Influence of halogen bonding interactions in crystalline networks of tetraarylethylene halobenzoyl esters

Article abstract of DOI:10.1021/cg200986v

Solid state halogen bonding interactions have been examined in structurally similar tetratopic haloarenes bearing a common tetraphenylethylene core. This study was designed with the aim of providing insight into the relative importance of fundamental solid state halogen bonding interactions (i.e., halogen...halogen, halogen...p, and halogen... carbonyl) in systems devoid of strong hydrogen bonding groups. The substrates used in this study all featured four halobenzoate substituents (halogen = Br or I) attached to the four para positions of tetraphenylethylene with conformationally flexible ester linkages. A total of nine crystal structures from five different tetraarylethylene substrates were obtained. While distinct and unique X...O and X...p halogen bonding interactions were identified in each structure, all structures displayed nominally similar packing arrangements generally consisting of one-dimensional ribbons aligned to generate non-interpenetrating twodimensional sheets. This feature may be a consequence of extensive edge-to-face arene-Arene interactions found in each structure and may indicate a greater structure-determining role for aryl-H...p interactions relative to halogen bonding contacts in this system.

Full text of DOI:10.1021/cg200986v

Article
pubs.acs.org/crystal
Influence of Halogen Bonding Interactions in Crystalline Networks of
Tetraarylethylene Halobenzoyl Esters
Published as part of the Crystal Growth & Design virtual special issue on Halogen Bonding in Crystal Engineering:
Fundamentals and Applications.
Pradeep P. Kapadia, Dale C. Swenson, and F. Christopher Pigge*
Department of Chemistry, University of Iowa, Iowa City, Iowa 52242, United States
S
* Supporting Information
ABSTRACT: Solid state halogen bonding interactions have
been examined in structurally similar tetratopic haloarenes
bearing a common tetraphenylethylene core. This study was
designed with the aim of providing insight into the relative
importance of fundamental solid state halogen bonding
interactions (i.e., halogen···halogen, halogen···π, and halogen···
carbonyl) in systems devoid of strong hydrogen bonding groups. The substrates used in this study all featured four halobenzoate
substituents (halogen = Br or I) attached to the four para positions of tetraphenylethylene with conformationally flexible ester
linkages. A total of nine crystal structures from five different tetraarylethylene substrates were obtained. While distinct and
unique X···O and X···π halogen bonding interactions were identified in each structure, all structures displayed nominally similar
packing arrangements generally consisting of one-dimensional ribbons aligned to generate non-interpenetrating two-
dimensional sheets. This feature may be a consequence of extensive edge-to-face arene−arene interactions found in each
structure and may indicate a greater structure-determining role for aryl-H···π interactions relative to halogen bonding contacts in
this system.
The importance of halogen bonding as a means to direct or
influence intermolecular recognition and self-assembly pro-
cesses in organic materials has been demonstrated in a range of
research areas. Similar to hydrogen bonding, peripheral halogen
groups in a molecule can effectively function as “sticky sites”
that direct intermolecular associations of larger supramolecular
assemblies. Thus, halogen bonding can play key roles in fields
where the design and manipulation of aggregation phenomena
are important. Toward this end, halogen bonding interactions
have been exploited in mediating solid state assemblies of
supramolecular architectures,7 liquid crystals,8 organic semi-
conductors,9 magnetic materials,10 nonlinear optical (NLO)
materials,11 and templates for solid state synthesis.12 Halogen
bonds have also been observed in solution phase in the context
of functional molecular receptors13 and in biological systems.14
Despite their significance, there are many fundamental
aspects of halogen bonding interactions that remain to be
elucidated. In particular, the relative importance of different
types of halogen bonding interactions in polyfunctional
organohalogens is not well-defined. As part of studies aimed
at determining the relevance of specific halogen bonding
synthons as a function of molecular structure, we have
previously reported the preparation and structural character-
ization of conformationally flexible tritopic haloarene derivatives
INTRODUCTION
■
Halogen bonding is a noncovalent interaction that takes place
between halogen atoms, functioning as electrophilic species, and
neutral or anionic electron donors.1,2 Organic halides feature an
anisotropic distribution of electron density around halogen atoms
such that regions of positive electrostatic potential (sometimes
referred to as the “sigma hole”)3 result along the axes of C−X
bonds. Halogen bonding interactions are principally electrostatic in
nature and are generally weaker than hydrogen bonds, but they are
highly directional in that Lewis bases (B) approach the halogen
bond donor (C−X) in a roughly linear fashion (i.e., C−X···B angle
∼ 180°). The strength of organic halogen bonding interactions
can be altered by neighboring substituents, particularly electron
withdrawing groups, as these substituents increase the electro-
philicity of halogen bond donors.4 Organohalogens also possess
regions of negative electrostatic potential along the equator of the
C−X bond. Consequently, halogens can display amphiphilic
character by acting as both electron acceptors and electron donors
in halogen bonding interactions.5 Experimental data from solid,
liquid, and gas phase studies confirm theoretical predictions that
halogen bond donor ability increases in the order of Cl < Br < I, a
trend that also correlates with halogen polarizability.2 Organo-
fluorines, however, do not typically display halogen bonding pro-
perties due to the small size, extreme electronegatvity, and limited
polarizability of fluorine atoms. The hybridization of carbons to
which halogens are attached also affects halogen bonding ability in
the order C(sp)−X > C(sp2)−X > C(sp3)−X.6
Received: July 29, 2011
Revised: December 14, 2011
Published: December 21, 2011
© 2011 American Chemical Society
698
dx.doi.org/10.1021/cg200986v | Cryst. Growth Des. 2012, 12, 698−706

Crystal Growth & Design
Article
of general structures 1−3.15−17 While common halogen
bonding motifs in the chloro and bromo derivatives were not
evident, extensive bifurcated halogen bonding interactions in
the iodo-substituted congeners were observed across all
substrates. These interactions took the form of I···I/I···OC
interactions involving amphiphilic iodo substituents in 1 and 2,
while iodo groups in 3 were found to function as bifurcated
halogen bond donors toward both OC and arene π
functionalities. Generation of this latter synthon assisted in
formation of trimeric arrays that further assembled into hexagonal
inclusion complexes with solvent-accessible channels of nanoscale
dimensions.17 We have now extended these studies to include
structural characterization of tetratopic haloarenes (X = Br, I)
affixed to a tetraphenylethylene core (4).
EXPERIMENTAL SECTION
■
Haloarene derivatives 6−10 prepared in this study are shown in Scheme 1.
Similar experimental procedures were used for each compound as detailed
in the representative procedure below.
Scheme 1. Haloarene TPE Derivatives Structurally
Characterized in This Study
We are interested in utilizing derivatives of tetraphenylethylene
(TPE) as starting materials in supramolecular approaches toward a
variety of functional materials. Substituted TPE frameworks can be
conveniently prepared by straightforward synthetic transforma-
tions so that functional groups important in intermolecular
interactions can be easily incorporated.18 Many derivatives of TPE
are known to possess interesting opto-electronic properties (such
as low redox potentials, solid state fluorescence, and aggregation-
induced emission) that further contribute to the attractiveness of
TPEs in supramolecular chemistry.19,20 For example, aggregation-
induced emission properties of TPEs have been exploited in
construction of solution-phase fluorescent sensors for metal ions
and biomolecules.21,22 Similarly, we have reported pyridine-
substituted TPE derivatives that display switchable emission as a
function of solvent and pH.23 We have also prepared solid state
organic semiconducting assemblies mediated by hydrogen bonding
between a TPE-based tetracarboxylic acid and various bis(pyridine)
components.24 Thus, an examination of the structural features
found in 4 may not only offer fundamental insight into halogen
bonding preferences but also suggest additional approaches for
influencing the solid state assembly of halo-substituted TPE
derivatives.
General Experimental Procedures. Tetraphenol 525 (100 mg,
0.25 mmol) was dissolved in 10 mL THF, and 0.211 mL (1.50 mmol)
Et3N, 3.1 mg (0.025 mmol) DMAP and 4.5 mol equiv of halobenzoyl
chloride were added under argon at room temperature. Reactions were
maintained for 12 h, and then concentrated in vacuo to afford white
solids. The solids were combined with 10 mL 10% aq. NaOH solution
and vigorously stirred for 15 min. Stirring was stopped and the solids
were allowed to settle at the bottom of the flask and the NaOH
solution was decanted. This procedure was repeated twice with 10 mL
of H2O. After the final treatment, the remaining solids were collected
by vacuum filtration, washed thoroughly with H2O, and dried in air.
Analytical samples were obtained by recrystallization from pyridine.
Solubility issues prevented collection of 13C NMR data.
4-Bromo Ester 6. mp > 220 °C. 1H NMR (DMF-d7, 300 MHz): δ
8.06 (d, J = 8.7 Hz, 8H), 7.93 (d, J = 8.4 Hz, 8H), 7.25 (s, 16H).
1
4-Iodo Ester 7. mp > 220 °C. H NMR (DMF-d7, 300 MHz): δ
8.06 (d, J = 8.7 Hz, 8H), 7.93 (d, J = 8.4 Hz, 8H), 7.25 (s, 16H).
HRMS (ESI+): Calcd for C54H32I4O8·Na ([M + Na]+), 1338.8174;
found 1338.8189.
699
dx.doi.org/10.1021/cg200986v | Cryst. Growth Des. 2012, 12, 698−706

Crystal Growth & Design
Article
Table 1. Crystallographic Data for 6 and 7
6·(Py)
7·(Py)
6·(DMF)2
81
triclinic
P1
7·(DMF)2
88
triclinic
7·(Py)3
crystallization yield (%)
88
88
triclinic
P1
79
crystal system
triclinic
monoclinic
P21/n
space group
a/Å
P1
P1
̅
̅
̅
̅
10.543(4)
16.296(5)
17.040(6)
112.180(16)
90.699(15)
106.481(19)
2576.0(16)
2
10.6242(12)
16.3746(17)
16.9432(18)
111.993(5)
91.015(5)
106.380(5)
2596.8(5)
2
10.2173(11)
16.4911(17)
19.045(2)
65.831(5)
85.161(5)
73.224(5)
2801.0(5)
2
10.2230(11)
16.4842(17)
19.0391(19)
65.799(5)
85.211(5)
73.177(5)
2798.9(5)
2
10.3097(11)
37.511(4)
16.7490(18)
90
b/Å
c/Å
α/°
β/°
γ/°
V/Å3
Z
107.176(5)
90
6188.4(11)
4
Dcalc
1.534
1.775
1.439
1.698
1.663
−1
μ (mm )
3.180
2.456
2.928
2.284
2.072
T/K
210(2)
12376
200(2)
190(2)
33797
200(2)
40387
190(2)
69935
no. of reflns
27748
no. of unique reflns
no. of reflns with I > 2σ(I)
no. of params
R1 [I > 2σ(I)]
wR2
3814
8664
7279
7290
11341
2715
6397
5250
4182
6764
202
650
687
666
714
0.1273
0.0523
0.0748
0.0589
0.0499
0.1047
0.3879
0.1189
0.2400
0.1335
Table 2. Crystallographic Data for 8−10
8·(DMF)
81
8·(Py)
9
10
crystallization yield (%)
81
triclinic
80
87
triclinic
crystal system
monoclinic
P21/n
monoclinic
P21/n
space group
a/Å
P1
̅
P1
̅
11.3913(12)
14.9677(16)
29.896(3)
90
11.9174(13)
15.3574(16)
16.0001(17)
65.224(5)
70.717(5)
77.858(5)
2500.8(5)
2
22.073(3)
8.6817(10)
23.886(3)
90
10.2588(11)
15.3024(16)
30.704(4)
96.614(5)
90.414(5)
95.087(5)
4768.4(9)
4
b/Å
c/Å
α/°
β/°
γ/°
V/Å3
Z
93.341(5)
90
94.603(5)
90
5088.7(9)
4
4562.5(10)
4
Dcalc
1.568
1.604
1.643
1.834
−1
μ (mm )
3.222
3.277
3.586
2.669
T/K
190(2)
45136
190(2)
29682
190(2)
54032
5974
190(2)
46871
no. of reflns
no. of unique reflns
no. of reflns with I > 2σ(I)
no. of params
R1 [I > 2σ(I)]
wR2
6649
8967
16697
4033
5412
3415
8161
642
677
595
1189
0.0519
0.1124
0.0478
0.0597
0.1178
0.0563
0.0886
0.0938
3-Bromo Ester 8. mp > 220 °C. 1H NMR (DMF-d7, 300 MHz): δ
8.28 (s, 4H), 8.17 (d, J = 8.1 Hz, 4H), 7.98 (d, J = 8.1 Hz, 4H), 7.62 (t,
J = 7.95 Hz, 4H), 7.28 (s, 16H). HRMS (ESI+) Calcd for
C54H32Br4O8·Na ([M + Na]+), 1148.8708; found, 1148.8710.
The remaining crystalline samples proved too fragile for PXRD
analysis and rapid transformation to amorphous material was observed
upon removal from their respective mother liquors. Diffraction data
were collected on a Nonius-Kappa CCD diffractometer. Crystallo-
graphic data are shown in Tables 1 and 2. Selected details concerning
structure solution and refinement are described below and full details
can be found in the Supporting Information (CIF).
6·(py). A partially occupied pyridine solvate is included in the structure
(occ = 0.78(4)). The pyridine was modeled as a rigid group (C(N)−C =
1.39 Å, C(N)−C(N)−C = 120°) with isotropic displacement parameters.
Data above 40% 2 theta were excluded from the final cycles of refinement
as few (<10%) were above background levels. Comparison of the final F2
(obs) vs F2 (calc) indicated that the crystal was a non-merohedral twin.
Attempts to determine the twin law were not successful. Because of the
limited data set phenyl rings were modeled as rigid groups and only the
Br atoms were modeled with anisotropic displacement parameters.
1
2-Bromo Ester 9. mp > 220 °C. H NMR (DMF-d7, 300 MHz): δ
8.08 (m, 4H), 8.02 (m, 4H) 7.86 (m, 4H), 7.61 (m, 4H), 7.29 (s, 16H).
·+
HRMS (EI) Calcd for C54H32Br4O8 ([M ]), 1123.8831; found, 1123.8840.
2-Iodo Ester 10. mp > 220 °C. 1H NMR (DMF-d7, 300 MHz): δ
8.15 (m, 4H), 8.04 (m, 4H), 7.82 (m, 4H), 7.63 (m, 4H), 7.29 (s,
16H). HRMS (ESI+) Calcd for C54H32I4O8·Na ([M + Na]+),
1338.8174; found 1338.8182.
X-ray Crystallography. Single crystals of 6−10 were grown by
slow evaporation of solutions prepared by dissolving 15 mg of
compound in 1 mL of either DMF or pyridine. Crystallization yields
are given in Tables 1 and 2. Bulk sample homogeneity of 6·(DMF)2,
7·(DMF)2, 8·(py), 8·(DMF), and 9 was confirmed by comparison of
calculated and measured powder X-ray diffraction (PXRD) patterns.
700
dx.doi.org/10.1021/cg200986v | Cryst. Growth Des. 2012, 12, 698−706

Crystal Growth & Design
Article
6·(DMF)2. The structure contains two sites partially occupied by
DMF solvates. One site (O81−C83) refined to 0.626(12) occupancy
while the other site (O91−C93) refined to 0.546(14) occupancy. The
two sites were restrained to have the same conformation. The
anisotropic displacement parameters were restrained with the rigid bond
restraint. A comparison of F2 (obs) with F2 (calc) indicated the existence
of non-merohedral twinning but attempts to identify the (probably
rotational) twinning proved unsatisfactory.
7·(py). The pyridine solvate in this structure was refined to
0.910(13) occupancy.
7·(DMF)2. The two DMF solvates were refined to have occupancies of
0.822(13) (O81−C83) and 0.751(14) (O91−C93). Both molecules were
restrained to have the same conformations. The higher occupancy site was
refined with anisotropic displacement parameters, while the other site was
refined with isotropic displacement parameters.
7·(py)3. Three pyridine solvates were identified in this structure.
Two pyridines refined to occupancy = 1.000 and were not disordered.
The third pyridine (C91−C96) was disordered over three sites. These
disordered sites were restrained to sum 1.000 and converged to give
partial occupancies of 0.433(16), 0.280(11), and 0.261(17). Each
pyridine was modeled as a rigid group (C(N)−C = 1.39 Å, C(N)−
C(N)−C = 120°).
8·(py). One bromobenzoate group in this structure was disordered
via ∼180° rotation about the C64−O67 bond. The disorder refined to
0.9185(17)/0.0915(17). The phenyl ring was modeled as a rigid group,
and the minor site benzoate was restrained to be flat and have the same
bond distances as the major site. All non-hydrogen atoms were assigned
the same isotropic displacement parameters. The pyridine solvate
molecule was also disordered over two sites (0.888(5)/0.111(5)). The
minor site was refined as a rigid group (C(N)−C = 1.39 Å, C(N)−
C(N)−C = 120°) and assigned the same isotropic displacement
parameters.
RESULTS AND DISCUSSION
■
While tetraphenylethylenes 6−10 were easily prepared via
acylation of tetraphenol 5, all compounds proved to be sparingly
soluble in common organic solvents. This characteristic initially
hampered efforts to grow X-ray quality single crystals. Eventually,
we found that dissolution of the haloarene substrates in warm
DMF or pyridine followed by slow evaporation over 1−5 days was
an effective crystallization procedure, and single crystals of 6−8
were obtained from each of these solvents as solvent-inclusion
complexes. Crystals of ortho-halobenzoate esters 9 and 10 were
obtained from DMF as close-packed materials.
Figure 1. (a) 1D chains present in 6·(py). Br···OC = 3.302 Å,
Br···πbond = 3.623 Å, C−Br···O = 166.22°, C−Br···πbond = 141.05°. (b) 1D
chains in 7·(py). I···OC = 3.401 Å, I···πbond = 3.574 Å, C−I···O =
163.68°, C−I···πbond = 142.88°. (c) View of 2D layers formed from
interdigitation of 1D chains along with pyridine solvate molecule in
7·(py). Individual chains are color-coded. Edge-to-face arene interactions
and additional interchain I···πbond interactions (d = 3.718 Å) indicated by
black lines. Similar 2D layers are found in 6·(py).
The inclusion complexes 6·(py) and 7·(py) obtained from slow
evaporation of pyridine solutions were found to be virtually
isostructural. In each case, TPE molecules adopt propeller-like
conformations typical of tetraphenylethylenes in the solid state.19
Individual molecules of 6/7 are engaged in two types of halogen
bonding interactions resulting in formation of one-dimensional
(1D) chains. As shown in Figure 1, these chain motifs are
mediated by complementary X···OC and X···π halogen
bonding (see Figure 1 caption for relevant distances and
angles). In the case of the halogen − π contacts, the closest
X···πarene interaction is to the midpoint of an arene π bond rather
than the arene centroid.26 One-dimensional chains are extended
into two-dimensional (2D) layers via a combination of arene
edge-to-face interactions between adjacent halobenzoyl moi-
eties and additional X···π (over bond) contacts as shown in
Figure 1c. Disordered pyridine solvate molecules are housed
within cavities formed at the chain−chain interface. While there
is considerable precedent for pyridyl N···X (especially X = I)
halogen bonds,1 pyridine solvates appear to be serving a space-
filling role in these structures and are not involved in halogen
bonding interactions.
While halogen bonding appears to play an important role in the
2D organization of 6·(py) and 7·(py), stacking of individual layers
in the third dimension is mediated by an extensive network of
edge-to-face arene contacts (Figure 2). In these structures 2D
layers are stacked parallel to the a axis in an abab pattern slightly
offset along a. Arene rings in the TPE core interact with arene
rings from adjacent TPE cores, while peripheral halobenzoyl rings
interact with peripheral halobenzoyl rings in adjacent layers.
Single crystals of 6 and 7 obtained from slow evaporation of
DMF exhibited a similar arrangement of 1D chains organized
into 2D sheets with included solvent molecules occupying
cavities at the interchain interface. A partial view of the 2D
sheet structure found in 7·(DMF)2 is shown in Figure 3a. A
linear network of I···OC and I···πarene halogen bonding inter-
actions similar to those found in the pyridine solvate described
above result in ribbon-like chains of individual molecules. Once
again, the I···πarene interaction involves approach of the I to the
midpoint of an arene π bond as indicated in Figure 3a. These
ribbon-like chains are then arranged in 2D layers via edge-to-face
701
dx.doi.org/10.1021/cg200986v | Cryst. Growth Des. 2012, 12, 698−706

Crystal Growth & Design
Article
pattern mediated by edge-to-face π-stacking interactions similar
to those shown in Figure 2. As a consequence of stacking
interactions, individual 2D layers are aligned in a slightly offset
fashion. This arrangement produces large rhomboid channels of
dimensions ∼13 × 7 Å that are filled with included DMF
solvates (Figure 3b). The presence of these channels produces a
relatively porous network with approximately 41% solvent
accessible void space as determined using PLATON calcu-
lations.27 The DMF inclusion complex obtained from 6 exhibited
a similar overall network architecture with Br···OC and
Br···πbond interactions comparable to those observed in the iodo
analogue.
We also attempted to prepare cocrystalline networks using a
combination of 7 and various compounds possessing two
potential halogen bond acceptor sites (e.g., dimethyl malonate,
methyl nicotinate, diethyl maleate, and several bis(pyridine)s).
These experiments involved mixing 7 and the cocrystallization
agent in DMF or pyridine. While no cocrystals were obtained, a
new pyridine inclusion complex of stoichiometry 7·(py)3 was
isolated and characterized from slow evaporation of a pyridine
solution containing 7 and dimethyl malonate. Unlike the
structures discussed above, all four iodoarene groups in 7·(py)3
were engaged in some form of halogen bonding that results in
linking each molecule of 7 to five other molecules (Figure 4a).
Two iodo groups are involved in distinct I···πarene interactions
with two different molecules of 7. One of these interactions is
Figure 2. (a) View of stacked 2D sheets in 7·(py) perpendicular to the
stacking axis. Edge-to-face arene contacts indicated with black lines.
(b) View of 7·(py) down a showing the relationship between two
adjacent layers. Light blue = top layer, violet = bottom layer.
to the midpoint of an arene bond (over bond interaction, dI···π
=
3.564 Å, C−I···π angle = 154.15°), while the other involves
interaction between an iodo group and an arene carbon (over
carbon π interaction, dI···C‑arene = 3.649 Å, C−I···Carene angle =
171.11°).26d One of these iodine atoms also serves as a halogen
bond acceptor toward an aryl iodide halogen bond donor from
a third molecule of 7 (dI···I = 3.795 Å, C−I···I angles = 168.24°
and 96.73°). A third iodine participates in a halogen bond to a
carbonyl group from a fourth molecule of 7 (dI···O = 3.380 Å,
C−I···O angle = 152.49°). Finally, the fourth iodine substituent
functions as a halogen bond donor toward a fifth molecule of 7.
Such an extensive array of halogen bonds about the semiflexible
TPE derivative produces a nonclose packed three-dimensional
(3D) architecture in which the pyridine solvates occupy voids
as shown in Figure 4b, and no I···pyridine halogen bonds are
present. Thermochemical characterization of 7·(py) and 7·(py)3
could not be performed due to the fragility of the crystals. On
the basis of calculated densities, however, it appears that 7·(py)
is the more close packed structure. It is certainly possible that
the tris(pyridine) inclusion complex represents a metastable
state along the path to the mono(pyridine) complex. If so, then
the marked differences in lattice architecture would indicate
that the 3D network of halogen bonding interactions in 7·(py)3
is supplanted in favor of more edge-to-face arene contacts in
7·(py) (Figure 2).
In order to investigate the effect of substitution pattern on
halogen bonding interactions, TPE derivative 8 was prepared
and characterized. As was the case with 6, two different
inclusion complexes were obtained from slow evaporation of
DMF or pyridine solutions. However, very few distinct halogen
bonding interactions are evident upon analysis of the resulting
crystal structures. In 8·(DMF), only one halogen bond between
a bromine and the carbonyl group of DMF is apparent (Figure 5a)
with a variety of other intermolecular contacts (e.g., C−H···O,
C−H···π, arene edge-to-face, and face-to-face) leading to the
generation of sheet-like assemblies as shown in Figure 5b. The
structure of 8·(py) is somewhat reminiscent of features found
Figure 3. (a) 2D sheets formed by parallel alignment of halogen
bonded chains in 7·(DMF)2. Relevant distances and angles: C−I···O
3.522 Å, 126.91°; C−I···πbond 3.535 Å, 149.56°. (b) View of the partial
packing of 7·(DMF)2 (down a) with channels occupied by included
DMF molecules (blue).
π-stacking of aromatic rings. Additional polar interactions (C−
H···O hydrogen bonding) with DMF solvates appear to further
reinforce this layered structure. No halogen bonding interactions
between the DMF solvates and the iodoarene moieties are
evident. The 2D layers stack parallel to the a axis in an abab
702
dx.doi.org/10.1021/cg200986v | Cryst. Growth Des. 2012, 12, 698−706

Crystal Growth & Design
Article
Figure 4. (a) Halogen bonding interactions linking 7 to five additional
molecules observed in 7·(py)3. (b) Extended packing in 7·(py)3 down c.
Pyridine solvates shown in blue.
in inclusion complexes of 6 and 7 in that 8 assembles to form
2D sheets that stack in an abab pattern slightly offset down the
a axis (Figure 5c). However, close intermolecular contact
between an aryl bromine residue and an arene carbon (over
carbon Br···π interaction) provides the only evidence for
halogen bonding (dBr···C‑arene = 3.310 Å, C−Br···Carene angle =
150.48°. In part, the absence of extensive halogen bonding
interactions in 8 may stem from the location of the aryl halide
substituents at electronically unactivated meta-positions of the
benzoate rings. Notably, halobenzoate TPE derivatives that
feature halogens at electronically activated 4-positions (6 and
7) and 2-positions (9 and 10, vide infra) exhibit significantly
more halogen bonding contacts. Steric factors likely play a role
in governing the observed halogen bonding patterns as well,
although the conformational flexibility of these TPE esters is
envisioned to attenuate this effect.16
Figure 5. (a) Halogen bonding interaction between 8 and DMF
solvate (dBr···O = 3.407 Å, C−Br···O angle = 163.6°). (b) Extended
packing in 8·(DMF) down b. (c) Extended packing of 8·(py) down a.
be obtained from slow evaporation of DMF or pyridine
solutions. Within each compound the same crystalline
modification was observed irrespective of crystallization solvent.
Additionally, each compound was obtained as a close-packed
structure without any included solvent. In the structure of 9,
two types of halogen bonding appear to be significant.
Individual molecules of 9 are organized into 1D ribbons via
intermolecular Br···Br halogen bonding (Figure 6a). To achieve
close packing, each 1D ribbon is connected in a slightly offset
manner to adjacent ribbons via Br···π (over carbon) contacts as
illustrated in Figure 6b (along with additional C−H···O
The final set of compounds included in this study features
TPE frameworks decorated with ortho-substituted bromo- or
iodobenzoyl rings. Once again, crystals of both 9 and 10 could
703
dx.doi.org/10.1021/cg200986v | Cryst. Growth Des. 2012, 12, 698−706

Crystal Growth & Design
Article
Figure 6. (a) Br···Br halogen bonding in 9. (b) Stacked sheet-like
packing reinforced with Br···π (over carbon) halogen bonding.
interactions not shown in Figure 6). Thus, one bromine atom
in each molecule is engaged in amphiphilic bifurcated halogen
bonding by acting as a halogen bond donor (electrophile)
toward an arene carbon (over carbon π interaction, 3.510 Å,
164.73°) and a halogen bond acceptor (nucleophile) in an
attractive Br···Br interaction. A third bromine from each
molecule of 9 is also positioned a short distance (3.340 Å) from
an arene π-bond in an adjacent ribbon; however, the C−Br···π
angle of 126.48° deviates substantially from the ideal halogen
bonding value. The fourth bromine does not appear to
participate in any significant intermolecular interactions.
The ortho-iodo analogue 10 adopts a slightly different
packing arrangement in which independent parallel ribbons are
aligned roughly in the bc plane to form undulating sheets.
Intermolecular interactions within each strand consist of multiple
C−H···O interactions along with iodine halogen bonding
(Figure 7a). In one ribbon, a halogen bond is observed
involving an iodine halogen bond donor and an ester carbonyl
halogen bond acceptor (dI···O = 3.322 Å, C−I···O = 149.53°).
The second unique ribbon features a single intermolecular over
Figure 7. (a) Parallel ribbons that generate 2D sheets in 10 mediated
by intermolecular C−H···O, I···Carene, and I···O interactions. (b) View
of stacked sheets in 10 (down b) color-coded to highlight abab
pattern.
carbon I···π interaction (dI···C‑arene = 3.347 Å, C−I···C−arene
=
156.13°). Undulating sheets are stacked down the a axis in an
abab pattern with additional interlayer over bond and over
carbon I···π contacts as shown in Figure 7b (dI···π‑bond = 3.332
and dI···C‑arene 3.563 Å, C−I···πbond angle = 170.40 and C−
I···Carene angle = 146.78°).
Scheme 2. Halogen Bonding Synthons Exhibited in 6−10
The substrates examined in this study were designed to
probe the interplay between specific types of halogen bonding
interactions and molecular structure in similar but electronically
distinct systems. Five basic halogen bonding synthons
(illustrated schematically in Scheme 2) were observed in the
TPE halobenzoyl esters examined. Table 3 provides a summary
of the halogen bonding synthons observed in 6−10. Although
all structures (with the exception of 7·(py)3) exhibited
nominally similar extended packing architectures consisting of
stacked 2D layers, consistent trends in halogen bonding as a
function of halogen or substitution pattern were generally not
observed. Only in the 1:1 solvent inclusion complexes of the 4-
halobenzoyl esters were similar halogen bonding motifs present
irrespective of structure. However, the halogen bonding
interactions in 6/7·(DMF) and 6/7·(py) were all confined to
the 2D sheet assemblies formed from parallel alignment of 1D
ribbons, and extensive arene edge-to-face contacts appear to
constitute the dominant solid state interactions in these
structures. Given the abundance of π systems in the substrates
6−10, perhaps it is not surprising that halogen···π synthons II
and III were the most frequently observed halogen bonding
motifs, followed by X···OC synthon I. Somewhat surprisingly,
the X···X halogen bonding motif (synthon IV) was observed
only in one structure. Our previous studies indicated that this
type of interaction was common in compounds somewhat
similar to 6−10.15−17 Moreover, in most structures reported here
at least one halogen in the tetra(halo) substrate does not exhibit
any significant intermolecular close contacts. One must assume
that the energetic value gained by engaging all four halogens in
some form of halogen bonding is offset by the disruption of
704
dx.doi.org/10.1021/cg200986v | Cryst. Growth Des. 2012, 12, 698−706

Crystal Growth & Design
Article
Many tetraphenylethylenes exhibit aggregation-induced
emission.20 In dilute solutions TPEs are generally nonfluore-
scent; however, upon addition of a poor solvent aggregation of
TPEs occurs resulting in a fluorescence signal. The origin
of this optical behavior is believed to reside in restricted
intramolecular motions (e.g., aryl bond rotations) of TPE
frameworks when in aggregated states. Luminescence of TPEs
also extends to the solid state, and this property was qualit-
atively apparent in crystals of 6−10 when illuminated with a
hand-held UV light. Single crystals of 7·(py) were further
examined using confocal microscopy, and a representative
image is shown in Figure 8. Solution phase aggregation-induced
emission of 7 was also probed. A sample of 7 was dissolved in
100% DMF and the fluorescence spectrum was recorded. The
change in fluorescence was then monitored as increasing
amounts of H2O were added to the solution (Figure 9). While
the solution was initially nonemissive, a relatively weak fluore-
scence signal centered at ∼460 nm was observed at 20% water
content. Continued addition of water produced enhanced
emission along with a slight red shift in the fluorescence
maxima. Haloarene-TPE derivatives 6 and 8−10 exhibited
similar fluorescence profiles (see Supporting Information).
Thus, use of TPE derivatives in crystal engineering applications
may offer a convenient means for construction or luminescent
organic and metal−organic frameworks, and studies along these
lines are underway.
Table 3. Summary of Solid State Halogen Bonding
Interactions (Synthons I−V) Observed in TPE Derivatives
6−10
I
II
III
---
IV
---
V
6·(DMF)2
7·(DMF)2
6·(py)
7·(py)
7·(py)3
8·(DMF)
8·(py)
9
+++
+++
+++
+++
---
+++
+++
+++
+++
+++
---
---
---
---
---
---
---
---
---
---
---
+++
---
---
+++
---
+++
---
---
---
+++
+++
+++
---
---
---
---
+++
+++
---
10
---
+++
CONCLUSIONS
■
This study was designed to assay the importance of specific halo-
gen bonding interactions in structurally related but electronically
differentiated tetratopic haloarenes. Substrates 6−10 were
prepared from a readily available tetraphenylethylene derivative
lacking strong hydrogen bonding groups in order to maximize the
influence of halogen bonding interactions. However, only the 4-
halobenzoyl-substituted compounds 6 and 7 displayed a high
correlation between molecular structure and preferred halogen bond-
ing motifs (X···OC and X···π). In general, halogen bonding
interactions observed in 6−10 appear to reinforce a common
stacked-sheet packing motif in cooperation with edge-to-face
arene interactions and C−H···O/π hydrogen bonding. The
presence in some crystals of solvates capable of serving as halo-
gen bond acceptors (i.e., pyridine and DMF) did little to disrupt
this packing, and no halogen bonds involving included solvates
(with the exception of 8·(DMF)) were observed. Future studies
Figure 8. Confocal microscope image of 7·(py).
other weak noncovalent associations (e.g., C−H···O hydrogen
bonding, edge-to-face π bonding). In this context, it may be
interesting to probe the effect of systematically increasing the
halogen bond donor ability of the halide substituents (e.g.,
through preparation of fluorinated and partially fluorinated
bromo/iodo benzyol esters) as a means to disrupt the packing
patterns observed in 6−10 in favor of additional (stronger)
halogen bonding interactions.
Figure 9. Fluorescence spectra of 7 in DMF and DMF/H2O mixtures (vol%). No fluorescence was observed until water content was 20%. [7] =
23.17 μM, λex = 375 nm.
705
dx.doi.org/10.1021/cg200986v | Cryst. Growth Des. 2012, 12, 698−706

Crystal Growth & Design
Article
(12) Caronna, T.; Liantonio, R.; Logothetis, T. A.; Metrangolo, P.;
Pilati, T.; Resnati, G. J. Am. Chem. Soc. 2004, 126, 4500−4501.
(13) (a) Mele, A.; Metrangolo, P.; Neukirch, H.; Pilati, T.; Resnati,
G. J. Am. Chem. Soc. 2005, 127, 14972−14973. (b) Chudzinski, M. G.;
McClary, C. A.; Taylor, M. S. J. Am. Chem. Soc. 2011, 133, 10559−
10567. (c) Cavallo, G.; Metrangolo, P.; Pilati, T.; Resnati, G.;
Sansotera, M.; Terraneo, G. Chem. Soc. Rev. 2010, 39, 3772−3783.
(14) (a) Voth, A. R.; Hays, F. A.; Ho, P. S. Proc. Natl. Acad. Sci.
U. S. A. 2007, 104, 6188−6193. (b) Lu, Y.; Shi, T.; Wang, Y.; Yang,
H.; Yan, X.; Luo, X.; Jiang, H.; Zhu, W. J. Med. Chem. 2009, 52, 2854−
2862 and references cited.
will examine the ability to attenuate the influence of these latter
two noncovalent attractions through the use of TPE derivatives
substituted with more potent (more electrophilic) halogen bond
donors.
ASSOCIATED CONTENT
* Supporting Information
■
S
X-ray data with details of refinement procedures (CIF), fluore-
scence spectra and confocal microscope images of 6−10, calculated
and observed PXRD patterns for 6·(DMF)2, 7·(DMF)2, 8·(py),
8·(DMF), and 9. This material is available free of charge via the
Internet at http://pubs.acs.org.
(15) (a) Kumar, V. S. S.; Pigge, F. C.; Rath, N. P. CrystEngComm
2004, 6, 102−105. (b) Pigge, F. C.; Vangala, V. R.; Swenson, D. C.
Chem. Commun. 2006, 2123−2125.
(16) Pigge, F. C.; Vangala, V. R.; Swenson, D. C.; Rath, N. P. Cryst.
Growth Des. 2010, 10, 224−231.
AUTHOR INFORMATION
Corresponding Author
*Phone: 319-335-3805. Fax: 319-335-1270. E-mail: chris-pigge@
uiowa.edu.
■
(17) Pigge, F. C.; Vangala, V. R.; Kapadia, P. P.; Swenson, D. C.;
Rath, N. P. Chem. Commun. 2008, 4726−4728.
(18) Banerjee, M.; Emond, S. J.; Lindeman, S. V.; Rathore, R. J. Org.
Chem. 2007, 72, 8054−8061 and references cited.
(19) Rathore, R.; Lindeman, S. V.; Kumar, A. S.; Kochi, J. K. J. Am.
Chem. Soc. 1998, 120, 6931−6939.
ACKNOWLEDGMENTS
■
We thank the Department of Chemistry, University of Iowa,
and Dr. Jonas Baltrusaitis for assistance with confocal
microscopy. F.C.P. thanks the College of Liberal Arts &
Sciences and the Obermann Center for Advanced Studies for
sponsorship of a Career Development Award.
(20) Hong, Y.; Lam, J. W. Y.; Tang, B. Z. Chem. Commun. 2009,
4332−4353.
(21) Liu, L.; Zhang, G.; Xiang, J.; Zhang, D.; Zhu, D. Org. Lett. 2008,
10, 4581−4584.
(22) (a) Chen, Q.; Bian, N.; Cao, C.; Qiu, X.-L.; Qi, A.-D.; Han,
B.-H. Chem. Commun. 2010, 46, 4067−4069. (b) Liu, Y.; Deng, C.;
Tang, L.; Qin, A.; Hu, R.; Sun, J. Z.; Tang, B. Z. J. Am. Chem. Soc.
2011, 133, 660−663. (c) Kato, T.; Kawaguchi, A.; Nagata, K.;
Hatanaka, K. Biochem. Biophys. Res. Commun. 2010, 394, 200−204.
(23) Kapadia, P. P.; Widen, J. C.; Magnus, M. A.; Swenson, D. C.;
Pigge, F. C. Tetrahedron Lett. 2011, 52, 2519−2522.
REFERENCES
■
(1) (a) Metrangolo, P.; Meyer, F.; Pilati, T.; Resnati, G.; Terraneo, G.
Angew. Chem., Int. Ed. 2008, 47, 6114−6127. (b) Metrangolo, P.;
Resnati, G. Science 2008, 321, 918−919. (c) Metrangolo, P.; Resnati,
G.; Pilati, T.; Biella, S. Struct. Bonding (Berlin) 2008, 126, 105−136.
(24) Kapadia, P. P.; Ditzler, L. R.; Baltrusaitis, J.; Swenson, D. C.;
Tivanski, A. V.; Pigge, F. C. J. Am. Chem. Soc. 2011, 133, 8490−8493.
(25) Schultz, A.; Diele, S.; Laschat, S.; Nimtz, M. Adv. Funct. Mater.
2001, 11, 441−446.
́
(d) Fourmigue, M. Curr. Opin. Solid State Mater. Sci. 2009, 13, 36−45.
(2) (a) Lommerse, J. P. M; Stone, A. J.; Taylor, R.; Allen, F. H. J. Am.
Chem. Soc. 1996, 118, 3108−3116. (b) Riley, K. E.; Merz, K. M. Jr.
J. Phys. Chem. A 2007, 111, 1688−1694. (c) Ramasubbu, N.;
Parthasarathy, R.; Murray-Rust, P. J. Am. Chem. Soc. 1986, 108,
4308−4314. (d) Cabot, R.; Hunter, C. A. Chem. Commun. 2009,
2005−2007. (e) Politzer, P.; Murray, J. S.; Clark, T. Phys. Chem. Chem.
Phys. 2010, 12, 7748−7757. (f) Sarwar, M. G.; Dragisic, B.; Salsberg, L.
J.; Gouliaras, C.; Taylor, M. S. J. Am. Chem. Soc. 2010, 132, 1646−
1653.
(26) (a) Schollmeyer, D.; Shishkin, O. V.; Ruhl, T.; Vysotsky, M. O.
̈
CrystEngComm 2008, 10, 715−723. (b) Swierczynski, D.; Luboradzki,
R.; Dolgonos, G.; Lipkowski, J.; Schneider, H.-J. Eur. J. Org. Chem.
2005, 1172−1177. (c) Prasanna, M. D.; Guru Row, T. N. Cryst. Eng.
2000, 3, 135−154. (d) Vasilyev, A. V.; Lindeman, S. V.; Kochi, J. K.
Chem. Commun. 2001, 909−910.
(27) Spek, A. L. PLATON − A Multipurpose Crystallographic Tool;
University of Utrecht: The Netherlands, 1999.
(3) (a) Murray, J. S.; Riley, K. E.; Politzer, P.; Clark, T. Aust. J. Chem.
2010, 63, 1598−1607. (b) Clark, T.; Hennemann, M.; Murray, J.;
Politzer, P. J. Mol. Model. 2007, 13, 291−296.
(4) (a) Riley, K. E.; Murray, J. S.; Politzer, P.; Concha, M. C.; Hobza,
P. J. Chem. Theory Comput. 2009, 5, 155−163 and references cited.
(b) Gavezzotti, A. Mol. Phys. 2008, 106, 1473−1485.
(5) (a) Auffinger, P.; Hays, F. A.; Westhof, E.; Ho, P. S. Proc. Natl.
Acad. Sci. U. S. A. 2004, 101, 16789−16794. (b) Metrangolo, P.; Pilati,
T.; Resnati, G. CrystEngComm 2006, 8, 946.
(6) Sun, A.; Lauher, J. W.; Goroff, N. S. Science 2006, 312, 1030
and references cited.
(7) (a) Rissanen, K. CrystEngComm 2008, 10, 1107−1113.
(b) Bertani, R.; Sgarbossa, P.; Venzo, A.; Lelj, F.; Amati, M.;
Resnati, G.; Pilati, T.; Metrangolo, P.; Terraneo, G. Coord. Chem. Rev.
2010, 254, 677−695.
(8) Bruce, D. W.; Metrangolo, P.; Meyer, F.; Pilati, T.; Prasang, C.;
̈
Resnati, G.; Terraneo, G.; Wainwright, S. G.; Whitwood, A. C.
Chem.Eur. J. 2010, 16, 9511−9524 and references cited.
́
(9) (a) Fourmigue, M. Struct. Bonding (Berlin) 2008, 126, 181−207.
́
(b) Fourmigue, M.; Batail, P. Chem. Rev. 2004, 104, 5379−5418.
(10) Hanson, G. R.; Jensen, P.; McMurtrie, J.; Rintoul, L.; Micallef,
A. S. Chem.Eur. J. 2009, 15, 4156−4164.
(11) (a) George, S.; Nangia, A.; Lam, C.-K.; Mak, T. C. W.; Nicoud,
J.-F. Chem. Commun. 2004, 1202−1203. (b) Cariati, E.; Forni, A.;
Biella, S.; Metrangolo, P.; Meyer, F.; Resnati, G.; Righetto, S.; Tordin,
E.; Ugo, R. Chem. Commun. 2007, 2590−2592.
706
dx.doi.org/10.1021/cg200986v | Cryst. Growth Des. 2012, 12, 698−706