B···π-aromatic and C-H···B interactions in co-crystals of aromatic amine N-oxides with p-phenylenediboronic acid

Article abstract of DOI:10.1016/j.molstruc.2008.11.028

Co-crystals of p-phenylenediboronic acid with four aromatic N-oxides namely pyridine N-oxide, quinoline N, N′-dioxide, isoquinoline N, N′-dioxide and 4,4′-dipyridine N, N′-dioxide are prepared and are structurally characterized. The stacking pattern in ea

Full text of DOI:10.1016/j.molstruc.2008.11.028

Journal of Molecular Structure 920 (2009) 350–354
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Bꢀꢀꢀ
p
-aromatic and C–HꢀꢀꢀB interactions in co-crystals of aromatic amine
N-oxides with p-phenylenediboronic acid
*
Rupam Sarma, Jubaraj Bikash Baruah
Department of Chemistry, Indian Institute of Technology Guwahati, 781 039 Assam, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 26 October 2008
Received in revised form 12 November 2008
Accepted 13 November 2008
Available online 24 November 2008
Co-crystals of p-phenylenediboronic acid with four aromatic N-oxides namely pyridine N-oxide, quino-
line N, N0-dioxide, isoquinoline N, N0-dioxide and 4,40-dipyridine N, N0-dioxide are prepared and are struc-
turally characterized. The stacking pattern in each case is found to be different. An interesting stacking
effect that, sandwiches the boronic acid groups by pyridine N-oxide rings and associated through g2
and g3 type B–
with p-phenylenediboronic acid Bꢀꢀꢀ
p
interactions is presented. In the structures of co-crystals of aromatic amine N-oxides
aromatic and C–HꢀꢀꢀB interactions are observed.
Ó 2008 Elsevier B.V. All rights reserved.
p
Keywords:
Diboronic acid
N-Oxides
Co-crystals
Weak interactions
C–HꢀꢀꢀB interactions
1. Introduction
have studied the structural aspects of four co-crystals of aromatic
amine N-oxide with p-phenylenediboronic acid.
The weak interactions are of general interest in chemistry and
biology [1–4]. Information gathered from structural studies of a
particular class of compounds helps in establishing new interac-
tions. The compounds containing boronic acid functional group
are important as precursor for organic transformations [5–11]
and they are also used in medicine [12–13]. Phenylboronic acids
are toxic to microorganisms but they are relatively harmless to
higher animals [14–17]. The hydroxy group of boronic acid can
be replaced by various diols and based on this reactivity towards
diols, sensors for sugars are devised [18–19]. Despite susceptibility
of boronic acid towards organic reactions, a good numbers of host–
guest chemistry of boronic acids are available [20–25]. The self-
assemblies of boronic acid have structural features that are similar
to analogous carboxylic acid and structural comparisons are being
made [26–30]. The framework structures of boronic acids with
4,40-bipyridine type linkers are studied [31]. On the other hand
the N-oxides are known to form inclusion compounds [32–34]
and some N-oxide co-crystals are of medicinal importance [35–
36]. Boron as a covalent center in a molecule has high affinity for
oxygen, thus, framework structures constructed with N-oxides
are expected to have new weak interactions. A nucleophile would
interact with boronic acid at the electron deficient boron center
and also with OH groups to form H-bond, thereby leading to chem-
ical reactions or host–guest complexes. With these objectives we
2. Materials and methods
2.1. General
The p-phenylenediboronic acid, pyridine N-oxide, quinoline N-
oxide, isoquinoline N, N0-dioxide, and 4,40-bipyridine N, N0-dioxide
were obtained from Sigma–Aldrich Chemical Co., USA and directly
used without further purifications.
UV–visible spectra were recorded on a Perkin-Elmer Lambda
750 UV/vis spectrometer.
1H NMR spectra were collected in a Varian 400 MHz FT-NMR
instrument. The X-ray single crystal diffraction data were collected
at 296 K with MoK radiation (k = 0.71073 Å) using a Bruker Nonius
a
SMART CCD diffractometer equipped with graphite monochroma-
tor. The SMART software was used for data collection and also
for indexing the reflections and determining the unit cell parame-
ters; the collected data were integrated using SAINT software. The
structures were solved by direct methods and refined by full-ma-
trix least-squares calculations using SHELXTL software. All the
non-H atoms were refined in the anisotropic approximation
against F2 of all reflections. The H-atoms, except those attached
to oxygen atoms were placed at their calculated positions and re-
fined in the isotropic approximation; those attached to oxygen
were located in the difference Fourier maps, and refined with iso-
tropic displacement coefficients. The crystal data for the co-crys-
tals are given in Table 1.
* Corresponding author. Tel.: +91 361 2582301; fax: +91 361 2690762.
E-mail address: juba@iitg.ernet.in (J.B. Baruah).
0022-2860/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2008.11.028

R. Sarma, J.B. Baruah / Journal of Molecular Structure 920 (2009) 350–354
351
Table 1
Crystallographic parameters of the co-crystals.
Compound No.
A
B
C
D
Formulae
Mol. wt.
Crystal system
Space group
a/Å
C16H18B2N2O6
355.94
Monoclinic
P21/c
10.685 (13)
7.111 (9)
12.140 (14)
90.00
115.05 (3)
90.00
835.6 (18)
2
1.415
0.106
None
372
C24H22B2N2O6
456.06
C42H36B2N4O8
746.37
C16H16B2N2O6
353.93
Triclinic
Triclinic
Triclinic
ꢀ
ꢀ
ꢀ
P1
P1
P1
6.807 (16)
7.777 (2)
11.578 (4)
106.447 (12)
99.51 (12)
101.72 (9)
559.2 (3)
1
1.354
0.096
None
238
8.104 (5)
10.057 (6)
12.627 (7)
84.15 (4)
78.47 (4)
67.19 (4)
929.17 (9)
1
1.334
0.092
None
390
6.669 (8)
7.598 (10)
8.285 (11)
100.16 (11)
106.99 (9)
92.94 (9)
392.85 (9)
1
1.496
0.112
None
184
b/Å
c/Å
a
/°
b/°
c
/°
V/Å3
Z
Density/Mgmꢁ3
Abs. Coeff. /mmꢁ1
Abs. correction
F(000)
Total no. of reflections
6351
4359
5296
2963
Reflections, I > 2
Max. 2h/°
r(I)
1632
26.50
2695
28.38
2431
23.10
1424
25.48
Ranges (h, k, l)
ꢁ13 <= h <= 13, ꢁ6 <= k <= 8,
ꢁ9 <= h <= 3, ꢁ8 <= k <= 10,
ꢁ8 <= h <= 8, ꢁ11 <= k <= 11,
ꢁ8 <= h <= 7, ꢁ9 <= k <= 9,
ꢁ10 <= l <= 10
97.6
ꢁ15 <= l <= 14
ꢁ15 <= l <= 15
ꢁ13 <= l <= 13
Complete to 2h (%)
Refinement method
Data/restraints/
parameters
94.9
96.1
93.3
Full-matrix least-squares on F2
1632/0/118
Full-matrix least-squares on F2
2695/0/156
Full-matrix least-squares on F2
2431/0/256
Full-matrix least-squares on F2
1424/0/120
Goof (F2)
1.529
1.074
1.069
1.067
R indices [I > 2
R indices (all data)
r
(I)]
0.1093
0.1304
0.0458
0.0626
0.0710
0.0821
0.0454
0.0622
2.2. Spectroscopic data for the co-crystals
quinoline N-oxide, and 4,40-bipyridine N, N0-dioxide are easily
prepared by mixing respective solution of the corresponding N-
oxide with the p-phenylenediboronic acid. The co-crystals have
characteristic IR absorptions in the range 1211–1253 cmꢁ1 due
to N–O stretching frequency. The structures of each of them are
determined and their packing patterns are shown in Fig. 1A–D.
Each of these adduct has the N–OꢀꢀꢀH hydrogen bond interaction
as the primary interactions to form a network structure; these
structures are further held by weak interactions.
The common point in each of these structures is that, the strong
hydrogen bonding interactions between the two oxygen atoms of
N-oxide from two independent N-oxide molecules with the two
B–OH groups of the p-phenylenediboronic acid molecules. This
type of interactions over-powers the original hydrogen bonding
interactions between the B–OH groups of parent p-phenylenedibo-
ronic acid molecules [26–30]. The hydrogen bond parameters for
these interactions are listed in Table 2. The packing patterns of
these co-crystals show that each structure is associated with differ-
ent types of weak interactions. The 1:1 co-crystal of pyridine N-
oxide has the B(OH)2 groups anchored to N-oxides through C–
By mixing p-phenylenediboronic acid (0.165 g, 1 mmol) and pyr-
idine N-oxide (0.190 g, 2 mmol) in a mixed solvent methanol/tolu-
ene (4:1) gave the corresponding 1:1 co-crystals (A). The crystals
were obtained after seven days. Yield (crystals) 46%. IR (KBr,
cmꢁ1): 3209 (b), 1615 (m), 1510 (m), 1472 (m), 1423 (m), 1401
(m), 1369 (s), 1340 (s), 1235 (s), 1192 (s) 1165 (s), 1192 (m), 1139
(m), 1094 (m), 1058 (m), 836 (s), 759 (m). 1H NMR (DMSO-d6,
400 MHz): 8.2 (2H, d, J = 8.0 Hz), 8.0 (4H, s), 7.7(4H,s), 7.4 (2H, t,
J = 8.0 Hz), 7.3 (1H, t, J = 8.0 Hz). Layering an aqueous solution of p-
phenylenediboronic acid (0.165 g, 1 mmol) over a quinoline N-oxide
(0.290 g, 2 mmol) solution in toluene yielded pure crystalline co-
crystals (B) (yield, 26%). IR (KBr, cmꢁ1): 3303 (b), 1638 (m), 1577
(m), 1514 (m), 1430 (m), 1399 (s), 1380 (s), 1329 (s) 1311 (s), 1263
(s), 1229(m), 1211(m), 1162 (s), 1135 (s), 1084 (m), 1043 (s), 1008
(s), 880 (m), 848 (s), 804 (s), 776 (s). 1H NMR (DMSO-d6, 400 MHz):
8.6 (1H, d, J = 8.0 Hz), 8.5 (1H, d, J = 8.0 Hz), 8.1 (1H, d, J = 8.0 Hz),
8.0 (4H, s), 7.9 (1H, d, J = 8.0 Hz), 7.8 (2H, m), 7.7 (4H, s), 7.4 (1H, q,
J = 8.0 Hz). Similarly, the co-crystals of isoquinoline N-oxide with
p-phenylenediboronic acid (2:1) (C) were obtained; but in very low
yield of crystalline pure product (2%). IR of the sample and NMR of
solution shows identical peak to that of the parent compounds, so
these are not listed. A dimethyl sulfoxide solution of p-phenylene-
diboronic acid (0.165 g, 1 mmol) and 4,40-bipyridine N, N0-dioxide
(0.376 g, 2 mmol) led to the formation of co-crystals (1:1). Yield of
the pure crystalline complex was found to be 82%. IR (KBr, cmꢁ1):
3400 (b), 1633 (s), 1508 (m), 1480 (s), 1437 (m), 1398 (m), 1361
(m), 1328 (s), 1257 (m), 1237 (s), 1195 (m), 1155 (s), 1116 (m),
1097 (m), 1051 (m), 1026 (m), 820 (s), 730 (m). 1H NMR (DMSO-d6,
400 MHz): 8.3 (4H, d, J = 8.0 Hz), 7.6 (4H, d, J = 8.0 Hz), 7.3 (8H, s).
HꢀꢀꢀO, and B–
sandwich a pyridine N-oxide ring between two B(OH)2 units
through interactions. The distance of separa-
2 and 3-type of B–
p interactions. The B–p interactions in the co-crystals
g
g
p
tion between the N-oxide containing rings and B(OH)2 units are
3.40 Å and 3.52 Å, respectively. On co-crystal formation with N-
oxide, the complementing properties among the parent boronic
acids are lost. The C–HꢀꢀꢀO interactions become dominating among
the weak interactions; the interactions are listed in Table 2.
The quinoline N-oxide forms a 1:1 co-crystal whereas isoquino-
line N-oxide forms 2:1 co-crystals with p-phenylenediboronic acid.
These co-crystals self-assembles through strong hydrogen bond
interactions between the N+–Oꢁ of N-oxide and the O–H of the
boronic acid groups. In both these cases extensive C–HꢀꢀꢀO and
O–HꢀꢀꢀO hydrogen bond interactions are observed (Fig. 1B and C).
3. Results and discussion
3.1. Structural study
However, significantly different
tals are observed. The co-crystal of quinoline N-oxide is devoid of
-interactions but in the case of the co-crystal of isoquinoline N-
oxide -stacking effect is predominant. In the lattice of the co-crys-
p-interactions in the two co-crys-
The co-crystals of p-phenylenediboronic acid with different aro-
matic N-oxides namely pyridine N-oxide, quinoline N-oxide, iso-
p
p

352
R. Sarma, J.B. Baruah / Journal of Molecular Structure 920 (2009) 350–354
Fig. 1. The weak interactions in the structures of co-crystals of p-phenylenediboronic acid with (A) pyridine N-oxide, (B) quinoline N-oxide, (C) isoquinoline N-oxide, (D) 4,40-
bipyridine N, N0-dioxide. In each case inset are the structures of the corresponding co-crystals.

R. Sarma, J.B. Baruah / Journal of Molecular Structure 920 (2009) 350–354
353
Table 2
Hydrogen bond parameters in co-crystals of p-phenylenediboronic acid.
D–HꢀꢀꢀA
dD–H (Å)
dHꢀꢀꢀ A (Å)
dD ꢀꢀꢀ A (Å)
<D–HꢀꢀꢀA (°)
With pyridine N-oxide
O2–H2AꢀꢀꢀꢀO1 [ꢁx, ꢁ1/2 + y, 1/2 ꢁ z]
O3–H3AꢀꢀꢀꢀO1 [ꢁx, 1 ꢁ y, ꢁz]
C1–H1ꢀꢀꢀꢀO3 [ꢁx, 1 ꢁ y, ꢁz]
C5–H5ꢀꢀꢀꢀO3 [ꢁx, 1/2 + y, 1/2 ꢁ z]
C6–H6ꢀꢀꢀꢀO1 [ꢁx, 1 ꢁ y, ꢁz]
0.82
0.99
0.93
0.93
0.93
1.92
1.71
2.60
2.35
2.47
2.69 (6)
2.70 (6)
3.29 (7)
3.26 (7)
3.37 (7)
158
176
131
165
161
With quinoline N-oxide
O2–H2ꢀꢀꢀꢀO1 [ꢁx, 1 ꢁ y, 1 ꢁ z]
O3–H3ꢀꢀꢀꢀO1 [1 ꢁ x, 1 ꢁ y, 1 ꢁ z]
C1–H1ꢀꢀꢀꢀO3 [x, y, 1 + z]
C5–H5ꢀꢀꢀꢀO2
0.82
0.82
0.93
0.93
0.93
2.03
2.11
2.59
2.42
2.49
2.81 (2)
2.81 (1)
3.50 (2)
3.26 (3)
3.34 (2)
157
144
168
150
152
C12–H12ꢀꢀꢀꢀO1 [ꢁx, 1 ꢁ y, 1 ꢁ z]
With isoquinoline N-oxide
O3–H3ꢀꢀꢀꢀO1 [1 ꢁ x, 1 ꢁ y, ꢁz]
O4–H4ꢀꢀꢀꢀO2 [x, y, ꢁ1 + z]
C10–H10ꢀꢀꢀꢀO1 [ꢁ1 + x, y, 1 + z]
C1–H1ꢀꢀꢀꢀO1
0.82
0.82
0.93
0.93
1.98
2.01
1.93
1.89
2.71 (4)
2.76 (3)
2.85 (4)
2.82
149
152
171
174
With 4,40-bipyridine N, N0-dioxide
O2–H2ꢀꢀꢀꢀO1
0.82
0.82
0.93
2.09
2.03
2.56
2.87 (3)
2.79 (2)
3.45 (3)
157
152
161
O3–H3ꢀꢀꢀꢀO1 [1 + x, y, z]
C5–H5ꢀꢀꢀꢀO2 [ꢁ1 + x, y, z]
tal of quinoline N-oxide and p-phenylenediboronic acid, the quin-
oline N-oxide molecules are placed in a head to tail arrangement,
whereas in the later case the isoquinoline N-oxide molecules are
positioned in head to head arrangement. The head to head sand-
wiched arrangement is electro-statistically unfavorable; but due
to the complementarities for hydrogen bond formation they prefer
to have the dimeric arrangement adopting a non-sandwiched
arrangement as shown in Fig. 1C. These dimers are formed through
C10–HꢀꢀꢀO1 and C1–HꢀꢀꢀO2 interactions. These dimeric pairs consti-
tute a layered structure that are held by the C–HꢀꢀꢀO and O–HꢀꢀꢀO
shows the interaction between the respective pairs. Fig. 2(a)
shows the effect of pyridine N-oxide on the absorption spectrum
of p-phenylenediboronic acid. The p-phenylenediboronic acid ab-
sorbs at 274 nm and 229 nm, but with the addition of pyridine N-
oxide solution the peak at 274 nm undergoes a blue shift to
263 nm and the peak at 229 nm shifts to 231 nm. Both the peaks
are accompanied by a change in the absorption with a hyperchro-
mic shift. The peak at 263 nm is characteristic of pyridine N-oxide
so increase in the intensity with concentration is obvious. How-
ever, the increase in the absorption coefficient of the peak at
231 nm may be attributed to the formation of the co-crystal. Also
the presence of the isobestic point at 222 nm shows the presence
of two species at equilibrium. To check the origin of hyperchro-
mic shift of the absorption peak at ꢂ231 nm we have checked
the absorption spectra of a mixture of components viz. p-phenyl-
enediboronic acid and ethylene glycol followed by the addition of
pyridine N-oxide solution (Fig. 2b). Interestingly no change in the
absorption coefficient of the peak at ꢂ231 nm is observed in this
case. From these observation it can be interpreted that ethylene
glycol interact with the diboronic acid first [18–19] and it renders
the pyridine N-oxide to bind with the acid; further evidence
comes from the disappearance of the isobestic point in this set
of experiments. Fig. 2c shows the absorption spectra of the 4,40-
bipyridyl N, N0-dioxide upon addition of p-phenylenediboronic
acid. In this case also the presence of the isobestic point at
288 nm shows the presence of two different species at equilib-
rium. The 4, 40-bipyridyl N, N0-dioxide absorbs at 223 nm and
330 nm. Upon addition of the p-phenylenediboronic acid the va-
lue of the absorption coefficient of the peaks changes, the inten-
sity of the peak at 223 nm increases, which is due to gradual
increase in the concentration of the p-phenylenediboronic acid.
However, the absorption coefficient of the peak at 330 nm de-
creases; which may be attributed to the formation of the co-
crystals.
interactions of boronic acid and
ers, one above another, and placed offset to each other. The
separation between the layers is 3.34 Å within the generally re-
ferred limit of -stacks [37]. In the co-crystals of quinoline N-oxide
p–p interactions between two lay-
p–p
p
and p-phenylenediboronic acid, the boronic acid groups are placed
parallel to each other. Two groups from two opposite ends of the
parent diboronic acid are parallel with two boron atoms placed
one above the other. The distance of separation between these
two parallel boron atoms is 3.98 Å. The hydrogen bond parameters
of the weak C–HꢀꢀꢀO interactions in the lattices of the co-crystals
are given in Table 2.
The co-crystals of the 4,40-bipyridyl N, N0-dioxide and p-phenyl-
enediboronic acid posses conventional O–HꢀꢀꢀO, C–HꢀꢀꢀO as well as
less conventional C–HꢀꢀꢀB [38] and Bꢀꢀꢀp interactions. The strong
NꢀꢀꢀOH interactions between the N-oxide and boronic acid O–H
namely O2–H2ꢀꢀꢀꢀO1 and O3–H3ꢀꢀꢀꢀO1 makes a sheet like structures
(Table 2). Generally, a B–O interaction is expected between the
lone pair of oxygen with a vacant p-orbital of boron atom. How-
ever, the aromatic rings in the co-crystal are oriented in such a
way that the oxygen atom of N-oxide is involved in O–HꢀꢀꢀO, C–
HꢀꢀꢀO to form layered structure. Among the layers the oxygen atom
of N-oxide occupies a space just above the boron atom with a dis-
tance of separation 3.10 Å, based on this distance of separation and
projection of the lone pair of oxygen of N-oxide (Fig. 1D) it is pro-
posed that there is a Bꢀꢀꢀ
p
interaction among the layers. It may be
mentioned that the Bꢀꢀꢀ
p interactions are rarely found interactions
4. Conclusions
[39–43].
In conclusion, structural aspects of few co-crystals of boronic
3.2. Solution study
acids with N-oxides are studied and observed that the interactions
in each case is different and some rare interactions such as Bꢀꢀꢀ
p
The ultraviolet spectra of solutions of p-phenylenediboronic
acid with pyridine N-oxide as well as with 4,40-bipyridyl N-oxide
interactions and C-HꢀꢀꢀB interactions are present in this class of

354
R. Sarma, J.B. Baruah / Journal of Molecular Structure 920 (2009) 350–354
Acknowledgement
The authors thank Department of Science and Technology, New
Delhi, India for financial support.
References
[1] T. Steiner, Angew. Chem. Int. Ed. 41 (2002) 748–765.
[2] G. Desiraju, Acc. Chem. Res. 35 (2002) 5731–5765.
[3] T. Threlfall, Analyst 120 (1995) 2435–2460.
[4] S.L. James, Encyclopedia of Supramolecular Chemistry, Mercel Dekker, New
York, 2004. pp. 1093–1099.
[5] A. Suzuki, H.C. Brown, Organic Syntheses via Boranes, Aldrich Chemical
Company, Milwaukee, 2003. Vol. 3.
[6] N. Miyaura, A. Suzuki, Chem. Commun. (1979) 866–867.
[7] N. Miyaura, T. Yanagi, A. Suzuki, Synth. Commun. (1979) 513–519.
[8] S.V. Ley, A.W. Thomas, Angew. Chem. Int. Ed. 42 (2003) 5400–5449.
[9] S. Itsuno, T. Matsumoto, D. Sato, T. Inoue, J. Org. Chem. 65 (2000) 5879–
5881.
[10] D. Hall, Boronic Acids: Preparation, Applications in Organic Synthesis and
Medicine, Wiley-VCH, Weinheim, Germany, 2005.
[11] T.D. James, M.D. Phillips, S. Shinkai, Boronic Acids in Saccharide Recognition,
RSC Publishing, Cambridge, UK, 2006.
[12] A.M. Doherty (Ed.), Annual Reports in Medicinal Chemistry, vol. 39, Elsevier
Inc., Netherlands, 2004, pp. 345–346.
[13] N.A. Petasis, Aust. J. Chem. 60 (2007) 795–798.
[14] A. Michaelis, P. Becker, Ber. 13 (1880) 58–61.
[15] A. Michaelis, P. Becker, Ber. 15 (1882) 180–185.
[16] W. Seaman, J.R. Johnson, J. Am. Chem. Soc. 53 (1931) 711–723.
[17] S. Gronowitz, T. Dalgren, J. Namvedt, C. Roos, B. Sjoberg, U. Forsgren, Acta
Pharm. Suecica 8 (1971) 377–390.
[18] O. Hirata, M. Yamamoto, K. Sugiyasu, Y. Kubo, M. Ikeda, M. Takeuchi, S. Shinkai,
J. Supramol. Chem. 2 (2003) 133–142.
[19] A.-J. Tong, A. Yamauchi, T. Hayashita, Z.-Y. Zhang, B.D. Smith, N. Teramae, Anal.
Chem. 73 (2001) 1530–1536.
[20] N. Christinat, R. Scopelliti, K. Severin, Angew. Chem. Int. Ed. 47 (2008) 848–1852.
[21] N. Iwasawa, H. Takahagi, J. Am. Chem. Soc. 129 (2007) 7754–7755.
[22] B. Victor, V. Raul, L. Rolando, G.-A. Carolina, H. Herbert, B.I. Hiram, Z.-R. Luis, S.
Rosa, F. Norberto, Inorg. Chem. 45 (2006) 2553–2561.
[23] K. Koumoto, T. Yamashita, T. Kimura, R. Luboradzki, S. Shinkai,
Nanotechnology 12 (2001) 25–31.
[24] K.E. Maly, N. Malek, J-H. Fournier, P. Rodriguez-Cuamatzi, T. Maris, J.D. Wuest,
Pure Appl. Chem. 78 (2006) 1305–1321.
[25] N. SeethaLekshmi, V.R. Pedireddi, Cryst. Growth Des. 7 (2007) 944–949.
[26] S.J. Rettig, J. Trotter, Can. J. Chem. 55 (1977) 3071–3075.
[27] J.H. Fournier, T. Maris, J.D. Wuest, W. Guo, E. Galoppini, J. Am. Chem. Soc. 125
(2003) 1002–1006.
[28] G. Rodriguez-Cuamatzi, P. Höpfl, Angew Chem. In. Ed. Eng. 43 (2004)3041–3044.
[29] P. Rodriguez-Cuamatzi, O.I. Arillo-Flores, M.I. Bernal-Uruchurtu, H. Hoepfl,
Cryst. Growth Des. 5 (2005) 167–175.
[30] P. Rogowska, M.K. Cyranski, A. Sporzynski, A. Ciesielski, Tetrahedron. Lett. 47
(2006) 1389–1393.
[31] V.R. Pedireddi, N. SeethaLekshmi, Tetrahedron Lett. 45 (2004) 1903–1906.
[32] B. Hatano, A. Aikawa, H. Katagiri, H. Tagaya, H. Takahashi, Chem. Lett. 36
(2007) 1272–1273.
Fig. 2. (a) UV-spectra of p-phenylenediboronic acid (10ꢁ3 M) upon addition of
pyridine N-oxide solution (10ꢁ3 M) (inset is the absorption spectra of p-phenyl-
enediboronic acid). (b) UV-spectra of p-phenylenediboronic acid (10ꢁ3 M), ethylene
glycol (10ꢁ3 M) upon additionꢁo3f pyridine N-oxide solution (10ꢁ3 M). (c) UV-spectra
of 4,40-bipyridyl N-oxide (10 M) upon addition of p-phenylenediboronic acid
solution (10ꢁ3 M).
[33] B. Hatano, A. Aikawa, H. Katagiri, H. Tagaya, H. Takahashi, CrystEngComm 7
(2005) 44–52.
[34] V. Videnova-Adrabinska, E. Janeczko, Chem. Commun. (1999) 1527–1528.
[35] L.S. Reddy, N.J. Babu, A. Nangia, Chem. Commun. (2006) 1369–1371.
[36] N.J. Babu, S.L. Reddy, A. Nangia, Mol. Pharm. 4 (2007) 417–434.
[37] C. Janiak, J. Chem. Soc. Dalton Trans. (2000) 3885–3896.
[38] S.M. Melikova, K.S. Rutkowski, P. Rodziewicz, A. Koll, Polish J. Chem. 76 (2002)
1271–1285.
[39] N. Kitamura, E. Sakuda, J. Phys. Chem. A 109 (2005) 7429–7434.
[40] P. Tarakeshwar, S.J. Lee, J.Y. Lee, K.S. Kim, J. Phys. Chem. B 103 (1999) 184–
191.
molecules and the study suggests about ample avenues for looking
at the new interactions in the co-crystals of boronic acids.
[41] S.X. Tian, H.-B. Li, Y. Bai, J. Yang, J. Phys. Chem. A 112 (2008) 8121–8128.
[42] M. Filthaus, I.M. Oppel, H.F. Bettinger, Org. Biomol. Chem. 6 (2008) 1201–
1207.
[43] B. Zarychta, J. Zaleski, A. Sporzynski, M. Dabrowski, J. Serwatowski, Acta Cryst.
Sec. C C60 (2004) o344–o345.
Supplementary data
The CIF files of the co-crystals are deposited to Cambridge Crys-
tallographic Database and have the CCDC Nos. 703292–703295.