Host channel framework determined by C-H?π interaction in the inclusion crystal of 2,5-bis(diphenylmethyl)hydroquinone and benzaldehyde

Article abstract of DOI:10.1016/j.molstruc.2004.08.013

A new kind of host compound, 2,5-bis(diphenylmethyl)hydroquinone is designed and prepared. The crystal structure of the inclusion compound formed by the host with benzaldehyde was determined by single crystal X-ray diffraction. The result shows that the host exhibits a stable conformation through intramolecular CH?π interactions in the inclusion crystal, and benzaldehyde guest molecules are accommodated in the channel which is constructed by the hosts, in which intermolecular C-H?π interactions between the hosts, play an important role in the architecture of channel framework besides van der Waal's forces. The complex structure is further stabilized by strong hydrogen bonding (O1-H1?O1′) and two weak C-H?O interactions (C5′-H5′?O1, C3- H3?O1′) between the host and guest.

Full text of DOI:10.1016/j.molstruc.2004.08.013

Journal of Molecular Structure 733 (2005) 143–149
www.elsevier.com/locate/molstruc
Host channel framework determined by C–H/p interaction
in the inclusion crystal of 2,5-bis(diphenylmethyl)hydroquinone
and benzaldehyde
*
Wen-Sheng Guo , Fang Guo, He-Nan Xu, Lei Yuan, Zhong-Hua Wang, Jian Tong
Institute of Chemical Science and Engineering, Liaoning University, Shenyang 110036, People’s Republic of China
Received 17 May 2004; revised 6 August 2004; accepted 9 August 2004
Available online 12 October 2004
Abstract
A new kind of host compound, 2,5-bis(diphenylmethyl)hydroquinone is designed and prepared. The crystal structure of the inclusion
compound formed by the host with benzaldehyde was determined by single crystal X-ray diffraction. The result shows that the host
exhibits a stable conformation through intramolecular CH/p interactions in the inclusion crystal, and benzaldehyde guest molecules
are accommodated in the channel which is constructed by the hosts, in which intermolecular C–H/p interactions between the hosts,
play an important role in the architecture of channel framework besides van der Waal’s forces. The complex structure is further
stabilized by strong hydrogen bonding (O1–H1/O10) and two weak C–H/O interactions (C50–H50/O1, C3–H3/O10) between the
host and guest.
q 2004 Elsevier B.V. All rights reserved.
Keywords: 2,5-Bis(diphenylmethyl)hydroquinone; Inclusion compound; Hydrogen bonding; Inter- and intra-C–H/p interactions
1. Introduction
functional groups that can form strong and stable intra-
and inter-molecular interactions, provide a lot of useful
models to study the function of weak CH/p interactions in
the aggregation of molecules [4].
In past years, there has been increasing interest in the
study of weak intra- and inter-molecular interactions,
because of their important roles played in the various fields
of chemistry and biochemistry, such as crystal engineering,
supramolecular chemistry, molecular recognition and self-
assembly of molecules [1]. Interactions such as C–H/X
(X: the proton acceptor, such as O, N) systems are
commonly recognized as weak hydrogen bonds. Of all the
weak hydrogen bonds, the CH/p interaction could be
regarded as the weakest [2]. In recent years, much attention
has been paid to the CH/p interaction as an important
factor in the crystal packing and in determining the structure
of clathrate compounds [3]. Crystalline inclusion com-
pounds, in particular, organic molecules with many
Herein, we report a crystal structure of an inclusion
compound, in which 2,5-bis(diphenylmethyl) hydro-
quinone is a new host molecule that conforms to Weber’s
rules for host design [5], bearing hydroquinone as the core
fragment, diphenylmethyl fragment as a large bulky space
group, and hydroxyl moieties as hydrogen-bonding donors.
The result of structural analysis of the inclusion crystal
formed by the title compound shows that this host
molecule facilitates the formation of a channel type host
framework by the interaction of CH/p between hosts,
which is obviously different from the layer type structures
constructed by 2,5-bis(2,4-dimethylphenyl) hydroquinone
[6] and 2,5-diphenyl hydroquinone [7]. The new evidence,
i.e. weak inter- and intra-molecular CH/p interaction
playing an indispensable role in the crystal packing and in
* Corresponding author. Tel.: C86 24 86813912; fax: C86 24 62202053.
E-mail address: wensguo@lnu.edu.cn (W.-S. Guo).
0022-2860/$ - see front matter q 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2004.08.013

144
W.-S. Guo et al. / Journal of Molecular Structure 733 (2005) 143–149
determining the structure of the lattice clathrate, is
provided in this paper.
heating. After cooling and standing for a few days, five
inclusion compounds with DMF, DMSO, THF, Benzal-
dehyde and acetophenone were crystallized, and the pure
crystalline materials were obtained by further recrystalliza-
tion as the same crystalline condition. The components and
ratios of the complexes were confirmed by measurement of
1
m.p., IR and H NMR data.
2.4. Crystal structure determination of host with
benzaldehyde
Crystals suitable for X-ray investigation were obtained
by slow evaporation at room temperature. X-ray
single crystal determination was obtained using a Bruker
Axs P4 X-ray diffractometer with graphite monochro-
˚
2. Experimental section
mated Mo Ka radiation (lZ0.71073 A) with q/2q
scan mode in the range 2.158!q!258, K1%h%8,
K11%k%11, K11%l%11. Three standard intensities
were monitored after each group of 100 reflections and
no evidence of crystal decay was observed. The structure
was solved by direct methods and refined on F2 by full-
matrix least-squares calculation. All non-hydrogen atoms
refined with anisotropic thermal displacement parameters.
All of the hydrogen atoms were located in difference
electron density map and their positions were allowed to
refine together with individual isotropic temperature
factors. The detailed data and structure refinement are
listed in Table 1. Selected bonds and angles are listed in
Table 2.
2.1. General methods
The 1H NMR and 13C NMR spectra were recorded on a
Varian YH 300 MB instrument in DMSO-d6. The IR
spectra were obtained with KBr pellets on a Perkin–Elmer
983 FT infrared spectrophotometer.
2.2. Synthesis
Diphenylmethanol (8.0 g, 0.49 mol), hydroquinone
(2.2 g, 0.2 mol), and p-toluenesulfonic acid (1.0 g) and
70 ml toluene were added into a tri-neck-flask and stirred
and refluxed for 4 h under the protection of N2. The
product was recrystallized from ethyl acetate to obtain
the white crystals of pure host 8.2 g, m.p. 278–279 8C,
yield 87%.
Table 1
Crystallographic data for host with benzaldehyde
1H NMR: d(DMSO-d6): 8.6 (2H, s, OH), 7.0–7.3 (20H,
m, ArH, substituted), 6.3 (2H, s, ArH, framework), 5.7
(2H, m, C–H); d 8.6 peak disappeared after being exchanged
for D2O.
Empirical formula
Formula weight
Crystal color, habit
Crystal dimensions (mm)
Crystal temperature (K)
Crystal system
(C32H26O2)1/2$C7H6O
327.40
Yellow, block
0.4!0.4!0.3
293
13C NMR: d (DMSO-d6) (ppm): 146.7 (Ar, 1,4-C), 143.9
(Ar, 2,5-C), 116.5 (Ar, 3,6-C), 128.5 (4 substituted phenyls
10-C), 128.1 (4 substituted phenyls o-C), 125.9 (4 sub-
stituted phenyls m-C), 120.9 (4 substituted phenyls p-C),
48.9 (CH2–C). There are eight chemical shifts for carbon
atoms, also confirming the symmetry of the host. IR: nmax
(KBr): 3531 (s, OH), 3059 (w, ArH), 1598, 1491, 1448
Triclinic
P-1
Space group
Z
˚
a (A)
˚
b (A)
˚
c (A)
2
9.394(8)
10.099(8)
10.838(9)
106.62(4)
112.48(5)
94.09(5)
891.2(13)
1.224
a (8)
b (8)
g (8)
(s, Ar), 1166 (s, ArO) cmK1
.
3
˚
V (A )
Dx (g cmK3
)
2.3. Inclusion complexes preparation
m (mmK1
F(000)
Rint
)
0.077
348
Potential guest solvents, such as methanol, ethanol,
1-propanol, 2-propanol, cyclopentanol, formaldehyde, acet-
aldehyde, benzaldehyde, acetone, cyclopentanone, aceto-
phenone, 2,5-hexanedione, N-methyl-2-pyrrolidone, ethyl
acetate, methyl benzoate, THF, 1,4-dioxane, pyridine,
cyclohexylamine, 1-chloro-2,3-epoxypropane), DMSO,
and DMF, were used to dissolve the host by stirring or
0.027
No. of collected data (unique)
No. of data with IO2s(I)
No. of parameters varied
S
2794
1913
302
1.012
Rf/wRf
0.0463/0.1148
0.0731/0.1309
All data Rf/wRf

W.-S. Guo et al. / Journal of Molecular Structure 733 (2005) 143–149
145
some extent: (h)$DMF: 71 cmK1; (h)$DMSO: 375 cmK1
(h)$THF: 269 cmK1 (h)$Benzaldehyde: 111 cmK1
(h)$acetophenone: 240 cmK1
;
;
Table 2
Selected bond lengths (A) and angles (8)
˚
;
;
(h)$2,5-hexanedione:
O(1)–C(2)
C(1)–C(3)
C(1)–C(2)
C(1)–C(4)
C(2)–C(3)#1
C(3)–C(2)#1
C(4)–C(11)
C(4)–C(5)
C(5)–C(6)
C(5)–C(10)
C(6)–C(7)
C(7)–C(8)
C(8)–C(9)
C(9)–C(10)
1.369(3) C(11)–C(12)
1.387(3)
1.391(3)
1.386(4)
1.377(4)
1.374(5)
1.386(4)
1.219(3)
1.464(4)
1.381(4)
1.389(4)
1.373(5)
1.370(5)
1.380(5)
1.368(5)
149 cmK1, showing that hydrogen bond interactions
between the host hydroxyl and the functional group of the
guests may be involved in the crystal.
1.390(3) C(11)–C(16)
1.398(3) C(12)–C(13)
1.526(3) C(13)–C(14)
1.393(3) C(14)–C(15)
1.393(3) C(15)–C(16)
O(10)–C(10)
1.524(3)
3.2. Crystal structure of host with benzaldehyde
C(10)–C(20)
1.530(3)
C(20)–C(70)
1.382(3)
C(20)–C(30)
1.385(3)
A perspective view of the complex crystal is depicted in
Fig. 1. The host is a symmetric molecule, and its symmetry
centre occupies a crystallographic symmetry centre, which
results in the asymmetric unit comprising half a host and
one guest, and the ratio of host and guest in the crystal is 1:2.
C(30)–C(40)
1.393(4)
C(40)–C(50)
1.356(4)
C(50)–C(60)
1.377(4)
C(60)–C(70)
1.381(4)
C(3)–C(1)–C(2)
C(3)–C(1)–C(4)
C(2)–C(1)–C(4)
O(1)–C(2)–C(3)#1
O(1)–C(2)–C(1)
C(3)#1–C(2)–C(1)
C(1)–C(3)–C(2)#1
C(11)–C(4)–C(1)
C(11)–C(4)–C(5)
C(1)–C(4)–C(5)
C(6)–C(5)–C(10)
C(6)–C(5)–C(4)
C(10)–C(5)–C(4)
C(5)–C(6)–C(7)
C(8)–C(7)–C(6)
C(7)–C(8)–C(9)
C(8)–C(9)–C(10)
C(9)–C(10)–C(5)
117.35(18) C(12)–C(11)–C(16) 117.8(2)
122.94(18) C(12)–C(11)–C(4)
119.70(18) C(16)–C(11)–C(4)
121.7(2)
120.4(2)
3.2.1. Strong hydrogen bond and weak C–H/O
120.97(19) C(13)–C(12)–C(11) 121.0(3)
117.87(18) C(14)–C(13)–C(12) 120.4(3)
121.16(18) C(15)–C(14)–C(13) 119.3(3)
121.48(19) C(14)–C(15)–C(16) 120.5(3)
112.33(17) C(15)–C(16)–C(11) 120.9(3)
interactions between host and guest in the inclusion crystal
As one of the most important factors in maintaining the
stability of the inclusion compound and decreasing the
crystal energy, a strong hydrogen bond between the host and
guest is involved in this crystal. Atom O1 of thehost at (x, y, z)
acts as hydrogen bonding donor to the atom O10 of the guest
O(10)–C(10)–C(20)
C(70)–C(20)–C(30)
C(70)–C(20)–C(10)
C(30)–C(20)–C(10)
C(40)–C(30)–C(20)
C(50)–C(40)–C(30)
C(40)–C(50)–C(60)
C(70)–C(60)–C(50)
C(60)–C(70)–C(20)
112.00(17)
113.68(17)
117.6(2)
124.9(3)
119.8(3)
121.2(3)
119.0(3)
120.2(3)
119.8(4)
120.1(4)
120.8(4)
119.3(3)
˚
at (x, yK1, zK1), with the length of 2.785 A and
123.83(19)
118.53(19)
120.9(2)
˚
hydrogen bond angle of 171.078 (O1–H1Z0.884 A,
0
˚
H1/O1 Z1.908 A).
120.6(3)
Apart from the conventional hydrogen bonding, the
inclusion complex is also further stabilized by two evident
C–H/O weak interactions between the host and guest. The
first C–H/O weak interaction occurs between the atom C50
of the guest molecule and O atom of hydroxyl group in
the host. The atom C50 of the guest molecule acts as
119.2(3)
120.5(3)
121.1(2)
Symmetry transformation used to generate equivalent atoms: #1 1Kx,
Ky, Kz.
hydrogen bonding donor to the atom O1 of0the h0ost at (1Kx,
3. Results and discussion
0
˚
˚
1Ky, Kz), C5 –O1Z3.590 A, C5 –H5 Z0.988 A,
0
˚
H5 /O1Z2.799 A, and the angle of D–H/A is 137.448.
3.1. Inclusion property of host
Meanwhile, the C3 atom in the core hydroquinone ring of
the host, which is located beside the hydroxyl group and O10
of carbonyl group in the guest, is also linked by C–H/O
The molar ratio of host/guest in each inclusion complex
1
was measured by H NMR, the molar ratio results and the
melting points were listed in Table 3.
0
˚
interaction, with the length of C3 and O1 is 3.538 A,
0
˚
˚
H3/O1 : 2.903 A, C3–H3: 0.953 A, and the bond angle of
C3–H/O10 is 125.168. Although the directionality of the
moderate and weak hydrogen bonds is much softer than that
of strong hydrogen bonding, it can still be identified by the
orientation of the lone electron pair. The oxygen lone
electron pair of carbonyl groups are located in the R2CZO
plane and form weak hydrogen bond angles of about 1208
with CaO bond [8]. Here, the bond angle of H3/O10–C10
is 134.258 and the torsion angle of H3–O10–C1–C20 is
11.658, showing that H3 is connected with lone electron pair
of sp2 orbital at O10 atom. The deviation of directionality of
this weak C–H/O interaction is 11.658 from the R2CaO
plane, and 14.258 from the criterion of 1208 of normal
contacting with sp2 orbital. The strong hydrogen bond and
the two weak C–H/O interactions between host and guest
in the inclusion complex are shown in Fig. 2 (Table 4).
The melting points of complexes are generally lower
than the host itself (278–279 8C), indicating that the new
inclusion compounds with different crystal lattices from the
host are formed.
IR absorption peaks of both host and guest are also found
in each inclusion compound, in which the hydroxyl group
absorption of the hosts was red shifted in each complex to
Table 3
Molar ratio of host/guest and melting points of complex structures
Inclusion complex
Molar ratio
m.p. (8C)
(h):DMF
1:2
1:2
1:1
1:2
1:2
267–268
274–275
270–271
258–259
262–263
(h):DMSO
(h):THF
(h):Benzaldehyde
(h):Acetophenone

146
W.-S. Guo et al. / Journal of Molecular Structure 733 (2005) 143–149
Fig. 1. Perspective view of the inclusion complex.
3.2.2. C–H/p interaction motif of host framework
the intermolecular C–H/p interactions between C13 in
substituted phenyl ring (C11–C16) of one host molecule and
C8 in phenyl ring (C5–C10) of another host molecule (1Kx,
1Ky, 1Kz) form half of the host framework. Due to the
symmetry of the host, the other half host framework is
formed by the symmetry. Here, cg0 is the centroid of the
phenyl ring of C5–C10, atom C13 aggregates at (x, y, z) acts
as hydrogen bonding donor to the centroid cg0 of another
Although the C–H/p interaction could be the weakest
hydrogen bond, it has been found in this complex crystal to
be an important contributive force to the formation of the
host framework besides the weak van der Waal’s force.
In the basic unit of the host framework, there
are altogether four host molecules constructing the
host framework as shown in Fig. 3(a), in which
Fig. 2. Packing diagram along the a axis of the inclusion complex, showing the O–H/O hydrogen bonding and C–H/O weak interactions between the host
and guest.

W.-S. Guo et al. / Journal of Molecular Structure 733 (2005) 143–149
147
Table 4
Intermolecular O–H/O, C–H/O and C–H/p contacts for the complex structure
D/A
D–H
H/A
D–H/A (8)
Symmetry code
Host–Guest
O1–H1/O10
C50–H50/O1
C3–H3/O10
2.785
3.590
3.538
0.884
0.988
0.953
1.908
2.799
2.903
171.07
137.44
125.16
x, yK1, zK1
1Kx, 1Ky, Kz
1Kx, 1Ky, 1Kz
Host–Host
C13–H13/cg0
C13–H13/C8
3.975
3.775
0.906
0.906
3.171
3.070
149.02
136.08
1Kx, 1Ky, 1Kz
1Kx, 1Ky, 1Kz
Note: cg0 designates the centroid of the phenyl ring (C5–C10).
0
˚
host at (1Kx, 1Ky, 1Kz), C13–cg : 3.975 A, C13–H13/
As shown in Fig. 2, we can roughly observe two distinct
contact gaps between the hosts, which could be due to the
existence result of van der Waal’s forces. The
0
0
˚
cg Z149.028, H13–cg Z3.171 A. The nearest atom in this
˚
phenyl ring from C13 is C8: C13–C8: 3.775 A, H13–C8:
˚
nearest distance of 3.991 A between C16 in the phenyl
˚
3.070 A, C13–H13/C8: 136.088. The second nearest atom
˚
rings (C11–C16) and C16A in the rings (C11A–C16A)
confirms the existence of van der Waal’s forces. Therefore,
the dispersion force also plays a necessary role in the
architecture of host framework.
from C13 is C9, C13–C9Z3.922 A, C13–H13/C9Z
160.168. The presence of C–H/p interaction is also
confirmed by the evaluation method proposed by Nishio
˚
˚
[3c] (DlinZ2.988 A!Dmax (3.05 A), qZ34.348!608, uZ
87.568), showing C–H/p weak interaction between the
hosts belongs to type ‘region 1’ [3e], namely, the hydrogen
atom is above the p-plane. The diagram of intermolecular
C–H/p interaction between the hosts is shown in Fig. 3(b).
In the lattice crystal, the equivalent isotropic displace-
ment parameters (Ueq) values of C8, C7 and C9 as acceptor
3.2.3. Structure and intra-molecular C–H/p interactions
in the host
Compared with compounds of similar structure [6,7], the
title host molecule forms a channel host framework, while
the latter form layer host frameworks. What factors could
cause this difference? The type of host framework may be
closely connected with the structure of the host. In the title
host of the inclusion crystal, the substituted phenyl rings are
connected to the core hydroquinone ring by C4 and C4A
(C3sp), with the bond angles about C4 (C4A) 112.33(17),
112.00(17) and 113.68(17)8, respectively, which all are
close to the standard tetrahedral bond angle of 109.58. More
importantly, the two substituted phenyl rings on the same
side which are linked by C4 (C4A) are almost perpendicular
with the dihedral angle of 93.22(1)8, and such conformation
is much more beneficial for the aromatic edge-face contact
in the host. Furthermore, when the host forms its inclusion
2
˚
atoms are 0.076, 0.080 and 0.080 A , respectively, gener-
ally, the Ueq value of C atom located in the p-position of
substituted phenyl ring is a little higher than that of the
o-position and m-position due to the comparably far
distance from the substituted position and it exhibits more
obvious thermal instability. However, here, atom C8 which
is located in the p-position has a comparably lower Ueq
value instead, which also indicates from another angle that
C8 is restricted and stabilized by C–H/p interaction, and
its disordered thermal motion is weakened to an extent. This
evidence further confirms the presence of the C–H/p
interaction between hosts.
Fig. 3. (a) Guest molecules which are accommodated in the channel hole formed by intermolecular C–H/p interaction; (b) intermolecular C–H/p
interaction in the host framework.

148
W.-S. Guo et al. / Journal of Molecular Structure 733 (2005) 143–149
other atoms with no C–H/p interaction involved, which
indicates that the disordered thermal motions of these C
atoms, as hydrogen bonding acceptors, have been decreased
to some extent by the restriction of the C–H/p interaction.
4. Conclusion
In the complex structure channel host framework depicted
here, conventional strong hydrogen bonding and weak
intermolecular C–H/O interaction play a very important
role in the decreasing the crystal energy and fixing the guest
molecules in the inclusion compound. The C–H/p weak
interactions are another important contribution to determin-
ing the shape of host framework and dominating the structure
of inclusion compounds. The orientations of substituted
phenyls of the host favour the formation of both intra- and
inter-molecular C–H/p weak interactions.
Fig. 4. Intramolecular C–H/p interactions in the host.
complex with benzaldehyde guest molecules, although the
strong hydrogen bonding and weak C–H/O interactions
between the host and guest are found in the crystals, the host
molecules still maintain a stable conformation, which could
indicate the possible existence of C–H/p interactions in
the host.
5. Supplementary material
Crystallographic data for this article have been
deposited in the Cambridge Crystallographic Data Centre
as supplementary publication No. 231489. Copies of this
information may be obtained free of charge from the
Director, CCDC, 12 Union Road, Cambridge CB21 EZ,
UK (fax: C44 1223 336 033; email: deposit@ccdc.
cam.ac.uk or www: http://ccdc.cam.ac.uk).
In the host, two kinds of intramolecular C–H/p
interactions are investigated. Firstly, C–H/p interaction is
found between the core hydroquinone ring and substituted
phenyl ring (C11–C16), here, cg00 designates the centroid of
the phenyl ring (C11–C16), C3 atom which is located in the
rich electron hydroquinone ringactsas hydrogen bond donor,
via H3, to the centroid 00cg00, C3–cg Z3.741 A,
00
˚
00
˚
C3–H3/cg Z127.498, H3–cg Z3.084 A. The distance
˚
between C3 and C12 of ring (C11–C16) is 3.391 A,
Acknowledgements
˚
H3–C12Z2.753 A, C3–H12/C12Z125.078. This
C–H/p interaction fixes the orientation of substituted
phenyl rings (C11–C16) with the dihedral angle between this
substituted phenyl and core hydroquinone of 94.66(1)8. At
the same time, the fixed orientation of phenyl ring C11–C16
results in another C–H/p interactions between this ring and
another substituted phenyl ring (C5–C10). C12 atoms of
phenyl ring (C11–C16), as hydrogen bond donor, is linked
with cg0 (the centroid of C5–C10), with the length of C12–cg0
This work is financially supported by the National
Natural Science foundation of China, grant number:
20372031.
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0
˚
is 3.842 A, and the angle of C12–H12/cg is 118.908. The
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˚
is 3.665 A, and the angle of C12–H12/C6 is 123.798. This
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