C(4) helices, Br...Br interaction and R42(10) ring in bromoipriflavone

Article abstract of DOI:10.1007/s10870-005-2797-0

The title compound, 8-bromo-7-isopropoxyisoflavone (bromoipriflavone), C₁₈H₁₅O₃Br, crystallizes in tetragonal crystal system, space group I4₁/a with cell constants a = 21.396(2) A, c = 13.588(2) A, V = 6220.2(14

Full text of DOI:10.1007/s10870-005-2797-0

Journal of Chemical Crystallography, Vol. 35, No. 2, February 2005 (ꢀC 2005)
DOI: 10.1007/s10870-005-2797-0
C(4) helices, Br· · ·Br interaction and R42(10)
ring in bromoipriflavone
Zun-Ting Zhang,(1)∗ Xiao-Bing Wang,(1) and Kai-Bei Yu(2)
Received July 20, 2004; accepted September 21, 2004
The title compound, 8-bromo-7-isopropoxyisoflavone (bromoipriflavone), C18H15O3Br,
crystallizes in tetragonal crystal system, space group I41/a with cell constants a =
3
˚
˚
˚
21.396(2) A, c = 13.588(2) A, V = 6220.2(14) A and Z = 16. Bromoipriflavone is com-
posed of a benzopyranone moiety, a phenyl moiety, an isopropoxy group and a bromine
atom. The benzopyranone ring is not coplanar with the phenyl ring with a dihedral angle
of 55.1◦. The molecules are stacked into a C(4) helices down [001] via π–π stacking and
hydrogen bonds, the C(4) helices are assembled into three-dimensional network via strong
Br· · ·Br interactions and synthons R42(10) formed by two tri-centered C H· · ·O hydrogen
bonds, resulting in a distinctive high-symmetry supramolecule. The title compound was
also characterized by IR and 1H NMR.
KEY WORDS: Ipriflavone; bromine; crystal structure; supramolecule; hydrogen bonds; π–π stacking.
Introduction
and has been shown to be effective in reducing
bone turnover rate mainly through an inhibition of
bone resorption.10 The title compound, 8-bromo-
7-isopropoxyisoflavone, is a derivative of ipri-
flavone with potential medical applications. In this
paper, we synthesized the title compound and its
crystal structure was determined by X-ray diffrac-
tion analyses. The determination results show that
there are a variety of weak but direction-specific
intermolecular forces, such as, hydrogen bonds,
π–π stacking interactions and Br· · ·Br interac-
tions. π–π Stacking interactions and C H· · ·O
hydrogen bonds link the title compound into a
C(4) helices, the C(4) helices assemble into a
three-dimensional network via strong Br· · ·Br in-
teraction and R42(10) formed by two tri-centered
hydrogen bonds at the inversion position, result-
ing in a distinctive high-symmetry supramolecule.
The preparation process of the title compound can
be expressed as Scheme 1.
Hydrogen bonds and π–π stacking in-
teractions are an important research content
in the supramolecular chemistry and crys-
tal engineering.1 They play an important role
in self-assembly and recognition of aromatic
compounds2,3 as an auxiliary stabilizing short
contact.4–6 Supramolecular synthon is an easy
way to describe the short contacts in the crys-
tal structure.7–9 Ipriflavone, a synthetic isoflavone,
is currently used in several countries for preven-
tion and treatment of involutional osteoporosis
(1) School of Chemistry and Materials Science, Shaanxi Normal Uni-
versity, Xi’an 710062, PRC.
(2) Analytical Center, Chengdu Branch of Chinese Academy of Sci-
ences, Chengdu 610041, PRC.
∗ All correspondence should be addressed to Zun-Ting Zhang,
School of Chemistry and Materials Science, Shaanxi Normal
University, Xi’an 710062, People’s Republic of China; e-mail:
zhangzunting@sina.com.
101
ꢀ
C
1074-1542/05/0200-0101/0 2005 Springer Science+Business Media, Inc.

102
Zhang, Wang, and Yu
Scheme 1.
ꢁꢁ
ꢁꢁ
Experimental
(1H, m, H C1 ), 1.35 (6H, d, J = 6.0 Hz, H C2 ,
ꢁꢁ
H C3 ).
Synthesis of the title compound
X-ray crystal structure determination
Ipriflavone was purchased from the State-
owned Pharmaceutical Company of Wu-Gong.
Other chemicals were of analytical reagent grade
and were used directly without further purifica-
tion. The infrared spectra were recorded as KBr
pellets on a Nicolet 170SX FT-IR spectropho-
tometer. The 1H NMR Spectra were recorded on a
Bruker Am-300 spectrometer with TMS as inter-
nal reference and DMSO-d6 as solvent. The crys-
tal structure was determined using Siemens P4
Diffractometer instrument.
The sample selected for investigation had
dimensions of 0.58 mm × 0.24 mm × 0.24 mm.
The data were collected with graphite monochro-
mated Mo Kα radiation (λ = 0.71073 A) at
˚
room temperature. A total of 3713 reflections
were collected to give 3062 independent reflec-
tions (Rint = 0.0412). The structure was solved
using direct methods with SHELXTL software
package13 and refined by full-matrix least-squares
techniques. The non-hydrogen atoms were as-
signed anisotropic displacement parameters in the
refinement. The hydrogen atoms were treated us-
ing a riding model. The structure was refined on
F2 using SHELX-97.14 The final R value (on F)
was 0.0377. The crystal used for the diffraction
study showed no decomposition during data col-
lection. The crystal and refinement data are list in
Table 1. Selected bond lengths, bond angles and
torsion angles are given in Table 2.
Ipriflavone (0.5 g) was dissolved in ethanol
(100 mL). Bromine (5 mL) was added dropwise
to the solution with strongly stirring. The mixture
was refluxed for half an hour. After cooling, the
mixture was poured into water (100 mL) and col-
orless precipitation appeared. The precipitate was
filtered and washed with water until the pH of the
filtrate was 7. After recrystallization from ethanol,
the products had melting point of 437 K. Crys-
tals of the title compound suitable for X-ray anal-
ysis were obtained from slow evaporation from
ethanol after three days at room temperature. IR
(KBr) υ: 3432, 2977, 1638, 1597, 1420, 1380,
1271, 1104, 1021, 781, 560 cm−1. The peaks at
1638 and 560 cm−1 belong to the C O11 and
Results and discussion
The title compound, 8-bromo-7-isopro-
poxyisoflavone, C18H15O3Br, possesses normal
geometrical parameters compared with its parent,
ipriflavone,15 in most of the bond distances and
bond angles. The title compound is composed of
a benzopyranone moiety, a phenyl moiety, an iso-
propoxy group and a bromine atom. (Fig. 1. The
subsequent discussion uses the crystallographic
atom naming scheme.) The atoms of benzopyra-
none ring, including ring A (C10 C15) and ring
12
C–Br vibration of the group in the title com-
1
pound, respectively. H NMR(DMSO-d6, ppm,
300 MHz): 8.58 (1H, S, H C2), 8.08 (1H, d,
J = 7.5 Hz, H C5), 7.58 (2H, d, J = 9.0 Hz,
ꢁ
ꢁ
ꢁ
H C2 , H C6 ), 7.47 (1H, d, J = 7.5 Hz, H C4 ),
ꢁ
7.42 (2H, dd, J = 9.0 Hz, J = 7.5 Hz, H C3 ,
ꢁ
H C5 ), 7.35 (1H, d, J = 7.5 Hz, H C6), 4.93

Bromoipriflavone
103
gle of 55.1◦, which is similar to its parent being
50.0◦. The bromine atom is located at atom C12
of ring A, which pushes the isopropyl to the other
side compared with its parent indicated by the
C16 O3 C13 C14 torsional angle of the title
compound being −17.91◦ and the corresponding
torsional angle of ipriflavone being 172.76◦. The
different orientations of the isopropyl groups be-
tween the title compound and its parent are the
result of the bromine substituent.
Table 1. Crystal Data and Structure Refinement for the Title
Compound
Compound
Bromoipriflavone
C18H15O3Br
CCDC-244989
359.21
Empirical formula
CCDC deposit no.
Formula weight
Temperature (K)
298(2)
˚
Wavelength (A)
0.71073
Tetragonal
I41/a
Crystal system
Space group
˚
˚
Unit cell dimensions
a = 21.396(2) A
b = 21.396(2) A
˚
The molecules of the title compound are
linked into a three-dimensional network by a va-
riety of weak but direction-specific intermolecu-
lar forces, and the formation of this framework is
readily analyzed by means of the supramolecu-
lar synthon.8 π–π Stacking interactions link the
molecules into C(4) helices along [0 0 1] together
with C H· · ·O hydrogen bonds. Furthermore, the
C(4) helices are assembled into a supramolecule
via the synthon R42(10) built by two tri-centered
C H· · ·O hydrogen bonds at the inversion posi-
tion and Br· · ·Br interactions (Fig. 2).
c = 13.588(2) A
3
˚
Volume, Z
6220.2(14) A , 16
Density (calculated)
Absorption coefficient
F(000)
1.534 Mg m−3
2.653 mm−1
2912
Crystal size
0.58 mm × 0.24 mm × 0.24 mm
Theta range for data collection 1.78–25.99◦
Limiting indices
0 ≤ h ≤ 26, 0 ≤ k ≤ 26,
−1 ≤ l ≤ 16
3713
Reflections collected
Independent reflections
Absorption correction
Maximum and minimum
transmission
3062 [Rint = 0.0412]
Empirical
0.9970 and 0.6064
Refinement method
Full-matrix least-squares on F2
3062/0/202
R1 = 0.0377, wR2 = 0.0432
R1 = 0.1339, wR2 = 0.0473
0.00205(3)
0.373 and −0.326 eA−3
Data/restraints/parameters
Final R indices [I > 2σ(I)]
R indices (all data)
Extinction coefficient
Largest diff. peak and hole
In the first submotif, the 41 screw axis down
[001] generates C(4) helical chains of molecules
of the title compound linked by π–π stack-
ing interactions and C H· · ·O hydrogen bonds
(Fig. 2). The adjacent benzopyranone moiety of
the molecules of the title compound are not com-
pletely parallel with a dihedral angle of 5.1◦ and
stacked with each other viewed down [0 0 1],
C (O1/C7 C11), are nearly coplanar with a mean
˚
deviation of 0.0191 A from its best least-square
˚
plane. The benzopyranone is not coplanar with
the phenyl ring B (C1 C6) with a dihedral an-
with a Cg–Cg# separation of 3.410 A [Cg is the
centroid of the benzopyranone moiety, including
◦
◦
˚
Table 2. Selected Bond Lengths (A), Bond Angles ( ) and Torsion Angles ( )
Br C(12)
O(1) C(7)
1.895(3)
1.360(4)
1.369(4)
1.230(4)
1.360(4)
1.449(4)
1.488(5)
1.336(4)
1.460(4)
1.464(5)
124.8(4)
116.4(4)
116.2(3)
C(13) O(3) C(16)
C(8) C(7) O(1)
C(11) C(12) Br
C(13) C(12) Br
120.1(3)
127.4(4)
121.3(3)
118.7(3)
O(1) C(11)
O(2) C(9)
O(3) C(13)
O(3) C(16)
C(6) C(8)
C(7) C(8)
C(8) C(9)
C(9) C(10)
O(3) C(13) C(14)
O(3) C(13) C(12)
C(7) O(1) C(11)
C(5) C(6) C(8) C(7)
C(5) C(6) C(8) C(9)
O(1) C(11) C(12) Br
C(10) C(11) C(12) Br
C(16) O(3) C(13) C(14)
C(16) O(3) C(13) C(12)
Br C(12) C(13) O(3)
Br C(12) C(13) C(14)
−125.4(5)
55.1(7)
1.9(7)
−177.2(3)
−17.9(8)
164.5(5)
−4.4(6)
177.9(4)

104
Zhang, Wang, and Yu
Fig. 1. Molecular structure and atomic numbering for the title compound. Displacement ellipsoids
are plotted at the 50% probability level.
Fig. 2. Part of the crystal structure of the title compound, showing the formation of the
C(4) helices, the synthon R42(10), the π–π stacking interactions, the hydrogen bonds
and the Br· · ·Br interactions. Atoms marked with an asterisk (∗), hash (#), ampersand
(&), dollar ($), at (@) and percent (%) are at the symmetry positions (1 − x, 1 − y,
1 − z), (0.75 − y, x + 0.25, 0.25 + z), (0.5 − x, 1 − y, 0.5 + z), (0.25 + y, 0.75 −
x, 1.75 − z), (y − 0.25, 0.75 − x, 0.75 + z) and (0.5 + x, y, 1.5 − z), respectively.
The horizontal dashed lines indicate the formation of the C(4) helices via the π–π
stacking interactions. Cg is the centroid of the benzopyranone moiety. For the sake
of clarity, some H atoms have been omitted.

Bromoipriflavone
105
atoms O1/C7 C15, symmetry code: (#) 0.75 − y,
0.25 + x, z + 0.25)]. The corresponding perpen-
dicular distances from Cg and Cg# to the best
least-squares ring planes of the other stacking ben-
tance is at the normal range compared with the
16
˚
reported criteria (3.40–3.70 A) of Br · · · Br in-
teraction, which shown that Br· · ·Br interaction
existsinthecrystalstructureofthetitlecompound.
˚
zopyranone moieties are 3.408 and 3.387 A, re-
spectively. The lateral displacement of Cg# rela-
tive to the normal from the Cg best least-square
ring plane at Cg to the Cg# best least-squares
Supplementary material
CCDC-244989 contains the sup-
plementary crystallographic data for this paper. These data
can be obtained free of charge at www.ccdc.cam.ac.uk/conts/
retrieving. html [or from the Cambridge Crystallographic Data
Centre (CCDC), 12 Union Road, Cambridge CB2 1EZ, UK; fax:
+44(0)1223-336033; e-mail: deposit@ccdc.cam.ac.uk].
˚
ring plane is 0.40 A. The perpendicular distances
and the lateral displacement are agreed with the
angle of Cg Cg# Cg& being 175.0◦ [symme-
try code: (&) 0.5 − x, 1 − y, z + 0.5]. The other
short contacts forming the helices are extensive
hydrogen bonds C1# H1#· · ·O2& with distance
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˚
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˚
˚
ing 2.64 A, C2$ · · · O2& being 3.503(1) A and
bond angle of 154.3◦. A tri-centric hydrogen bond
is formed by hydrogen bonds C2$ H2$ · · ·O2&
and C1# H1# · · · O2&. Combination of these tri-
centered hydrogen bonds at the inversion position
generates the second motif R42(10) (Fig. 2).
The last substructure is C12 Br · · · Br∗ syn-
thon (Fig. 2). Two bromine atoms link the ad-
jacent C(4) heli∗ces at the same layer together
˚
with a Br · · · Br distance of 3.651 A and an-
gles of 168.10◦ [angles of C12 Br· · ·Br∗ and
C12∗ Br* · · · Br are all of 168.10◦; symmetry
code: (*) 1 − x, 1 − y, 1 − z]. The Br · · · Br dis-