Mixed Bromine–Chlorine Induced Great Dielectric and Second-Order

Sep 22, 2017 - Mixed Bromine–Chlorine Induced Great Dielectric and Second-Order Nonlinear Optical Properties Changes in Phase Transitions Compounds ...
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Mixed Br-Cl Induced Great Dielectric and Second-Order Nonlinear Optical Properties Changes in Phase Transitions Compounds [H2mdap][BiBr5(1-x)Cl5x] (x = 0.00-1.00) Ya Wang, Chao Shi, and Xiang-Bin Han J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.7b05126 • Publication Date (Web): 22 Sep 2017 Downloaded from http://pubs.acs.org on September 22, 2017

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Mixed Br-Cl Induced Great Dielectric and Second-Order Nonlinear Optical Properties Changes in Phase Transitions Compounds [H2mdap][BiBr5(1-x)Cl5x] (x = 0.00−1.00) Ya Wang*, Chao Shi, Xiang-Bin Han College of Chemistry and Chemical Engineering, Southeast University, Nanjing 211189, China. E-mail: [email protected].

Abstract: Doping/mixing method plays an important role in modulating the structures and physical properties of functional materials. Herein, we report that the mixed crystals [H2mdap][BiBr5(1-x)Cl5x] (H2mdap = protonated N-methyl-1,3-diaminopropane, x = 0.00−1.00) undergo phase transitions with the trend that the larger x, the higher phase transition temperature. Variable-temperature structure analysis shows that anionic and cationic moieties in the crystal lattice contribute to the phase transition. Room-temperature structure comparisons reveal that phase transition point moving to a higher temperature is mainly due to the decrease of the Bi−Cl/Br−Bi angles in the anionic chains and slightly alter the intermolecular interactions with mixed different components of halogen atoms Cl and Br. Dielectric and Second harmonic generation experiments demonstrate their similar phase transition behaviours and coexistence of switchable dielectric behaviors and bistable nonlinear optical effects. Mixed Br-Cl induced great dielectric and second-order nonlinear optical properties changes which makes [H2mdap][BiBr5(1-x)Cl5x] (x = 0.00−1.00) become potential tunable and multifunctional optical-electrical coupled materials.

Introduction Phase transitions materials are multifunctional stimuli-responsive materials with a range of applications in sensors, actuators, optical and memory devices and so on.1-8 Much attention has been paid to improve the performances of the materials. Doping/mixing method is the most convenient and efficient approach, especially for the control of the phase transition temperature (Tc) and properties.9-12 For example, pure inorganic perovskite (LnCa)MnO3 doped with A-site lanthanide (Ln) exhibits multiferroic properties13,14 and ceramic BaTiO3 doped with Sr ion at Ba site makes the paraelectric-ferroelectric Tc shift to a lower temperature region.1 For molecule-based phase transition compound (NH2NH3)[Mn(HCOO)3], a downward shift of Tc (355 K) and the diffuse dielectric behaviors was observed when mixed with CH3NH3 cation,15,16 while the

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phase

transitions

and

(CH3NH3)[Mn(HCOO)3]

dielectric

properties

disappeared

Page 2 of 18

when

become

the

17,18

. The layered perovskites of compositions (CHA)2PbBr4-4xI4x (x ≤ 0.175,

CHA = cyclohexylammonium), varying the ratio of the Br and I ions cause changes in the Tc, dielectric constant and second-order nonlinear optical properties, nevertheless, there is a phase separation during the mixing x = 0.175.19 Mixing of the B’-site alkali metals in the hybrid double perovskite crystals (CH3NH3)2[K1-xRbxCo(CN)6] (x = 0.23–0.62) results in a fine tuning of the phase transition temperatures and therefore the switchable dielectric constant properties.20 Although there are many methods to control, modulate, or optimize the properties, reports that induced multi-properties systematic changes in organic-inorganic hybrid phase transitions compounds are still scare. Organic-inorganic hybrid phase transition materials have attracted much attention due to their advantages

on

easy-processing,

tunability,

cheapness,

environmental

friendliness

and

multifunctionality. Halogenoantimonates(III) and halogenobismuthates(III), Aa[MmXn], where A is the protonated amine cation or its analogues, M is the ion Bi(III) or Sb(III), and X is the halogen anion, constitute an attracting family of multifunctional materials.21-24 By doping/mixing the A, M and/or X components, the phase transition-related properties can be finely tuned.25-27 However, there is no detail explanation between the microscopic crystal structure and the properties changes. Herein,

we

report

a

series

of

Bi(III)-based

organic-inorganic

hybrid

compounds

[H2mdap][BiBr5(1-x)Cl5x] (H2mdap = protonated N-methyl-1,3-diaminopropane; x = 0.00–1.00). [H2mdap][BiCl5] (x = 1.00) shows a ferro- to paraelectric transition at Tc = 372 K with the structure changes from a polar phase to a nonpolar phase.28 The compounds [H2mdap][BiBr5(1-x)Cl5x] (x = 0.00–1.00) undergo phase transitions due to both the relative displacements of the Bi and Cl/Br ions in the anionic chains and order-disorder transformation of the organic cation. They display systematic changes in structure, phase transition behavior, dielectric and second-order nonlinear optical properties upon variation of the x. The Tc increases with the increase of the molar ratio x. Measurements Elemental analysis (EA) for C, H and N was performed on a Vario MICRO analyzer. Thermogravimetric analysis (TGA) was performed on a DSC/DTA-TG STA 449 F3 instrument at the rate of 10 K min−1 under air atmosphere. Differential scanning calorimetry (DSC) measurements was carried out on a NETZSCH DSC 200F3 under nitrogen atmosphere at 0.1 MPa in aluminum crucibles with a heating/cooling rate of 10 K min−1. Thermal gravimetric analysis was performed on a TA Instruments Q500. Powder X-ray diffraction (PXRD) patterns were obtained on a Rigaku SmartLab X-ray diffraction instrument. Dielectric constant curves were

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collected on crystalline-powdered samples and single crystal samples by a Tonghui TH2828A impedance analyser in the frequency range of 500 Hz to 1 MHz. Second harmonic generation (SHG) experiment was carried out on an Ins 1210058, INSTEC Instrument with the laser Vibrant 355 II, OPOTEK (pulsed Nd:YAG at 10 Hz repetition rate , 5 ns pulse duration, a wavelength of 1064 nm, 1.6 MW peak power). The numerical value of the nonlinear optical coefficients for SHG has been determined by comparison with a KDP reference. All of the above measurements were performed on a sample in the same batch. Synthetic procedures The mixed halogen compounds of [H2mdap][BiBr5(1-x)Cl5x](x = 0.00–1.00) were prepared by the Bi2O3 (2.84 g, 10 mmol) and H2mdap (1.02 g, 10 mmol) with the mixture of concentrated HBr and HCl solution in different molar ratios. Block crystals (yields: 75−80 %) were harvested by slowly evaporating at room temperature. Crystallographic data and structural refinement details showed homogeneous and uniform morphology. The phase purity of the samples was confirmed by PXRD (Figure S1). Element analyses of C/H/N obtained the x values in the crystal products. Calcd.(%) for x = 0.00: C 6.88, H 2.02, N 4.01; found: C 6.87, H 2.05, N 4.06. x = 0.38: C 7.82, H 2.30, N 4.56; found: C 7.84, H 2.32, N 4.57. x = 0.64: C 8.63, H 2.54, N 5.03; found: C 8.63, H 2.58, N 5.02. x = 0.72: C 8.92, H 2.62, N 5.20; found: C 8.90, H 2.66, N 5.09. x = 0.78: C 9.15, H 2.69, N 5.33; found: C 9.14, H 2.70, N 5.30. Single-crystal X-ray crystallography Variable-temperature single-crystal diffraction data of [H2mdap][BiBr5(1-x)Cl5x](x = 0.00–1.00) were collected on a Rigaku Saturn 724+ diffractometer operating with Mo-Kα (λ = 0.71075 Å) radiation and equipped with a graphite monochromator and Rigaku low-temperature gas spray cooler device. Data were processed including empirical absorption correction and using the CrystalClear software package (Rigaku, 2005). The structures were solved using direct methods and successive Fourier synthesis and then refined using full-matrix least-squares refinements on F2 using the SHELXTL software package. Cl and Br atoms randomly occupy the halogen sites and their ratio is decided by elemental analysis (the Experimental Section), corresponding to the refinement of the site occupancy factors. All non-hydrogen atoms were refined anisotropically and the positions of the hydrogen atoms were given geometrically. Summary of crystallographic data, selected bond lengths and bond angles and details of hydrogen bonding interactions are given in Tables S1–4.

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Results and discussion Thermal measurements Thermal stability of [H2mdap][BiBr5(1-x)Cl5x] (x = 0.00–1.00) was checked by TGA measurement. It shows that the samples begin to decompose at about 530 K with residues corresponding to Bi2O3 (Figure S2). The structural phase transitions were firstly checked by DSC measurements in the temperature range of 280–400 K (Figure 1). The phase transitions are reversible and the Tc values increase from 315 K for [H2mdap][BiBr5] (x = 0.00) to 372 K for [H2mdap][BiCl5] (x = 1.00)28. The Tc values increase with the increase of x (Figure 1). The corresponding estimated enthalpy and entropy changes (∆H and ∆S) are 3.86 KJ mol−1 and 12.3 J mol−1 K−1 for x = 0.00 and 6.47 KJ mol−1 and 17.4 J mol−1 K−1 for x = 1.00. In addition, there is a thermal hysteresis of the endo- and exothermal peaks (8 K for x = 0.00, 9 K for x = 1.00), exhibiting a characteristic of first-order phase transition.

Figure 1. DSC curves of [H2mdap][BiCl5xBr5(1-x)] (x = 0.00–1.00). Crystal Structures In order to further reveal the microscopic origin of phase transitions, variable-temperature X-ray crystal structures were determined at low temperature phase (LTP) and high temperature phase (HTP) to investigate the structural changes on [H2mdap][BiBr5(1-x)Cl5x] (x = 0.00–1.00) (Table 1 and Table S1). [H2mdap][BiCl5xBr5(1-x)] (x = 0.00–0.78) crystallize in the orthorhombic space group Pna21 at LTP and transform to space group Pnma at HTP. Although those compounds undergo similar cell parameters change in the vicinity of Tc between the two phases, a significant change of the symmetry with the point group from D2h in the HTP to C2v in the LTP, indicating the symmetry breaking occurs. The doped compounds from x = 0.38–1.00 are

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isomorphic with that of x = 0 at LTP and HTP demonstrating that phase transition of [H2mdap][BiBr5(1-x)Cl5x] (x = 0.00–1.00) originates from cationic disordering and anion deformation. Table 1 Crystallographic data and structural refinement details for [H2mdap][BiBr5(1-x)Cl5x] (x = 0 – 0.78) x

0.00

0.00

0.38

0.64

0.72

0.78

T/K

293 K

343 K

293 K

293 K

293 K

293 K

Formula

C4H14BiBr5N2

C4H14BiBr5N2

C4H14BiBr3.1Cl1.9N2

C4H14BiBr1.8Cl3.2N2

C4H14BiBr1.4Cl3.6N2

C4H14BiBr1.1Cl3.9N2

CCDC

1534848

1534849

1541243

1541244

1541245

1541246

Formula weight

698.65

698.65

614.20

556.41

538.63

525.30

Crystal system

orthorhombic

orthorhombic

orthorhombic

orthorhombic

orthorhombic

orthorhombic

Space group

Pna21

Pnma

Pna21

Pna21

Pna21

Pna21 18.209(4)

a/Å

18.297(4)

17.899(14)

18.160(4)

18.109(4)

18.120(4)

b/Å

10.234(2)

7.930(6)

10.074(2)

9.998(2)

9.950(2)

9.975(2)

c/Å

7.8231(16)

10.381(8)

7.6542(15)

7.5855(15)

7.5357(15)

7.5491(15)

α /°

90.00

90.00

90.00

90.00

90.00

90.00

β /°

90.00

90.00

90.00

90.00

90.00

90.00

γ /°

90.00

90.00

90.00

90.00

90.00

90.00

V / Å3

1464.9(5)

1473(2)

1400.3(5)

1373.4(5)

1358.7(5)

1371.2(5)

4

Z

4

Flack

0.27(2)

4

4

4

4

0.14(3)

1.02(3)

1.04(2)

0.18(2)

Dcalc / g cm−3

3.168

3.148

µ / mm−1

25.638

25.480

2.913

2.691

2.633

2.545

21.762

18.658

17.764

F (000)

1240

16.785

1240

1103.2

1009.6

980.8

959.2 3.029−27.479

θ range / °

3.278−27.476

3.005−27.500

3.020−27.480

3.035−27.480

3.041−27.475

Reflns collected

9796

15378

9330

9085

9138

9048

Indep. reflns (Rint)

3358 (0.0894)

1814 (0.1022)

3208(0.0838)

3151(0.0830)

3123(0.0688)

3144(0.0542)

No. of parameters

113

78

112

113

113

113

R1a, wR2b [I > 2σ(I)]

0.0492, 0.0791

0.0545, 0.1148

0.0605, 0.1265

0.0603, 0.1441

0.0481, 0.1135

0.0446, 0.1040

R1, wR2 [all data]

0.0722, 0.0851

0.0669, 0.1200

0.0867, 0.1355

0.0788, 0.1531

0.0627, 0.1192

0.0571, 0.1094

GOF

0.997

1.183

1.048

1.046

1.090

1.068

2.081, −1.275

0.962, −1.180

2.213, −2.223

2.651, −2.525

2.327, −1.355

2.513, −1.187

∆ρc / e Å−3

[a] R1 = Σ| |Fo| − |Fc| | / |Fo|. [b] wR2 = [Σw(Fo2−Fc2)2] / Σw(Fo2)2]1/2. [c] Maximum and minimum residual electron density.

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Figure 2. Structural comparison of [H2mdap][BiBr5] (x = 0.00) between the LTP and HTP: (a, b) basic structural unit; (c, d) [BiBr5]n2− zigzag chain with hydrogen-bonding interactions with the cations; H atoms were omitted for clarity. The two-site disorder, related by a mirror plane, of the cation in the HTP are shown in two colors of the bonds. Dotted lines represent hydrogen bonds. Taking [H2mdap][BiBr5] (x = 0.00) as an example, the asymmetric unit consists of one BiBr52− anion and one H2mdap cation at LTP (Fig. 2a). Each of the Bi3+ ion is hexa-coordinated with six bromide atoms forming a octahedral configuration. The octahedron is sterically interfered by the lone-pair electrons on Bi3+ in the BiBr52− moiety that lead the Bi3+ to deviate from the crystallographic centre of the octahedron.29,30 The deformed inorganic BiX6 octahedral units establish rich structural flexibility like anionic discrete bioctahedra, corner/edge/face-connected chains or layers.21,22,31,32 Here, the BiBr6 octahedron is distorted with Bi−Br bond distances in the range of

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2.734(2)−3.026(2) Å and Br−Bi−Br angles with two cis-positioned Br ions varying from 84.53(3)° to 95.46(7)° (Table S1). Br1 behaves as bridging linkers in a cis-mode and form a one-dimensional zigzag chains that extending along the c axis with the Bi1−Br1−Bi1 bond angle of 154.02(9) ° and Bi1−Br1 bond lengths of 2.960(2) Å and 3.026(2) Å (Figure 2c). The H2mdap, keeping in completely ordered state, are located in the free space enclosed by inorganic frameworks through weak N−H···Br hydrogen bonds with donor-acceptor distances of 3.451(2)−3.595(2) Å (Table S2). Nevertheless, upon heating, the appearance of the mirror paralleled to the ac plane causes the basic unit a prominent difference of basic unit structure compared with that in the LTP (Figure 2b). The central Bi1 atom and two terminal Br atoms (Br1 and Br3) are situated in the mirror plane with the bond lengths of Bi−Br varying from 2.750(2) Å to 2.976(2) Å and bond angles of Bi−Br−Bi ranging from 83.57(6)° to 92.12(5)° (Table S2). The bridging Br4 atom locates on the center of inversion and the bond angle of Br4−Bi−Br4 of the [BiBr5]n2− zigzag chain becomes linear compared with its LTP value of 154.02(9)°(Figure 2d). The gradually elongated displacement ellipsoids of C2 and C3 atoms when heating display a mirror-related orientational disorder at two equal site occupancies in HTP, demonstrating dynamic hopping-like motions for H2mdap groups that results in the disordering of organic cations (Figure 2b).33,34 This behavior is very similar to the organic-inorganic hybrid compounds [NH3(CH2)5NH3]SbX5 (X = Cl or Br) and [C5N2H16]2SbBr5 in the HTP.23,35,36

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Figure 3. Influence of x on the Bi–Cl/Br–Bi angle, the length of the bridged Br/Cl and Bi dBi–Br/Cli and Bi dBi–Br/Cli value, the distance of adjacent Bi dBi-Bi value of the [BiBr5(1-x)Cl5x]n2-(x =0.00−1.00).

In the lattice parameters of room temperature structures, with the increase of x, the b and c axes decrease slightly and the a axis changes little (Figure S5). The unit cell volumes have a shrinkage with the increase of x from 0.00 to 1.00, giving a gradually reduced volume space to accommodate cationic chains and anions. According to comparison of the bond length and angle of the H2mdap, there is no obvious regular change with the increase of the Cl component (Figure S6). For the one-dimensional zigzag chains, with increased Cl ions concentration, the lengths dBi-Bi of neighboring Bi···Bi in one chain shrink from 5.833(2) Å (x = 0.00) to 5.495(7) Å (x = 1.00), as well as the distances between the bridged Br/Cl and the adjacent Bi in two deformed octahedrons also have a significant decrease with the range from 2.789(3) Å to 2.960(2) Å and from

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2.909(3) Å to 3.026(2) Å, respectively (Figure 3). The Bi–Cl/Br–Bi angle of the [BiBr5(1-x)Cl5x]n2- deceases from 154.02(9) Å to 149.32(2) Å with the increase of x from 0.00 to 1.00. Through the above structural analysis, it appears that the contribution of cationic moiety to the change of phase transition temperature is negligible. Meanwhile, hydrogen bonding is sensitive and significant for the regulation of physical properties.37,38 With the increase of the doping component Cl, the interaction of the hydrogen bonds between anion and cation has changed. For instance, donor-acceptor distances of N1−H···Cl/Br hydrogen bonds are varying from 3.242(11) Å to 3.880(19) Å with increased Cl ions concentration (Table S3). The elongation or shortening of the hydrogen bond generates an increase or decrease in the ionic displacement similar to other compounds, may respond to activate order parameter.39,40 Most probably, hydrogen-bonded interaction affects the anionic distortion and the cationic order-disorder process. In this case, changes in each component are thought come from the different ionic radii of the halogen ions, though the difference between Cl (1.81 Å) and Br (1.95 Å) is small. The difference of radii between Br and Cl causes the cell volumes of series compounds declining from [H2madp][BiBr5] (1464.9(5) Å3) to [H2madp][BiCl5] (1323.6(5) Å3), giving rise to obviously decreasing the cavities occupied by the H2mdap. An increase of the phase transition temperature was observed due to the more and more difficult movement of cations. In addition, the larger and less electronegative Br ion in the anionic chain structure lengthens the Bi−Br bond, increases the Bi−Cl/Br−Bi angles and slightly alters the intermolecular interactions. We assume that smaller of Bi−Cl/Br−Bi angles at the LTP requires more energy to become straight at HTP. This is an important reason for the Tc shift to higher temperature. Similar PXRD patterns and same space group at LTP and HTP further indicate that no large structural changes occurred via doping bromide into chloride (Figure S1, Table 1, Table S1). Bromide-chlorine mixing effect in compounds [H2mdap][BiBr5(1-x)Cl5x] (x = 0.00–1.00) does not play an

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important role in huge structure change (Table 1). However, the mixing effect brings great physical property change, it is noteworthy that the Tc rise from 315 K to 372 K, and dielectric constant and SHG response all show regulated change with the molar ratio x increases from 0.00 to 1.00. Dielectric constant

Figure 4. Temperature dependence of real part (ε') of the dielectric permittivity of [H2mdap][BiBr5(1-x)Cl5x] (x =0.00–1.00) measured on powdered samples at 1 MHz. The inset shows the effect of x on the Tc of [H2mdap][BiBr5(1-x)Cl5x] (x = 0.00–1.00).

The temperature-dependent dielectric constant ε curves (ε = ε' − iε'', in which ε' is the real part and ε'' is the imaginary part) for [H2mdap][BiBr5(1-x)Cl5x] (x = 0.00–1.00) were measured on pressed-powder polycrystalline samples in a cooling mode at selected frequencies (Figure 4 and Figure S3–5). At 1 MHz, the values of peak temperature / ε'max / x are 315 K / 14.5 / 0.00, 317 K / 17.0 / 0.38, 333 K / 17.8 / 0.64, 342 K / 18.4 / 0.72, 344 K / 18.8 / 0.78 and 367 K / 19.9 / 1.00. The increase of the Cl content shifts distinctly the Tc towards higher temperature, consistent with the DSC result. The peak values are equal with the increase of the electric field frequency and no shift of the Tc with the variation of frequency was observed, illustrating no relaxation process occurs during the

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The Journal of Physical Chemistry

phase transition (Figure S3; Figure S5). In addition, single crystal sample anisotropy measurement of [H2mdap][BiBr5] (x = 0.00) is shown in the Figure S3. The dielectric curve exhibits a marked peak at 315 K along the c-axis upon cooling, while a sharp jump in the a-axis and b-axis. The values of ε' along the a and b axis are obviously smaller than that along the c-axis, indicating the polar change during the phase transitions along c-axis.

Nonlinear optical property

Figure 5. The temperature-dependence of the SHG intensity measured on the polycrystalline samples of [H2mdap][BiBr5(1-x)Cl5x] (x = 0.00–1.00).

From the aforementioned structural analyses, the disappearance of the mirror plane and deformation of anionic chains lead to the symmetry breaking. SHG experiments were performed with the crystalline powdered samples of [H2mdap][BiBr5(1-x)Cl5x]

(x

=

0.00–1.00)

(Figure

5)

to

prove

their

noncentrosymmetric (LTP) and centrosymmetric (HTP) structures and nonlinear optical property. Above the Tc, the SHG signals are negligible, corresponding to centrosymmetric structures of the HTP. With the decrease of the temperature, the signals undergo a step-like increase at the Tc and then quickly

reach

almost

saturation,

indicating

the

occurrence

of

noncentrosymmetric structures. The saturation values of the SHG intensity are

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estimated to be 1.10 times (x = 0.00), 1.00 times (x = 0.48), 0.75 times (x = 0.64), 0.50 times (x = 0.72), 0.40 times (x = 0.78), 0.26 times (x = 1.00), as large as that of the reference KH2PO4, revealing a quadratic NLO switching property.

Conclusions In conclusion, a series of mixed crystals [H2mdap][BiBr5(1-X)Cl5x] (x = 0.00– 1.00)

(H2mdap

=

protonated

N-methyl-1,3-diaminopropane)

has

been

successfully synthesized and exhibit a reversible phase transition from Tc = 315 K to 372 K with the increase of the molar ratio of x. Their structures are featured by anionic zigzag chains of [BiBr5(1-x)Cl5x]n and the origin of the phase transition includes both the relative displacements of the Bi and Cl or Br ions in the anionic chains and order-disorder transformation of the organic cations. Through comparing room-temperature structures, we found that the driving force for moving the Tc to room temperature is that the larger size and less electronegativity of Br ion than the Cl ion in the anionic chains generally lengthen the Bi−Br bond, increase the Bi−Cl/Br−Bi angles and slightly alter the intermolecular interactions and cell volumes. These systematic changes in structure induced great dielectric and second-order nonlinear optical properties changes.

Supporting Information Available XRD powder pattern, TGA curve, dielectric spectra of x = 0.00, dielectric spectra of x = 0.38−0.78 at various frequencies, and Influence of x on the cell parameters (Figures S1−S5, respectively), crystal data and structural refinement details in HTPs, Hydrogen-bond, Selected bond lengths and angles (Table S1−S4, respectively)(PDF) Crystallographic data of x = 0.00: CCDC deposition numbers 1534848, 1534849 (CIF)

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Crystallographic data of x = 0.38−0.78: CCDC deposition numbers 1541243−1541246, 1566455−1566458 (CIF)

Acknowledgements This work was supported by the Southeast University of China.

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