Halogen-Bonded Assemblies of Arylene Imides and Diimides: Insight from Electronic, Structural, and Computational Studies

Article abstract of DOI:10.1002/chem.202001706

Halogen-bonding interactions in electron-deficient π scaffolds have largely been underexplored. Herein, the halogen-bonding properties of arylene imide/diimide-based electron-deficient scaffolds were studied. The influence of scaffold size, from small (phthalimide) to moderately sized (pyromellitic diimide or naphthalenediimides) to large (perylenediimide), axial-group modification, and number of halo substituents on the halogen bonding and its self-assembly was probed in a set of nine compounds. The structural modification leads to tunable optical and redox properties. The first reduction potential (Formula presented.) ranges between ?1.09 and ?0.17 V (vs. SCE). Two of the compounds, that is, 6 and 9, have deep-lying LUMOs with values reaching ?4.2 eV. Single crystals of all nine systems were obtained, which showed Br???O, Br???Br, or Br???π halogen-bonding interactions, and a few systems are capable of forming all three types. These interactions lead to halogen-bonded rings (up to 12-membered), which propagate to form stacked 1D, 2D, or corrugated sheets. A few outliers were also identified, for example, molecules that prefer C?H???O hydrogen bonding over halogen bonding, or noncentrosymmetric rather than centrosymmetric organization. Computational studies based on Atoms in Molecules and Natural Bond Orbital analysis provided further insight into the halogen-bonding interactions. This study can lead to a predictive design tool-box to further explore related systems on surfaces reinforced by these weak directional forces.

Full text of DOI:10.1002/chem.202001706

Accepted Article
Accepted Article
Title: Halogen Bonded Assemblies of Arylene-imides and -diimides:
Insight from Electronic, Structural and Computational studies
Authors: Pritam Mukhopadhyay, Kalyanashis Mandal, Deepak Bansal,
Yogendra Kumar, Jyoti Shukla, and Rustam Niazi
This manuscript has been accepted after peer review and appears as an
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of the final Version of Record (VoR). This work is currently citable by
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content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.202001706
Link to VoR: https://doi.org/10.1002/chem.202001706
01/2020

10.1002/chem.202001706
Chemistry - A European Journal
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Halogen Bonded Assemblies of Arylene-imides and -diimides:
Insight from Electronic, Structural and Computational studies
Kalyanashis Mandal,[a] Deepak Bansal,[b] Yogendra Kumar,[a] Rustam,[a] Jyoti Shukla[a] and Pritam
Mukhopadhyay*[a]
Nowadays, halogen bonding interactions are fast emerging as an
efficient alternative to hydrogen bonding (HB) interactions.[1,5] In
contrast to a HB, halogen bond constitutes a covalently linked
electron rich halogen atom directionally interacting with electron
rich nucleophilic species such as anion/lone pairs. Such unique
mode of interaction is conceivable by the presence of positive
region on halogen atom, conceptualized as σ-hole by Politzer in
2007.[6] In the last two decades, there have been a persistent
effort by several research groups to rationalize this enigmatic
nature of halogen bonding. In 2003, Resnati and coworkers
reported halogen bonded architecture comprising of Br∙∙∙Npyridyl
interaction,[7] while, in 2004, Bruce and coworkers reported
formation of liquid crystals with a halogen bond.[8] In 2007, Zou
and coworkers theoretically proved the biologically relevant
Br∙∙∙Ophosphate interaction between adenine-5-bromouracil and
organic phosphate ion.[9] Findings by the Diederich[10] and
Parish[11] groups demonstrated the biological significance of
halogen bonding in proteins and DNA. Interestingly, Rissanen[4b]
and Diederich[12] have independently demonstrated construction
of supramolecular cages using halogen bond interaction. A recent
work from the Beer’s group demonstrated the importance of
halogen bonding in anion recognition by a chiral [2]rotaxane.[12] In
addition, presence of halogen atoms on the periphery of
organic/inorganic synthons has attracted scientific community to
augment the construction of supramolecular self-assemblies.[13]
Very recently, Molina and co-workers reported the generation of
interlocked supramolecular polymers assisted by halogen
bonding.[14] Bowling and coworkers reported the stabilization of a
triangular system via halogen bond interaction where rigidity of
halogen bond bridge depends upon the nature of donor halogen
atoms as well as the acceptor carbonyl groups.[15] Therefore, the
strength of halogen bonds can be fine-tuned by varying the motif
covalently bound to halogen atom.
In this context, inherently electron deficient aryleneimides/
arylenediimides π-scaffolds (naphthalenediimides: NDIs and
perylenediimides: PDIs)[16] provide promising platform towards
the rational synthesis of halogen bonded self-assemblies.
Moreover, these scaffolds are envisaged to hold significant
number of directionally aligned halogen atoms which can have
important ramifications in the formation of halogen bonded
architectures and their opto-electronic properties. A preliminary
investigation towards this effort was done by our group with the
PDI scaffold.[3b] Recently, the Gade group demonstrated twisting
of the π-rings in tetraazaperopyrenes (TAPP) by varying number
of halogen atoms.[3c,d] However, there are no systematic studies
till date, which delineates the effect of the size of the arylene-
imide/-diimide π-scaffolds, changes in its constituent atoms, its
number and the peripheral substituents on the halogen bonding.
Herein, we have studied the halogen bonding properties of
diverse range of di-, tetra- and octa-brominated arylene-imide/-
diimide-based systems (Schemes 1-2). We have explored the
Abstract: Halogen bonding interactions in electron deficient π-
scaffolds has largely been underexplored. Herein, we have studied
the halogen bonding properties of arylene-imide/-diimide-based
electron deficient scaffolds. We probed the influence of: scaffold size,
e.g.
from
small
phthalimide
(PTMI),
moderately-sized
pyromelliticdiimide (PMDI) or naphthalenediimides (NDIs) to large
perylenediimide (PDI); axial-group modifications; varied number of
halogens, etc. on the halogen bonding and its self-assembly in a set
of nine molecules. The structural modification leads to tunable optical
as well as redox property. The first reduction potential, E1 range
1/2
between -1.09 to -0.17 V (vs SCE). Two of the molecules, e.g. 6 and
9
embrace deep-lying LUMOs with values reaching -4.2 eV.
Gratifyingly, we realized single crystals of all the nine systems, which
revealed Br∙∙∙O, Br∙∙∙Br or Br∙∙∙π halogen bonding interactions, with
few systems capable of forming all the three-types. These interactions
lead to halogen bonded rings (up to 12-membered), which propagate
to form stacked 1D-, 2D- or corrugated sheets. We also identified few
outliers, e.g. molecule which prefer CH∙∙∙O hydrogen bonding over
halogen bonding; or a non-centrosymmetric organization over the
centrosymmetric ones. Computational studies based on Atoms in
Molecules (AIM) and Natural Bond Orbital (NBO) analysis provided
further insight into the halogen bonding interactions. This study can
lead to a predictive design tool-box to further explore related systems
on surfaces reinforced by these weak directional forces.
Introduction
Halogen bonding (XB) has gained widespread importance as a
non-covalent interaction as it manifests multitude of interesting
physico-chemical properties.[1] These interactions have been
widely exploited in the solid state for manipulating electronic,
magnetic, nonlinear optical properties, crystal-to-crystal
conversion, and recently for chiral information transfer.[2] Halogen
bonding can also modulate electron deficiency of the π-scaffolds
with electron mobility (e) reaching up to 8.6ꢀcm2ꢀV−1ꢀs−1.[3]
Whereas, in solution phase, effect of halogen bonding
interactions have been utilized in understanding cation or anion
binding interactions, anion transport, drug designing, etc.[4]
[a]
Dr. K. Mandal, Dr. J. Shukla, Dr. Y. Kumar, Mr. Rustam, and Dr. P.
Mukhopadhyay
Supramolecular and Material Chemistry Lab,
School of physical sciences, Jawaharlal Nehru University,
Delhi -110067, India.
E-mail: m_pritam@mail.jnu.ac.in
[b]
Dr. D. Bansal
Institute of Resource Ecology, Helmholtz-Zentrum Dresden-
Rossendorf, Bautzner Landstraße 400, 01328 Dresden – Germany.
Supporting information for this article is given via a link at the end of
the document.
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10.1002/chem.202001706
Chemistry - A European Journal
FULL PAPER
influence of:
a)
scaffold size
(phthalimide:
PTMI,
viable 1,3-Dibromo-5,5-dimethylhydantoin (DBH) as a source of
bromine with different starting materials to afford various di- and
tetra-bromo substituted precursors. These precursors were
further treated with the respective amines either in acetic acid or
DCM-PBr3 mixture to obtain different class of di-, terta- and octa-
bromo substituted imidized products such as PTMI, PMDI, NDI
and PDI (Scheme 2). Applying DBH as a brominating reagent all
the compounds were synthesized in good yields and
characterized using different analytical techniques such as FTIR,
UV-Vis, NMR and Mass spectroscopy (Figures S1-S16; ESI).
Interestingly, FTIR spectra also suggests the influence of
molecular modulation as well as potential intra- or inter-molecular
Br∙∙∙Oimide interactions on the C=O stretching frequency (c=o) of
the molecules (Figure S17; ESI). Notably, c=o stretches for the
brominated imides were observed in the range between 1563 cm-
1 to 1771 cm-1. To our observation, 1 exhibit single c=o stretch at
1688 cm-1 whereas its diimide counterpart 2, exhibit two c=o
stretches at higher energy of 1771 cm-1 and 1705 cm-1. This is in
accordance with the crystal structure which reveals the presence
of two unequal intra-molecular Br∙∙∙Oimide interaction in 2 (3.199 Å
and 3.238 Å) resulting in the appearance c=o stretches at two
different positions. Similarly, tetra bromo NDIs 7 and 8 also exhibit
two c=o stretches due to the presence of two different intra-
molecular Br∙∙∙Oimide interactions. On the other hand, considerable
influence of inter-molecular Br∙∙∙Oimide interaction is observed in
the structurally comparable dibromo NDIs 3-6. While taking 3 as
a reference where the inter-molecular Br∙∙∙Oimide is 3.256 Å and its
C=O group stretches at 1671 cm-1 and 1563 cm-1. The
intermolecular Br∙∙∙Oimide separation in 4 increased to 3.736 Å
resulting in the appearance of c=o stretches at 1705 cm-1 and
1647 cm-1. Similarly, comparison of inter-molecular Br∙∙∙Oimide
interaction in 3 with 5 (3.513 Å) also exhibits increase in C=O
stretching frequency to 1721 cm-1 and 1671 cm-1. Understandably,
increased inter molecular separation leads to dimmining of C=O
interaction with other molecule(s) thus having more of double
bond character and therefore higher stretching frequency.
However, 6 exhibit closer Br∙∙∙Oimide separation of 3.175 Å to 3
which corroborates with the comparable c=o stretching of 1688
cm-1 in 6. These observations suggest the potential influence of
intermolecular XB interaction on electronic properties of the
molecules.
pyromelliticdiimide: PMDI, naphthalenediimide: NDI and
perylenediimide: PDI), b) axial-group modifications (imide N-R: R
= H; n-Butyl; n-Hexyl; Mesityl), c) varying the number of halogens,
d) H atoms in combination with the halogen atoms, and e) imide
carbonyl oxygen atom versus sulfur atoms, on the halogen
bonding and its self-assembly. The molecules revealed presence
of two type of halogen bonding interactions: i) Br…Br and ii)
Br…Oimide. Computational studies were performed to identify the
electronic and energy density functions of the halogen bonding
interactions using AIM analysis and extent of the orbital overlaps
by NBO analysis and their interactions by Hirshfeld crystal surface
analysis.
Scheme 1. Top: General schematic representation of intermolecular halogen
bonding interaction (X = Br and Y = Br/O). Bottom: Variations engineered
through: -scaffold size, axial groups, imide (C=O/C=S) groups and variation of
no. of halogen atoms.
The absorption spectra of the compounds were recorded in
DCM to understand the influence of π-scaffold size, axial and core
modulation on the UV-vis profile (Figure 1). However, due to poor
solubility of 3 in DCM, its spectrum was analyzed in DMF. Notably,
all the compounds, except 6 and 9, exhibited predominant π-π*
absorption features within the range of 330-450 nm (Table 1).
Interestingly, while tetrabromo-phthalimide (1) exhibit sharp π-π*
responses at 330 nm and 340 nm, dibromo-PMDI (2) exhibits
similar absorption features red-shifted by ca. 20 nm. Moreover, in
dibromo-NDI (3) both these absorption features were further red-
shifted by ca. 10 and 40 nm, respectively. Such observations
suggest decrease in π-π* energy gap with increased electronic
delocalization.
Scheme 2. Molecular structures of 1- 9.
Results and Discussion
Halogenation and perhalogenation of electron deficient π-
scaffolds entail major synthetic drawbacks such as use of
hazardous and corrosive molecular bromine, high temperatures,
and low yields.[17-20] We have exploited effective synthetic
pathways by reacting commercially available and economically
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10.1002/chem.202001706
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Table 1. Absorption data in solution and solid-state 1-9.
Molecule
λ
max(sol) [nm]
ε
sol [M-1cm-1] (x104)
λ
max(solid) [nm]
1
2
3
4
5
6
7
8
9
331, 340
350, 365
361, 400
362, 405
362, 405
486, 513
398, 424
396, 425
470, 536
0.29, 0.30
0.46, 0.51
1.68, 0.35
1.31, 0.86
1.95, 0.12
0.84, 0.82
1.25, 1.21
0.81, 0.73
1.59, 1.97
332
365
365
347, 416
365, 410
485, 515
427
Figure 1. Absorption spectra of 1, 2, 4-9 (0.3 µM) in DCM, 3 (0.3 µM) in DMF.
427
Furthermore, the axial group(s) modification in the NDI display
weak electronic influence on its absorption profile. For example,
in 3, having only hydrogen at the axial position, displays band at
360 nm along with a shoulder at ca. 400 nm, while, these bands
were found at similar positions in 4 and 5 substituted with axial n-
hexyl chain and aromatic mesityl group, respectively (see table 1).
In contrast, replacement of the two diagonally opposite O atoms
of the carbonyl groups in 5 with sulphur atoms (6) induces
significant effect on the electronic transitions with absorption
bands at 486 and 513 nm, which is red-shifted by ca. 120 nm and
100 nm compared to corresponding bands in 5. Moreover,
tetrabromo-NDIs 7 and 8, being analogous counterparts of
dibromo-NDIs 4 and 5, displayed π-π* absorption peaks red
shifted by ca. 40 nm and 20 nm, respectively. Furthermore,
increased aromaticity as well as perbromination in octabromo-PDI
9 exhibits highly red-shifted absorption spectrum. Interestingly,
solid state absorption of all the compounds were recorded to
identify the presence of potential H-type or J-type stacking (Figure
2). Interestingly, in case of compounds 1, 3 and 4, the absorption
bands are blue-shifted by ca. 8 nm, 35 nm and 15 nm,
respectively. These blue shifted values indicate their potential to
form H-aggregates (Table 1). While, the compounds 5, 6, 8 and 9
showed red-shifted absorption in their solid-state, indicating J-
type stacking interactions. These observations are supported by
the solid-state packing of the molecules. For example, while
molecules 1, 3 and 4 were observed stacked parallel to each other
via π-π interaction, the others show more of a slipped or off-set
π-π stacking interactions.
477, 550
Electrochemical Studies
Next, we determined the redox properties of compounds 1-9 by
performing cyclic voltammetry studies (Figure 3, Tables 2). Most
of the compounds exhibited highly reversible redox response(s)
toward the negative potential of the voltammogram. Interestingly,
electrochemical studies could explicitly differentiate between the
structural modulations in terms of the nature of the π -scaffold,
axial- and core-substitution in these compounds. For examples,
while 1 exhibits single quasi-reversible redox response at E1/2 = -
1.09 V having peak to peak separation of 103 mV (∆Ep), its diimide
counterpart, 2, exhibits a reversible redox signal at E1/2= -0.68 V
(∆Ep = 72 mV) comparatively shifted by 410 mV towards positive
potential. Moreover, in case of the axial-modified NDIs 3-5, no
considerable electronic influence was observed. In case of 3,
napthalenediimide exhibits two redox waves at E1 = -0.47 (∆Ep=
1/2
105 mV) and E2 = -0.90 V (∆Ep= 140 mV). Whereas in 4, both
1/2
these redox waves were observed at E1 = -0.49 V (∆Ep= 66 mV)
1/2
and E2 = -0.95 V (∆Ep= 67 mV). Moreover, these redox
1/2
potentials were found to be at E1 = -0.44 V (∆Ep = 61 mV) and
1/2
E2 = -0.91 V (∆Ep= 72 mV) in case of 5. These values suggest
1/2
that redox potential remain negligibly shifted by ca. ± 0.02 V (E1
)
1/2
and ca. ±0.04 V (E21/2) on changing the axial groups. Interestingly,
such observations corroborate our findings in absorption studies
toward the negligible influence of axial modification on the
electronic properties of these compounds, as expected for lack of
electronic communication between the pendant axial groups and
the π-scaffold. However, in case of 6, considerable shift towards
less negative potentials at E1 = -0.20 V (∆Ep= 79 mV) and E2
1/2
1/2
= -0.56 V (∆Ep= 79 mV) was observed. Moreover, in case of tetra-
bromoNDIs 7 and 8, both exhibits two reversible redox responses
at E1 = - 0.38 V (∆Ep= 59 mV) and E2 = - 0.73 V (∆Ep= 74 mV)
1/2
1/2
in 7 and E1 = - 0.32 V (∆Ep= 57 mV) and E2 = -0.71 V (∆Ep=
1/2
1/2
65 mV) in 8. Gratifyingly, as compared to their dibromo
counterpart 4 and 5, the E1 and E2 potential values were
1/2
1/2
cathodically shifted by ca. 115 mV and ca. 190 mV, respectively.
Apart from that, modulation effect was also investigated on
Figure 2. Solid state absorption spectra of 1-9.
the wave separation (ΔE) between both the redox signals (E1
1/2
and E21/2). For example, in dibromo NDIs 3, 4 and 5, ΔE values
were observed to be 490 mV, 460 mV and 470 mV, respectively.
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O1΄
O2
4΄
3΄
N1
O2
5
O1
1
1
8
Br1
Br1΄
2
2΄
1΄
2
7
5
3
Br4
Br1
4
5΄
6
3
O2΄
N1
4
O1
Br3
Br2
2
1
Figure 3. Cyclic voltammogram of 1, 2, 4–9 in DCM and 3 in DMF 0.1 M
Bu4NPF6, potential is referenced against standard calomel electrode (SCE).[31]
Whereas, this separation is reduced to 360 mV for sulphur
substituted NDI (6). On the other hand, traversing from dibromo
NDIs 4 and 5 to their respective tetrabromo counterparts 7 and 8
respectively, exhibit comparatively compressed E1 and E2
O1
O2΄
2΄
N1΄
O1
N1΄
7΄ 6
1΄
O2΄
N1΄
7΄
1΄
6
4
O1΄
Br1΄
O2
7΄ 6
1΄ 4
4
Br1
1/2
1/2
2΄
5 3
Br1
3
2
5
5
3
2΄
separation of 350 mV (7) and 380 mV (8). These results further
established the large electronic impact on modification in the NDI-
core. Furthermore, the octabrominated perylenediimide (9)[3b]
showed further shifts in redox potentials towards the positive side
Br1΄
5΄
2
3΄ 5΄
4΄
Br1
1
7
5΄
1
Br1΄
1
3΄
2
4΄
6΄
3΄
4΄
7
O1΄
O2
6΄
7
O2
6΄
O1΄
N1
O1
O2΄
N1
of voltammogram with E1 at -0.17 V (∆Ep= 97 mV) and E21/2 at -
N1
1/2
0.34 V (∆Ep= 105 mV). These results suggest that increase in the
number of π-rings as well as the core-substitution of bromine
atom(s) affords more electron deficient scaffolds, which in turn
facilitates the electron accepting properties of the imides.
3
5
4
Table 2. Cyclic voltammetry studies of 1 – 9.
Molecule
E11/2 (V)
E21/2 (V)
ΔE
LUMO (eV)a
1
2
3
4
5
6
7
8
9
-1.09
-0.68
-0.47
-0.49
-0.44
-0.20
-0.38
-0.32
-0.17
---
---
-3.304
-3.491
-3.989
-3.874
-4.018
-4.197
-3.962
-4.076
-4.229
O1΄
O2
S1
N1΄
N1΄
O1΄
O1΄ N1΄
O2
4΄
3΄
5΄
1΄
---
---
7΄ 6
1΄
7΄ 6
1΄
4
Br1΄
2΄
4
Br2
Br1
-0.90
-0.95
-0.91
-0.56
-0.73
-0.71
-0.34
0.49
0.46
0.47
0.36
0.35
0.38
0.17
Br1΄
Br2΄
Br2
Br1
Br1΄
Br2΄
3
2
2΄
5
7
6΄
6
7
3
5
2΄
5΄
4΄
6΄
2
1
2
1
5΄
4΄
6΄
Br1
1
3΄
3
4
3΄
S1
7
O1
O2΄
5
7
O2΄
O1
N1
N1
N1
O1
Condition: 1, 2, 4–9 in DCM and 3 in DMF 0.1 M Bu4NPF6; aCalculated for
reduction potential: -(4.4+E1red).
7
8
6
Figure 4. Single crystal X-ray structures of molecules 1-8. Thermal ellipsoids
are drawn at 50% probability level.
Single crystal X-ray Crystallography Studies
Gratifyingly, we could obtain good quality single crystals of all the
compounds and investigate their propensity to form halogen
bonding interactions by X-ray diffraction studies. Figure 4 shows
the molecular structures of compounds 1-8.[21,32]
Interestingly, all the compounds showed multiple Br∙∙∙Br and/or
Br∙∙∙Oimide halogen bonding interactions (Table S1). Modulation in
the size of the imide rings (five Vs six) and the π-scaffold reflected
considerable influence on the intramolecular Br∙∙∙Oimide separation.
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Further, all the compounds exhibit extensive intermolecular
halogen bonding interactions resulting in the formation of self-
assembled structures (Figures S18-S25; ESI). Moreover,
depending upon the angle formed between the two CX∙∙∙YC (X
= Br and Y = Br/O) synthons (Figure 6), these interactions are
classified as type I (symmetrical interactions where θ1 ≈ θ2) and
type II (bent interactions where θ1 ≈ 180° and θ2 ≈ 90°).[23,24]
In case of 1, two molecules in one-dimension (1D) layer
(shown in same colour) interacts via intermolecular Br∙∙∙Oimide
separation of 3.052 Å (Br1'∙∙∙O1) and Br∙∙∙Br separation of 3.696
Å (Br1∙∙∙Br1') and 3.686 Å (Br1∙∙∙Br2') (Figure 7a). In Br∙∙∙O
interaction, C3—Br1∙∙∙O1 (θ1) and C1—O1∙∙∙Br (θ2) were
found to be ~ 177⁰ and 158⁰ respectively, suggesting type I
interaction (Figure 6). Whereas, for the Br∙∙∙Br interaction, a non-
ideal type II like interaction was observed with the θ1 (C3—
Br1∙∙∙Br2) and θ2 (C4—Br2∙∙∙Br1) of ~ 177 ⁰ and ~ 122 ⁰,
respectively. As a reference, the sum of the van der Waals radii
of two Br atoms has been found to be 3.74 Å.[22]
Figure 5. A side view of the single crystal X-ray structure of molecule 9.
Thermal ellipsoids are drawn at 50% probability level.
Notably, crystal structure of 1 displays intramolecular Br∙∙∙O
separation of avg. 3.175 Å (Br1∙∙∙O1 = 3.173 Å and Br4∙∙∙O2 =
3.178 Å) which increases to 3.199 Å (Br1׳∙∙∙O1) and 3.238 Å
(Br1∙∙∙O2) in 2. However, in the NDI-based compounds 3-8 a
considerable decrease in the intramolecular Br∙∙∙O separation in
the range 2.861–2.937 Å was observed. Tetrabromination at the
core in 7 and 8 influence the intramolecular Br∙∙∙O separation as
well as the planarity of the NDI scaffold. For example, 7 shows
Br∙∙∙O separations of 2.861 Å (Br2∙∙∙O2) and 3.025 (Br1∙∙∙O1) Å,
while 8 exhibits Br∙∙∙O separation of 2.919 Å (Br2∙∙∙O2) and 2.937
Å (Br1∙∙∙O1). Likewise, Br∙∙∙O interactions in 9 was found to be
2.831 and 2.870 Å (Figure 5). It is important to note that the
intramolecular Br∙∙∙O interactions revealed in 1-9 are considerably
shorter than the sum of the van der Waals radii of Br and O atoms
(3.45 Å).[22] Structural analysis of 7 and 8 reveals highly twisted
NDI scaffolds with torsional angle (θ) of 16.65° (O1-C5-C1-C7)
and 7.23° (O2-C4-C3-C6) in 7 and 23.44° (O2-C6-C4-C3) and
19.90° (O1-C7-C1-C2) in 8. The increased torsion angle in 8 is
possibly influenced by the bulky mesityl rings. Notably, such
twisted non-planar arrangement of the aromatic core was also
observed in case of octa-brominated PDI 9.[3b]
X……….Y
C
C
X
θ1
θ2
θ2
θ1
C
Y
C
Type II
Type I
Figure 6. Type I and type II interactions in halogen bonded systems.
Moreover, the 1D arrangement in 2 involves type I intermolecular
Br∙∙∙Br and Br∙∙∙O interactions having separation of 3.707 Å
(C2'—Br1'∙∙∙Br1—C2; θ1 = θ2 = 121.49⁰) and 2.981 Å (C2'—
Br1'∙∙∙O2—C5; θ1 = ~177⁰, θ2 = ~158⁰), respectively (Figure 7b).
Interestingly, type I interactions in 3 displays 1D arrangement
having Br∙∙∙Br (3.707 Å) separation identical to 2, but the Br∙∙∙O
separation increased to 3.256 Å (C2'—Br1'∙∙∙O2—C7) due to the
possible increase in size of the π-scaffold (Figure 7c). In contrast,
presence of alkyl and bulky mesityl groups in the axial positions
of 4 and 5 respectively, shows layered structure involving only
weak Br∙∙∙O and no Br∙∙∙Br intermolecular interaction with the
separation of 3.736 Å in 4 and 3.513 Å in 5 (Figures 7d-e).
Importantly, both 4 and 5, demonstrate type II interaction with θ1
(C2—Br1∙∙∙O2) = ~86⁰ and θ2 (C6—O2∙∙∙Br1) = ~141⁰ in 4 and
θ1 (C3—Br1∙∙∙O2) = ~87⁰ and θ2 (C7—O2∙∙∙Br1) = ~137⁰ in 5.
Interestingly, 5 shows Br∙∙∙π interactions with distances ranging
between 3.190-3.389 Å. However, 6 demonstrates Br∙∙∙Br and
Br∙∙∙O intermolecular interaction of type I separated by 3.602 Å
and 3.175 Å respectively, resulting in the generation of 1D layer
(Figure 8a). Moreover, structural complexity in 7 gets reflected in
its intermolecular interaction where one molecule is connected to
symmetrically arranged four adjacent neighbors in a zig-zag
manner via four Br∙∙∙O (Br2'∙∙∙O1A: 3.081Å) and eight Br∙∙∙Br
(Br1∙∙∙Br2': 3.633 Å and Br2∙∙∙Br1': 3.433 Å) interactions (Figure
8b). Interestingly, while Br∙∙∙O interaction followed type I mode of
interaction, Br∙∙∙Br shows type II interaction.
Table 3. Halogen bonding interactions and torsion angle in 1 - 9.
Intramolecular separation
Intermolecular separation
Mo
lec
ule
Torsion
anglea
Br∙∙∙Oimide
Br∙∙∙Br
Br∙∙∙Oimide
Br∙∙∙Br
3.695(9)
3.686(1)
3.670
3.316(1)
3.275(1)
3.306(1)
3.173(5),
3.178(4)
3.051(6)
1
2.68
3.713
3.199(2)
3.238(2)
2
3
4
5
2.981(2)
3.244(3)
---------
3.707(4)
3.705(8)
---------
4.45
0.32
5.76
2.28
0.14
--------
--------
--------
--------
2.888(4)
2.912(2)
2.935(2)
2.907(2)
3.513(2)
---------
6
7
8
3.175(2)
3.081(8)
3.101(5),
3.602(3)
--------
3.025(1)
2.861(1)
2.937(6),
2.919(5)
3.433(1),
3.633(1)
12.90,
3.25
5.69,
2.11
3.197(1)
3.174(1)
----------
3.210
3.238
3.357
2.831
2.870
3.255(4)
2.794(3)
9
----------
------
a(O—C1—C2—C3—Br), (Br—C2—C4—Br)
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the Br atoms at the bay positions participate in halogen bonding
Br∙∙∙O type I interactions with θ1 and θ2 being ~163⁰ and ~174⁰
(Figure 8d).
Consequently, the question is how does these halogen
bonding interactions influence or drive the hierarchical self-
assembly? Considering the self-assembly of 1, the Br∙∙∙Br
interactions form 5-, 9- and 12-membered large-sized rings to
propagate the two distinct 1D layers, as highlighted with different
color codes (Figure 7a, Table S2). The 5-membered rings are
shaped via three Br atoms with distances of 3.686 and 3.696 Å,
amongst which one of the Br atoms forms a bifurcated, or a three-
center halogen bonding interaction. Interestingly, the 12-
membered rings which are formed through the participation of six
Br atoms have two 9-membered rings inscribed in it. The 9-
membered rings are formed through halogen bonding interactions
between five Br atoms. In contrast, a smaller 6-membered ring is
formed by the participation of one O atom and two Br atoms, with
Br1’ forming a bifurcated halogen bonding interaction. As a result,
two distinct 1D layers are formed, which are connected via Br∙∙∙Br
(Br2∙∙∙Br2': 3.713 Å and 3.670 Å) interactions resulting in the
formation of 1D sheets (Figure S18a; ESI). Interestingly, these 1D
sheets form infinite π-stacks via interlayer H-bonding between
alkyl hydrogen (H10) and Oimide (O1) atoms (Figure S18b; ESI). In
case of 2, a large 10-membered ring is formed via the formation
of two short Br∙∙∙O (2.981 Å) interactions. This large ring has two
6-membered rings inscribed in it that is linked via a Br∙∙∙Br
interaction (3.707 Å). These halogen bonded rings continue to
form infinite 1D layers, which are connected via interlayer H-
bonds between hydrogen atoms (H9a and H9b) of the axial alkyl
chains and Oimide (O1) of another layer (Figure S19; ESI). Likewise,
3 forms similar supramolecular halogen bonded rings, which
replicate to form infinite 1D layers. Further, these layers form π-π
stacking interactions to afford 2D sheets (Figures S20; ESI). In
contrast, 4 forms a 1D layer aided by 10-membered rings carved
out of two complementary CH∙∙∙O H-bonding interactions, while
extremely weak Br∙∙∙O interactions were observed. These 1D
layers further π-stack via the naphthyl rings to afford 2D sheets
(Figure S21; ESI). Such preference of H-bonding has been seen
in pyridine-N-oxide versus halogen bonding in pyridine-based
scaffolds substituted with halogen atoms.[25] In case of 5, the 1D
layer is formed by a combination of CH∙∙∙O H-bonded 10-
membered rings, weak 5-membered Br∙∙∙O rings and multiple
Br∙∙∙π halogen bonding interactions. Thus, the bulky axial mesityl
groups in 5 entails complexity in the infinite supramolecular
organization (Figure S22; ESI). In 6, the halogen bonded rings are
formed in a similar fashion to that of 3, while surprisingly the
mesityl rings do not induce any Br∙∙∙π interactions. Moreover, H-
bonding interactions involving hydrogen atom (H10) of the axial
mesityl group with the Oimide (O1) of another layer assist formation
of 2D sheets (Figures S23c; ESI). In the case of 7, multiple Br∙∙∙O,
Br∙∙∙Br and Br∙∙∙π interactions result in the propagation of the
supramolecular assembly. In particular, highly unusual trifurcate
type of halogen bonding interactions, in which a Br atom forms
two Br∙∙∙Br and one Br∙∙∙O type of interaction, while the adjacent
Br atom can form another trifurcate type of halogen bonding
Figure 7. Representation of Br∙∙∙O, Br∙∙∙Br and Br∙∙∙π halogen bonding
interactions in molecules 1-5 and their self-assembly. Color code: H, White; C,
Gray; N, Blue; O, red and Br, orange.
While 8 having bulky mesityl groups in the axial positions, interact
symmetrically with four neighboring molecules only through Br∙∙∙O
(Br1∙∙∙O2': 3.101 Å) forming type I interactions with no observable
Br∙∙∙Br interactions akin to that of 5 (Figure 8c). Finally, in 9 only
interactions with two Br∙∙∙Br and one
Br∙∙∙π interactions.
Interestingly, the NDI ring participates to form the Br∙∙∙π
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interaction. The supramolecular packing of 7 shows the presence
of 2D arrangement comprising
of vertically propagating two different layers (shown in green and
blue colour) (Figure S24b; ESI). In sharp contrast, 8 forms a
supramolecular assembly in which the essential halogen bonding
interactions are very different to that of its congener 7. Molecule
8 assembles involvement of four Br∙∙∙O interactions and an equal
number of Br∙∙∙π interactions in a radial manner. This results in a
2D sheet type of an arrangement (Figure S25a; ESI). Interestingly,
the well-aligned 2D sheets are placed over one another via π-
stacking of xylene solvent molecules (with distance of ca. 3.473
Å and 3.541 Å) (Figures S25b and c; ESI). Noteworthy here is,
that the asymmetric supramolecular packing in 8 produces a non-
centrosymmetric Fdd2 space group, while all the other molecules
considered here crystallizes in a centrosymmetric manner (Table
S5-6). Notably, 9 having the largest π-surface amongst all the
considered molecules, shows multiple Br∙∙∙O and Br∙∙∙π halogen
bonding interactions. The Br atoms at the non-bay positions (Br1,
Br4) form Br∙∙∙π halogen bonding interactions with the PDI rings
of the neighboring molecules with Br1∙∙∙C12 and Br4∙∙∙C3
distances being 3.516 and 3.347 Å, respectively. The Br atoms at
the bay positions (Br2, Br3) form Br∙∙∙O halogen bonding
interactions with Br2∙∙∙O2 and Br3∙∙∙O1 distances being 2.794 and
3.255 Å, respectively. The increased number of Br∙∙∙π halogen
bonding interactions is possibly due to the ring contortion brought
about by the perbromination as also observed in the case of 7.
The contortion drives large overlapping of the π-surfaces and the
consequent 2D corrugated sheet-like self-assembly. The Br∙∙∙π
interactions observed in case of 5, 7, 8 and 9 can be termed as
multi-center halogen bonding as the Br atom forms multiple sub
van der Waals interactions (3.64 Å).
Hirshfeld surface analysis
Hirshfeld crystal surface analysis and fingerprint plots facilitates a
comparison of the inter and intra-molecular non-covalent
interactions such as Br···O, Br···Br, π···π, O···H interactions
within the molecules.[26,27] In order to gain insight into these
interactions, Hirshfeld analysis for all the synthesised molecules
were performed (Figure S26-S35). As shown in table 4, molecule
1 exhibit highest value for intermolecular Br···Br interaction of
26.4% whereas 7 displays maximum Br···O interaction of 10.0%.
Importantly, surface analysis clearly showed absence of Br···Br
interactions in 4 and 5, while sparser Br···O interaction. In general,
traversing from 1-9, the Br···O interaction is significantly more
common (except that for 1) than Br···Br interaction. Hirshfeld
analysis also captured significant amount of Br···C interactions in
the crystal structure, out of which, significant proportion arise from
well-defined Br···π interactions.
Topological Analysis
Next, we performed computational topological analysis for all the
halogen bonded systems.[28,29] Topological calculation of the
electron density supports the presence of potential halogen bonds
in all the compounds. Importantly, the bond critical points (BCP)
were observed existing in a bond path of two interacting atoms
(e.g. Br ···O and Br···Br). Table 4 and S3 describe the calculated
local properties at Br···O and Br···Br BCPs in all the halogenated
Figure 8. Representation of Br∙∙∙O, Br∙∙∙Br and Br∙∙∙π halogen bonding
interactions in molecules 6-9 and their self-assembly. In case of 9, the central
PDI molecule is colored Pink to aid in deciphering the interactions. Color code:
H, White; C, Gray; N, Blue; O, red and Br, orange.
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systems. Primarily, these properties at the BCPs are analysed
based on the different parameters: the electron density ρ(rc) and
Laplacian ∇2ρ(rc), the densities of kinetic energy, G(rc), potential
energy, V(rc), total energy, H(rc) = V(rc) + G(rc), and the
|V(rc)|/G(rc) ratio. Notably, the Laplacian of the electron density is
related to the measure of the local curvature of ρ(rc), and
illustrates whether the electron density is locally depleted (∇2(rc)
> 0) or concentrated (∇2(rc) < 0) at any given point in the space.
Furthermore, the Laplacian is related to the local potential (V(rc))
and kinetic (G(rc)) energy components of the total energy via virial
theorem (1/4)∇2ρ(rc) = 2G(rc) + V(rc) (in a.u.). Thus, when the
∇2ρ(rc) is negative, the electronic charge is concentrated and thus
potential energy largely dominates the local total electronic
energy E(rc) as well as the local virial relationship. Moreover,
when the ∇2ρ(rc) is positive, the electronic charge is locally
depleted and the kinetic energy is in local excess. According to
Bader and Essen, the former condition occurs in shared
interactions, while the later situation is the characteristic of closed-
shell interactions.[28]
AIM studies were performed by considering all the
molecules in their dimeric form. The parameters obtained from the
calculation are shown in table 4 and figures 9, S36 and S37. For
intermolecular interaction, the values of ρ(rc) are calculated to be
in a range of 0.0038-0.0217 au, whereas the values of ∇2ρ(rc) are
all positive, ranging from 0.0134 to 0.0758 au. These values are
within the common accepted values for H-bonding interactions [28]
and indicate closed-shell interactions in these molecules. In order
to gain insight of non-covalent interaction, it is more appropriate
to understand in terms of electron energy density E(rc). The sign
of E(rc) at BCP indicates whether the interaction is electrostatic
(E(rc) > 0) or covalent dominant (E(rc) < 0). From table S3, it is
evident that for all the dimeric system in molecules 1 to 9, the E(rc)
values are all greater than zero, which suggests that the halogen
bonding interaction in these molecules are potentially electrostatic
in nature. Notably, the intermolecular Br···O interaction (cp1) of
molecule 4 (0.0007) and 9 (0.0023) exhibit minimum and
maximum E(rc) values, respectively. Moreover, molecules 1
(0.0092), 2 (0.0107), 7 (0.0108) and 9 (0.0161) with axial alkyl
chain, displays considerably increased electron density (ρ(rc)) in
the intermolecular Br···O interaction as compared to other
molecules. These observations were also noted in the laplacian
electron density ∇2(rc) for the intermolecular Br···O interaction at
the same BCP with molecule 9 exhibiting highest ∇2(rc) value of
0.0677 a.u. This value suggests strongest halogen bonding
interaction which is also demonstrated by the shortest
intermolecular Br···O distance of 2.831 Å in 9. In addition, the ρ(rc)
values of the Br···O interaction can be seen to be dependent on
the electron deficiency of the molecule. For example, 6 which is
the second-most electron deficient molecule in the series (from
CV studies), shows a ρ(rc) value of 0.0073 compared to 0.0038
and 0.0056 for 4, and 5, respectively. On the other hand, AIM
results predict the absence of Br···Br intermolecular interaction in
4, 5 and 8 which is in further support of our crystallographic
findings. Interestingly, in 7, significantly high Br···Br interactions
with electron density 0.0048, 0.0080 and 0.0099 a.u. at cp2, cp3
and cp4 respectively, were observed. Figure 9, S36 and S37
displays molecular critical points and contour maps of all the nine
molecules. Thus, topological analysis at the BCPs validates
intermolecular Br···Oimide as well as Br···Br interactions in these
systems.
Natural Bond Orbital analysis
NBO analyses provide an efficient tool in understanding intra and
intermolecular bonding and interaction among bonds, as well as
provides a convenient ground for investigating conjugative
interactions or charge transfer in molecular systems.[30] Moreover,
NBO method provides advantage in getting information about
interactions in both filled and virtual orbital spaces that could
influence the intra and intermolecular interactions analysis.
Herein, we have identified two representative molecules 1 and 3
based on their small size and structural diversity to perform NBO
analysis. The second order Fock matrix aids to evaluate the
donor-acceptor orbital interactions.[30,31]
Table 4: Intra and Intermolecular cp (critical point) values, Potential energy difference, Second order perturbation energy, Hirshfeld interactions.
Total E2
kcal/mol
ρ(rc)a
Hirshfeld surface (%)
b
ΔEb
Entry
kcal/mol
cp1
cp2
cp3
cp4
cp5
Br···O
Br···Br
Br···O
Br···Br
Br···C
1
2
3
4
5
6
7
8
9
0.0092
0.0107
0.0059
0.0038
0.0056
0.0073
0.0108
0.0089
0.0161
0.0113
0.0067
0.0064
0.0085
0.0092
0.0081
0.0048
0.0183
0.0063
0.0112
0.0101
0.0189
0.0038
0.0092
0.0073
0.0080
0.0177
0.0217
0.0069
0.0107
---
0.0058
---
0.80
1.90
1.71
1.13
---
1.61
1.57
4.7
7.2
5.1
0.0
0.8
3.4
10.0
5.3
8.6
26.4
1.5
2.5
---
19.4
13.9
0.0
----
---
1.29
0.50
0.0183
0.0056
0.0185
0.0099
0.0195
0.0080
---
----
----
----
----
----
----
5.2
0.0176
0.0185
0.0147
---
---
4.2
---
1.0
6.4
0.8
6.2
---
---
14.9
4.9
---
---
---
17.5
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Figure 9. Molecular critical point and contour line diagrams for the dimeric form of 1-4 molecules.
The E2 value represents the extent of interaction between electron
donors and acceptors. As shown in figure 10, two adjacent
molecules of 1 exhibits interaction of non-bonding orbital of imide
O lone-pair to antibonding Br-C orbital (nOlp→σ*Br-C) and the non-
bonding Br lone-pair to antibonding Br-C orbital (nBrlp→σ*Br-C) with
second order perturbation energy, E2 of around ca. 1.61 kcal/mol
and 1.57 kcal/mol, respectively. The 3D (Figure 10 a,c) and 2D
(Figure 10 b,d) representations clearly showed non-bonding and
antibonding orbital overlaps.
Figure 11. NBO 2D and 3D representation of intermolecular donor–acceptor
O∙∙∙Br and Br∙∙∙Br interactions in 3. (a, b) Overlap between n and σ* orbitals in
O∙∙∙Br. (c and d) Insufficient overlapping between n and σ* orbitals in Br∙∙∙Br.
Whereas, the dimeric form of 3, exhibits nOlp→σ*Br-C interaction
within the ten-membered cyclic ring with E2 of 1.29 kcal/mol
(Figure 11 a-b) and nBrlp→σ*Br-C interaction with greatly reduced
E2 value of 0.50 kcal/mol (Figure 11 c-d). The calculations
revealed greater stabilization from the Br···O interactions vis-à-
vis the Br···Br interactions. The NBO calculations also clearly
established the donor-acceptor type of interactions between the
non-bonding lone-pair orbitals of O/Br and the antibonding
orbitals of Br-C.
Figure 10. NBO 2D and 3D representation of intermolecular donor–acceptor
O∙∙∙Br and Br∙∙∙Br interactions in 1. (a, b) Overlap between n and σ* orbitals in
O∙∙∙Br. (c and d) overlapping between n and σ* orbitals in Br∙∙∙Br.
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A Predictive Design Tool-Box?
non-centrosymmetric packing (vide, example 8). In the next level,
predictive computational tools aid in determining and validating
the (r)/E(2) parameters of the halogen bonding interactions. A
systematic logical understanding can thus assist to establish a
predictive structural tool-box in these systems.
With the information in hand, is it possible to arrive at a general
tool-box that can aid or help to forecast the various probable
halogen bonding interactions in the solid-state for arylene-imide/-
diimide-based systems? Towards this, we consider here a simple
flow-chart that starts with the various available input variables in
the molecular structure (Figure 12).
Conclusions
In summary, we explored the halogen bonding properties of di-,
tetra- and octa-brominated arylene-imide/-diimide-based electron
deficient π-scaffolds of varying sizes, e.g. from the small PTMI, to
the moderately-sized PMDI and NDIs, to the large PDI. In a set of
nine molecules, we also varied the axial-groups, number of
halogens, and imide carbonyl O versus S atoms to examine how
these diverse modifications influence the halogen bonding and its
self-assembly. The molecules showed tunable optical and redox
properties and also demonstrated deep-lying LUMOs with values
reaching -4.2 eV. Importantly, we realized single crystals of all the
nine systems and X-ray diffraction studies revealed three-types of
halogen bonding interactions viz. Br∙∙∙O, Br∙∙∙Br or Br∙∙∙π. Notably,
few of the systems could exhibit a combination of all the three-
type of interactions. In general, the Br∙∙∙O interactions outnumber
the Br∙∙∙Br interactions. The Br∙∙∙π interactions evolve as a result
of the mesityl groups at the axial positions, or as a result of the
contortion in the arylenediimide rings. Interestingly, we observed
5-, 6-, 9-, 10- and 12-membered diverse halogen bonded rings.
The mono-, bifurcated- or multi-center halogen bonds further
propagate to form stacked 1D-, 2D- or corrugated sheets. The
study also recognized few outliers, e.g. molecule which prefer
CH∙∙∙O hydrogen bonding over halogen bonding interactions; or
a
non-centrosymmetric organization over the majority of
centrosymmetric ones. Such non-centrosymmetric arrangement
would be of great interest from the point of view of designing new
class of supramolecular NLO systems.[32] Atoms in Molecules
(AIM) and Natural Bond Orbital (NBO) analysis provided insight
into the halogen bonding interactions. The ρ(rc) values also
reflected the effect of the electron deficiency of the molecule on
the halogen bonding interactions. The findings outlined here, can
be considered as a predictive design tool-box for higher-order
arylenediimides and for other related halogen bonded electron
deficient π-systems.
Figure 12. A flow-chart for halogen bonding (XB) in arylene-imides and -
diimides to accomplish a predictive structural design tool-box.
Experimental Section
The system can then form halogen bonding of different types
including complex possibility of a combinational halogen bonding
that utilizes all the three types e.g., Br···O, Br···Br and Br∙∙∙π
interactions. The interactions can then form hierarchical assembly
depending on the halogen bonded ring-size, no. of different
halogen bonded rings, a simple two-center versus three-center
(bifurcated) or multi-center interactions. These interactions can
lead to the self-assembled D/2D sheets or non-planar corrugated
sheets. At this point, we can consider the possible outlier(s),
which provide orthogonal insight into the halogen bonding
interactions. For example, a molecular system (vide, example 4)
that prefers to form CH∙∙∙O H-bonding interaction over halogen
bonding interaction. There can be other outliers that result from
asymmetric hierarchical assembly of the molecules to result in
General: All starting materials and reagents were purchased from
commercial sources and used without further purification, unless otherwise
stated. NMR spectra were recorded on a Bruker 500 MHz spectrometer.
1H, 13C, DEPT-135 and APT NMR spectra were recorded using TMS as
an internal standard. Spectra were referenced to residual solvent peaks.
Chemical shifts (δ) were expressed in ppm. Coupling patterns were
designated as s, singlet; d, doublet; t, triplet; m, multiplet. TOF-MS-ES
mass spectral data were obtained using a Synapt G2 HDMS mass
spectrometer.
UV-Vis-NIR
spectra
were
recorded
on
a JASCO V-670 Spectrophotometer; path lengths of 10 mm were used.
Wavelengths reported in nanometers (nm). UV-Grade solvents were used
for the spectroscopic experiments. FTIR spectra were recorded on a
Varian 7000 FTIR spectrometer. Samples were prepared in a dry condition.
A background scan of air was collected prior to analysis while FTIR in neat
were taken using Bruker Tensor 37 FTIR Spectrometer.
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Electrochemical measurements: Cyclic voltammetry (CV) and
Differential Pulse Voltammetry (DPV) were carried out using a computer
controlled potentiostat (CHI 650C) and a standard three electrode
arrangement consisted of platinum as a working and auxiliary electrodes
and SCE as reference electrode. All the electrochemical measurements
were carried out in Ar-purged solvents containing nBu4NPF6 (0.1 M) as the
supporting electrolyte. The scan rate for CV experiments was typically 200-
300 mV/s. DPV was carried out keeping peak amplitude 50 mV, peak width
0.01 sec, pulse period 0.05 sec and increment E at 20 mV.[33]
163.50, 136.18, 114.07, 38.86, 30.25, 20.06, 13.58. FTIR (neat, cm-1):
2919, 2853, 1771, 1705, 1439, 1364, 1181. ESI-MS: calculated exact
mass for [C18H20Br2N2O4 + 2H+], 485.9779, found 485.8675.
Synthesis of 3: A mixture of Br2NTCDA (1.00 gm, 2.34 mmol) and
ammonium acetate (2.80 g, 37.52 mmol) in acetic acid (25.0 ml) was
stirred at 80 °C for 6 h. The reaction mixture was cooled to room
temperature to afford yellow precipitates. These precipitates were filtered
and washed with methanol (three times) followed by acetone (one time)
and was air dried under vacuum to obtain yellow product. Yield: 397 mg
(40 %). M.P.>300 ˚C,1H NMR (500 MHz, DMSO-d6, TMS): δ (ppm) = 12.28
(d, 2H, ArH-axial), 8.63 (d, 2H, ArH). FTIR (neat, cm-1): 3202, 3078, 2869,
1671, 1563, 1414, 1247. ESI-MS: calculated exact mass for
[C14H4Br2N2O4 + 2H+], 423.8683, found 423.5392.
X-ray Crystallography: The intensity data were obtained with Bruker
APEX-II CMOS diffractometer for 1-8 by using graphite-monochromated
Mo-Kα radiation (λ = 0.71073 Å). Intensity data were corrected for Lorentz
polarization effects and an empirical absorption correction (SADABS) was
applied. The structures were solved by direct methods and refined by full-
matrix least-squares refinement techniques on F2 by using the programs
SHELXL-2016 in the WinGX module.[34] All hydrogen atoms were fixed at
calculated positions with isotropic thermal parameters, whereas all non-
hydrogen atoms were refined anisotropically. In 7, four carbon atoms (C8,
C9, C10, C11) of butyl alkyl chain and two imidic oxygen atoms O1 and
O2 were found disordered and were fixed at two positions using part
command. In addition, one nitrogen (N1) and a carbon atom (C5) were
refined isotropically. Moreover, in 3, 6 and 7, some disordered electron
density was observed which could not be resolved. In case of 3 and 6,
disordered electron density was removed using solvent masking
procedure ‘SQUEZE’ in PLATON showing the electron recovery of 72 in 3
and 46 in 6. These electron counts closely corresponds to one
dimethylacetamide and dichloromethane solvent molecule in 3 and 6,
respectively. Whereas in case of 7, squeezing the electron density lead to
unstable structural refinement, and therefore are not squeezed due to
which the CHECK CIF displays B-level alert of residual electron density.
However, in case squeezed, the squeeze command leads to the recovery
of electron count of 89 corresponding to a toluene molecule. All the
crystallographic details and refinement parameters are provided in tables
S4 and S5; ESI. CCDC 1869948-1869955 contains supporting
crystallographic data for this paper.
Synthesis 4: A reaction procedure similar to 3 was performed in acetic
acid with the following reagents; Br2NTCDA (1.00 gm, 2.34 mmol) and
hexylamine (1.22 ml, 9.36 mmol). Reaction mixture was stirred for 90 min
followed by regular workup with methanol and acetone to afford yellow
colour product. Yield: 485 mg (35 %), Rf = 0.72 (CHCl3/Hexane 7:3),
M.P.>300 ˚C, 1H NMR (500 MHz, CDCl3, 298 K): δ = 9.02 (s, 2H, Ar-H),
4.22 (d, 4H, Ar-H), 1.763-1.049 (16H), 0.93 (2xCH3). 13C NMR (125 MHz,
CDCl3, 300 K): δ = 160.77, 160.73, 139.07, 128.33, 127.75, 125.38, 124.12,
41.62, 31.46, 29.70, 27.86, 26.74, 22.54, 14.01. FTIR (neat, cm-1): 3052,
2919, 2845, 1705, 1647, 1555, 1430, 1372. ESI-MS: calculated exact
mass for [C26H30Br2N2O4 + 2H+], 592.0561, found 592.7904.
Synthesis of 5: Reaction procedure similar to 4 was utilized for the using
following reagents: Br2NTCDA (1.00 gm, 2.34 mmol) and mesitylamine
(1.32 ml, 9.36 mmol). Yield: 710 g (46 %), Rf = 0.52 (CHCl3), M.P.>300 ˚C,
1H NMR (500 MHz, CDCl3, 298 K): δ = 9.04 (s, 2H, Ar-H), 7.01 (s, 4H,
MesBz-H), 2.31(s, 6H, Mes-pCH3), 2.03(d, 12H, Mes-CH3). 13C NMR (125
MHz, CDCl3, 300 K): 161.20, 160.57, 160.26, 160.22, 139.58, 139.37,
139.17, 138.99, 134.90, 134.81, 132.22, 131.52, 131.26, 130.55, 130.25,
130.11, 129.88, 129.68, 129.43, 129.04, 128.62, 127.14, 126.58, 126.44,
126.25, 124.49, 21.22, 17.82, 17.77. FTIR (neat, cm-1): 2919, 1721, 1671,
1563, 1406, 1297, 1223. ESI-MS: calculated exact mass for
[C32H26Br2N2O4 + 2H+], 660.0248, found 660.9420.
Synthesis
Synthesis for 3,6-Dibromopyromellitic acid precursor for the 1 and 2 as
well as Br2NTCDA and Br4NTCDA was performed according to the
literature report.(20) Whereas, 9 was synthesised as reported earlier by our
group.(3b)
Synthesis of 6: Suspension of N,N’-dimesityl-1,4,5,8-tetracarboxylic acid
bisimide (0.50 g, 0.76 mmol) and Lawesson’s reagent (LR) (2.00 gm, 3.03
mmol) in dry and degassed toluene (20.0 ml) was heated at 85 ˚C for 36 h
under N2 atmosphere. The resulting brown solution was allowed to attain
room temperature and concentrated under vacuum to afford brown solid.
This solid was purified by column chromatography (100-200 mesh) with
CHCl3/Hexane (2:1) as an eluent. Yield: 102 mg (20%), Rf = 0.56
(CHCl3/Hexane 6:4), M.P.>300 ˚C, 1H NMR (500 MHz, CDCl3, 298 K): δ =
9.34 ( 2H, Ar-H), 6.99 ( 4H, MesBz-H), 2.31 (6H, Mes-pCH3), 1.99 (12H,
Mes-oCH3), 13C NMR (125 MHz, CDCl3, 300 K): δ = 189.30, 158.08,
143.68, 139.15, 135.38, 134.06, 129.77, 128.33, 128.27, 127.17, 123.54,
21.29, 17.72, 17.67. FTIR (neat, cm-1): 2911, 1688, 1414, 1331, 1214. MS
(MALDI-TOF, matrix- α-cyano-4-hydroxycinnamic acid): 552.46 (m/z).
Synthesis of 1: A mixture of tetrabromophthalic anhydride (1.00 gm, 2.10
mmol) and butyl amine (8.60 mmol) in acetic acid (25.0 ml) was stirred at
800C for 3h. The reaction mixture was cooled and filtered to afford dirty
white precipitates. These precipitates were thoroughly washed with
methanol and then acetone (one time) and air dried under vacuum to
obtain off-white crystalline solid. Yield: 380 mg (30 %), Rf = 0.57
(CHCl3/Hexane 8:2), M.P.>300 ˚C, 1H NMR (500 MHz, CDCl3, 298 K): δ =
3.63 (t, 2H, J = 7.0 Hz), 1.61-1.53 (m, 2H), 1.32-1.25 (m, 2H), 0.87 (t, 3H,
J = 7.0 Hz). 13C NMR (125 MHz, CDCl3, 300 K): δ = 163.88, 143.30, 137.43,
130.88, 130.67, 130.50, 128.96, 128.79, 128.39, 125.42, 121.21, 63.22,
38.87, 30.39, 30.25, 20.05, 13.59. FTIR (neat, cm-1): 2936, 2853, 1688,
1331, 1156. ESI-MS: calculated exact mass for [C12H10Br4NO2 + H+],
515.7440, found 515.3732.
Synthesis of 7: A mixture of Br4NTCDA (1.00 gm, 1.71 mmol) and butyl
amine (0.35 ml, 3.61 mmol) were taken in DCM (25.0 ml) and was refluxed
for 2h. To the resulting reaction mixture PBr3 (0.34 ml, 3.61 mmol) was
added followed by stirring for another 1h. The mixture was allowed to attain
room temperature. The resulting reaction mixture was poured onto ice cold
water to afford yellow precipitate. This precipitate was filtered and washed
with methanol (three times) and finally with acetone (one time). The
obtained solid was dried under vacuum to obtain yellow crystalline solid.
Yield: 392 mg (33 %), Rf = 0.68 (CHCl3/Hexane 8:2), M.P. 300 ˚C, 1H NMR
(500 MHz, CDCl3, 298 K): δ = 4.14 (t, 4H, J = 7.5 Hz), 1.70-1.64 (m, 4H),
1.42-1.35 (m, 4H), 0.94 (t, 6H). 13C NMR (125 MHz, CDCl3, 300 K): δ =
159.82, 138.90, 135.60, 128.12, 127.67, 126.67, 125.66, 42.70, 42.29,
41.86, 37.11, 36.98, 32.80, 31.94, 29.99, 29.90, 29.71, 29.38, 27.28, 27.10,
Synthesis of 2: A mixture of 3,6-dibromopyromellitic acid (1.00 gm, 2.60
mmol) butyl amine (10.60 mmol) and acetic acid (25.0 ml) was stirred at
800C for 3h. The mixture was cooled to room temperature, the precipitated
was collected by filtration and washed with three times methanol and once
with acetone and dried under vacuum to obtain off-white crystalline solid.
Yield: 391 mg (33 %), Rf = 0.72 (CHCl3/Hexane 8:2), M.P.>300 ˚C, 1HNMR
(500 MHz, CDCl3, 298 K): δ = 3.67 (t, 4H, J = 7.0 Hz), 1.64-1.55 (m, 4H),
1.34-1.27 (m, 4H), 0.90 (t, 6H). 13C NMR (125 MHz, CDCl3, 300 K): δ =
This article is protected by copyright. All rights reserved.

10.1002/chem.202001706
Chemistry - A European Journal
FULL PAPER
22.71, 20.41, 20.35, 14.14, 13.79. FTIR (neat, cm-1): 2919, 2861, 1705,
1655, 1364, 1272, 1189, 1147. ESI-MS: calculated exact mass for
[C22H22Br4N2O4 + 4H+], 693.8291, found 693.7791.
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Synthesis of 8: Synthetic procedure similar to 7 was adopted for the
synthesis of 8 using following reagents: Br4NTCDA (1.00 gm, 1.71 mmol)
and mesitylamine (1.32 ml, 9.38 mmol). Yield: 630 mg (45 %), Rf = 0.66
(CHCl3), M.P. 300 ˚C, 1H NMR (500 MHz, CDCl3, 298 K): δ = 7.01 (s, 4H,
MesBz-H), 2.29 (s, 6H, Mes-pCH3), 2.04 (d, 12H, Mes-oCH3). 13C NMR
(125 MHz, CDCl3, 300 K): 159.81, 159.59, 139.50, 139.34, 139.28, 136.00,
134.74, 130.85, 129.71, 127.28, 126.25, 21.19, 17.90, 17.81. FTIR (neat,
cm-1): 3252, 2919, 1721, 1671, 1380, 1223.
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Acknowledgements
P.M. thanks DST, GOI for the SwarnaJayanti Fellowship
(DST/SJF-02/CSA-02/2013-14). K. M. and D. B. thanks UGC and
DST-SERB NPDF, respectively, for research fellowships. We
thank DST-FIST, DST PURSE, UPE-II for financial assistance
and AIRF, JNU for the instrumentation facilities.
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Keywords: π-conjugated systems • opto-electronic property •
Halogen bonding • self-assembly • theoretical calculations
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Entry for the Table of Contents
FULL PAPER
Herein, we explored the halogen
bonding properties of arylene-
imide/-diimide-based electron
deficient scaffolds. We probed
the influence of: scaffold size,
axial-groups, number of
Kalyanashis Mandal, Deepak
Bansal, Yogendra Kumar, Rustam,
Jyoti Shukla and Pritam
Mukhopadhyay*
Page No. – Page No.
halogens, and imide carbonyl O
versus S atoms, on the halogen
bonding and its self-assembly in
a set of nine molecules. Single
crystal X-ray data along with
AIM and NBO analysis provide
insight into these interactions.
Halogen Bonded Assemblies of
Arylene-imides and -diimides:
Insight from Electronic,
Structural and Computational
studies
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