figure 1).

Figure 1. Local coordination environment of Zn(II) in 1a. The guest water molecules and nitrate anions are omitted (Zn = pink, O = yellow, N = blue, C = gray).

The L-trp ligand acts as a bridging ligand and adopts a synanti mode (mode II in Scheme 2) by exhibiting a monodentate and chelate coordination, which leads to the formation of a 1D chiral chain (Figure 2a). Adjacent chiral chains are then mutually connected via μ2-bpe bridges to form an extended neutral 2D coordination layer of {Zn2(L-trp)2(bpe)2} having a homochiral rectangle-like (4,4) topology (Figure 2b). It is noteworthy that {Zn2(L-trp)2(bpe)2} layers are precisely stacked atop of each other to give an AAA type of packing 1574

dx.doi.org/10.1021/cg401472k | Cryst. Growth Des. 2014, 14, 1572−1579

Crystal Growth & Design

Article

Figure 2. (a) 1D chiral chain having L-trp units arranged in a syn-anti mode. (b) Homochiral two-dimensional metal-tryptophanate coordination (4,4)-layer structure in 1a along the a axis.

Figure 3. (a) Topological representation of 1a showing a rectangle-like (4,4) net stacked on each other forming AAA packing. (b) Sequentially arranged guest molecules occupying free spaces between two stacked layers.

Table 1. Summary of Crystal Data and Refinement Results compound

1a

1b

2

empirical formula formula weight Mr crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) vol (Å3) Z Dcalc (g/cm3) μ/mm−1 T/K R1 [I > 2σ(I)] wR2 (on F2, all data)

Zn2C46H50N10O14 1097.70 monoclinic P21 8.4181(2) 10.3794(2) 13.6828(3) 90.00 103.6970(10) 90.00 1161.53(4) 1 1.569 1.113 200 0.0286 0.0984

CoC23H25N5O7 542.41 monoclinic P21 8.4008(9) 10.3355(11) 13.6770(15) 90.00 103.716(8) 90.00 1153.7(2) 2 1.561 0.800 200 0.0755 0.1392

CoC23H27N5O7 544.43 monoclinic P21 8.4484(6) 10.3292(7) 13.6867(9) 90.00 104.576(4) 90.00 1155.9(14) 2 1.564 0.799 100 0.0491 0.1167

the existence of a significant relationship between structure and properties for these types of materials. Dielectric and Impedance Studies. We measured the real and imaginary part of the complex dielectric constant and dielectric loss for compounds 1a and 1b (Figure 5a,b) within

the frequency range of 40 Hz to 1 MHz. In our case, the dielectric constant (real part) of 1a (κ = 2.53 at 1 MHz) was found to be lower than 1b (κ = 3.30 at 1 MHz). Since compounds 1a and 1b were isostructural, the low dielectric constant in 1a in comparison to 1b can be attributed to the 1575

dx.doi.org/10.1021/cg401472k | Cryst. Growth Des. 2014, 14, 1572−1579

Crystal Growth & Design

Article

Figure 4. (a) Emission spectra of compounds 1b and 2 compared with the ligands. (b) Emission spectrum of 1a compared with that of bpe ligand.

Figure 5. (a) Plots of dielectric constant νs frequency for compounds 1a and 1b. (b) Plots of dielectric loss νs frequency for 1a and 1b.

Figure 6. (a) Impedance plots for compounds 1a and 1b. (b) Impedance vs frequency plots for 1a and 1b.

degrees, depending upon which type of polarization mechanism is dominant.19 In the present case, a lowering of the κ value on increasing the frequency may be due to a gradual loss of space charge polarization. However, the variation in dielectric loss with frequency can be associated with the dipole alignment when a field is applied.20 At low frequencies, it is much easier for the dipoles to switch alignment under a changing field. An increase in the frequency results in rigid dipoles, and a reduction in the degree of rotation with the applied field occurs, thus reducing their contribution to the polarization field. A lower value of dielectric loss at higher frequencies is generally expected in samples with good optical qualities.21

presence of the zinc metal center. The total polarization of a dielectric arises from four sources of charge displacement: (a) electronic displacement, (b) ionic displacement, (c) orientation of permanent dipoles, and (d) space charge displacement.17 In many compounds, the dielectric constant exhibits a large variation with frequency, and a low dielectric constant is required to minimize cross-talk noise and propagation delay. The high dielectric constant in the lower frequency region in both samples under investigation can be attributed to the presence of interfacial or a space charge polarization mechanism.2b,18 In addition, the dielectric constant always decreases with increasing frequency, although with varying 1576

dx.doi.org/10.1021/cg401472k | Cryst. Growth Des. 2014, 14, 1572−1579

Crystal Growth & Design

Article

Figure 7. (a) Plot of FTIR spectra for compound 1a soaked in different anion solutions. (b) The corresponding PXRD patterns.

Figure 8. (a) Plots of dielectric constant for 1a treated with different anion solutions. (b) Plots of corresponding dielectric loss.

Information). The IR spectra for 1a after treatment with KSCN revealed the appearance of a new peak at 2087 cm−1, consistent with the incorporation of SCN− in the structure, while treatment with NaN3 revealed a peak at 2053 cm−1 (Figure 7a). In the case of SO42− and HCO3− the strong peaks at ∼1100 cm−1 and ∼1630 cm−1 was probably overlapped with the peak of 1a in the same region, while the incorporation of H2PO4− led to a sharpening of the peak at 1616 cm−1 and the appearance of new characteristic peaks at 1155, 1072, 894 cm−1, indicating the incorporation of H2PO4− in 1a. The PXRD patterns of 1a-SCN−, 1a-N3−, 1a-SO42−, and 1a-HCO3− are similar to that of 1a, whereas the corresponding PXRD pattern of 1a-H2PO4− showed a significant peak shift in going from 13.7° to 9.2° (Figure 7b). The dielectric properties of chiral MOFs have been largely unexplored. In particular, changes in dielectric properties on the introduction of different anions have not been studied so far. Therefore, by applying the same procedure as was done for 1a and 1b, we measured the real and imaginary part of the dielectric constant (κ) for compounds 1a-SCN−, 1a-N3−, 1aSO42−, 1a-HCO3−, and 1a-H2PO4− within a frequency range of 40 Hz to 1 MHz. In our case, the dielectric constant of 1a (κ = 2.53 at 1 MHz) was found to increase on treatment with these anions (Figure 8a).

To further investigate the dielectric behavior of compounds 1a and 1b, impedance spectroscopic studies (Z′ vs Z″) were carried. Impedance plots have a semicircular arc in the lower resistance region corresponding to bulk material properties and are followed by a spike in the higher resistance region, which corresponds to the formation of an electrical double layer (EDL) capacitances at the electrode/sample interface.22 As indicated by the plots, the impedance values for compound 1a have a much steeper slope (Figure 6a). Impedance vs frequency plots are shown in Figure 6b. The impedance Z of an ideal capacitor is shown by the formula Z = 1/jωC, where ω is the angular frequency and C is the electrostatic capacitance of the capacitor. According to the said formula, the amount of impedance decreases inversely with the frequency. Anion Exchange Studies and Anion Controlled Dielectric Measurements. In the structures of chiral MOFs 1 and 2, NO3− anions are present between the 2D layers. The exchange of these encapsulated anions in 1a against various anions was examined. Crystals of 1a were immersed in an aqueous solution (0.2 mol L−1) of KSCN, NaN3, NaClO4, Na2SO4, NaHCO3, and KH2PO4, respectively. The solution was exchanged with fresh anion solution every day for one week. The SCN−, N3−, SO42−, HCO3−, and H2PO4− treated samples displayed a change in color, and transparency was completely lost in some of the samples (Figure S7, Supporting 1577

dx.doi.org/10.1021/cg401472k | Cryst. Growth Des. 2014, 14, 1572−1579

Crystal Growth & Design

Article

L.; Chen, F.; Wiktor, P.; Ferry, D. K.; Tao, N. J. Nano Lett. 2010, 10, 5060. (d) Zhou, Y.; Tian, C.; Meng, S.; Yue, Z.; Li, L. J. Am. Ceram. Soc. 2012, 95, 1665. (e) Yang, B.-H.; Xu, H.-Y.; Yang, Z.-Z.; Zhang, C. J. Mater. Chem. 2010, 20, 2469. (f) Volksen, W.; Miller, R. D.; Dubois, G. Chem. Rev. 2009, 110, 56. (g) Maex, K.; Baklanov, M. R.; Shamiryan, D.; lacopi, F.; Brongersma, S. H.; Yanovitskaya, Z. S. J. Appl. Phys. 2003, 93, 8793. (h) Cava, R. J. J. Mater. Chem. 2001, 11, 54. (2) (a) See www.itrs.net, Chapter Interconnect, Table INTC2. (b) Hoefflinger, B. Chips 2020; Hoefflinger, B., Ed.; Springer: Berlin Heidelberg, 2012. (3) Havemann, R. H.; Hutchby, J. A. Proc. IEEE 2001, 89, 586. (4) (a) Su, C.-Y.; Goforth, A. M.; Smith, M. D.; Pellechia, P. J.; zur Loye, H.-C. J. Am. Chem. Soc. 2004, 126, 3576. (b) Luo, T.-T.; Wu, H.C.; Jao, Y.-C.; Huang, S.-M.; Tseng, T.-W.; Wen, Y.-S.; Lee, G.-H.; Peng, S.-M.; Lu, K.-L. Angew. Chem., Int. Ed. 2009, 48, 9461. (c) Lee, C.-H.; Huang, H.-Y.; Liu, Y.-H.; Luo, T.-T.; Lee, G.-H.; Peng, S.-M.; Jiang, J.-C.; Chao, I.; Lu, K.-L. Inorg. Chem. 2013, 52, 3962. (d) Zhang, H.-X.; Wang, F.; Tan, Y.-X.; Kang, Y.; Zhang, J. J. Mater. Chem. 2012, 22, 16288. (e) Ma, S.; Zhou, H.-C. Chem. Commun. 2010, 46, 44. (f) Chae, H. K.; Siberio-Perez, D. Y.; Kim, J.; Go, Y.; Eddaoudi, M.; Matzger, A. J.; O’Keeffe, M.; Yaghi, O. M. Nature 2004, 427, 523. (g) Li, H.; Eddaoudi, M.; O’Keeffe, M.; Yaghi, O. M. Nature 1999, 402, 276. (h) Eddaoudi, M.; Kim, J.; Rosi, N.; Vodak, D.; Wachter, J.; O’Keeffe, M.; Yaghi, O. M. Science 2002, 295, 469. (5) (a) Zhu, W.; He, C.; Wu, P.; Wu, X.; Duan, C. J. Chem. Soc., Dalton Trans. 2012, 41, 3072. (b) Wang, C.; Zheng, M.; Lin, W. J. Phys. Chem. Lett. 2011, 2, 1701. (c) Song, F.; Wang, C.; Lin, W. Chem. Commun. 2011, 47, 8256. (d) Ma, L.; Falkowski, J. M.; Abney, C.; Lin, W. Nat. Chem. 2010, 2, 838. (e) Jeong, K. S.; Go, Y. B.; Shin, S. M.; Lee, S. J.; Kim, J.; Yaghi, O. M.; Jeong, N. Chem. Sci. 2011, 2, 877. (f) Dang, D.; Wu, P.; He, C.; Xie, Z.; Duan, C. J. Am. Chem. Soc. 2010, 132, 14321. (g) Seo, J. S.; Whang, D.; Lee, H.; Jun, S. I.; Oh, J.; Jeon, Y. J.; Kim, K. Nature 2000, 404, 982. (6) (a) Zhou, X.; Li, H.; Xiao, H.; Li, L.; Zhao, Q.; Yang, T.; Zuo, J.; Huang, W. J. Chem. Soc., Dalton Trans. 2013, 42, 5718. (b) Zheng, M.; Tan, H.; Xie, Z.; Zhang, L.; Jing, X.; Sun, Z. ACS Appl. Mater. Interfaces 2013, 5, 1078. (c) Wang, M. X.; Long, L. S.; Huang, R. B.; Zheng, L. S. Chem. Commun. 2011, 47, 9834. (d) Mahata, P.; Natarajan, S. Inorg. Chem. 2007, 46, 1250. (e) Li, Z. Z.; Du, L.; Zhou, J.; Zhu, M. R.; Qian, F. H.; Liu, J.; Chen, P.; Zhao, Q. H. J. Chem. Soc., Dalton Trans. 2012, 41, 14397. (f) Wu, P.; Wang, J.; Li, Y.; He, C.; Xie, Z.; Duan, C. Adv. Funct. Mater. 2011, 21, 2788. (7) (a) Nagaraja, C. M.; Haldar, R.; Maji, T. K.; Rao, C. N. R. Cryst. Growth Des. 2012, 12, 975. (b) Sibille, R.; Mazet, T.; Malaman, B.; Gaudisson, T.; Francois, M. Inorg. Chem. 2012, 51, 2885. (c) Kurmoo, M. Chem. Soc. Rev. 2009, 38, 1353. (d) Ferrando-Soria, J.; SerraCrespo, P.; de Lange, M.; Gascon, J.; Kapteijn, F.; Julve, M.; Cano, J.; Lloret, F.; Pasan, J.; Ruiz-Perez, C.; Journaux, Y.; Pardo, E. J. Am. Chem. Soc. 2012, 134, 15301. (8) Duan, X.; Meng, Q.; Su, Y.; Li, Y.; Duan, C.; Ren, X.; Lu, C. Chem.Eur. J. 2011, 17, 9845. (9) (a) Ye, Q.; Fu, D.-W.; Tian, H.; Xiong, R.-G.; Chan, P. W. H.; Huang, S. D. Inorg. Chem. 2008, 47, 772. (b) Pan, C.; Nan, J.; Dong, X.; Ren, X.-M.; Jin, W. J. Am. Chem. Soc. 2011, 133, 12330. (10) (a) Yang, P.; He, X.; Li, M.-X.; Ye, Q.; Ge, J.-Z.; Wang, Z.-X.; Zhu, S.-R.; Shao, M.; Cai, H.-L. J. Mater. Chem. 2012, 22, 2398. (b) Tang, Y.-Z.; Huang, X.-F.; Song, Y.-M.; Chan, P. W. H.; Xiong, R.G. Inorg. Chem. 2006, 45, 4868. (c) Qu, Z. R.; Ye, Q.; Zhao, H.; Fu, D. W.; Ye, H. Y.; Xiong, R. G.; Akutagawa, T.; Nakamura, T. Chem.Eur. J. 2008, 14, 3452. (11) Farrugia, L. J. Appl. Crystallogr. 1999, 32, 837. (12) Sheldrick, G. M. SHELX-97, A Program for Crystal Structure Solution and Refinement; University of Göttingen: Göttingen, Germany, 1997. (13) (a) Nettleman, J. H.; Supkowski, R. M.; LaDuca, R. L. J. Solid State Chem. 2010, 183, 291. (b) Wang, H.; Zhang, D.; Sun, D.; Chen, Y.; Zhang, L.-F.; Tian, L.; Jiang, J.; Ni, Z.-H. Cryst. Growth Des. 2009, 9, 5273. (c) Zhang, J.; Li, Z. J.; Kang, Y.; Cheng, J. K.; Yao, Y. G. Inorg. Chem. 2004, 43, 8085.

It is noteworthy that a small but significant increase in the dielectric constant was observed for 1a-SCN−, 1a-N3−, 1aSO42−, and 1a-HCO3− as compared with that of 1a sample. The results of an elemental analysis revealed that the NO3− ions in 1a were partially exchanged with SCN−, N3−, SO42−, and HCO3− ions (Table S1, Supporting Information). Their structures basically remained intact as evidenced by IR, PXRD, and luminescence data. The increase in the dielectric constant may be attributed to the disturbance of the original well-ordered hydrogen bonding as the result of the incorporation of different anions. This random distribution may increase the mobility of anions in the structure and, hence, the polarization.17 On the contrary, the NO3− ions in 1a were found to be completely exchanged for H2PO4− as evidenced by EA, IR, PXRD, and luminescence data. In particular, the PXRD pattern of 1a-H2PO4− showed that the peak shift from 13.7° to 9.2° can be attributed to the expansion between two-dimensional layers to accommodate H2PO4− anions. The O−H groups and the large size of the incorporated H2PO4− anions enhance polarizability, thereby resulting in a high value of the dielectric constant (20.79 at 40 Hz and 3.46 at 1 MHz) as shown in Figure 8a.

■

CONCLUSION We successfully synthesized three 2D homochiral MOFs which are highly thermal stable and emissive. The presence of chiral centers in the reactants resulted in the formation of the noncentrosymmetric compounds 1a, 1b and 2, where compound 1a has very versatile properties. Compound 1a is not only a very luminescent material but is also sensitive toward certain anions. It is a good low-κ dielectric material, and its unique anion controlled dielectric behavior is demonstrated for the first time. In addtion, 1a displays fair nonlinear optical properties in comparison to 1b. This work may exploit facile entry for incorporation of anions into chiral MOFs for the preconceived needs in future material design.

■

ASSOCIATED CONTENT

S Supporting Information *

TGA, PXRD patterns, SHG curve, optical microscope pictures of 1a after treatment with different anions and their corresponding elemental analysis, luminescence and XPS plots, and crystallographic data. This material is available free of charge via the Internet at http://pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Authors

*(K.-L.L.) Fax: 886-2-27831237. E-mail: [email protected]. tw. *(Y.-C.L.) Fax: 886-2-23636359. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS We thank Academia Sinica, Taiwan International Graduate Program, and the National Science Council, Taiwan, for financial support.

■

REFERENCES

(1) (a) Xu, T.; Wu, Y.-K.; Luo, X.; Guo, L. J. Nat. Commun. 2010, 1, 59. (b) Stengel, M.; Spaldin, N. A. Nature 2006, 443, 679. (c) Xia, J. 1578

dx.doi.org/10.1021/cg401472k | Cryst. Growth Des. 2014, 14, 1572−1579

Crystal Growth & Design

Article

(14) (a) Zhang, L.-Y.; Liu, G.-F.; Zheng, S.-L.; Ye, B.-H.; Zhang, X.M.; Chen, X.-M. Eur. J. Inorg. Chem. 2003, 2965. (b) Bertoncello, R.; Bettinelli, M.; Casarin, M.; Gulino, A.; Tondello, E.; Vittadini, A. Inorg. Chem. 1992, 31, 1558. (15) Zhao, J.; Wang, X.-L.; Shi, X.; Yang, Q.-H.; Li, C. Inorg. Chem. 2011, 50, 3198. (16) Kurtz, S. K. J. Appl. Phys. 1968, 39, 3798. (17) (a) Böttcher, C. J. F.; van Belle, O. C.; Bordewijk, P.; Rip, A.; Yue, D. D. J. Electrochem. Soc. 1974, 121, 211C. (b) Akutagawa, T.; Koshinaka, H.; Sato, D.; Takeda, S.; Noro, S.-I.; Takahashi, H.; Kumai, R.; Tokura, Y.; Nakamura, T. Nat. Mater. 2009, 8, 342. (c) Zhang, W.; Cai, Y.; Xiong, R.-G.; Yoshikawa, H.; Awaga, K. Angew. Chem., Int. Ed. 2010, 49, 6608. (18) Srivatsan, T. S. Processing and Fabrication of Advanced Materials, XVII: Part 8: Polymer-Based Composites and Nano Composites; I.K. International Publishing House: New Delhi, India, 2009; Vol. II. (19) Cardarelli, F. Materials Handbook: A Concise Desktop Reference; Springer London, Limited: London, 2008. (20) Hill, R. M.; Dissado, L. A. Nature 1979, 281, 286. (21) (a) Kanagathara, N.; Anbalagan, G. Int. J. Opt. 2012, 1. (b) Feng, I. W.; Zhao, W.; Li, J.; Lin, J.; Jiang, H.; Zavada. J. Appl. Opt. 2013, 52, 5426. (22) Sengwa, S. C. R. J. Ind. J. Pure Appl. Phys. 2011, 49, 204.

1579

dx.doi.org/10.1021/cg401472k | Cryst. Growth Des. 2014, 14, 1572−1579