A role for π-Br interactions in the solid-state molecular packing of para-halo-phenoxy-boronsubphthalocyanines

Article abstract of DOI:10.1039/c0ce00796j

We report the synthesis and characterization of a series of para-halo-phenoxy-boronsubphthalocyanines (BsubPcs). Across this series, a crystal polymorph of p-bromophenoxy-BsubPc (α-BrPhO-BsubPc) contains a clear and discernible π-Br interaction directing crystallization into a motif not previously seen for phenoxy-BsubPcs.

Full text of DOI:10.1039/c0ce00796j

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COMMUNICATION
A role for p–Br interactions in the solid-state molecular packing of
para-halo-phenoxy-boronsubphthalocyanines†
a
Andrew S. Paton, Alan J. Lough and Timothy P. Bender
b
ab
*
Received 29th October 2010, Accepted 28th March 2011
DOI: 10.1039/c0ce00796j
distinctive 1-dimensional columns of molecules aligned roughly
perpendicular to the plane of the BsubPc ligand—distinctly different
from their corresponding perhydrogenated analogs.3 In summation,
there are two commonly observed motifs for BsubPc in the
crystalline state: dimeric or ribbon motifs arranged concave-concave
common to perhydrogenated derivatives and 1D columns common
to perfluorinated derivatives.
We report the synthesis and characterization of a series of para-
halo-phenoxy-boronsubphthalocyanines (BsubPcs). Across this
series, a crystal polymorph of p-bromophenoxy-BsubPc (a-BrPhO-
BsubPc) contains a clear and discernible p–Br interaction directing
crystallization into a motif not previously seen for phenoxy-
BsubPcs.
Recently, the importance of intermolecular halogen (X) interac-
tions in influencing crystal packing has been recognized. In particular,
C–X/p, C–H/X, and X/X interactions have been shown to be
important in influencing crystal structures. A survey of the Cam-
bridge Structural Database was performed in 200010 that searched for
the occurrence of C–X/p interactions in compounds with a C–X
group and at least one 6-membered aromatic group. The study
showed that there are particular orientations through which these
interactions occur, and that the average distances for these intermo-
lecular C–X/p interactions are 3.224 ꢀ 0.025, 3.525 ꢀ 0.007,
Boron is unique amongst the atoms of the periodic table as only its
halides (Cl, Br) template the formation of the trimeric sub-
phthalocyanine (subPc) ligand on reaction with phthalonitrile.1
Researchers have utilized the unique chemical and physical properties
of the resulting boronsubphthalocyanine (BsubPc) for application in
non-linear optics,2a organic light emitting diodes (OLEDs),2b,c organic
field effect transistors (OTFTs),2d–f and solar cells.2g,h Commonly, the
BsubPc derivative is used in the solid state and as such an under-
standing of its solid state molecular packing motifs and methods to
influence or even control the motifs are of interest.
ꢀ
3.625 ꢀ 0.009, and 3.698 ꢀ 0.013 A for X ¼ F, Cl, Br, and I,
Regarding common solid state molecular packing of BsubPcs, we
have recently highlighted that typical motifs for crystals of phe-
noxy-substituted boron subphthalocyanines (phenoxy-BsubPcs) are
the formation of dimers or of ribbons associated through their
concave faces.‡,3 Others have shown that tert-butoxy-BsubPc and
ethoxy-BsubPc also form the dimer motif.4,5 Even one of the few
crystal structures of the related alkoxy-tribenzosubporphyrins
arranges into a similar concave-face to concave-face dimer motif.6
Two polymorphs of methoxy-BsubPc have been found, one of
which possesses the dimeric motif and the other arranges into
a ribbon motif associated through the concave faces, not unlike the
ribbon structure observed in some phenoxy-BsubPcs.3,7 Peripheral
perfluorination of the BsubPc ligand on the other hand results in
a wholly different motif for the crystal structures of phenoxy-
F12BsubPc8 and 4-methylphenoxy-F12BsubPc.9 This packing struc-
ture consists of phenoxy-to-concave-face p-stacking that forms
respectively. Specifically, C–Br/p and C–I/p intermolecular
interactions have been shown to mediate a tris-(halophenoxy)triazine
and trihalobenzene guest-host inclusion complex, with the trihalo-
benzene molecule held in channels created by three triazine deriva-
tives.11 Also, a group of four C–X/p (X ¼ Br, I) intermolecular
interactions working in concert has been shown to construct
a building block for a series of staircase inclusion compounds.12 The
C–H/X and X/X interactions have also been shown to affect the
crystal packing structure and solid-state molecular structure of three
(2,20-bipyridine-N,N)-dibromo-cis-bis[1,1-diphenylhydrazido]-
molybdenum(VI) derivatives.13
There are three reported crystal structures that suggest halogen–
boron or halogen–p interactions may influence the crystallization of
BsubPc derivatives: Cl-F12BsubPc,14 Br-F12BsubPc,15 and
F-F12BsubPc.16 Each is arranged in a concave to convex arrangement
ꢀ
having halogen–boron distances of 3.671(3), 3.721(3), and 3.228(5) A,
respectively, which are all below the sum of their respective B/X van
der Waals radii.17 However, it is difficult to determine whether this
arrangement is formed under the thermodynamic direction of
a halogen-boron interaction, a halogen–p interaction or rather that it
is the preferred crystallization motif of perfluorinated BsubPcs based
solely on geometric considerations. Additionally, these halo-BsubPc
derivatives do not offer an opportunity for synthetic variation and
thus also do not allow for the examination of the use of halogen–
boron interactions to engineer crystals of BsubPc.
aDepartment of Chemical Engineering and Applied Chemistry, The
University of Toronto, 200 College St., Toronto, Ontario, Canada M5S
3E5. E-mail: tim.bender@utoronto.ca
bDepartment of Chemistry, University of Toronto, 80 St. George St.,
Toronto, Ontario, Canada M5S 3H6
† Electronic supplementary information (ESI) available. CCDC
reference numbers 799250–799252, and 814720. For ESI and
crystallographic data in CIF or other electronic format see DOI:
10.1039/c0ce00796j
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It would be of interest to see whether boron-halogen interactions
could be used to crystal engineer BsubPcs bearing synthetically
variable halogenated fragments preferably resulting in arrangements
within the crystal not previously seen. Furthermore, it would be of
interest to see evidence to the affirmative or to the contrary of the role
of direct halogen–boron or halogen–p interactions. Given our recent
experience with phenoxy-BsubPcs,3 the incorporation of halogens
onto a phenoxy moiety would allow us to study the effect of halo-
genation as well as have multiple reference structures for comparison.
Furthermore, if the carbon spacer is a phenoxy unit or higher aryloxy
unit, specific angular (meta- and para-) and distal options are possible
for future studies. In our previous study we synthesized and char-
acterized 4-fluorophenoxy-BsubPc (FPhO-BsubPc, compound 2a,
Scheme 1). For this derivative there was no evidence of halogen-
boron interactions and the derivative crystallized into an arrangement
nearly identical to phenoxy-BsubPc itself.3
molecule is located nearly in the centre of the concave-side of the
neighbouring molecule beneath the boron atom (Fig. 1c). A closer
examination of the geometry (Fig. 2) shows the separation between
the bromine and the boron in the neighbouring molecule is 3.850(5)
17
ꢀ
A, which is equal to the sum of the van der Waals radii. There is also
ꢀ
a measurable C–Br/p interaction at a distance of 3.380(5) A
between the bromine and the centroid (Cg) of the concave-side of the
five-membered p-ring consisting of C9–C10–C15–C16–N3 of the
BsubPc (see numbering Fig. S3).† Additionally, between the rows of
molecules there is a convex-side to convex-side p–p interaction
ꢀ
between two BsubPc molecular fragments at a distance of 3.716(3) A
(Fig. 1c). An examination of the bond angles of this molecule
(in particular the B1–O1–C25 angle) reveals no bond angle strain is
present. Unlike other cases of phenoxy-BsubPcs where the phenoxy
molecular fragment is positioned between lobes of the BsubPc ligand,
in this case it is positioned over a lobe (above N5–C24–C23–C18–
C17). This form of BrPhO-BsubPc will hereafter be referred to as
a-BrPhO-BsubPc.x Single crystals of BrPhO-BsubPc were also
obtained from dichloromethane/pentane diffusion crystallization. In
this case a second polymorph was found wherein the solid-state
arrangement is again dominated by the formation of discernible
dimers and for which the overall arrangement is identical to that
obtained for IPhO-BsubPc (Fig. 1d). This form of BrPhO-BsubPc
will hereafter be referred to as b-BrPhO-BsubPc.{ Using a commer-
cial software package (Materials Studio version 5.0, Accelrys Inc.) we
calculated the energy difference between a-BrPhO-BsubPc and
b-BrPhO-BsubPc to be ꢁ4.35 kcal molꢂ1, with b-BrPhO-BsubPc
being lower in energy. This indicates that each polymorph is relatively
close in energy and that a-BrPhO-BsubPc might be kinetically
favoured whereas b-BrPhO-BsubPc might be thermodynamically
favoured (assuming the solvent systems used for growth does not
favour one polymorph over the other).
In this communication, we wish to report the synthesis, crystalli-
zation and characterization of the three additional para-halogenated-
phenoxy-BsubPcs. The syntheses were carried out according to
a procedure outlined previously (Scheme 1).3 Briefly, Cl-BsubPc (1,
Scheme 1) was reacted with the appropriate para-halophenol at reflux
in toluene. Purification was carried out via Kauffman column chro-
matography on standard basic alumina as the adsorbant and
dichloromethane as the eluent yielding compounds 2b–d (Scheme 1).
Finally, all crystallizations were performed via vapour diffusion with
benzene as the solvent and heptane as the anti-solvent. For
compound 2c a further vapour diffusion crystallization was also
performed using dichloromethane as the solvent and pentane as the
anti-solvent. In all cases, within one to two weeks, high quality single
crystals suitable for X-ray diffraction were grown.
The molecular arrangements within the crystal (extended beyond
the unit cell) for 4-chlorophenoxy- (ClPhO-) and 4-iodophenoxy-
(IPhO-) BsubPc (compounds 2b and 2d) are illustrated in Fig. 1b and
1e, respectively. The arrangement of the previously reported FPhO-
BsubPc is redrawn in Fig. 1a for comparison. As was the case for the
solid state molecular packing of FPhO-BsubPc (and other para-
phenoxy-BsubPcs),3 ClPhO-BsubPc and IPhO-BsubPc orient them-
selves into distinct dimers; however, each is distinctly different in its
arrangement of the dimers relative to one another. Despite the larger
size of the iodine atom, IPhO-BsubPc arranges into a nearly identical
crystal structure as FPhO-BsubPc as can been seen by a comparison
of Fig. 1a and 1d. In the case of ClPhO-BsubPc, while it does
organize into discernible dimers, the arrangement of dimers relative
to one another is markedly different than in the case of FPhO-BsubPc
and IPhO-BsubPc.
In an effort to explain the uniqueness of BrPhO-BsubPc and what
structural features might be influencing its formation, we computed
the electrostatic potential surface for each of FPhO-BsubPc, ClPhO-
BsubPc and BrPhO-BsubPc using the 6-31G* basis set with the
B3LYP DFT method (as implemented in the commercial software
package Spartan ’06) and IPhO-BsubPc using instead the 6-311G*
basis set, the results of which are illustrated in Fig. S9, S10, 3 and S11,
respectively.† According to these calculations, considering first
BrPhO-BsubPc, a region of relative electron deficiency is present in
the p-system at the boron atom on the underside of the molecule,
while a moderate yet noticeable electron surplus is present around the
circumference of the bromine atom (Fig. 3). If we consider the spatial
arrangement of these two areas of electron deficiency and surplus
within the crystal structure, they are oriented in such a way and at
In contrast, when grown from benzene/heptane the crystal struc-
ture of BrPhO-BsubPc (Fig. 1c) does not show the association of
pairs of BsubPc molecular fragments into dimers; rather, it is
arranged into 1D ribbons of BsubPc molecules. The bromine of one
ꢀ
ꢀ
a suitable distance (Br–B 3.850 A and Br–p 3.380 A, as mentioned
above) to constitute an electrostatic interaction between the bromine
atom and the p-system of the BsubPc molecular fragment. However,
the same electrostatic distribution can also be found in the remaining
derivatives (see Fig. S7, S8 and S9 for FPhO-BsubPc, ClPhO-BsubPc
and IPhO-BsubPc, respectively).† Clearly, it is not simply the elec-
trostatic interaction which is motivating the formation of the unique
solid-state molecular packing of a-BrPhO-BsubPc.
Examination and comparison of Fig. S9, S10, 3 and S11† will also
show the expected change in size of the halogen on going from
fluorine to iodine. We are therefore left with the following explana-
tion in an attempt to describe the uniqueness of a-BrPhO-BsubPc: it
is not only the electrostatic interaction between the BsubPc molecular
Scheme
1 Synthesis of para-halophenoxy-BsubPcs (2a–d) from
Cl-BsubPc (1). Conditions: (i) 5 equiv. toluene, reflux, HCl.
3654 | CrystEngComm, 2011, 13, 3653–3656
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Fig. 1 Illustration of the molecular packing arrangement within the single crystal (extended beyond the unit cell) of (a) FPhO-BsubPc, (b) ClPhO-
BsubPc, (c) a-BrPhO-BsubPc, (d) b-BrPhO-BsubPc and (e) IPhO-BsubPc. Colours: carbon ¼ grey; nitrogen ¼ blue; boron ¼ light brown; fluorine ¼
violet; chlorine ¼ green; bromine ¼ yellow; iodine ¼ dark brown. Hydrogens omitted for clarity. (a) Redrawn from ref. 3.
fragment and the halogen atom but rather the unique combination of
the electrostatics of the molecule, the size of the bromine atom and
the size of the underside of the bowl of the BsubPc ligand which leads
to the formation this new molecular packing arrangement. This new
packing motif does place the phenoxy fragment over a lobe of the
BsubPc ligand; it can be formed without placing strain on the bond
angles within the BrPhO-BsubPc molecule.
In summary, we have observed a new crystal packing motif for
BsubPcs. This different packing structure occurs only in the case of
BrPhO-BsubPc and not for the other para-halophenoxy-BsubPcs
This journal is ª The Royal Society of Chemistry 2011
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ꢃ
ꢃ
ꢃ
3
ꢀ
(2) , b ¼ 78.811(2) , g ¼ 68.0100(19) , V ¼ 1184.74(8) A , T ¼ 150(1)K,
ꢁ
space group P1, Z ¼ 2, 12 718 reflections measured, 5379 independent
reflections (Rint ¼ 0.0437). The final R1 value was 0.0413 (I > 2s(I)). The
final wR(F2) value was 0.0906 (I > 2s(I)). The final R1 value was 0.0659
(all data). The final wR(F2) value was 0.1009 (all data).
ꢂ ꢂ
1 C. G. Claessens, D. Gonzalez-Rodrıguez, B. del Rey and T. Torres,
Chem. Rev., 2002, 102, 835–853.
ꢂ
ꢂ
ꢂ
2 (a) C. G. Claessens, D. Gonzalez-Rodrıguez, T. Torres, F. Agullo-
Lopez, I. Ledoux, J. Zyss, V. R. Ferro and J. M. G. de la Vega, J.
ꢂ
Phys. Chem. B, 2005, 109, 3800–3806; (b) G. E. Morse,
M. G. Helander, J. F. Maka, Z. H. Lu and T. P. Bender, ACS
ꢂ
Appl. Mater. Interfaces, 2010, 2(7), 1934–1944; (c) D. D. Dıaz,
H. J. Bolink, L. Cappelli, C. G. Claessens, E. Coronado and
T. Torres, Tetrahedron Lett., 2007, 48, 4657–4660; (d)
K. L. Mutolo, E. I. Mayo, B. P. Rand, S. R. Forrest and
M. E. Thompson, J. Am. Chem. Soc., 2006, 128, 8108–8109; (e)
H. Kumar, P. Kumar, R. Bhardwaj, G. D. Sharma, S. Chand,
S. C. Jain and V. Kumar, J. Phys. D: Appl. Phys., 2009, 42, 015103;
(f) H. Gommans, D. Cheyns, T. Aernouts, C. Girotto,
J. Poortmans and P. Heremans, Adv. Funct. Mater., 2007, 17, 2653–
2658; (g) T. Yasuda and T. Tsutsui, Mol. Cryst. Liq. Cryst., 2007,
462, 3–9; (h) H. Gommans, T. Aernouts, B. Verreet, P. Heremans,
A. Medina, C. G. Claessens and T. Torres, Adv. Funct. Mater.,
2009, 19, 3435–3439.
Fig. 2 Illustration of the area of the bromine atom and the boron of its
nearest neighbour in a-BrPhO-BsubPc.
3 A. S. Paton, G. E. Morse, A. J. Lough and T. P. Bender,
CrystEngComm, 2011, 13, 914, DOI: 10.1039/C0CE00599A.
4 R. Potz, M. Goldner, H. Huckstadt, U. Cornelissen, A. Tutass and
H. Homborg, Z. Anorg. Allg. Chem., 2000, 626, 588–596, CCDC
reference KAJPEQ.
5 K. Kasuga, T. Idehara, M. Handa, Y. Ueda, T. Fujiwara and K. Isa,
Bull. Chem. Soc. Jpn., 1996, 69, 2559–2563, CCDC reference
RUGJOS.
6 Y. Inokuma, J. H. Kwon, T. K. Ahn, M. C. Yoo, D. Kim and
A. Osuka, Angew. Chem., Int. Ed., 2006, 45, 961–964, CCDC
reference PEFWAZ.
7 M. K. Engel, J. Yao, H. Maki, H. Takeuchi, H. Yonehara and C. Pac,
Rep. Kawamura Institute of Chem.Res., 1997, 9, 53. CCDC reference
UCIJOF.
Fig. 3 Electrostatic potential 3D mapped isosurface plot of BrPhO-
BsubPc generated using the 6-31G* basis set with the B3LYP DFT
method. Areas of electron deficiency are coloured blue; areas of electron
excess are colored red.
presented in this study. Given the similar electrostatic distributions
for all compounds in this study, we must conclude the unique motif
observed (a-BrPhO-BsubPc) is a result of the combination of the
electrostatics and the particular size of the bromine atom giving
a favourable p–Br interaction that directs its solid-state packing.
Based on computer aided modelling, indications are that this new
form is a kinetically favoured polymorph.
8 C. G. Claessens and T. Torres, Angew. Chem., Int. Ed., 2002, 41,
2561–2677.
9 A. S. Paton, G. E. Morse, J. F. Maka, A. J. Lough and T. P. Bender,
Acta Crystallogr., Sect. E: Struct. Rep. Online, 2010, 66,
o3059.
10 M. D. Prasanna and T. N. Guru Row, Cryst. Eng., 2000, 3, 135–
154.
11 R. K. R. Jetti, A. Nangia, F. Xue and T. C. W. Mak, Chem. Commun.,
2001, 919–920.
12 A. Noman, M. M. Rahman, R. Bishop, D. C. Craig and
M. L. Scudder, CrystEngComm, 2003, 5(75), 422–428.
13 C. Bustos, C. Sanchez, E. Schott, M. T. Garland and L. Alvarez-
Thon, Acta Crystallogr., Sect. E: Struct. Rep. Online, 2006, 62,
m3104–m3106.
Notes and references
‡ For a description of the terminology used to describe BsubPcs,
specifically concave and convex face, see ref. 1.
x Crystal data for a-BrPhO-BsubPc: C30H16BBrN6O, M ¼ 567.21,
14 T. Fukuda, J. R. Stork, R. J. Potucek, M. M. Olmstead, B. C. Noll,
N. Kobayashi and W. S. Durfee, Angew. Chem., Int. Ed., 2002, 41,
2565–2568.
15 G. E. Morse, J. F. Maka, A. J. Lough and T. P. Bender, Acta
Crystallogr., Sect. E: Struct. Rep. Online, 2010, 66, o3057–o2974.
16 M. S. Rodriguez-Morgade, C. G. Claessens, A. Medina, D. Gonzalez-
Rodriguez, E. Gutierrez-Puebla, A. Monge, I. Alkorta, J. Elguero and
T. Torres, Chem.–Eur. J., 2008, 14, 1342–1350.
ꢀ
ꢀ
ꢀ
monoclinic, a ¼ 15.7312(12) A, b ¼ 10.2246(9) A, c ¼ 16.4141(13) A, a ¼
ꢃ
ꢃ
ꢃ
3
ꢀ
90 , b ¼ 113.281(5) , g ¼ 90 , V ¼ 2425.2(3) A , T ¼ 150(1) K, space
group P21/n, Z ¼ 4, 14 248 reflections measured, 5448 independent
reflections (Rint ¼ 0.0961). The final R1 value was 0.0638 (I > 2s(I)). The
final wR(F2) value was 0.1388 (I > 2s(I)). The final R1 value was 0.1368
(all data). The final wR(F2) values were 0.1690 (all data).
{ Crystal data for b-BrPhO-BsubPc: C30H16BBrN6O, M ¼ 567.21,
ꢀ
ꢀ
ꢀ
17 A. Bondi, J. Phys. Chem., 1964, 68, 441–451.
triclinic, a ¼ 10.1389(4) A, b ¼ 11.0056(4) A, c ¼ 11.6749(5) A, a ¼ 86.929
3656 | CrystEngComm, 2011, 13, 3653–3656
This journal is ª The Royal Society of Chemistry 2011