Lamellar Packing in Cocrystals of Arylbipyridines with

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Columnar/Lamellar Packing in Cocrystals of Arylbipyridines with Diiodoperfluorobenzene Remya Ramakrishnan, Ajith R. Mallia, Niyas M. A., Ramarani Sethy, and Mahesh Hariharan Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.6b00968 • Publication Date (Web): 15 Sep 2016 Downloaded from http://pubs.acs.org on September 20, 2016

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Crystal Growth & Design

Columnar/Lamellar

Packing

in

Cocrystals

of

Arylbipyridines with Diiodoperfluorobenzene Remya Ramakrishnan,⊥ Ajith R. Mallia,⊥ Niyas M. A., Ramarani Sethy† and Mahesh Hariharan*

School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram, CET Campus, Sreekaryam, Thiruvananthapuram, Kerala, India 695016. Abstract Stimulated by strongly directional C-I•••N noncovalent halogen bonding, π−hole•••π and π−π interactions, cocrystals of non-planar 4-arylated-2,2’-bipyridine (ArB) derivatives with 1,4diiodo-tetrafluorobenzene (D) were generated which exhibits promising columnar/lamellar packing arrangement. Hirshfeld surface (HS), quantum theory of atoms in molecules (QTAIM) and electrostatic potential surface (ESP) analyses were employed to examine the weak intermolecular interactions governing the packing arrangement in ArB crystals and corresponding cocrystals with D (ArB•D). Cocrystals of 4-phenyl-2,2’-bipyridine (PhB) and 4(naphthalen-1-yl)-2,2’-bipyridine (NaB) with D [PhB•D1, PhB•D2, (NaB)2•D2.5 and (NaB)3•D2] exhibited C-I•••N directed infinite one-dimensional chains of alternate ArB and D units. In contrast, C-I•••N interactions guide the formation of termolecular complexes in the cocrystal of 4-(phenanthren-9-yl)-2,2’-bipyridine with D (PhenB•D0.5). Successful implementation of C-I•••N interactions aided by 2,2’-bipyridine and D enabled the tuning of three dimensional close packing in planar polyaromatic hydrocarbons into columnar/lamellar arrangement suitable for optoelectronic devices.

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Keywords Crystal engineering, packing motifs, quantum theory of atoms in molecules, halogen bonding. Corresponding Author *[email protected]

Introduction Construction of supramolecular self-assembled solid state architectures1-3 has gained much attention in terms of its potential applications in various crystal engineering fields.4-5 Highly directional6 intermolecular interactions such as hydrogen bonding,7-8 dihydrogen3 and halogen bonding interactions8 play pivotal role in driving the formation of supramolecular scaffolds for the design of functional materials.9 Cocrystallization10 is one such bottom up approach in understanding the intermolecular interactions and producing aggregated supramolecular crystal structures. A condicio sine qua non for the formation of binary,11 ternary12 or multi13 cocrystals is the availability of strong hydrogen or halogen bond donors and acceptors.14 Diiodotetrafluorobenzene (D)5,

15

is a well-recognized coformer which can induce strong C-

H•••F interactions16 and halogen bonds14 via iodine atoms.14 Potential applications of cocrystals17 range from drug delivery10, 18 to optical and electronic devices.15, 19-21 Relative orientation of molecules in the crystal structure can be tuned in a geometry based design of cocrystals, which is a relatively less explored path that has potential applications in the development of novel hybrid functional materials.9,

22

Molecular packing motifs largely

determine the intrinsic charge transfer behaviors and the intermolecular electronic coupling for the efficient functioning of organic devices such as organic semiconductors, organic field effect transistors (OFET),23 photoconductors5, 21 etc. Most of the polyaromatic hydrocarbons (PAH’s) crystallize in edge-to-face (C-H•••π) herringbone packing imparting a low intermolecular charge


2

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mobility.24 Attempts in understanding the factors responsible for the improved charge mobility in PAH’s establishes that face-to-face (π−π) stacking is preferred over herringbone arrangement (C-H•••π).24-28 Pioneering works by Schollhorn,5 Metrangolo,29 Resnati29 and coworkers exploited the nitrogen-halogen (C-X•••N) closed shell interactions in investigating the nature of various planar bipyridine and D containing cocrystals. Jin and coworkers30-31 demonstrated the significance of halogen•••π interactions in driving the cocrystallization of D30-31 with different PAH’s such as naphthalene, phenanthrene and pyrene. Our continued efforts in modulating the packing arrangement in near-orthogonal bichromophores32-34 and PAH’s35-41 encouraged us to engineer halogen bonded cocrystals and explore the close packing. Inspired by the packing motif riddles and instigated by the interplay of intermolecular interactions, we set out to investigate the crystal structures of non-planar nitrogen containing PAH’s and its cocrystals in a geometry based approach. Regulation of intermolecular interactions to achieve columnar/lamellar arrangement in PAH’s is an emerging area of research. The precursor units PAH, bipyridine and D display herringbone/sandwich-herringbone arrangement. We presume that the novel cocrystals of arylated-2,2’-bipyridine with D would possess emergent properties facilitated by crystal packing.

Results and Discussion Suzuki−Miyaura cross-coupling of 4-bromo-2,2’-bipyridine (BrB) with corresponding arylboronic acids furnished 4-phenyl-2,2’-bipyridine (PhB), 4-(naphthalen-1-yl)-2,2’-bipyridine (NaB), 4-(anthracen-9-yl)-2,2’-bipyridine (AnB), 4-(phenanthren-9-yl)-2,2’-bipyridine (PhenB) and 4-(pyren-9-yl)-2,2’-bipyridine (PyB) derivatives in moderate to high yields (30-90%)


3


Br N

Ar F

F

F

F

2M K2CO3, Pd(PPh3)4

B HO

N

N

Ar

+

I

OH

24 h, 70 oC, THF

N

I BrB

ArB

*

*

*

D

*

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

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*

Ar =

Ph

Na

An

Phen

Py

Figure 1. Syntheses scheme for ArB derivatives and respective chemical structures. 1,4diiodotetrafluorobenzene (D), coformer used for cocrystallization of ArB derivatives. (Figure 1, see Supporting Information, SI). 1,4-diiodotetraflurobenzene (D) was used as the coformer in an attempt to generate cocrystals of arylated 2,2’-bipyridine (ArB) derivatives by slow evaporation method using appropriate solvents. Novel cocrystals (ArB•D) of PhB, NaB and PhenB were obtained with formula PhB•D, (NaB)2•D2.5, (NaB)3•D2 and PhenB•D0.5 with yields between 62-96%. Two polymorphic forms of PhB•D were harvested under different crystallization conditions (PhB•D1 and PhB•D2, SI). Slow evaporation of ArB derivatives from 1:3 dichloromethane:hexane mixture under ambient conditions provided corresponding crystals of ArB. Single-crystal X-ray diffraction analyses of ArB derivatives indicated solvent free crystals wherein PhB and PyB correspond to centrosymmetric space group P21/c (monoclinic crystal system) with four molecules in the unit cell. Crystalline AnB and PhenB belong to


4

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Table 1. Crystal data and structure refinement parameters of ArB derivatives and their cocrystals.

Unit cell parameters

PhB

AnB

PhenB

PyB

PhB••D1

PhB••D2

(NaB)2•D2.5

(NaB)3•D2

PhenB••D0.5

Empirical formula

C16 H12 N2

C24 H16 N2

C24 H16 N2

C26 H16 N2

C22 H12 F4 I2 N2

C22 H12 F4 I2 N2

C55 H28 F10 I5 N4

C72 H42 F8 I4 N6

C27 H16 F2 I N2

Formula weight

232.28

332.39

332.39

356.41

634.14

634.14

1650.71

533.32

Crystal system

Monoclinic

Triclinic

Triclinic

Monoclinic

Orthorhombic

Monoclinic

Triclinic

Monoclinic

Triclinic

Space group, Z

P21/c, 4

P -1, 2

P -1, 2

P21/c, 4

Pna21, 4

P21/c, 8

P -1, 2

P21/c, 4

P -1, 2

a (Å)

13.8210(11)

6.0864(2)

6.8593(6)

29.4499(6)

15.4231(12)

26.0077(12)

13.9409(3)

27.6708(11)

4.11530(10)

b (Å)

11.6660(9)

12.2098(5)

10.8425(9)

4.27690(10)

13.8007(15)

20.8066(10)

14.6174(3)

7.2439(3)

12.5278(3)

c (Å)

7.5753(6)

13.0559(6)

12.4936(1)

14.2475(3)

9.9092(9)

7.9192(3)

14.9787(4)

31.0834(10)

20.7571(6)

α, deg

90

115.489(2)

111.282(4)

90

90

90

81.9970(10)

90

79.5750(10)

β, deg

96.288(2)

99.859(2)

93.162(4)

96.219(10)

90

96.406(2)

85.4870(10)

99.603(2)

89.1280(10)

1569.31


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γ, deg

90

94.047(2)

90.703(4)

90

90

90

67.220(10)

90

84.799(10)

Volume (Å 3)

1214.06(17)

851.44(6)

863.97(13)

1783.97(7)

2109.2(3)

4258.6(3)

2785.83(11)

6143.2(4)

1048.15(5)

Temperature (K)

296

296

296

296

296

296

296

296

296

Calculated density (g/cm3)

1.271

1.297

1.278

1.327

1.997

1.978

1.871

1.785

1.690

Reflections collected

9550

12739

13829

13668

9674

33565

44664

49526

16967

Unique reflections

2126

2963

3026

3130

3474

7515

10889

12050

4082

Number of parameters

163

235

235

253

271

541

667

811

289

R1 (I >2σ(I))

0.0525

0.0387

0.0571

0.0395

0.0373

0.0358

0.0455

0.0546

0.0269

wR(F2) (I>2σ(I))

0.1439

0.1206

0.1876

0.1144

0.0958

0.0611

0.1290

0.0828

0.0627

R (F %)

5.24

3.87

5.71

3.95

3.73

3.58

4.55

5.46

2.69

Goodness-of-fit on F2

1.084

1.138

1.032

1.067

1.030

1.011

1.036

0.985

1.043

CCDC number

1486837

1486830

1486831

1486834

1486836

1486833

1486838

1486835

1486832


6

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Figure 2. Intermolecular interactions existing in ArB derivatives. Intermolecular (a) C-H•••N interaction in PhB, (b) C-H•••H-C, π− −π, C-H•••N and C-H•••C interactions in AnB, (c) C-H•••N interaction in PhenB and (d) C-H•••N interactions in PyB. centrosymmetric space group P-1 (triclinic crystal system) with two molecules in the unit cell (Table 1). Qualitative single crystal X-ray structure analyses of ArB derivatives reveal the significance of intermolecular C-H•••N hydrogen bonding interaction in directing the three dimensional arrangement in ArB crystals. C-H•••N (dC-H•••N=2.61 Å) interaction dictates the packing arrangement in PhB. C-H•••N (dC-H•••N=2.73 Å), C-H•••C (dC-H•••C=2.86 Å) and C-H•••HC (dC-H•••H-C=2.24 Å) closed shell intermolecular interactions are found to influence the packing in AnB. π− −π interactions operating at 3.39-3.80 Å further contribute to packing in AnB. C-H•••N (dC-H•••N=2.70 Å) and π−π (dπ•••π=3.49-3.54 Å) interactions direct the packing arrangement in PhenB. Intermolecular C-H•••C (dC-H•••N=2.82 Å) and C-H•••N (dC-H•••N=2.70 Å) interactions drive the packing arrangement in PyB (Figure 2). The torsional angle between bipyridine and aryl rings varies between 9.65o in PhB to 74.25o in AnB (Figure S1, Table S1, SI).Packing efficiency (ߟ) of ArB crystals was found to be in the range of 0.678-0.692 (Table S2, SI).


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Figure 3. Close packing in crystalline (a) PhB, (b) AnB, (c) PhenB and (d) PyB. Quantum theory of atoms in molecules (QTAIM) analyses35, 39-40, 42 of ArB crystals were performed to examine bond paths and (3,-1) bond critical points (BCP). The nature of intermolecular interactions in ArB derivatives was studied using dimer models (Figure S2a-g, Table S3, SI). Positive values of electron density [ρ(r)],42 its Laplacian [∇2ρb(r)]42 at the BCP and the interaction distance (d) confirms the existence of closed shell intermolecular interactions.42-43 Intermolecular C-H•••N hydrogen bonding interaction with ρ(r) of 0.0076 a. u. in PhB and 0.0072 a. u. in PyB form zigzag patterns that propagate along b and c-axis respectively. C-H•••N interaction with ρ(r) of 0.0064 a. u. in PhenB forms extended chain like C-H•••N contacts along a-axis. C-H•••N hydrogen bonding interaction having ρ(r), 0.0067 a. u., and C-H•••C (edge-to-face) interaction with ρ(r), 0.0051 a. u., together dictate the propagation of AnB along a-axis. Apart from C-H•••N and C-H•••C interaction, nonpolar intermolecular CH•••H-C closed shell interaction with ρ(r), 0.0048 a. u. exists in AnBb (Figure 2a-d). C-H•••H-C closed shell interaction was further examined with Pendas’ interacting quantum atoms (IQA) approach43-45 in a bid to characterize the interaction based on the degree of stabilization. Interaction energy (EIQA) of C-H•••H-C was estimated to be -0.17 kcal/mol thus indicating the


8

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Figure 4. 2D-fingerprint plots of crystalline (a) PhB, (b) AnB, (c) PhenB and (d) PyB obtained from Hirshfeld analyses. stabilizing43 nature of this interaction (Table S4, SI). QTAIM calculations also confirmed the existence of C•••C contacts in AnB and PhenB that correspond to π−π interactions (Table S3, SI). Hirshfeld surface (HS)46 and two-dimensional (2D) fingerprint analyses were carried out to explore the packing motifs existing in the crystalline ArB (Figure 3a-d). Investigation of 2Dfingerprint plots derived from HS analyses implied that C•••N (0.2-3.3%), C•••C (5.7-15.3%), CH•••N (6.9-13.1%), C-H•••C (20.6-32.4%) and C-H•••H-C (47.4-54.3%) interactions influence the packing in crystalline ArB (Figure 4a-d and Table S5, SI). The sharp spikes and a pair of wings observed in the 2D-fingerprint plots of ArB derivatives correspond to C-H•••N (Figure S3a-d, SI) and C-H•••C interactions (Figure S4a-d, SI), respectively. C-H•••H-C contacts emulated in the middle of scattered points contribute significantly to the total Hirshfeld surfaces (Figure S5a-d, SI). C•••C contacts presented as distinct flower like patterns at the center of the 2D-fingerprint plots correspond to π−π interaction (Figure S6a-d, SI). PhB displays offset stacking along a-axis and edge-to-face σ−π interaction along b-axis forming a sandwich herringbone arrangement. Crystal packing in AnB and PhenB constitute edge-to-face C-


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H•••π interaction resulting in a herringbone arrangement. PyB exhibits lamellar motif with infinite face-to-face π−π stacking along b-axis and edge-to-face herringbone arrangement along a-axis (Figure 3a-d, Table S6, SI). Crystalline PhB•D1 belongs to Pna21 space group (orthorhombic crystal system) with four PhB•D moieties in the unit cell (Table 1). The X-ray crystal structure of PhB•D1 reveals a torsion angle (Φ) of 39.79° between bipyridine and phenyl rings, which is higher than that in crystalline PhB (Φ=9.65°, Figure S1, Table S1, SI). The crystal structure of PhB•D1 possesses alternating PhB and D chains directed by C-I•••N interactions as characterized by I•••N distances of 3.163 and 3.095 Å along a-axis. The two iodine atoms in D form trifurcated and tetrafurcated interactions respectively, justifying the presence of C-I•••N interactions of different strengths.

(a) b a c

(b)

c a b

Figure 5. (a) 2D corrugated sheet47 formed by crystalline PhB•D1 and (b) Intermolecular interactions existing in PhB•D1.


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The polymer chains are cross-linked by weak C-H•••F hydrogen bonding interactions (dC-H•••F=2.567 Å) forming a two-dimensional corrugated sheet (Figure 5a).47 One fluorine atom of D forms bifurcated interactions with adjacent carbon atoms of a nearby D unit (dF•••C’=3.06 Å, dF•••C’’=2.90 Å). The C•••F interaction and π−hole•••π31, 47 and/or π−π interactions (3.49-3.80 Å) existing between carbon atoms of D and bipyridine cores of PhB contribute to the packing of the molecules in three dimension. Packing efficiency (ߟ) of the compound is evaluated to be 0.675 (Table S2, SI).

(a)

c a b

(b)

b a c Figure 6. (a) 2D π−π stacking of wave-like chains in crystalline PhB•D2 and (b) Intermolecular interactions existing in PhB•D2.


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Crystalline PhB•D2 belongs to P21/c (monoclinic crystal system) with eight PhB•D entities in the unit cell (Table 1). The cocrystals PhB•D2 comprises of two types of PhB units exhibiting torsion angles of 35.21° and 32.81° between bipyridine and phenyl rings (Figure S1, Table S1, SI). PhB•D2 forms wave-like chains propagated by three different C-I•••N halogen bonding (dN•••I=2.93-3.08 Å) and a distinct C-I•••π halogen bonding along a-axis (Figure 6a). The resultant I•••C distances are 3.44 and 3.61 Å with C-I•••C bond angles of 163.88° and 155.70° respectively. The polymer chain is further stabilized by bifurcated C-H•••F hydrogen bonding and C•••F interactions (dH•••F=2.53 Å and dC•••F=3.10 Å). The two-dimensional network constructed by C-H•••F hydrogen bonding interactions are characterized by H•••F distances of 2.577 and 2.581 Å (Figure 6b). π−π interactions (3.50-3.90 Å) dictate the packing in threedimension along c-axis. Packing efficiency (ߟ=0.670) of PhB•D2 is found to be almost identical to the PhB•D1 polymorph (ߟ=0.675, Table S2, SI). (NaB)2•D2.5 crystallizes in triclinic space group P-1 with

Z=2 (Table 1). The

stoichiometry of (NaB)2•D2.5 remains independent of the precursor ratio of NaB and D, when isolated before total evaporation of the solvent. The crystal system consists of two types of NaB units exhibiting torsion angles of 32.41° and 34.44° between bipyridine and naphthalene rings (Figure S1, Table S1, SI). Infinite one-dimensional chains are generated by three different CI•••N halogen bonding interactions with distances ranging from 3.09 to 3.16 Å along a-axis. The successive chains are flipped with respect to C-I•••N halogen bonding interactions and linked to each other through D by C-H•••F hydrogen bonding interactions (dC-H•••F=2.61 Å, Figure 7) forming duplex structures. C-F•••F-C interhalogen interactions (dC-F•••F-C=2.52 Å) characterized by C-F•••F bond angles of 158.84° and 144.89° and a torsion angle of 170.99° is also observed. π−hole•••π31, 47 and π−π interactions operating at 3.44-3.54 Å afford three-


12

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c a b Figure 7. Intermolecular interactions forming the two-dimensional network in (NaB)2•D2.5. dimensional packing arrangement along b-axis. (NaB)2•D2.5 is found to possess void spaces occupying 8.4% of the unit cell with a void volume of 235.17 Å3 (Figure S7, SI). Consequently, (NaB)2•D2.5 exhibits a lower packing efficiency of 0.626 compared to other ArB•D cocrystals (Table S2, SI). Upon performing X-ray diffraction measurements at low temperature, (NaB)2•D2.5 exhibits residual electron density corresponding to solvent molecules in the voids. However, efforts in deciphering a complete picture of the disordered solvent molecules occupying voids turned out to be unsuccessful. (NaB)3•D2 adopts the monoclinic space group P21/c with Z=4 (Table 1). The crystal system consists of three types of NaB units with torsion angles 2.51°, 27.88° and 31.57° between bipyridine and naphthalene units (Figure S1, Table S1, SI). Four different C-I•••N halogen bonding interactions with distances varying between 3.06 and 3.14 Å direct the formation of


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a c b Figure 8. Intermolecular interactions forming the two-dimensional network in (NaB)3•D2. two kinds of polymer chains along c-axis. The polymer chains are linked to each other via CH•••F hydrogen bonding interactions operating at 2.57 and 2.66 Å. The conjoined pair of polymer chains is cross-linked through bipyridine units of NaB by C-H•••F and C•••F interactions ensuing the formation of a complex two dimensional network (Figure 8). Three dimensional packing arrangement in (NaB)3•D2 is determined by π−hole•••π14,

31, 47

and π−π

interactions (3.47-3.59 Å) along b-axis. Even though short C•••I distance (dC•••I=3.664 Å) exists in (NaB)3•D2, the C-I•••C bond angle being 78.97° eliminates the possibility of π•••σ* interaction.5 (NaB)3•D2 exhibits a packing efficiency of 0.681 (Table S2, SI). PhenB•D0.5 crystallizes in centrosymmetric space group P-1 (triclinic crystal system) with Z=2 (Table 1). The observed stoichiometry of PhenB•D0.5 is independent of the precursor ratio,


14

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(b)

(a)

a

b

c

c a

b

Figure 9. (a) Top view of the π−π stacked structure of crystalline PhenB•D0.5 and (b) C-H•••F interactions linking the termolecular complexes. when isolated before total evaporation of the solvent. The torsion angle between the bipyridine and Phen units in PhenB•D0.5 is found to be 51.15o (Figure S1, Table S1, SI). Analyses of the crystal structure of PhenB•D0.5 revealed the presence of C-I•••N halogen bonding interaction (d C-I•••N

=3.08 Å) which dictates the formation of a termolecular complex (donor-acceptor-donor)

in crystalline PhenB•D0.5. Even though B adopts a conformation with two N atoms anti to each other (torsion angle 11.33o) it does not favour the formation of a polymeric complex (Figure 9a). Both the iodine atoms in D form trifurcated interactions. C-H•••F hydrogen bonding and π−π interactions operating at 2.65 Å and 3.574-3.83 Å respectively result in termolecular units (PhenB-D-PhenB) stacking one above the other along a-axis (Figure 9b). Packing efficiency of PhenB•D0.5 is estimated to be 0.701 thus showing a marginal increase when compared to that of its parent crystal PhenB (ߟ=0.678, Table S2, SI). To establish the halogen bond formation between ArB and D in ArB•D cocrystals infrared (IR) spectra of ArB crystals is recorded and compared with that of the corresponding cocrystals. Halogen bond formation induces a small shift for XB-donor associated bands to lower frequencies and XB-acceptor bands to higher frequencies.48-49 This effect is evident for the bipyridine moiety (the XB-acceptor) involved in the halogen bond wherein the νCbipyr-H stretching in PhB, NaB and PhenB undergoes a shift from 3053, 3051 and 3049 cm-1 respectively to 3057


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and 3055 cm-1 in PhB•D1and PhB•D2 respectively, to 3053 cm-1 in (NaB)2•D2.5 and (NaB)3•D2 and to 3061 cm-1 in PhenB•D0.5 (Figure S8, SI). The fundamental band of the ring sextet νC–C stretch of D is downshifted from 1468 cm-1 to 1462, 1463, 1465, 1462 and 1462 cm-1 in PhB•D1, PhB•D2, (NaB)2•D2.5 , (NaB)3•D2 and PhenB•D0.5 respectively. Transfer of charge from nitrogen of bipyridine unit to the σ-hole14 of D results in halogen bond formation, with a consequent increase in the electron density of the benzene ring leading to the lowering of ring sextet νC–C stretch vibrational frequency.47 The IR active νC–F stretching mode of D50 is slightly upshifted from 939 cm-1 to 941 cm-1 in PhB•D1 and (NaB)2•D2.5 and to 943 cm-1 in PhB•D2, (NaB)3•D2 and PhenB•D0.5 (Figure S9, SI). The nature of intermolecular interactions in ArB•D cocrystals is studied by QTAIM analyses using dimer, trimer and pentamer models (Figure S10a-i, Table S7, SI). Intermolecular interactions which are evident from the crystal structure are validated by QTAIM calculations. Apart from these interactions, trimers PhB•D1a and PhB•D1b exhibit one C-H•••H-C closed shell interaction each whereas pentamer PhB•D2a shows five C-H•••H-C closed shell interactions. Trimer (NaB)3•D2a shows three C-H•••H-C closed shell interactions. Along with F•••F interaction, trimer (NaB)2•D2.5b exhibits I•••I interaction that appears parallel to the F•••F interaction. F•••F and I•••I interhalogen interactions are further analysed with Pendas’ interacting quantum atoms (IQA) approach.44-45 Interaction energies (EIQA) of F•••F and I•••I are estimated to be 33.0 kcal/mol and 2.68 kcal/mol respectively, thus indicating the destabilizing43 nature of these interactions (Table S4, SI). Coulombic interaction energy (ECIQA) constitutes the major contribution

to

EIQA

substantiating

the

destabilizing

nature

of

F•••F

and

I•••I interhalogen interactions in (NaB)2•D2.5.


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Figure 10. Close packing in cocrystalline (a) B•D,5 (b) PhB•D1, (c) PhB•D2, (d) (NaB)2•D2.5, (e) (NaB)3•D2 and (f) PhenB•D0.5. Hirshfeld surface analysis of ArB•D and Β•D5 cocrystals was performed to investigate intermolecular interactions and to probe the packing motifs (Figure 10a-f). Detailed analyses of 2D-fingerprint plots obtained from HS analysis indicated the presence of C•••N (1.33.4%),C•••C (5.4-15%), C-H•••N (2.9-3.4%), C-H•••C (7.2-22%) ,C- H•••H-C (14.2-38.9%), CH•••F (14.9-22%), C-H•••I (7.2-16.3%), C•••F (2.7-7%), C•••I (0.8-4.7%), C-I•••N (1.4-4.3%) and F•••F (0.3-4.3%) interactions which influence the packing arrangement in cocrytals (Table S8, SI). Sharp spikes at the base and middle portion of 2D-fingerprint plots correspond to CH•••F and C-H•••I interactions respectively (Figure 11a-f). C-H•••F and C-H•••I interactions along with C-H•••H-C closed shell interactions contribute significantly to the total Hirshfeld surfaces (Figure S11-S13, SI). Ratio of percentage of C-H•••C (edge-to-face) and C•••C (face-toface) was used to determine the packing arrangement in cocrystals (Figure 10a-f and Table S9,


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Figure 11. 2D-fingerprint plots of crystalline (a) B•D,5 (b) PhB•D1, (c) PhB•D2, (d) (NaB)2•D2.5, (e) (NaB)3•D2 and (f) PhenB•D0.5 obtained from Hirshfeld analyses. SI). B•D5 and PhB•D1 follows sandwich herringbone arrangement while PhB•D2 exhibits lamellar close packing. (NaB)2•D2.5 and (NaB)3•D2 exhibit columnar stacking along b-axis. PhenB•D0.5 displays columnar arrangement with π−π stacking along a-axis. Electrostatic surface potential (ESP) maps were generated for different ArB monomers, dimers and ArB•D cocrystals (Figure S14a-n, SI). ESP was constructed using 0.0002e/a.u. isodensity surface with colours varying from red to blue indicating increasing electrostatic potential from negative to positive respectively. The intense red region encompassing nitrogen atom indicates the localised electron density distribution around nitrogen atom and the blue portion which forms a belt around the aromatic rings are strong positive potential regions. Electron donating nature of nitrogen and electron accepting nature of hydrogen makes the


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intermolecular C-H•••N interaction attractive which can be traced from the crystal structure and QTAIM analyses of ArB derivatives. The introduction of 1,4-diiodotetrafluorobenzene (D) as a coformer induces more hydrogen (C-H•••F) and halogen bonds in cocrystals owing to the presence of fluorine and iodine. The strong positive potential region centred on the outermost region of Y-I (Y is an electron donor) bond otherwise called σ−hole (Figure S14e, SI)14,

51

observed in D makes it a potential halogen bond donor confirming the attractive nature of CI•••N halogen bonding interaction. Another positive potential region indicated in blue seen perpendicular to the σ framework of D corresponds to π−hole14 (Figure S14e, SI) which forms π−hole•••π47 intermolecular interaction31 with electron rich π systems in ArB. C-H•••F hydrogen bonding and C-H•••π interactions can be inferred to be attractive as evidenced from ESP analysis wherein fluorine and the electron rich π cloud of the ArB aromatic rings (yellow regions in the ESP maps of monomeric ArB and D; Figures S14a-e, SI) are attracted to electron deficient hydrogens (blue region). The σ−hole14 bonds, π−hole•••π and C-H•••F interactions formed by D results in the diverse packing of cocrystals.UNI intermolecular potentials, calculated using UNI (unified) force field52-53 in the Mercury CSD 3.8 gave total packing energy of ArB crystals and ArB•D cocrystals (Table S2, SI). Total packing energy of PhB•D1 and PhB•D2 is estimated to be -219.2 kJ/mol and -211.9 kJ/mol suggesting slightly greater stability of the PhB•D1 compared to PhB•D2. Conclusion Crystalline arylated 2,2’-bipyridines and corresponding cocrystals with the coformer 1,4diiodotetrafluorobenzene were successfully synthesized and the nature of intermolecular interactions were closely investigated by HS, QTAIM and ESP analysis. Subtle interactions like C-H•••H-C in AnB, F•••F and I•••I interhalogen interactions observed in (NaB)2•D2.5 were


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characterized by QTAIM-IQA method. The studies indicate that the strongly directional and energetically favorable C-I•••N interactions direct formation of co-ordination networks in most of the cocrystals while the C-H•••N hydrogen bonding controls the close packing in ArB derivatives. The hydrogen bonded chains linked by C-H•••F interactions contribute to the twodimensional packing in cocrystals. Three-dimensional packing arrangement undergoes a transition from sandwich herringbone and herringbone in ArB to lamellar (γ-motif) and columnar (β-motif) in ArB•D cocrystals owing to the greater contribution of π−hole•••π and π−π (face-toface) interactions. The predominant C-I•••π halogen bonding observed in Na•D and Phen•D cocrystals remains dormant in most of the ArB•D cocrystals due to the stronger C-I•••N interactions

relative

to

C-I•••π interaction.

Tailoring

of

C-I•••N,

C-H•••F,

π−hole•••π and π−π interactions enabled successful design of three-dimensional self-assembled architectures suitable for optoelectronic device applications. ASSOCIATED CONTENT Supporting Information. Detailed description of synthesis and characteristics of compounds.http://pubs.acs.org. Author Contributions ⊥These †

authors contributed equally.

Present address: Graduate school of Material Science,Nara Institute of Science and Technology

(NAIST), 8916-5 Takayama, Ikoma, Nara 630-0192, Japan. Funding Sources


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M. H. acknowledges Kerala State Council for Science, Technology and Environment (KSCSTE) for the support of this work, 007/KSYSA-RG/2014/KSCSTE. ACKNOWLEDGMENT Remya Ramakrishnan and Ajith R. Mallia acknowledge UGC and CSIR respectively for financial assistance; Niyas. M. A. is thankful for INSPIRE fellowship. The authors also thank Dr. Babu Varghese, IIT-Madras and Dr. Sunil Varughese, NIIST-Trivandrum, for valuable suggestions. Authors thank Alex P. Andrews, IISER-TVM for single crystal X-ray structure analyses and Prof. Angel Martin Pendas, University of Oviedo, Spain for fruitful discussions on IQA analysis. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.

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For Table of Contents Use Only Columnar/Lamellar Packing in Cocrystals of Arylbipyridines with Diiodoperfluorobenzene Remya Ramakrishnan,⊥ Ajith R. Mallia,⊥ Niyas M. A., Ramarani Sethy† and Mahesh Hariharan*

Synopsis: Arylated 2,2’-bipyridines and corresponding cocrystals with the coformer 1,4diiodotetrafluorobenzene were successfully synthesized and characterized. The cocrystals exhibited promising columnar/lamellar arrangements in contrast to the precursor units that possess herringbone/sandwich herringbone arrangement. Tailoring of C-I•••N, C-H•••F, π−hole•••π and π−π interactions enabled successful design of three-dimensional self-assembled architectures that could be suitable for optoelectronic device applications.


23

Lamellar Packing in Cocrystals of Arylbipyridines with

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