Interplay of Halogen Bonding and Hydrogen Bonding in the Cocrystals

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Interplay of Halogen Bonding and Hydrogen Bonding in the Cocrystals and Salts of Dihalogens and Trihalides with N,N'-bis(3-pyridyl-acrylamido) Derivatives: Phosphorescent Organic Salts ANINDITA GOSWAMI, Mousumi Garai, and Kumar Biradha Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.8b01786 • Publication Date (Web): 15 Feb 2019 Downloaded from http://pubs.acs.org on February 17, 2019

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Crystal Growth & Design

Interplay of Halogen Bonding and Hydrogen Bonding in the Cocrystals and Salts of Dihalogens and Trihalides with N,N'-bis-(3-pyridyl-acrylamido) Derivatives: Phosphorescent Organic Salts Anindita Goswami, Mousumi Garai and Kumar Biradha*

Department of Chemistry, Indian Institute of Technology, Kharagpur-721302, India

ABSTRACT.

N,N'-bis-(3-pyridyl-acrylamido)

derivatives

cocrystals and salts with dihalogens I2 and Br2.

are

shown

to

form

The detailed structural

analyses of the cocrystals and salts reveal that the amide-to-amide N-H···O hydrogen bonding takes the major role in the cocrystals while N-H···N hydrogen bonding predominates in the salts.

With increase of the halogen content in the

lattice the interactions involved with halogens (N-H···X hydrogen bonding, N···X

ACS Paragon Plus Environment

1

Crystal Growth & Design 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

Page 2 of 70

and X···X halogen bonding) found to overpower the conventional N-H···O and N-H···N hydrogen bonding.

In one such heavy halogen content salt, it is found

that the water acts as a mere space filling species and does not involve in any conventional hydrogen bonding such as N-H···N or N-H···O hydrogen bonds or halogen bonding.

All the cocrystals and salts are found to exhibit solid state

photoluminescence which can be attributed to the charge transfer due to halogen bonding.

Further the tetra brominated salts are found to exhibit

phosphorescence at 77 K in a rigid matrix and also at room temperature owing to triplet producing carbonyls and triplet stabilizing heavy atom perturbations (CBr···Br-C, Br···Br, C-H···Br) in their crystal lattice.

INTRODUCTION Halogen bonding1,2 is emerging as one of the prominent interactions in the field of supramolecular chemistry and crystal engineering in designing new solid state

architectures

with

variety

of

properties

in

the

context

of

organic

catalysis,3,4 solid state synthesis,5-7 porous and organic inclusion systems,8-10 nanoparticles,11-13 analytical chemistry and separation processes,14-17 polymers


2

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and thin flims,18,19 liquid crystals,20-22 optical and optoelectronic systems,23,24 conductive and magnetic materials,25,26 molecular recognition,27,28 designing of drugs,29

and

in

pharmaceutical

industry.30

The

nature

and

geometrical

properties of halogen bonds are well researched area since the beginning of 20th century and still it is continuing to be of interest to several researchers to understand this phenomenon.31-37

Halogen bonding is a noncovalent interaction

acting between polarizable halogen atom (X), where the X functions as electrophilic species (Halogen bond donor) and an electron rich atom, which could be anionic or a neutral species, for e.g. a lone pair or a π system (Halogen bond acceptor).

In halogen bonding, Xs play the role of hydrogen

atom in the hydrogen bonding.

When the X atom is involved in formation of

one covalent bond, the formation of σ hole on the elongation of the covalent bond is the key in the context of halogen bond, making X as an electrophilic species and halogen bond as highly directional, tunable (similar to hydrogen bond) and hydrophobic (complementary to hydrogen bond).


3


Page 4 of 70

Through the journey of halogen bonding, the most emphasis has been on iodine-diiodine (I-···I-I) as halogen bond acceptor as well as formation of different polyiodides,38-41 owing to the high polarizability and greater anisotropic charge distribution on the electrostatic potential surface42,43 among group XVII elements.

Notable, not many cocrystals44,45 of dihalogen molecules are reported

to date given their tendency for the formation of salts46,47 with organic bases. One of the classic example for X2 containing cocrystal is the one between I2 and 4-alkoxystilbazoles that exhibits liquid crystalline properties.48

Among the

heterocycles, the pyridine functionality is most exploited functionality for the halogen bonding with dihalogens or haloaromatics.49,50

In organic salts of

nitrogen bases, the halide ions act as proton acceptor to form N-H···X interactions. On the other hand halogen bonding interactions are shown to assist phosphorescence of organic materials in number of cases.51-60

Such assistance

originates from the enhancement of the spin-orbit coupling (Ts and Ss) as the halogen bonding and other intermolecular interactions of X-atom increases the


4

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probability

of

T1—›S0

radiative

decay

of

phosphorescence.

The

direct

attachment of halogen atom with the chromophores (internal heavy atom effect) or within the surroundings of the chromophores (external heavy atom effect) play a significant role by a charge transfer either from chromophores to perturbers (X or C-X) or perturbers to chromophores.

The interaction between

the chromophores and perturbers takes place either through the lone pair (n) orbitals of the X or through the σ and σ‫ ٭‬orbital of the C-X bonds.

In addition

to halogen bonding, the intermolecular interactions such as C-X···X-C, N-H···X, C-H···X, X···X are also important in stabilization of the triplet state in the context of this unique emission behavior.

Our recent studies on several bis-(3-pyridyl-acrylamido) derivatives containing various alkyl/aryl spacers in between amide functionalities reveal that they exhibit two types of amide-amide hydrogen bonding architectures depending on the spacers: -sheet or 2D-layers via amide-to-amide hydrogen bonds. 2D-layers

have

been

utilized

by

us

to

self-template


solid

state

The [2+2]

5


Page 6 of 70

polymerization reactions in SCSC manner in pure organics as well as in their coordination polymers.61-64

In this report, the related derivatives are studied to

examine their capability of maintaining their amide-to-amide hydrogen bonding patterns while the pyridyl groups form halogen bonding with I2 or Br2 or being protonated forming salts.

In this contribution we intend to examine the interplay

of salt vs cocrystal and halogen bonding vs N-H···O hydrogen bonding by studying the complexation reactions of bis-(3-pyridyl-acrylamido) derivatives (PAED, PAXD and PAH, Scheme 1) with I2 and Br2 and their crystal structures. The organic molecules are selected such that they fall into three categories in terms of their spacers: PAED contains flexible ethyl spacer (aliphatic) and PAXD contains flexible xylyl spacer (aromatic-aliphatic) in between the amide groups while the amide groups are directly linked in PAH.

In case of

cocrystals, the halogen bonding is expected to increase the dimensionality from one-dimensional -sheet to two-dimensional layer and from two-dimensional NH···O hydrogen bonding to three-dimensional networks. (Scheme 2).


6

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O N H N

O

H N

N

O HN

NH

O

PAED

PAXD

N

N N

O H N N H N

O

PAH

Scheme 1. Structural drawing of PAED, PAXD and PAH.

a)

H N X

N

X

O Y

O

N

X X

O Y

O

N

X X

O

N

N

X

X

H

H N

N

X

H

H N

N

X

O Y

N

N

X

X

H


7


H b)

X

X

N

N O

O N

N

H

Y

H

O

X N

X

X

O Y

X

N

N X

H O

N

Page 8 of 70

N N H

Y

X

X

X

X N

H N O

X

Scheme 2. Halogen bond extending the N-H···O hydrogen bonded a) -sheets to two-dimensional layer; b) 2D-sheets to three-dimensional network (Y= spacer, X= halogen).

Our studies reveal that these derivatives have a tendency to form cocrystals and salts with I2 depending on the reaction conditions.


However, with Br2 they

8

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found to form only mono or tribromide salts of the tetra brominated PAED and PAXD.

The crystal structures of these derivatives reveal that as the content of

halogens increases, the interactions involved with halogens dominate the crystal packing over the conventional N-H···O and N-H···N hydrogen bonds.

The

crystal structures of these materials are analyzed in terms of interaction interference, N-H···O, N-H···N and N-H···X hydrogen bonding, N···X halogen bonding and X···X contacts. state

absorption

and

These materials are found to exhibit good solid

luminescence

properties.

In

particular,

the

tetra

brominated salts of PAED and PAXD have exhibited efficient phosphorescence both at 77K in a rigid glass matrix and at room temperature. RESULTS AND DISCUSSION The molecules PAED, PAXD and PAH were synthesized by condensation reactions of 3-pyridine acrylic acid with ethylenediamine, p-xylylenediamine and hydrazine hydrate, respectively, in the presence of triphenyl phosphite.

The as

synthesized materials of PAED was recrystallized from MeOH-DCM and PAXD and

PAH

were

recrystallized

from

MeOH-DMF


solvent

system.

The

9


Page 10 of 70

complexation reactions of I2 (two equiv.) with PAED, PAXD and PAH (one equiv.) in MeOH-CHCl3 resulted in single crystals of complexes PAED.2I2, 1, PAXD.2I2, 2 and [HPAH][PAH][I3˗], 3 respectively.

Our efforts to obtain the

cocrystals of PAH with I2 by changing the reaction conditions in terms of concentrations, ratios and solvents were unsuccessful.

However, we were

successful in obtaining single crystals of triiodide salts [H2PAED][I3˗]2, 4 and [HPAXD][I3˗], 5 of PAXD and PAED, respectively, by repeating the reactions in the presence of one equiv. of KI in MeOH-CHCl3.

The complexation reactions

of Br2 with PAED and PAXD resulted in the formation of single crystals of [H2Br4PAED][Br˗]2·2H2O, 6 and [H2Br4PAXD][Br3˗]2,7 respectively.

We note here,

in these structures both the double bonds of PAED and PAXD were found to be fully brominated.

The reactions of Br2 with PAH were found to result in

precipitates but not suitable single crystals.

Further, the presence of KBr in

these reactions resulted in the similar out comes that is formation of single crystals of 6 and 7.

The pertinent crystallographic parameters for all the

complexes 1-7 are given in Table 1 and 2.

In the cocrystals of I2 (1 and 2), it


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is observed that the molecules are assembled into 2D-hydrogen bonding layers while I2 participates in halogen bonding with pyridine N-atom as anticipated. The crystal structure analyses of the salts 3-5 reveal that the N-H···N hydrogen bonding prefers over N-H···O hydrogen bonding.

Whereas in crystal structures

of salts 6 and 7, N-H···Br- and Br···Br interactions found to play a significant role over other conventional interactions. Complexes 1 and 2 crystallized in P21/c space group with a difference in the asymmetric unit contents.

The asymmetric unit of 1 contains one unit of PAED

and two units of I2, whereas the asymmetric unit of 2 contains half unit of PAXD and one disordered I2 with two orientations, one with 0.75 occupancy and the other with 0.25 occupancy.

In both the structures the bis-(pyridine-

acrylamido) molecules are found to have amide-to-amide hydrogen bonding layers in which the double bonds are aligned for photo polymerization with centroid to centroid distance of double bonds are 3.532 Å and 4.070 Å in 1 and 2 respectively (Figure 1a,2a).

In 1, the two I2 molecules are found to

have halogen bonding interaction with pyridine N-atoms with one of their ends


11


(N···I: 2.479(4) Å, 2.580(4) Å; Figure 1b,1d).

Page 12 of 70

The second end of I2 involves in

I···I interactions, interestingly each I is involved in three such contacts (trifurcated) to form a tetramer of I2 (3.9682(9) Å, 4.1910(9) Å, 4.1952(10) Å, Figure 1c).

These tetramers reside between the layers and connect them via

halogen bonding.

In 2, the I2 with 0.75 occupancy involved in halogen bonding

(N···I: 2.551(18) Å) while the I2 with 0.25 occupancy involved in interaction (C···I: 2.85(2) Å, H···I: 2.000 Å, C-H···I: 150.696°).

pyC-H···I

Here too the

other end is involved in I···I (I···I: 3.286(6) Å) contacts to form layer of I2 in between the organic layers of PAXD (Figure 2b,c).

Although, the double bonds

are aligned for solid state [2+2] polymerization in 1 and 2, they have been found to be unreactive despite of prolonged irradiations.

We would like to note

here that the PAED and PAXD molecules form β-sheets in their crystal structures which are photo-inactive as the double bonds are not within reactive distances. a)


12

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b)

c)

d)

Figure 1. Illustrations for the crystal structure of 1: a) 2D-layer of N-H···O hydrogen bonding; b) & d) halogen bonding interactions of I2 with pyridine Natoms (pyN···I, shown in red color); c) tetramer of I2 (I···I interactions, shown in blue color).


13


Page 14 of 70

a)

b)

c)

Figure 2. Illustrations for the crystal structure of 2: a) 2D-layer of N-H···O hydrogen bonding; b) layer of I2 in between the organic layer of PAXD; c) halogen bonding interactions of I2 with pyridine N-atoms (pyN···I, shown in red color) and I···I interactions (shown in blue color).


14

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The triiodide salt 3 crystallizes in P-1 space group and the asymmetric unit is constituted by one neutral PAH, one monoporotonated PAH (HPAH) and one I3˗ ion.

The PAH and HPAH units form β-sheets via amide-to-amide hydrogen

bonds. Two of these β-sheets are joined together via N-H···N hydrogen bonds (N···N: 2.665(5) Å, H···N: 1.81 Å, N-H···N: 176°) to form a dimer of the sheets (Figure 3a). Å; Figure 3c).

The I3˗ form linear 1D-chains via I···I interactions (I···I: 3.7412(7) Two of such chains of I3˗ are enclathered within four dimers of

β-sheets via plethora of other weak interactions (Figure 3b). a)

b)


15


Page 16 of 70

c) Figure 3. Illustrations for the crystal structure of 3: a) dimer of β sheets, through N-H···N hydrogen bonds; b) further joining of dimer of β-sheets by

pyC-

H···O=C interactions; c) 1D-chain of I3˗.

The triodide salts 4 and 5 also crystallized in P-1 space group with a difference in their asymmetric unit contents.

In 4, the asymmetric unit contains

one I3˗ and half of protonated PAED while that of 5 contains half unit each of triiodide and protonated PXAD. sheet like structure via

In 4, The HPAED units join to form a 1D-

pyN-H···O=C

hydrogen bonds (N···O: 2.673(4) Å, H···O:

1.98(6) Å, N-H···O: 170(7)°, Figure 4a). corrugated

2D-layer

These sheets further linked to

via weak electrostatic interaction between

(N···O: 3.138(4)) Å; Figure 4b).

pyN

+···O=C

The triodide anions form dimers via I···I

(3.7476(5) Å) interactions and enclathered between the layers via (O=C)-N-H···I (N···I: 3.667(3) Å, H···I: 2.88 Å, N-H···I: 153°).and C-H···I (C···I: 4.086(4) Å,


16

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H···I: 3.385 Å, C-H···I: 131°) interactions and by plethora of other weak interactions (Figure 4c,d).

In 5, the HPAXD moieties form one-dimensional zig-

zag chain via

hydrogen bonds.

pyN···H···Npy

These chain stack on each other

via three types of interactions: O=C-NH···π: 4.184 Å,

pyC-H···π:

4.062 Å and

offset π···π: 3.562 Å to form corrugated 2D-layers (Figure 5a,b).

The triiodide

ions do not form any dimer or 1D-chain as observed in 3 and 4 but are encapsulated in between the organic layers via N-H···I (N···I: 3.908(5) Å, H···I: 3.082 Å, N-H···I: 157°) and

pyC-H···I

(C···I: 3.428(7) Å, H···I: 3.27 Å, C-H···I:

175°) and plethora of other weak interactions (Figure 5c). a)

b)


17


Page 18 of 70

c)

d) Figure 4. Illustrations for the crystal structure of 4:a) 1D-chain via N+H···C=O interactions;

b)

linking

of

1D-chains

electrostatic interactions between

pyN

to

+···O=C;

corrugated

2D-layer

via

weak

c) packing of I3˗ within the lattice;

d) dimer of I3˗.

a)

b)


18

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c)

Figure 5. Illustrations for the crystal structure of 5:a) one-dimensional zig-zag chain via charge assisted

pyN···H···NPy

hydrogen bonds, further stacking of 1D-

chains on each other to form corrugated 2D-layers; b) linking of 2D-layers via pyC-H···O=C

interactions; c) packing of I3- within the lattice.

The reaction of PAED with Br2 resulted in the formation of single crystals of HBr salt of tetra brominated PAED (TBPAED), 6.

The crystal structure

analyses reveal that the asymmetric unit contains half of the H2TBPAED and one each of Br- and H2O.

In the crystal structure,


pyC-H···O=C

(C···O:

19


Page 20 of 70

3.237(14) Å, H···O: 2.40 Å, C-H···O: 150°) and BrC-H···O=C (C···O: 3.268(16) Å, H···O: 2.370 Å, C-H···O: 152°) and in combination with N+H···Br˗ (N···Br: 3.183(11) Å, H···Br: 2.34 Å, N-H···Br: 168°) interaction form one-dimensional sheets (Figure 6a,b).

These one-dimensional sheets interact with each other

via plethora of C-Br···Br˗: 3.574(2) Å and NH···Br˗ (N···Br: 3.317(9) Å, H···Br: 2.46 Å, N-H···Br: 173°) interactions to form 3D-lattice.

Further, it is interesting

to note here that the included water molecule does not have any strong hydrogen bonding either with amide groups or with C-Br bonds or Br˗ ions (Figure 6c).

Generally, in the presence of H2O molecules, amide groups and

pyridinium ions are expected to lead to a structure a)

b)


20

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c)

Figure 6. Illustrations for the crystal structure of 6: a) formation of 1D-chain through

pyC-H···O=C

and BrC-H···O=C in combination of NH+···Br˗ interactions;

b) 1D-sheets; c) linking of one-dimensional sheets with each other via plethora of

C-Br···Br˗

and

NH···Br˗

interactions

to

form

a

3D-lattice.

(Note;

no

conventional hydrogen bond with H2O molecule).

containing strong N-H···O, N-H···N and O-H···O hydrogen bonds.

However, in

the present case none of these hydrogen bonds are seen to form as the PAED is fully loaded with halogen atoms and therefore NH+···Br˗, C-Br···Br˗ and NH···Br˗ interactions are dominating in the lattice and H2O molecules are playing the role of mere space filling.


21


Page 22 of 70

In contrast, the same reaction of Br2 with PAXD produced single crystals of tribromide salt of protonated and tetra brominated PAXD, (H2Br4PAXD), 7.

It

crystallizes in P-1 space group and the asymmetric unit is constituted by half unit of H2Br4PAXD and one Br3˗ ion.

Interestingly, the tribromide ions are

found to be highly unsymmetrical unlike the triiodide ions.

All these trianions

found to be linear, the I3˗ unit exhibit I-I distances of 2.9159(6) Å & 2.9396(6) Å; 2.8459(5) Å & 3.0063(5) Å and 2.9137(5) Å & 2.9137(5) Å in 3-5 respectively.

Whereas in 7, Br3˗ unit exhibits Br-Br distances of 2.388(3) Å and

2.850(2) Å (Figure 7e).

The terminal Br of Br3˗ that has longer distance acts

as Br- and participates in NH+···Br˗ (N···Br: 3.185(8) Å, H···Br: 2.34 Å, N-H···Br: 166°) and (O=C)-N-H···Br˗ (N···Br: 3.386(8) Å, H···Br: 2.61 Å, N-H···Br: 150°) interactions to form 1D-sheets in a similar manner to that of 6 (Figure 7a). The terminal Br that forms a shorter distance involves in Br···Br interaction with C-Br bonds.

Further, the H2TBPAXD molecules aggregate into 1D-chains along

X-axis to form 1D-sheet similar to that of 6.

Similar to 6 the packing is


22

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governed by N-H+···Br˗, (O=C)-N-H···Br˗, Br···Br and C-Br···Br-C contacts, no conventional strong hydrogen bonds are observed (Figure 7b,c,d). a)

b)

c)

d)

e) 7.67 Å


23


Page 24 of 70

Figure 7. Illustrations for the crystal structure of 7: a)1D-chain through N+H···Br3-interactions and NH···Br3- interactions; b) formation of 1D-network by C-Br···Br-C: 4.0775(18) Å interactions in the perpendicular direction of 1D-chain formed by N+H···Br3˗ and NH···Br3˗ interactions; c) aggregation of 2D-layer through Br3˗···Br3˗: 3.595(3) Å contacts; d) further aggregation of 2D-layers to form a 3D-lattice along X axis; e) 1D-chain of Br3˗ ion within the 2D-layer of H2TBPAXD.

Mechanochemical Grinding: The synthesis of salts and co-crystals by mechanochemical dry or wet grinding

is

of

significant

interest

owing

to

effectiveness and green route of synthesis.65,66

their

facile

synthesis,

cost

We and several others have

shown that mechanochemical grinding is an alternate synthetic route to produce organic cocrystals and salts which are identical to conventionally crystallized materials.67-70

Here to explore the utility of mechanochemical synthesis in this

iodine containing cocrystals and salts, the solvent drop (MeOH-CHCl3in 1:1 ratio) assisted mechanochemical grinding experiments have been performed for


24

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the complexation reactions of I2 and PAED, PAXD and PAH with and without KI by manual grinding in an agate mortar and pestle taking the solid materials in 2:1 ratios.

During the grinding process, MeOH-CHCl3 solvent was added

dropwise and the manual grinding was continued for 30 min.

Comparison of

the XRPD patterns of the grinded samples with those of respective simulated patterns reveal that complexes 1 and 2 (Figure S1,S2) can be produced by this methodology but could not produce the complexes 3-5 despite of several trails by changing time duration of grinding, ratios of the components, and the amount of solvents.

The experimental XRPD patterns for the grinded materials

corresponding to 3-5 have shown no significant peaks in the powder diffraction pattern.

The powder diffraction patterns and colors of the grinded materials

analogous to 1 and 2 are found to be identical with those of conventionally produced 1 and 2. DRS and Solid State Luminescence Organic solid state luminescent materials have drawn a lot of attention owing to their enormous application in the field of optoelectronics and sensing


25


properties. be

an

Page 26 of 70

It was shown that halogen bonding based crystal engineering can

efficient

chromophores interactions.71-73

tool

in

in

their

fine

tuning

the

emissive

solid

state

through

properties

noncovalent

of

halogen

organic bond

As early as in 1950, R. Mulliken has developed the Charge

Transfer theory (CT) to explain the spectroscopic properties and the dipole moment behavior of the halogen bonded adducts.74-76

In case of halogen

bonding, the charge transfer between halogen bond donors and acceptors occurs through n→σ* interactions.

The charge transfer phenomenon in the

halogen bonded adduct is the key in fine tuning their emission behavior. Herein, in order to get some insights into optical absorption and emission behavior of PAED, PAXD, PAH and cocrystals and salts 1-7, diffuse reflectance spectroscopy (DRS) and solid state photoluminescence studies were performed on the grinded powder material of the samples.

From the DRS it has been

observed that these materials exhibit distinct absorption bands reflecting their different colors in solid state.

PAED and PAXD are colorless and PAH is of

bright yellow and the cocrystals and salts of I2 1-5 are of deep brown color


26

Page 27 of 70 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


whereas the salts 6 and 7 are of red color.

The absorption bands of PAED

and PAXD are located at around 310 and 320 nm respectively, indicating their white color.

On the other hand PAH has a broad absorption band, ranging

from around 320 to 400 nm confirming its bright yellow color.

Cocrystals and

salts 1-5 have broad range of absorption ranging from 360 to 680 nm showing their deep brown color.

Salts 6 and 7 of red color have shown absorption in

the region of 320 to 550 nm. (Figure S9a,b.c). The solid state photoluminescence of these powder materials were recorded under identical conditions at room temperature upon excitation at 320 nm wavelength.

The observed red-shift of the emission maxima of cocrystals and

salts 1-7 compared to PAED, PAXD and PAH can be correlated to the n→σ* charge transfer in the ambience of halogen bonding noncovalent interaction. PAED, PAXD and PAH have emission maxima at about 410, 416 and 470 nm respectively (Figure 8a,b,c).

The emission behavior of these three can be

referred to the pyridine moiety, xylyl spacer and hydrazine spacer.


27


Owing to the charge transfer from pyridine nitrogen atom to the σ* orbital of I2 (n→σ*), 1 and 2 have shown red-shift in the emission behavior.

1 has

emission maxima at about 515 nm and 2 has emission maxima at about 511 nm (Figure 8a,b).

The emission profile of 3, 4, and 5 can be explained by the

charge transfer from I˗ to the σ* orbital of I2 in triiodide moiety.

3 shows

emission maxima at about 475 nm, similar to PAH, which can be attributed to the overall effect of PAH based emission and charge transfer in I3˗ (Figure 8c). 4 and 5 have emission maxima at about 510 and 470 nm respectively, indicating the similar charge transfer in triiodide moiety and within the crystal lattice (Figure 8a,b). PAED b) 1 4 1.0 6

a) 1.0 0.8

Normallized Intensity


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

Page 28 of 70

0.6 0.4 0.2 0.0 350

PAXD 2 5 7

0.8 0.6 0.4 0.2

400

450 500 Wave Length (nm)

550

600

0.0 350

400

450

500

550

600

Wave Length (nm)


28

Page 29 of 70

1.0

c)


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


PAH 3

0.8 0.6 0.4 0.2 0.0

420 440 460 480 500 520 540 560 580 600

Wave Length (nm)

Figure 8.Solid state luminescence spectra: a) for PAED and 1, 4, 6; b) for PAXD and 2, 5, 7; c) for PAH and 3.

The emission behavior of 6 and 7 can be explained in a similar way, by the overall effect of charge transfer of Br˗ to σ* orbital of C-Br bond and charge transfer of Br˗ to the σ* orbital of Br2 in Br3˗ moiety.

6 has two emission

maxima at about 470 and 520 nm (Figure 8a) and 7 also has two emission


29


Page 30 of 70

maxima at about 470 and 570 nm (Figure 8b), corresponding to charge transfer effect within the crystal lattice.

Phosphorescence Study These materials are anticipated to exhibit bright phosphorescence owing to i) triplet producing carbonyl; ii) triplet stabilizing heavy halogen atoms and iii) intermolecular interactions involving halogen bonding interactions.

Therefore

phosphorescence behavior of cocrystals and salts 1-7 has been explored.

The

grinded samples of 1-7 are dispersed in MeOH and EtOH (1:4) solvent mixture to record phosphorescence emission and time-resolved spectra at 77K in liquid N2 atmosphere and also at room temperature in saturation with N2 gas with an excitation wave length of 260 nm.

Out of seven complexes, the tetra

brominated salts 6 and 7 have shown significant green phosphorescence emission centered at about 500 nm both at 77 K and at room temperature (Figure 9c,d), where as other cocrystals and salts 1-5 have not shown any significant peaks in their phosphorescence emission profiles.


In an identical

30

Page 31 of 70 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


condition, 6 and 7 have exhibited weak fluorescence emission having emission maxima at about 350 nm, upon excitation with wave length 260 nm (Figure 9a,b).

It also shows that at room temperature the phosphorescence emission

intensities drastically decrease and the maxima also get broaden which can be referred to the lack of rigidification induced triplet stabilization and several nonradiative dacay paths being feasible through molecular vibrational, collisional and thermal motions, compared to in a rigid glass solvent matrix at 77 K. The unique phosphorescence emission behavior of 6 and 7 can be attributed to the presence of C-Br bond adjacent to carbonyl choromophore (Figure 6a,7a) which helps in stabilizing the excited triplet sate, perturbation through the σ and σ* orbital and consequently increasing the probability of T1—›S0 radiative transition by promoting Sn→Tn ISC. luminogens

are

locked

in

the

crystal

Further in 6 and 7, the organic lattice

by

various

intermolecular

interactions such as C-Br···Br-C, C-H···Br, N-H···Br and Br···Br (Figure 6c,7d) which obviously play a significant role in insitu generation and stabilization of the triplet state.


31


Page 32 of 70

Time-resolved PL spectra of 500 nm emission has been recorded for 6 and 7 to gain a deeper insight into the nature of the green emission at 77 K and at room temperature.

The luminescence decay curves of 500 nm emission with

excited state lifetime are found to be as long as 0.244 and 0.603 ms for 6 and 7, respectively, at 77 K prove that the green emission is originating from triplet to singlet radiative transitions (Figure 10a,c).

The luminescence decay features

at room temperature also follow the same trend as at 77 K, though having shorter triplet excited lifetime 0.153 and 0.247 ms than those measured at 77 K (Figure 10b,d).

The comparison of excited state lifetime at both 77 K and

room temperature of 6 and 7 shows that 7 has longer lifetime at the triplet excited state which can be attributed to the additional perturbation of Br˗···Br2 in the heavier Br3˗ in the crystal lattice of 7.


32

Page 33 of 70

a)

fluorescence emission profile of 7 phosphorescence emission profile of 7

1.0 Normallized Intensity


b)

fluorescence emission profile of 6 phosphorescence emission profile of 6

1.0 0.8 0.6 0.4

0.8 0.6 0.4 0.2

0.2 300

350

400 450 500 Wave Length (nm)

500000 c)

550

0.0 300

600

350

700000

d)

77 K room temperature


550

600

77 K room temperature

600000

400000

500000

300000

Intensity

Intensity

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


200000

400000 300000 200000

100000 100000

0

400


600

650

0

400



600

33


Page 34 of 70

Figure 9. Fluorescence and phosphorescence profiles. a) for 6 and b) for 7; comparison of phosphorescence emission profile of c) for 6 and d) for 7at 77 K and at room temperature.

a)

b)


34

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c)

d)

Figure 10. Time-resolved phosphorescence decay profile of emission of 500 nm: a) for 6 at 77 K; b) for 6 at room temperature; c) for 7 at 77 K; d) for 7 at room temperature.

All the time-resolved emissions follow the 2nd order

exponential decay law.


35


Page 36 of 70

CONCLUSIONS The crystal structure of cocrystals and salts of dihalogens and trihalides with N,N'-bis(3-pyridyl-acrylamido)

derivatives

have

been

explored

thoroughly

understand the interplay of halogen bonding versus hydrogen bonding.

to

The N-

H···O hydrogen bond layer, that is similar to one observed in the bis-amide derivatives (Scheme 2), found to form in the cocrystals of I2 (1 and 2).

The

pydridyl groups halogen bonded to I2 in both the cases, but only one end of I2 involved in it preventing the formation of 3D-network composed of halogen bonding and hydrogen bonding (Scheme 2).

In the crystal structures of salts

(3, 4 and 5), the N-H···N and N-H···X hydrogen bonding found to be predominant over amide-to-amide N-H···O hydrogen bonds.

The N-H···Br˗, C-

Br···Br˗ and Br···Br˗ interactions found to play a crucial role in the tetra brominated salts (6 and 7) given that the components are heavily loaded by halogen atoms.

Interestingly, the conventional hydrogen bonding such as N-


36

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H···O and N-H···N are not observed in these structures.

In addition, the

enclathered water in 6 found to be a mere space filling unit as it doesn’t involve in any sort of interactions with itself or with amides or with halogens. The solid state luminescence property has been studied attributing to the charge transfer phenomenon between the halogen bond donor and halogen bond acceptor in the context of electronic properties of halogen bonding. tetra

brominated

salts

6

and

7

have

been

found

to

exhibit

The

efficient

phosphorescence at 77K and also at room temperature that can be attributed to the crystallization induced phosphorescence (CIP) phenomenon of pure organic luminogens through heavy halogen atom perturbation. EXPERIMENTAL SECTION All the chemicals, and solvents such as Malonic acid, Ethylenediamine, pXylylenediamine, Hydrazine hydrate (80%in H2O), solid I2, liquid Br2, Potassium Iodide (KI), Methanol (MeOH), Ethanol (EtOH), Tetrahydrofuran (THF), N,N′dimethylformamide (DMF), were purchased from local chemical suppliers and used without purification.

FTIR spectra were recorded with a Perkin-Elmer


37


Instrument Spectrum Rx Serial No. 73713.

Page 38 of 70

The XRPD patterns had been

recorded at room temperature with a BRUKER-AXS-D8-ADVANCE diffractometer (Cu target).

Melting points were taken using a Fisher Scientific melting point

apparatus, cat. no. 12-144-1.

The solid state luminescence spectra were

recorded with a Spex Fluorolog-3 (model FL3-22) spectrofluorimeter.

The

diffuse reflectance spectra (DRS) were recorded with a Cary model 5000 UVvis-NIR spectrophotometer.

The Phosphorescence spectra and the time-

resolved PL spectra were recorded with a Spex Fluorolog-3 (model FL3-22) spectrofluorimeter.

The solution state luminescence spectra were collected with

a Shimadzu RF-6000 spectrofluorophotometer.

The solution state absorbance

spectra were recorded with the use of a Shimadzu (model no. UV2450) UV-vis spectrophotometer.

Vapor of solid I2 and liquid Br2 is very health hazardous

and should be handled with care. Preparation of PAED, PAXD, PAH: PAED, PAXD, PAH were synthesized and purified by recrystallization by procedure reported by us earlier.61-64


38

Page 39 of 70 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


General Procedure for the Synthesis of Complexes 1-3: The complexation reactions were carried out by slow solvent evaporation process of a mixture of 3 mL methanolic solution of PAED, PAXD or PAH (0.05 mmol) and I2 (0.1 mmol) in 5 mL of CHCl3.

Brown colored needle like

crystals suitable for X-ray diffraction were obtained within 6-10 days in about 60-70% yield. PAED.2I2, 1. 2926.76(w),

Yield 65-70%.

1616.57(s),

FT-IR (KBr) υmax/cm-1; 3262.44(w), 3064.90(w),

1544.32(s),

1416.63(m),

1346.35(m),

1228.30(s),

962.01(m), 801.97(m), 638.48(s). PAXD.2I2, 2. 1622.89(m),

Yield 60-65%. 1542.82(s),

FT-IR (KBr) υmax/cm-1; 3230.76(w), 1659.82(m),

1415.66(s),

1322.38(m),

969.72(m),

798.40(m),

υmax/cm-1;

3008.08(w),

748.78(s), 637.37(s). [HPAH][PAH][I3˗],

3.

Yield

60-65%.

FT-IR

(KBr)

1537.73(s), 1464.18(s), 963.32(s), 796.26(m), 670.04(s).

General Procedure for the Synthesis of Complexes 4 and 5:


39


Page 40 of 70

The complexation reactions were carried out by slow solvent evaporation process of a mixture of 3 mL methanolic solution of PAED or PAXD (0.05 mmol) with KI (0.05 mmol) and I2 (0.1 mmol) in 5 mL CHCl3.

Brown colored

needle like crystals suitable for X-ray diffraction were obtained within 7-10 days in about 50-60% yield. [H2PAED][I3˗]2, 1661.62(s),

4.

Yield

1613.07(s),

50-55%.

1520.81(s),

FT-IR

(KBr)

1413.65(s),

υmax/cm-1;

3247.25(w),

1225.00(m),

966.78(m),

υmax/cm-1;

3230.76(w),

802.54(m), 699.46(m). [HPAXD][I3˗],

5.

Yield

50-60%.

FT-IR

(KBr)

1621.90(m), 1515.23(s), 1412.92(s), 969.41(w), 751.10(s), 671.84(s). General Procedure for the Synthesis of Complexes 6 and 7: The complexation reactions were carried out by slow solvent evaporation process of a mixture of 3 mL methanolic solution of PAED or PAXD (0.05 mmol) with 0.5 mL liquid Br2 in 5 mL THF.

Red colored rectangular block

shaped crystals suitable for X-ray diffraction were obtained within 6-8 days in about 70-75% yield.


40

Page 41 of 70 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


[H2Br4PAED][Br˗]2·2H2O, 6. 2743.41(w),

1661.19(s),

Yield 70-75%. 1554.77(s),

FT-IR (KBr) υmax/cm-1; 3249.10(w),

1360.79(w),

1229.74(w),

808.95(w),

682.70(s), 568.78(s). [H2Br4PAXD][Br3˗]2, 7.

Yield 70-75%.

FT-IR (KBr) υmax/cm-1;3269.23(w),

2798.12(m), 1686.24(s), 1535.16(s), 1229.11(m), 803.30(s), 674.41(s), 567.23(m). Crystal Structure Analysis by Single crystal X-ray: All the single-crystal data were collected on a Bruker-APEX-II CCD X-ray diffractometer that uses graphite monochromated Mo Kα radiation (λ= 0.71073 Å) at room temperature and low temperature by the hemisphere method.

The

structures were solved by direct methods and refined by least-squares methods on F2 using SHELX-2014.77

Non-hydrogen atoms were refined anisotropically

and hydrogen atoms were fixed at calculated positions and refined using a riding model.

The H atoms attached to C, N and O are located whereever

possible and refined using the riding model. Preparation of Stock Solutions for Phosphorescence and Time-Resolved PL measurement:

The finely grinded crystals were dispersed in MeOH+EtOH (1:4)


41


Page 42 of 70

mixture to make 10-4 M solution by sonication for 1hr.

The 1 mL of each

stock solution saturated with N2 were subjected to record phosphorescence and time-resolved PL measurement under liquid N2 atmosphere at 77 K and at room temperature with 3/2 slit.

Table 1. Crystallographic Parameters for 1-4

1

2


3

4

42

Page 43 of 70 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


Formula C18H18I4N4O2

C24H22I4N4O2

C32H29I3N8O4

C18H20I6N4O2

Mol.Wt.

829.96

906.05

970.33

1085.78

T (k)

293(2)

293(2)

293(2)

293(2)

Crystal

monoclinic

monoclinic

Triclinic

Triclinic

P21/c

P21/c

P-1

P-1

a (Å)

12.6387(19)

10.004(3)

9.4656(9)

8.5414(8)

b (Å)

18.473(3)

9.440(3)

10.0632(9)

9.5268(9)

c (Å)

10.3527(15)

15.616(4)

18.4396(18)

9.9050(9)

α (°)

90

90

102.905(3)

67.547(2)

β (°)

95.733(4)

106.300(8)

99.192(3)

73.554(2)

γ (°)

90

90

96.797(3)

78.142(2)

V (A3)

2405.0(6)

1415.4(6)

1668.3(3)

710.09(12)

Z

4

2

2

1

D

2.2922(6)

2.1258(11)

1.9317(3)

2.5391(4)

0.0360

0.0655

0.0380

0.0228

0.1115

0.1744

0.1086

0.0840

System Space group

(g/cm3) R1[I >2σ(I)] wR2(on F2

,all

data)


43


Page 44 of 70

Table 2. Crystallographic Parameters for 5-7

5

6

7

Formula

C24H23I3N4O2

C18H24Br6N4O4

C24H24Br10N4O2

Mol.Wt.

780.16

839.87

1199.57

T (k)

150(2)

293(2)

299(2)

Crystal

Triclinic

Triclinic

Triclinic

P-1

P-1

P-1

a (Å)

4.6395(4)

8.4101(13)

7.6691(10)

b (Å)

11.9797(8)

9.9874(16)

8.7405(12)

c (Å)

12.0323(10)

10.981(3)

13.4101(17)

α (°)

106.124(5)

111.427(7)

87.191(9)

β (°)

91.369(5)

97.985(6)

79.254(9)

γ (°)

99.859(5)

111.357(4)

84.985(9)

System Space group


44

Page 45 of 70 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


V (A3)

631.15(9)

759.3(3)

879.3(2)

Z

1

1

1

D(g/cm3)

2.0500(3)

1.8366(7)

2.2652(5)

> 0.0402

0.0699

0.0733

0.1094

0.2102

0.1861

R1

[I

2σ(I)] wR2(on F2

,all

data)


45


Page 46 of 70

Table 3. Hydrogen Bonding Parameters in the Crystal Structure of 1-7

Complex

Type

H···A (Å)

D···A (Å)

D-H···A (deg)

N-H···O

2.12

2.910(5)

153

2.05

2.892(4)

165

C-H···Oa

2.53

2.845(5)

100

N-H···O

1.91

2.73(2)

159

C-H···Oa

2.58

2.92(2)

102

C-H···Na

2.50

2.833(19)

101

2.07

2.833(5)

147

2.10

2.843(6)

144

1

2


46

Page 47 of 70 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


N-H···O

2.10

2.879(5)

151

2.10

2.850(5)

145

1.81

2.665(5)

176

2.51

2.850(6)

102

2.53

2.864(6)

101

2.54

2.859(6)

100

2.52

2.857(6)

101

2.54

3.400(8)

153

C-H···N

2.58

3.433(7)

153

C-H···I

3.05

3.762(5)

135

Type

H···A (Å)

D···A (Å)

D-H···A

N-H···N

3 C-H···Oa

Complex

(deg)

4

5

N-H···O

1.98(6)

2.673(4)

170(7)

C-H···Oa

2.49

2.822(5)

101

N-H···I

2.88

3.667(3)

153

2.45

3.208(8)

136

C-H···O

2.60

3.395(8)

142

C-H···Oa

2.44

2.799(8)

102

N···H···N

-

2.642

-

2.34

3.183(11)

168

2.46

3.317(9)

173

N-H···Br


47


6

2.40

3.237(14)

150

2.37

3.268(16)

152

a2.47

a2.833(15)

a102

2.79

3.664(13)

157

2.34

3.185(8)

166

N-H···Br

2.61

3.386(8)

150

C-H···Oa

2.49

2.835(16)

101

C-H···Na

2.53

2.870(12)

102

C-H···O

C-H···Br

7

Page 48 of 70

aIntramolecular.

ASSOCIATED CONTENT

Supporting Information: Comparison of XRPD patterns, FT-IR Data, Diffuse Reflectance Spectra (DRS) and Solution state UV-vis. absorbance spectra.

AUTHOR INFORMATION

Corresponding Author *E-mail: [email protected].


48

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Fax: +91-3222- 282252. Tel.: +91-3222-283346.

ORCID Kumar Biradha: 0000-0001-5464-1952

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT

We acknowledge SERB (EMR/2017/001499), DST, New Delhi, India, for financial support, DST-FIST for the single crystal X-ray diffractometer. acknowledges IIT KGP for a research fellowship.

A. G.

We are also thankful to Mr.

Saurav Kayal and Mr. Arghajit Pyne, Department of Chemistry, IIT Kharagpur, for helping with phosphorescence and time-resolved PL measurement.

REFERENCES


49


Page 50 of 70

1. Cavallo, G.; Metrangolo, P.; Milani, R.; Pilati, T.; Priimagi, A.; Resnati, G.; Terraneo, G. The Halogen Bond. Chem. Rev. 2016, 116, 2478-2601. 2. Gilday, L. C.; Robinson, S. W.; Barendt, T. A.; Langton, M. J.; Mullaney, B. R.; Beer, P. D. Halogen Bonding in Supramolecular Chemistry. Chem.

Rev. 2015, 115, 7118-7195. 3. Kuwano, S.; Suzuki, T.; Hosaka, Y.; Arai, T. A Chiral Organic Base Catalyst with Halogen-Bonding-Donor Functionality: Asymmetric Mannich Reactions of Malononitrile with N-Boc Aldimines and Ketimines. Chem.

Commun. 2018, 54, 3847-3850. 4. Matsuzawa,

A.;

Takeuchi,

S.;

Sugita,

K.

Iodoalkyne-Based

Catalyst-

Mediated Activation of Thioamides through Halogen Bonding. Chem. Asian

J. 2016, 11, 2863-2866. 5. Zhu, B.; Wang, J. -R.; Zhang, Q.; Mei, X. Greener Solid-State Synthesis: Stereo-Selective

[2+2]

Photodimerization

of

Vitamin

K3

Controlled

by

Halogen Bonding. CrystEngComm. 2016, 18, 6327-6330.


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6. Sinnwell, M. A.; Blad, J. N.; Thomas, L. R.; MacGillivray, L. R. Structural Flexibility of Halogen Bonds Showed in a Single-Crystal-to-Single-Crystal [2+2] Photodimerization. IUCrJ. 2018, 5, 491-496. 7. Sinnwell,

M.

A.;

MacGillivary,

L.

R.

Halogen-Bond-Templated

[2+2]

Photodimerization in the Solid State: Directed Synthesis and Rare SelfInclusion of a Halogenated Product. Angew. Chem., Int. Ed. 2016, 55, 34773480.

8. Turunen, L.; Peuronen, A.; Forsblom, S.; Kalenius, E.; Lahtinen, M.; Rissanen,

K.

Tetrameric

and

Dimeric

[N···I+···N]

Halogen-Bonded

Supramolecular Cages. Chem. Eur. J. 2017, 23, 11714-11718. 9. García, M. D.; Martí-Rujas, J.; Metrangolo, P.; Peinador, C.; Pilati, T.; Resnati, G.; Terraneo, G.; Ursini, M. Dimensional Caging of Polyiodides: Cation-Templated Synthesis Using Bipyridinium Salts. CrystEngComm 2011, 13, 4411-4416.


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Table of contents use only:

Synopsis: The salts and cocrystals of N,N'-bis-(3-pyridyl-acrylamido) derivatives with dihalogens have been explored in terms of N-H···O, N-H···N and N-H···X


69


hydrogen bonding and N···X halogen bonding.

Page 70 of 70

The cocrystals exhibit halogen

bonding as well as N-H···O while in salts the N-H···N and N-H···X hydrogen bonding predominates.

These materials exhibit solid-state luminescence and

phosphorescence properties given the interactions involved with halogens.


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Interplay of Halogen Bonding and Hydrogen Bonding in the Cocrystals

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