Various Ionic Crystals from the Combination of 1,3-Bis

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Various Ionic Crystals from the Combination of 1,3Bis(dicyanomethylidene)indan Anion and #-Electronic Cations Yuka Tanaka, Keisuke Ichijo, Sota Kodama, Shun Aoyama, Tsukasa Yoshida, Ryohei Yamakado, and Shuji Okada Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.9b00841 • Publication Date (Web): 16 Aug 2019 Downloaded from pubs.acs.org on August 20, 2019

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Crystal Growth & Design

Various Ionic Crystals from the Combination of 1,3-Bis(dicyanomethylidene)indan Anion and π-Electronic Cations Yuka Tanaka, Keisuke Ichijo, Sota Kodama, Shun Aoyama, Tsukasa Yoshida, Ryohei Yamakado*, and Shuji Okada* Department of Organic Materials Science, Graduate School of Organic Materials Science, Yamagata University, Yonezawa 992-8510, Japan [email protected]; [email protected] KEYWORDS. ionic crystals, charged π-electronic systems, charge-segregated assemblies

ABSTRACT. 1,3-Bis(dicyanomethylidene)indan anion (CMI–) is a stable π-electronic anion that prepared by the self-deprotonation. A series of ion-pairing assemblies based on CMI– were investigated by various π-electronic cations. The packing structures were revealed by the single-crystal X-ray analysis, and charge-by-charge and charge-segregated assemblies were obtained. Interestingly, cation-cation and/or anion-anion stacking formations were observed in all crystal structures, although the electrostatic repulsion affects between identically charged species. The stabilization of the identical charged stackings by the dipole-dipole interactions was explained from the DFT calculation. In addition, the delocalization of negative or positive charge through the face-to-face stacking and hydrogen bonding between the different charged species also play an important role for the formation of various assemblies.

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Introduction Charged organic molecules construct various nanoarchitectures based on electrostatic interactions, and provide ion-pairing materials.1–3 Especially, well defined arrangements of ion-pairing assemblies were achieved by the peripheral modification of the ionic species as the building units.4–6 Organic ionic crystals, one of the multicomponent co-crystals, have attracted much attention as nonlinear optical (NLO), ferroelectric, and superelastic materials.7–9 Organic ionic crystals have advantages for controlling the properties and the orientation of the molecules by the combination with various counter ions. In addition, crystals comprising πelectronic ions, which have delocalized charge in the -conjugation system and are distinguished from the electrically-neutral aromatics substituted by ionic groups, would have potentials for the organic electronics materials with improved properties due to enhanced polarization, electrostatic -facial interactions and the resulting steric interactions of the electronic ions. The π-electronic cations, whose positive charge is delocalized in the conjugation system, are easily prepared by the N-alkylation of heterocyclic amines (e.g. Nmethyl stilbazolium and cyanine dyes). Meanwhile, conventional organic anions have ionic groups such as sulfonate, carboxylate, and phosphate. It is difficult to synthesize stable πelectronic anions, whose negative charge is delocalized in the -conjugation system, because of their electron-rich character that facilitates their transformation into other species. To stabilize the π-electronic anions, π-extended anions and the anions having electronwithdrawing

groups

(e.g.

Kuhn’s

pentamethoxycarbonyl-substituted

anion,10,11

pentacyanocyclopentadienide,

cyclopentadienide12–20)

were

and

developed.

Bis(dicyanomethylidene)indan anion (CMI–), prepared by the self-deprotonation of 1,3bis(dicyanomethylene)indan (CMI),21–23 is also a fairly stable π-extended anion. It has been studied as a small near-infrared (NIR) dye, which shows light absorption and fluorescence in


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the red to NIR region. However, to the best of our knowledge, there are only one report of the single crystal structure including CMI–.24 We therefore focused on CMI– as an effective π-electronic anion for constructing organic ionic crystals in this study. Various ionic crystals based on CMI– were fabricated with contributions from alternated and segregated stacking, depending on the counter cations (Figure 1).

Experimental Section General information Starting materials were purchased from Kanto Chemical, TCI, and Sigma-Aldrich, and used without further purification unless otherwise stated. 1H and 13C nuclear magnetic resonance (NMR) spectroscopies were investigated on JEOL ECX-500 500 MHz and ECZ-600 600 MHz spectrometers using DMSO-d6 (δ 2.50 and 39.5 for 1H and

13C

NMR, respectively) as the

internal standards. Ultraviolet (UV)-visible (Vis) absorption spectra were recorded on a JASCO V-560 spectrometer using a 10 mm quartz cell. UV-vis-NIR diffuse reflectance spectra were recorded on a JASCO V-570 spectrometer using powdered samples. Samples were supported on filter paper, which was also used to provide the background reference.

Synthesis. Preparation

of

4-[2-(4-cyanophenyl)ethenyl]-1-methylpyridinium

1,3-

bis(dicyanomethylidene)indan-2-ide (1a+-CMI–). 1,3-Bis(dicyanomethylidene)indan (72.2 mg, 0.298 mmol) was added to a suspension of NaOH (15.0 mg, 0.375 mmol) in MeOH (20


3


mL).

Page 4 of 24

The mixture was heated at 60 °C to complete dissolution.

Then, 4-[2-(4-

cyanophenyl)ethenyl]-1-methylpyridinium iodide25 (10.4 mg, 0.298 mmol) was added and the mixture was stirred overnight at r.t. After removing the solvents, the residue was recrystallized from MeOH to afford 1a+-CMI– (22.8 mg, 66.0 µmol, 22%) as a purple powder. M.p.: 208 °C. 1H

NMR (600 MHz, DMSO-d6, ): 4.28 (3H, s), 5.70 (1H, s), 7.42–7.43 (2H, m), 7.74 (1H, d,

J = 16.2 Hz), 7.90–7.92 (4H, m), 7.96 (2H, d, J = 8.4 Hz), 8.10 (1H, d, J = 16.2 Hz), 8.24 (2H, d, J = 6.9 Hz), 8.92 (2H, d, J = 6.9 Hz).

13C

NMR (150 MHz, DMSO-d6, ): 47.14, 50.37,

102.73, 111.98, 117.81, 117.92, 118.64, 121.56, 124.07, 126.73, 128.56, 130.13, 132.96, 138.30, 138.32, 139.59, 145.41, 151.64, 158.14. Preparation

of

1-methyl-4-[2-(4-nitrophenyl)ethenyl]pyridinium

bis(dicyanomethylidene)indan-2-ide

(1b+-CMI–).

1,3-

1,3-Bis(dicyanomethylidene)indan

(0.121 g, 0.500 mmol) was added to a suspension of NaOH (20.0 mg, 0.500 mmol) in MeOH (20 mL). The mixture was heated at 60 °C to complete dissolution. Then, 1-methyl-4-[2-(4nitrophenyl)ethenyl]pyridinium iodide25 (0.184 g, 0.500 mmol) was added and the mixture was stirred overnight at r.t. After removing the solvent, the residue was recrystallized from MeOH to afford 1b+-CMI– (0.118 g, 0.375 mmol, 75%) as a purple powder. M.p.: 205 °C. 1H NMR (500 MHz, DMSO-d6, ): 4.28 (3H, s), 5.70 (1H, s), 7.41–7.45 (2H, m), 7.74 (1H, d, J = 16.8 Hz), 7.90–7.92 (2H, m), 7.99 (2H, d, J = 8.4 Hz), 8.10 (1H, d, J = 16.8 Hz), 8.27 (2H, d, J = 6.9 Hz), 8.34 (2H, d, J = 6.9 Hz), 8.93 (2H, d, J = 6.9 Hz).

13C

NMR (125 MHz, DMSO-d6,

): 47.22, 50.42, 102.79, 117.92, 118.00, 121.57, 124.21, 124.26, 127.46, 128.97, 130.13, 137.76, 137.83, 141.50, 145.45, 147.78, 151.52, 158.15. Preparation

of

4-{2-[4-(dimethylamino)phenyl]ethenyl}-1-methylpyridinium

1,3-

bis(dicyanomethylidene)indan-2-ide (1c+-CMI–). 1,3-Bis(dicyanomethylidene)indan (0.242 g, 1.00 mmol) was added to a suspension of NaOH (40.0 mg, 1.00 mmol) in MeOH (20 mL).


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Then, 4-{2-[4-

(dimethylamino)phenyl]ethenyl}-1-methylpyridinium iodide25 (0.366 g, 1.00 mmol) was added and the mixture was stirred overnight at r.t. After removing the solvents, the residue was recrystallized to afford 1c+-CMI– (0.418 g, 0.870 mmol, 87%) as a purple powder. M.p.: 225 °C. 1H NMR (500 MHz, DMSO-d6, ): 3.02 (6H, s), 4.16 (3H, s), 5.70 (1H, s), 6.78 (2H, d, J = 9.2 Hz), 7.16 (1H, d, J = 16.5 Hz), 7.42–7.44 (2H, m), 7.58 (2H, d, J = 9.2 Hz), 7.90 (1H, d, J = 16.5 Hz), 7.90–7.92 (2H, m), 8.03 (2H, d, J = 6.5 Hz), 8.67 (2H, d, J = 6.5 Hz).

13C

NMR (125 MHz, DMSO-d6, ): 46.34, 50.39, 102.77, 111.92, 117.07, 117.86, 117.96, 121.57, 122.10, 122.42, 130.11, 137.84, 141.86, 144.30, 151.84, 153.34, 158.14. Some 13C peaks were overlapped. Preparation

of

4-[2-(4-cyanophenyl)ethenyl]-1-methylquinolinium


(2a+-CMI–).

1,3-


(0.242 g, 1.00 mmol) was added to a suspension of NaOH (40.0 mg, 1.00 mmol) in MeOH (40 mL).


Then, 4-[2-(4-

cyanophenyl)ethenyl]-1-methylquinolinium iodide25 (0.398 g, 1.00 mmol) was added and the mixture was stirred overnight at 50 °C. The resulting precipitate was collected by filtration and washed with MeOH. Filtrate was recrystallized by MeOH to afford 2a+-CMI– (0.400 g, 0.780 mmol, 78%) as a purple powder. M.p.: 243 °C. 1H NMR (600 MHz, DMSO-d6, ): 4.58 (3H, s), 5.69 (1H, s), 7.40–7.42 (2H, m), 7.87–7.89 (2H, m), 8.01 (2H, d, J = 8.4 Hz), 8.09 (1H, dd, J = 7.8, 8.4 Hz), 8.16–8.19 (3H, m), 8.30 (1H, dd, J = 7.8, 9.0 Hz), 8.48–8.52 (3H, m), 9.06 (1H, d, J = 9.5 Hz), 9.43 (1H, d, J = 8.0 Hz).

13C

NMR (150 MHz, DMSO-d6, ): 45.47, 50.36,

102.71, 112.14, 117.12, 117.80, 117.90, 119.48, 121.57, 123.56, 126.54, 126.55, 129.23, 129.55, 130.10, 132.84, 135.16, 137.76, 138.74, 139.84, 140.37, 148.54, 151.80, 158.09. Some 13C

peaks were not clearly observed.


5


Preparation

of

Page 6 of 24

1-methyl-4-[2-(4-nitrophenyl)ethenyl]quinolinium


(2b+-CMI–).

1,3-


(0.121 g, 0.500 mmol) was added to a suspension of NaOH (20.0 g, 0.500 mmol) in MeOH (20 mL). The mixture was heated at 60 °C to complete dissolution. Then, 1-methyl-4-[2-(4nitrophenyl)ethenyl]quinolinium iodide25 (0.208 g, 0.500 mmol) was added and stirred overnight at 60 °C. The resulting precipitate was collected by filtration and washed with MeOH. Filtrate was recrystallized from MeOH to afford 2b+-CMI– (0.243 mg, 0.456 mmol, 91%) as a dark purple powder. M.p.: 255 °C. 1H NMR (600 MHz, DMSO-d6, ): 4.58 (3H, s), 5.65 (1H, s), 7.39–7.41 (2H, m), 7.86–7.88 (2H, m), 8.09 (2H, dd, J = 7.8, 7.8 Hz), 8.20– 8.25 (3H, m), 8.30 (1H, dd, J = 7.8, 7.8 Hz), 8.37 (2H, d, J = 9.0 Hz), 8.48–8.55 (3H, m), 9.06 (1H, d, J = 8.4 Hz), 9.45 (1H, d, J = 7.2 Hz).

13C

NMR (150 MHz, DMSO-d6, ): 45.01, 50.37,

102.72, 117.28, 117.80, 117.91, 119.50, 121.53, 124.10, 124.37, 126.55, 129.63, 129.64, 130.10, 135.19, 137.79, 138.75, 139.79, 141.76, 147.92, 148.60, 151.71, 158.09. Some 13C peaks were not clearly observed. Preparation

of

4-{2-[4-(dimethylamino)phenyl]ethenyl}-1-methylquinolinium

1,3-

bis(dicyanomethylidene)indan-2-ide (2c+-CMI–). 1,3-Bis(dicyanomethylidene)indan (0.242 g, 1.00 mmol) was added to a suspension of NaOH (40.0 mg, 1.00 mmol) in MeOH (20 mL). The mixture was heated at 60 °C to complete dissolution.

Then, 4-{2-[4-

(dimethylamino)phenyl]ethenyl}-1-methylquinolinium iodide25 (0.416 g, 1.00 mmol) was added and the mixture was stirred overnight at 50 °C. After removing the solvent, the residue was recrystallized from MeOH to afford 2c+-CMI– (0.530 g, 0.628 mmol, 63%) as a purple powder. M.p.: 244 °C. 1H NMR (600 MHz, DMSO-d6, ): 3.07 (6H, s), 4.44 (3H, s), 5.70 (1H, s), 6.83 (2H, d, J = 9.0 Hz), 7.42 (2H, m), 7.87 (2H, d, J = 9.0 Hz), 7.89 (2H, m), 7.98 (2H, dd, J = 16.8, 16.8 Hz), 8.02 (1H, d, J = 15.6 Hz), 8.17 (1H, d , J = 15.6 Hz), 8.21 (1H, dd, J = 16.2, 12.0 Hz), 8.34 (2H, d, J = 9.0 Hz), 9.03 (1H, d, J = 10.5 Hz), 9.10 (1H, d, J = 8.0 Hz).


6

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13C

NMR (150 MHz, DMSO-d6, ): 44.27, 50.70, 103.00, 111.90, 113.11, 113.92, 117.81,

117.92, 118.97, 121.57, 123.34, 126.32, 128.55, 130.14, 131.33, 134.61, 136.86, 137.82, 144.69, 146.78, 152.30, 153.16, 158.14. Some 13C peaks were not clearly observed. Preparation

of

1,1’-(ethane-1,2-diyl)bis(4-methylpyridinium)

bis(dicyanomethylidene)indan-2-ide) (3a2+-2CMI–).

bis(1,3-

To a MeOH (20 mL) solution of

sodium salt of 1,3-bis(dicyanomethylidene)indan (49.3 mg, 0.187 mmol) was added 1,1’(ethane-1,2-diyl)bis(4-methylpyridinium) dibromide26 (34.9 mg, 93.0 µmol) and the mixture was stirred overnight at 50 °C. After removing the solvents, the residue was recrystallized from MeOH to afford 3a2+-2CMI– (33.0 mg, 50.3 µmol, 54%) as a purple powder. M.p.: 247 °C. 1H NMR (400 MHz, DMSO-d6, ) 2.62 (4H, s), 5.10 (6H, s), 5.71 (2H, s), 7.44 (4H, dd, J = 5.2, 6.0 Hz), 7.92 (4H, dd, J = 5.2, 5.2 Hz), 8.03 (4H, d, J = 6.4 Hz), 8.75 (4H, d, J = 6.4 Hz).

13C

NMR (150 MHz, DMSO-d6, ): 21.60, 50.38, 59.00, 102.73, 117.93, 121.59,

128.70, 130.16, 137.85, 144.15, 158.16, 160.14. Preparation of 1,1’-(propane-1,3-diyl)bis(4-methylpyridinium) dibromide bis(1,3bis(dicyanomethylidene)indan-2-ide) (3b2+-2CMI–).


sodium salt of 1,3-bis(dicyanomethylidene)indan (63.8 mg, 0.203 mmol) was added 1,1’(propane-1,3-diyl)bis(4-methylpyridinium) dibromide26 (78.7 mg, 0.203 mmol) and the mixture was stirred overnight at 50 °C.

After removing the solvents, the residue was

recrystallized from MeOH to afford 3b2+-2CMI– (37.8 mg, 52.8 µmol, 52%) as a purple powder. M.p.: 190 °C. 1H NMR (600 MHz, DMSO-d6, ) 2.62 (2H, quint, J = 2.6 Hz), 2.63 (6H, s), 4.58 (4H, t, J = 7.2 Hz), 5.70 (2H, s), 7.43 (4H, dd, J = 3.6, 3.0 Hz), 7.91 (4H, dd, J = 3.6, 3.0 Hz), 8.03 (4H, d, J = 5.8 Hz), 8.84 (4H, d, J = 5.8 Hz).

13C

NMR (150 MHz, DMSO-d6, ):

21.41, 31.38, 50.39, 56.77, 102.74, 117.94, 121.60, 128.46, 130.18, 137.85, 143.93, 158.14, 159.22.


7


Page 8 of 24

Preparation of 1-ethyl-2-{3-[1-ethyl-2(1H)-quinolinylidene]-1-propen-1-yl}quinolinium 1,3-bis(dicyanomethylidene)indan-2-ide (4+-CMI–).


sodium salt of 1,3-bis(dicyanomethylidene)indan (5.50 mg, 17.0 µmol) was added 1-ethyl-2{3-[1-ethyl-2(1H)-quinolinylidene]-1-propen-1-yl}quinolinium iodide27 (8.17 mg, 17.0 µmol) and the mixture was stirred overnight at 50 °C. After removing the solvents, the residue was recrystallized from MeOH to afford 4+-CMI– (12.0 mg, quant) as a dark purple powder. M.p.: 257 °C. 1H NMR (400 MHz, DMSO-d6, ) 1.43 (6H, t, J = 7.2 Hz), 4.47 (4H, br. m), 5.70 (1H, s), 6.57 (2H, d, J = 12.7 Hz), 7.42(2H, m), 7.46 (4H, ddd, J = 7.2, 7.2, 1.4 Hz), 7.76 (2H, ddd, J = 8.6, 7.2, 1.4 Hz), 7.84 (2H, dd, J = 7.7, 1.4 Hz), 7.89 (2H, d, J = 8.6 Hz), 7.90 (2H, m), 8.00 (2H, d, J = 9.6 Hz), 8.30 (2H, d, J = 9.6 Hz), 8.71 (1H, t, J = 12.7 Hz).

13C

NMR (150

MHz, DMSO-d6, ): 12.48, 43.86, 50.39, 102.73, 105.39, 116.09, 117.94, 120.05, 121.59, 124.69, 124.91, 129.14, 130.16, 132.50, 135.59, 137.85, 138.55, 147.52, 151.97, 158.16. X-ray Crystallography. Crystallographic data for the ion pairs of 1a+-CMI–, 1c+-CMI–, 2a+-CMI–,

2b+-CMI–, 3a2+-2CMI–, 3b2+-2CMI–, and 4+-CMI– are summarized in Table 1. Single

crystals of 1a+-CMI–, 1c+-CMI–, and 3b2+-2CMI– were obtained by the vapor diffusion of hexane into the methanol solutions. Single crystals of 2a+-CMI– and 2b+-CMI– were obtained by the slow evaporation of the methanol solutions. A single crystal of 3a2+-2CMI– was obtained by the vapor diffusion of hexane into the acetone solution. A single crystal of 4+CMI– was obtained by the slow evaporation of the acetone solution. The data for 2b+-CMI– was collected at r.t. on a Rigaku RAPID-II diffractometer with graphite monochromated MoK radiation ( = 0.71075 Å). The data for 1a+-CMI–, 1c+-CMI–, 2a+-CMI–, 3b2+-2CMI–, and 4+-CMI– were collected at 100 K on Rigaku PILATUS3 with Si (111) monochromated synchrotron radiation ( = 0.4139 and 0.4249 Å) at BL02B1 (SPring-8) and the data for 3a2+2CMI– was collected at 90 K on DECTRIS EIGAR monochromated synchrotron radiation (


8

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= 0.811069 Å) at BL40XU (SPring-8). These structures were solved using the direct methods. The non-hydrogen atoms were refined anisotropically. In this paper, the π-plane distances out of parallel orientations have been defined as the average lengths between non-hydrogen atoms of π units and the mean planes of their neighboring π units. The CIF files (CCDC- 1935495– 1935501) can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.


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Page 10 of 24

Table 1 Crystallographic details for 1a+-CMI–, 1c+-CMI–, 2a+-CMI–, 2b+-CMI–, 3a2+-2CMI–, 3b2+-2CMI–, and 4+-CMI–. 1a+-CMI–

1c+-CMI–

2a+-CMI–

2b+-CMI–

formula

C30H18N6

C31H24N6

C34H20N6

C33H20N7O2

fw

462.50

480.56

512.56

546.56

crystal size, mm crystal system

0.500  0.500  0.200 monoclinic

0.150  0.030  0.010 triclinic

0.100  0.020  0.010 triclinic

0.300  0.050  0.050 monoclinic

space group

C2/c (no. 15)

P-1 (no. 2)

P-1 (no. 2)

C2/c (no. 15)

a, Å

25.9399(19)

8.871(10)

7.315(2)

31.813(7)

b, Å

17.2485(12)

12.408(15)

7.943(2)

6.9307(14)

c, Å

10.4006(7)

12.780(2)

22.402(9)

27.838(6)

, ° , ° , °

90

112.56(6)

85.56(3)

90

92.479(7)

99.29(4)

81.49(3)

117.945(5)

90

101.828(10)

84.41(15)

90

V, Å3

4649.1(6)

1226(3)

1279(7)

5422(2)

calcd, gcm

1.322

1.302

1.331

1.339

Z

8

2

2

8

T, K

100(2)

100(2)

100(2)

296(2)

, mm–1

0.036 (synchrotron)

0.037 (synchrotron)

0.037 (synchrotron)

no. of reflns

51863

18012

9715

0.088 (Mo-K) 24306

no. of unique reflns

5332

5573

5355

6153

variables

327

338

363

375

, Å

0.4139 (synchrotron)



R1 (I > 2(I))

0.0359

0.0878

0.0968

0.71075 (Mo-K) 0.1457

wR2 (I > 2 (I)) GOF

0.1015

0.2658

0.2537

0.4085

1.044

1.033

1.020

1.034

3a2+-2CMI–

3b2+-2CMI–

4+-CMI–

formula

C44H28N10

C45H30N10·2((H2)O)

C40H30N6· CH3CN

fw

348.38

768.79

633.75

crystal size, mm crystal system

0.060  0.020  0.020 triclinic

0.200  0.050  0.050 orthorhombic

0.240  0.050  0.050 triclinic

space group

P-1 (no. 2)

C2221 (no. 20)

P1 (no. 1)

a, Å

8.3232(3)

12.385(13)

4.9376(10)

b, Å

9.7414(4)

24.55(3)

13.1267(4)

c, Å

10.7328(4)

13.744(15)

26.7289(9)

, ° , ° , °

87.690(3)

90

102.96(3)

83.628(3)

90

90.077(3)

84.506(3)

90

90.193(2)

V, Å3

860.48(6)

4179(8)

1688.27(9)

calcd, gcm–3

1.345

1.181

1.251

Z

1

4

2

T, K

90(2)

100(2)

100(2)

, mm–1

0.110 (synchrotron)

0.034 (synchrotron)

0.035 (synchrotron)

no. of reflns

9300

43882

65402

no. of unique reflns

3134

4458

20096

variables

245

255

889

, Å




R1 (I > 2(I))

0.0412

0.0489

0.1813

wR2 (I > 2 (I)) GOF

0.0964

0.1454

0.4769

1.085

1.072

1.768

–3


10

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Computation detail. Ab initio calculations at B3LYP/6-31+G(d,p) and B3LYP-GD3/631+G(d,p) levels were carried out by using the Gaussian 09 program.28

Results and Discussion The salts of CMI– combined with stilbazolium cations (1a+–1c+), styrylquinolinium cations (2a+–2c+), dications based on pyridinium (3a2+ and 3b2+), and cyanine dye (4+) were prepared by the ion exchanges using sodium salt of 1,3-bis(dicyanomethylidene)indan (Na+-CMI–) and iodide or bromide salts of cations (Figure 1). The identifications were performed by 1H and 13C

NMR spectra. In all compounds, the UV/vis absorption maximum at ca. 580 nm derived

from CMI– was observed in the methanol solutions (0.05 mM). These absorption spectra were matched with the summed spectra of Na+-CMI– and corresponding iodide or bromide salts of cations. In addition, we measured the diffuse reflectance spectra in the solid state, and the summed spectra of Na+-CMI– and corresponding iodide or bromide salts of cations were also observed. These results indicated that there was no specific interaction, such as chargetransfer, between the anion and the cation. All compounds synthesized were screened by several crystallization methods (e.g. slow evaporation, vapor diffusion, and slow cooling), and seven single crystals (1a+-CMI–, 1c+CMI–, 2a+-CMI–, 2b+-CMI–, 3a2+-2CMI–, 3b2+-2CMI–, and 4+-CMI–) appropriate for X-ray crystallographic analysis were obtained. Ion pairs of 1a+-CMI– and 1c+-CMI– crystallize in the monoclinic C2/c and triclinic P-1 space groups, respectively. In the packing structure of 1a+-CMI–, an alternately stacking structure of two pairs of cations and anions were observed (Figure 2a). The distances of cation–cation and anion–anion are 3.30 Å and 3.37 Å, respectively. The cation dimer forms the opposite (anti-)


11


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directional stacking, resulting in the negligible dipole moment cancelled by each other. On the other hand, CMI– forms the same (syn-) directional stacking, and the dipole moments are totally cancelled in the crystal. In the packing structure of 1c+-CMI–, a pair of the cations with centrosymmetric relation, where the -conjugated planes of the cations are on the same plane, stack along the a axis with inclination (Figure 2b). The distance between faced -conjugated planes of the adjacent cations are 3.58 Å. The anions form the anti-directional dimer with a distance of 3.36 Å between the paired anions. The dimers are arranged in the side-by-side manner along the a axis. Charge-by-charge assemblies, defined as the mode comprising alternately stacking positively and negatively charged species, were observed in 2a+-CMI– and 3a2+-2CMI–, which crystalized in the triclinic P-1 space group (Figure 3).

In 2a+-CMI–, the planarity of

styrylquinolinium in comparison with that of stilbazolium is low due to steric hindrance. The dihedral angles between average ring planes calculated from the related sp2 atoms of quinolinium (10 atoms) and phenyl (six atoms) moieties is 5.61°. In the packing structure, CMI– locates upon the quinolinium moiety with the stacking distances of 3.30 Å and 3.39 Å. In addition, the partial π-π stacking between phenyl rings of 2a+ was also observed (d = 3.44 Å).

Meanwhile, the structure of a set of 3a2+-2CMI– has the point symmetry around the

center of the dication. One pyridinium ring of 3a2+ is overlapped with the five-membered ring of CMI– with distance of 3.43 Å, and this pyridinium ring faces to that of the adjacent 3a2+ on the opposite side. However, overlapping between these pyridinium rings is quite small. The other side of CMI– face to CMI– and they form the anti-directional dimeric structure with distance of 3.36 Å. Thus, 3a2+-2CMI– is concluded to have the inclined cation– anion–anion–cation type stacking unit.


12

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It should be noted that charge-segregated assemblies resulted from the stacking of identically charged species were constructed in 2b+-CMI–, 3b2+-2CMI–, and 4+-CMI–, crystalized in the monoclinic C2/c space group, the orthorhombic C2221 space group, and the triclinic P1 space group, respectively (Figure 4). Ion pairs 2b+-CMI– and 4+-CMI– form both anion and cation columns. The anti-directional stacking for both species were observed in 2b+-CMI–, whereas the syn-directional stacking for both species were observed in 4+-CMI–. For 4+-CMI–, there are two anion and two cation arrays along the a axis in a unit cell, and anion and cation directions in the different arrays are not opposite resulting in asymmetrical arrangement of ion pairs along the b axis. The distances of cation–cation are 3.43 Å for 2b+-CMI– and 3.50 Å and 3.51 Å for 4+-CMI–, and those of anion–anion are 3.46 Å for 2b+-CMI– and 3.43 Å and 3.48 Å for 4+-CMI–, respectively. On the other hand, in 3b2+-2CMI–, only the columnar structure of CMI– along the c axis, containing alternating sequence of anti- and syn-directional stacking structures with the corresponding π-π stacking distances of 3.43 Å and 3.46 Å, respectively, were observed. Dication 3b2+ forms the apparent network structure with a zig-zag plane parallel to the (010) plane but there are no strong interactions among the dications. Dications in the zig-zag plane are helically arranged along the c axis, which causes a chiral space group of the 3b2+-2CMI– crystal. Interestingly, except the case of 2a+-CMI–, identical charged stacking including dimeric forms and columns were obtained although the electrostatic repulsion is existing between the identical charged species. In addition, two kinds of stacking modes of CMI–, anti- and syndirectional stackings, were observed. To understand the stability of the packing structures, theoretical calculations were performed by using the B3LYP/6-31+G(d,p) level for theory. First, we focused on the dipole-dipole interactions which stabilize the stacking formations. The dipole moments of 1a+, 1b+, 2a+, and 2b+ having electron-withdrawing groups are very large, i.e., 17.6, 20.8, 14.7, and 17.8 debye, respectively, whereas those of 1c+ and 2c+ having


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electron-donating groups are small, i.e., 6.7 and 2.9 debye, respectively. Therefore, the stacking distances between cations of 1a+ and 2b+ are slightly shorter than those of 1c+ in the crystal structures. We also focused on the stabilities and dipole moments of the stacking forms of CMI– which observed in the crystals with 1a+, 1c+, 2b+, 3a2+, and 3b2+ as a counter cation. To consider the dispersion energy, theoretical calculation was performed at the B3LYP-GD3/631+G(d,p) level. As shown in Table 2, negligible dipole moments of the anti-directional stackings indicated that the dipole-dipole interactions would stabilize the dimeric forms. Interestingly, the stability of the syn-directional stackings is similar to that of anti-directional stackings. These results can be explained by the large offset distances, which provide the interaction between π-electronic anion as donor and cyano moieties as acceptor. Next, we calculated the electrostatic potential (ESP) mappings of CMI–, 1a+, 1c+, 2a+, 2b+, and 4+. In CMI–, negative charge is delocalized in the π-electronic system, and cyano substituents as acceptor stabilized the negative charge. On the other hand, although the positive charge in 4+ delocalized in the π-electronic systems, those in 1a+, 1c+, 2a+, and 2b+ partially localized on the pyridinium and the quinolinium rings, resulting in the formation of the antidirectional stackings in the crystal structures. To understand the effect of counter ions, ESP mapping based on single-crystal X-ray structures of the ion pairs were investigated. Figure 5 displays ESP mapping on the stacking structures of 1a+-CMI– and 2b+-CMI–. In 1a+-CMI–, face-to-face stacking of cations and anions delocalizes the negative and positive charges each other, and the electrostatic repulsion between identically charged species is decreased. On the other hand, in 2b+-CMI–, the stabilization of charged π-electronic species in the chargesegregated assembly is not by face-to-face stacking but by the hydrogen bonding between cyano moieties and protons on cationic species. In fact, the negative charge on the hydrogenbonded nitrogens is lower than that of the corresponding moieties without such hydrogen bond.


14

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Thus, the delocalization of the negative charge through the hydrogen bond is suitable for the formation of the charge-segregated assembly.

Figure 1 Chemical Structures of (a) 1,3-bis(dicyanomethylidene)indan anion (CMI–) and (b) cations 1a+–1c+, 2a+–2c+, 3a2+, 3b2+, and 4+.


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Figure 2 Single-crystal X-ray structures of (a) 1a+-CMI– and (b) 1c+-CMI–: (i) packing diagrams, where the magenta and cyan parts represent the anions and the cations, respectively. For (b), the projections viewed along a (left) and c (right) axes are shown; (ii) stacking structures (top and side views) of CMI–; (iii) stacking structures (top and side views) of cations. Atom color code: gray, blue and pink refer to carbon, nitrogen, and hydrogen, respectively.


16

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Figure 3 Single-crystal X-ray structures of (a) 2a+-CMI– and (b) 3a2+-2CMI–: (i) packing diagrams, where the magenta and cyan parts represent the anions and cations, respectively; (ii) stacking structures (top and side views) of anion–cation–anion for 2a+-CMI– and anions for 3a2+-2CMI–. Atom color code: gray, blue and pink refer to carbon, nitrogen, and hydrogen, respectively.


17


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Figure 4 Single-crystal X-ray structures of (a) 2b+-CMI–, (b) 3b2+-2CMI–, and (c) 4+-CMI–: (i) and (ii) packing diagrams, where the magenta and cyan parts represent the anions and the cations, respectively; stacking structures of (iii) CMI– and (iv) cations (top and side views). Atom color code: gray, blue, red and pink refer to carbon, nitrogen, oxygen, and hydrogen, respectively.

Figure 5 Electrostatic potentials (ESP) mapped onto the electron density isosurfaces (δ = 0.01) (top and side views) calculated at the B3LYP/6-31+G(d,p) level for stacking structures of (a) 1a+-CMI– and (b) 2b+-CMI– derived from the single-crystal X-ray structures. Table 2 The stacking directions, distances, dipole moments, and calculated total energies at B3LYP-GD3/631+G(d,p) of two CMI– for 1a+-CMI–, 1c+-CMI–, 2b+-CMI–, 3a2+-2CMI–, 3b2+-2CMI–, and 4+-CMI–. 1a+-CMI– syn 3.37 13.3

1c+-CMI– anti 3.36 0.0

2b+-CMI– anti 3.46 0.0

direction distance (Å) dipole moment (Debye) Energy (hartree) –1587.325 –1587.340 –1587.266 aOne of two independent stacking structures was used for the calculation.

3a2+-2CMI– anti 3.36 0.0

3b2+-2CMI– syn 3.46 13.5

anti 3.43 0.3

–1587.324

–1587.313

–1587.304

4+-CMI– a syn 3.43 14.3 –1587.306

Conclusion


18

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Various ion pairs based on 1,3-bis(dicyanomethylidene)indan anion were prepared by the ion exchanges using sodium salt of 1,3-bis(dicyanomethylidene)indan and iodide or bromide salts of π-electronic cations. Seven ionic crystals were obtained, and assembled structures were revealed by single-crystal X-ray analysis. In all ionic crystals, cation-cation and/or anion-anion stacking formations were observed, although the electrostatic repulsion affects between identically charged species.

Moreover, three charge-segregated assemblies, wherein

negatively charged components form column structures of identically charged species, were obtained. The key factors to achieve such assembled structures are 1) the dipole-dipole interactions and 2) the delocalization of negative or positive charge through the face-to-face stacking and hydrogen bonding between the different charged species. Thus, we demonstrated the potential of 1,3-bis(dicyanomethylidene)indan anion as the component for the fascinating ionic crystals. Further examination for novel ionic crystals and the application for organic electronic materials, are currently ongoing in our laboratory.

Supporting information, which includes UV/vis absorption spectra of the compounds in methanol and UV/vis/NIR diffuse reflection spectra of the compounds, is available.

Funding Sources A part of this work was supported by Advanced Next Generation Energy Leadership (ANGEL) project (2016–17) and Japan-Ukraine Bilateral Joint Research Project from Japan Society for the Promotion of Science (JSPS).


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ACKNOWLEDGMENT Theoretical calculations were performed using Research Center for Computational Science, Okazaki, Japan. The synchrotron radiation experiments were performed at the BL02B1 (2018B1714, 2019A1704) and BL40XU (2019A1211) of SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) with the supports by Dr. Kunihisa Sugimoto, JASRI/SPring-8, Dr. Nobuhiro Yasuda, JASRI/SPring-8, and Mr. Kei Muzuguchi, Yamagata University.

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For Table of Contents Use Only

Various Ionic Crystals from the Combination of 1,3-Bis(dicyanomethylidene)indan Anion and π-Electronic Cations

Yuka Tanaka, Keisuke Ichijo, Sota Kodama, Shun Aoyama, Tsukasa Yoshida, Ryohei Yamakado, and Shuji Okada

A series of ion-pairing assemblies based on 1,3-bis(dicyanomethylidene)indan with various πelectronic cations were investigated. Their packing structures studied by the single-crystal Xray analysis were found to be charge-by-charge and charge-segregated assemblies. Interestingly, cation-cation and/or anion-anion stackings, which are electrostatically unfavorable, are formed in all crystal structures, and the reasons were verified by the DFT calculation.


24

Various Ionic Crystals from the Combination of 1,3-Bis

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