Crystal and molecular structures of three 2,2′-thio-and 2,2′-sulfonyl-bis(1,3-diarylprop-2-en-1-ones)

Article abstract of DOI:10.1023/A:1013795006690

The X-ray crystal structures of 2,2′-thio- and 2,2′-sulfonylbis(1,3-diarylprop-2-en-1-ones) are determined [1: 2,2′-thiobis(3-(p-chlorophenyl)-1-phenylprop-2-en-1-one), C₃₀H₂₀Cl₂O₂S, space group C2/c, a = 14.275(3), b = 6.280(1), c = 26.533(5) A, β = 94.55(3)°, Z′ = 1/2; 2: 2,2′-sulfonylbis(1,3-diphenylprop-2-en-1-one), C₃₀H₂₂O₄S, space group P1, a = 9.652(1), b = 12.044(1), c = 12.182(1) A, α = 61.985(6), β = 77.511(5), γ = 74.340(6)°, Z′ = 1; 3: 2,2′-sulfonylbis(3-(p-chlorophenyl)-1-phenylprop-2-en-1-one), C₃₀H₂₀Cl₂O₄S, space group P, a = 8.294(1), b = 13.175(2), c = 13.470(1) A, α = 62.870(9), β = 83.796(7), γ = 85.282(8)°, Z′ = 1]. The C=C double bonds are all clearly defined. The sulfide 1 crystallizes on a crystallographic twofold axis, leading to a symmetric molecular conformation. The sulfones 2 and 3 crystallize on general positions, with different and irregular conformations.

Full text of DOI:10.1023/A:1013795006690

Journal of Chemical Crystallography, Vol. 31, No. 2, February 2001 (�C 2002)
0
Crystal and molecular structures of three 2,2 -thio-
0
and 2,2 -sulfonyl-bis(1,3-diarylprop-2-en-1-ones)
(
1)
(1)
(2)
(2)
M. Gnanadeepam, S. Selvaraj, Antoine M.M. Schreurs, Jan Kroon,
(
3)
(1)
Thomas Steiner, * and S. Perumal
Received November 28, 2000
0
0
The X-ray crystal structures of 2,2 -thio- and 2,2 -sulfonylbis(1,3-diarylprop-2-en-
0
1
-ones) are determined [1: 2,2 -thiobis(3-(p-chlorophenyl)-1-phenylprop-2-en-1-one),
˚
C30H20Cl2O2S, space group C2/c, a = 14.275(3), b = 6.280(1), c = 26.533(5) A,
�
0
0
�
= 94.55(3) , Z = 1/2; 2: 2,2 -sulfonylbis(1,3-diphenylprop-2-en-1-one), C30H22O4S,
¯
˚
space group P1, a = 9.652(1), b = 12.044(1), c = 12.182(1) A, � = 61.985(6), � =
�
0
0
7
2
˚
7.511(5), � = 74.340(6) , Z = 1; 3: 2,2 -sulfonylbis(3-(p-chlorophenyl)-1-phenylprop-
¯
-en-1-one), C30H20Cl2O4S, space group P1, a = 8.294(1), b = 13.175(2), c = 13.470(1)
�
0
A, � = 62.870(9), � = 83.796(7), � = 85.282(8) , Z = 1]. The C C double bonds are all
clearly defined. The sulfide 1 crystallizes on a crystallographic twofold axis, leading to a
symmetric molecular conformation. The sulfones 2 and 3 crystallize on general positions,
with different and irregular conformations.
KEY WORDS: Crystal structure; organosulfur compounds.
Introduction
double bond in these compounds by conventional
methods is difficult because the alkene function
0
2
,2 -Thiobis(1,3-diarylprop-2-en-1-ones)are
is trisubstituted. In this context, we have deter-
mined the crystal structures of three compounds
from this family, one sulfide, 1, and two sulfones,
2 and 3. The crystal structures shall not only de-
fine the molecular constitution unequivocally, but
also give information on steric distortions of the
prop-2-ene moieties.
1
� 5
excellent synthons
for the synthesis of a va-
riety of heterocyclic compounds containing two
hetero atoms like thiazines, thianes, and dithianes
whose applications as tranquilizers, sedatives, and
other applications are reported in the literature.6
An unequivocal stereochemical assignment of the
(
(
1)
2)
School of Chemistry, Madurai Kamaraj University, Madurai,
Tamil Nadu 625021, India.
Department of Crystal and Structural Chemistry, Bijvoet Center
for Biomolecular Research, Utrecht University, Padualaan 8, 3584
CH Utrecht, The Netherlands.
Institut f u¨ r Chemie-Kristallographie, Freie Universit a¨ t Berlin,
Takustra�e 6, D-14195 Berlin, Germany.
To whom correspondence should be addressed; e-mail: steiner@
chemie.fu-berlin.de
Experimental
The thiobis compound 1 was obtained
by condensation of bis(benzoylmethyl)sulfide
with p-chlorobenzaldehyde. The sulfonylbis
compounds 2 and 3 were obtained by oxidation
of the corresponding thiobis compounds with
(
3)
*
87
1
074-1542/02/0200-0087/0 �C 2002 Plenum Publishing Corporation

8
8
Gnanadeepam, Selvaraj, Schreurs, Kroon, Steiner, and Perumal
Table 1. Crystallographic Data for 1, 2, and 3
1
2
3
Formula
CCDC deposite no.
MW
C30H20Cl2O2S
CCDC-1003/6004
515.42
C30H22O4S
CCDC-1003/6005
478.54
C30H20Cl2O4S
CCDS-1003/6006
547.42
Diffractometer
Temperature, K
Crystal system
Space group
Kappa CCD
125
monoclinic
C2/c (No. 15)
Turbo-CAD4
RT
Turbo-CAD4
RT
triclinic
triclinic
¯
¯
P1 (No. 2)
P1 (No. 2)
Unit cell dimensions
˚
a, A
14.275(3)
6.280(1)
26.533(5)
90
94.55(3)
90
2371.1(8)
4
1/2
9.652(1)
12.044(1)
12.182(1)
61.985(6)
77.511(5)
74.340(6)
1197.1(2)
2
8.294(1)
13.175(2)
13.470(1)
62.870(9)
83.796(7)
85.282(8)
1301.4(3)
2
˚
b, A
˚
c, A
�
�
�
, deg
, deg
, deg
˚
3
Volume, A
Z
Z
0
1
1
�
3
Dc, g/cm
, mm
1.444
0.390
1.328
0.171
1.397
0.365
�
1
�
Crystal size, mm
0.45 � 0.2 � 0.15
0.3 � 0.3 � 0.15
0.2 � 0.2 � 0.1
Measured reflections
Unique reflections
Unique with I > 2�(I)
4060
7307
9791
2435
2259
0.33
0.039
5491
2597
0.22
0.068
5966
1772
0.23
0.093
˚
� 3
4
�max, e A
R [for I > 2�(I)]
Rw [for all data]
0.088
0.167
0.289
Table 2. Fractional Atomic Coordinates of 1 and Equivalent
hydrogen peroxide (30%) in glacial acetic
Isotropic Displacement Parameters
7
0
acid.
[1; 2,2 -thiobis(3-(p-chlorophenyl)-1-
0
Ueqa
phenylprop-2-en-1-one), 2: 2,2 -sulfonylbis(1,3-
diphenylprop-2-en-1-one), 3: 2,2 -sulfonylbis
x/a
y/b
z/c
0
S
Cl
O1
C1
C2
C3
C11
C21
C31
C41
C51
C61
C13
C23
C33
C43
C53
C63
0.5000
0.66735(3)
0.62200(8) � 0.33552(17) 0.77711(4)
0.19979(8) 0.7500
0.56905(7) 0.528274(14) 0.02792(13)
0.01413(13)
(3-(p-chlorophenyl)-1-phenylprop-2-en-1-one)].
Crystals were grown from solutions in CHCl3–
0.0214(2)
0.0150(3)
0.0144(3)
0.0166(3)
0.0151(3)
0.0191(3)
0.0232(3)
0.0245(4)
0.0244(3)
0.0199(3)
0.0159(3)
0.0192(3)
0.0206(3)
0.0194(3)
0.0199(3)
0.0186(3)
MeOH [2:1 (v/v)]. X-ray diffraction data were
0.60439(10) � 0.1519(2)
0.78791(5)
0.74705(5)
0.71166(5)
0.84150(5)
0.85879(5)
0.90940(6)
0.94249(6)
0.92563(6)
0.87523(6)
0.66812(5)
0.62368(6)
0.58023(5)
0.58210(5)
0.62607(6)
0.66904(6)
0.59372(10)
0.65634(11)
0.0157(2)
0.0165(2)
collected at 125 K on a Nonius Kappa CCD
diffractometer for 1, and at RT on a Nonius
Turbo-CAD4 diffractometer for 2 and 3 (Mo K�
0.59442(10) � 0.0876(2)
0.61222(11)
0.60443(12)
0.57761(12)
0.1199(3)
0.1692(3)
0.0135(3)
˚
radiation with � = 0.71073 A). Diffraction
power of 2 and 3 was only moderate, leading
0.55994(12) � 0.1923(3)
to a relatively large number of weak reflections.
0.56940(11) � 0.2436(3)
8
9
The structures were solved and refined with
standard methods (anisotropic refinement for
non-H atoms, H atoms treated in the riding
model, no absorption correction). Relevant
crystallographic data are given in Table 1,
and fractional atomic coordinates are given in
Tables 2–4.
0.66108(10)
0.69364(11)
0.69472(11)
0.66557(11)
0.63697(11)
0.63451(11)
0.1594(2)
0.0774(2)
0.1995(3)
0.4095(3)
0.4986(2)
0.3740(2)
aUeq is defined as one-third of the trace of the orthogonalized
Ui j tensor.

Organosulfur compounds
89
Table 3. Fractional Atomic Coordinates of 2 and Equivalent
Table 4. Fractional Atomic Coordinates of 3 and Equivalent
Isotropic Displacement Parameters
Isotropic Displacement Parameters
x/a
y/b
z/c
Ueqa
x/a
y/b
z/c
Ueqa
S
0.27083(10) 0.43036(9) 0.42178(8) 0.0453(3)
S
0.0152(2)
0.43149(15) 0.30718(16) 0.0744(6)
O1
O1
O2
O3
C1
C2
C3
0.3852(3)
0.3077(3)
0.3144(2)
0.1795(2)
0.2764(3)
0.1867(3)
0.0607(3)
0.2348(3)
0.0943(4)
0.0609(5)
0.1679(5)
0.3080(5)
0.3422(4)
� 0.0276(4)
0.0261(5)
� 0.0621(5)
� 0.2015(5)
� 0.2556(4)
� 0.1702(4)
0.4070(4)
0.4290(3)
0.5532(4)
0.5064(3)
0.5258(4)
0.6139(4)
0.6815(4)
0.6606(4)
0.5747(3)
0.6929(3)
0.8184(4)
0.9505(4)
0.9609(5)
0.8375(5)
0.7050(4)
0.6718(2)
0.3854(3)
0.4612(2)
0.3380(2)
0.6788(3)
0.5765(3)
0.5814(3)
0.7811(3)
0.8213(3)
0.9224(4)
0.9782(4)
0.9358(4)
0.8387(3)
0.6849(3)
0.7868(3)
0.1846(2)
0.1880(3)
0.50802(19) 0.0564(7)
0.0622(7)
0.0826(9)
Cl
Cl
� 0.8130(3)
0.72666(18) � 0.07281(18) 0.1140(8)
0
0
� 0.3833(3) � 0.08246(17) 0.92397(18) 0.1190(8)
O1
O1
O2
O3
C1
C2
C3
C11
C21
C31
C41
C51
C61
C13
C23
C33
C43
C53
C63
� 0.3091(6)
� 0.0112(5)
0.0950(5)
0.5172(4)
0.1594(4)
0.4918(4)
0.4022(4)
0.5741(6)
0.5130(5)
0.5155(5)
0.6959(6)
0.4085(4)
0.3649(4)
0.3519(4)
0.2234(4)
0.3162(6)
0.2517(6)
0.1608(6)
0.2690(7)
0.1724(8)
0.1329(9)
0.1013(17)
0.0978(16)
0.0877(14)
0.1004(16)
0.0704(19)
0.0633(17)
0.0674(18)
0.073(2)
0
0.4682(2)
0.2547(3)
0.3063(3)
0.2748(3)
0.2982(3)
0.3383(3)
0.3694(3)
0.3670(3)
0.3323(3)
0.2964(3)
0.1787(3)
0.0781(3)
0.0598(7)
0.0418(8)
0.0381(8)
0.0430(8)
0.0394(8)
0.0490(9)
0.0611(10)
0.0684(12)
0.0655(11)
0.0539(10)
0.0423(8)
0.0571(10)
0.0670(11)
0.0681(12)
0.0605(10)
0.0507(9)
0.0476(9)
0.0389(8)
0.0422(8)
0.0404(8)
0.0546(10)
0.0697(12)
0.0740(12)
0.0635(11)
0.0491(9)
0.0398(8)
0.0488(9)
0.0618(11)
0.0708(12)
0.0653(11)
0.0528(9)
0.0984(5)
� 0.2412(8)
� 0.1638(7)
� 0.2109(8)
� 0.2249(8)
C11
C21
C31
C41
C51
C61
C13
C23
C33
C43
C53
C63
� 0.1340(11) 0.7578(7)
� 0.1224(13) 0.8734(9)
� 0.2036(17) 0.9298(9)
� 0.2932(14) 0.8664(10)
0.105(3)
0.142(4)
0.1906(13) 0.164(7)
0.2839(13) 0.165(6)
� 0.3077(9)
� 0.3559(8)
0.7520(8)
0.5721(5)
0.3269(8)
0.1031(6)
� 0.0109(7)
� 0.0665(6)
� 0.0036(7)
0.1066(6)
0.1627(5)
0.3877(5)
0.4174(6)
0.5199(7)
0.3878(5)
0.3670(5)
0.3631(6)
0.3783(6)
0.3995(6)
0.4053(5)
0.6212(6)
0.6444(6)
0.7364(7)
0.8116(6)
0.7942(6)
0.7018(6)
0.123(3)
0.0692(19)
0.084(2)
0.083(2)
0.0759(19)
0.076(2)
0.0696(18)
0.0633(17)
0.0625(17)
0.0691(19)
0.0531(15)
0.0697(18)
0.089(2)
0.085(2)
0.078(2)
0.0672(18)
0.0619(17)
0.0686(18)
0.074(2)
0.079(2)
0.087(2)
0.0752(19)
0.8766(4) � 0.0123(4)
0.8671(4) � 0.0062(4)
� 0.3599(10) 0.6059(6)
0.7677(4)
0.6770(3)
0.3309(3)
0.3796(3)
0.3981(3)
0.2137(3)
0.1986(4)
0.0910(4)
� 0.0040(4)
0.0099(4)
0.1191(3)
0.3817(3)
0.3340(3)
0.3182(3)
0.3529(4)
0.4048(4)
0.4184(3)
0.0925(4)
0.1841(3)
0.2526(3)
0.3389(3)
0.3516(3)
0.2490(3)
0.1399(3)
0.1349(4)
0.2370(5)
0.3458(4)
0.3511(3)
0.2803(3)
0.3387(3)
0.2728(4)
0.1468(4)
0.0868(4)
0.1524(3)
� 0.4986(11) 0.6575(5)
� 0.6379(9)
� 0.6399(9)
� 0.5019(8)
� 0.1113(7)
� 0.0613(6)
� 0.0725(6)
� 0.2871(7)
� 0.3339(7)
� 0.4939(9)
� 0.6102(8)
� 0.5649(7)
� 0.4047(7)
� 0.1391(7)
� 0.1141(8)
� 0.1853(8)
� 0.2853(8)
� 0.3110(9)
� 0.2352(8)
0.6688(5)
0.6352(6)
0.5849(5)
0.2184(5)
0.3068(5)
0.2988(5)
0.2039(5)
0.1187(5)
0.1047(6)
0.1776(7)
0.2611(6)
0.2773(5)
0.2025(6)
0.0878(6)
0.0031(6)
0.0265(6)
0.1375(6)
0.2231(6)
0
C1
0
0
C2
0
0
0
C3
C1
C2
C3
0
0
0
0
0
0
0
0
0
0
0
0
C11
C21
C31
C41
C51
C61
C13
C23
C33
C43
C53
C63
0
0
0
0
0
0
0
0
0
0
0
0
C11
C21
C31
C41
C51
C61
C13
C23
C33
C43
C53
C63
aUeq is defined as one-third of the trace of the orthogonalized
Ui j tensor.
aUeq is defined as one-third of the trace of the orthogonalized
Ui j tensor.
Results and discussion
single and double bonds, respectively, confirm-
ing the expected molecular constitution. The
7
The molecular structures of 1, 2, and 3 as
observed in the crystal structures are shown in
Fig. 1. Relevant geometrical parameters are given
in Table 5. The sulfide 1 crystallizes on a twofold
crystallographic axis, forcing the conformation to
be symmetrical (Fig. 1(a)). The bond angle at
p-chlorophenyl groups are bonded to C3 in cis po-
sition with respect to S (Scheme 1). The resulting
stericconflictS���C11leadstoappreciablewiden-
�
ing of the S C2 C3 angle to 124.9(1) , whereas
�
the angle C3 C2 C1 is narrowed to 117.9(1) .
�
the S atom is normal [98.7(1) ]. In the propene
The torsion angle S C2 C3 C13 is only slightly
�
groups, the bond lengths of C3 C2 = 1.347(2)
twisted from the ideal value to � 1.6(2) . The two
˚
and C2 C1 = 1.519(2) A point at well-defined
prop-2-ene groups at S are mutually arranged in

9
0
Gnanadeepam, Selvaraj, Schreurs, Kroon, Steiner, and Perumal
(a)
Scheme 1.
an antiparallel fashion, so that the p-chlorophenyl
groups point in opposite directions, and the same
is true for the two unsubstituted phenyl rings. The
C O groups point in almost the same directions,
0
with an intramolecular O1���O1 separation of
(b)
˚
only 3.662(3) A. Because of the roughly paral-
lel alignment of the C O dipoles, this is an un-
favourable arrangement. A further interesting fea-
ture of 1 are intramolecular stacking interactions
of the phenyl and p-chlorophenyl rings (Fig. 2).
In this interaction, the midpoint of the phenyl
˚
ring has a normal distance of 3.92 A from the
p-chlorophenyl least squares plane.
The stereochemistry of the sulfones 2 and
3
differs from 1 in that the aromatic groups at
the C3 C2 bonds are attached trans with re-
(c)
Fig. 1. Molecular structure and atomic numbering scheme
of 1, 2, and 3 shown in views roughly along the bisector of
the C S C angle. Thermal ellipsoids are drawn at the 50%
probability level for 1 and the 30% probability level for 2
and 3.
spect to S (Scheme 2). Now, the steric conflict
is not with S but with C1 and the phenyl ring at-
tached to it, so that the angles C3 C2 C1 and
0
0
0
�
Scheme 2.
C3 C2 C1 are widened to values above 125

Organosulfur compounds
91
Table 5. Selection of Geometric Parameters
1
2
3
Bond lengths
S C2
S C2
1.775(2)
1.769(3)
1.770(3)
1.435(2)
1.434(2)
1.509(4)
1.496(4)
1.331(4)
1.330(4)
1.213(3)
1.213(3)
1.778(6)
1.746(6)
1.428(4)
1.444(4)
1.500(8)
1.493(8)
1.311(8)
1.329(8)
1.221(7)
1.202(6)
0
S O2
S O3
C2 C1
1.510(2)
1.347(2)
1.219(2)
0
0
C2 C1
C3 C2
C3 C2
0
0
C1 O1
C1 O1
0
0
Bond angles
C2 S1 C2
S C2 C3
0
98.7(1)
124.9(1)
103.9(1)
102.8(3)
118.5(2)
117.1(2)
112.1(2)
116.2(2)
129.4(3)
126.5(3)
130.0(3)
127.2(3)
119.0(3)
119.3(3)
118.4(5)
117.8(5)
113.8(5)
116.7(5)
127.7(6)
125.5(6)
128.1(6)
125.2(6)
118.6(6)
118.8(5)
0
0
S C2 C3
S C2 C1
S C2 C1
117.1(1)
117.9(1)
128.7(1)
118.9(1)
0
0
C3 C2 C1
0
0
0
C3 C2 C1
C2 C3 C13
0
0
0
0
C2 C3 C13
C2 C1 C11
0
0
C2 C1 C11
Torsion angles
0
C2 S C2 C1
� 53.7(1)
� 1.6(2)
� 65.1(2)
� 72.4(3)
� 175.7(3)
� 170.6(3)
� 102.5(3)
� 137.4(3)
73.3(3)
80.5(5)
81.7(5)
0
0
C2 S C2 C1
S C2 C3 C13
S C2 C3 C13
S C2 C1 C11
S C2 C1 C11
S C2 C1 O1
177.3(5)
177.7(4)
105.5(6)
� 104.9(6)
� 71.4(7)
75.7(7)
110.1(8)
� 105.3(8)
154.4(7)
39.2(9)
� 4.5(10)
� 176.3(6)
� 4.2(11)
� 1.3(10)
0
0
0
0
� 43.4(2)
137.6(1)
� 43.4(2)
� 146.3(2)
� 25.7(2)
179.4(1)
0
0
0
0
0
S C2 C1 O1
O1 C1 C2 C3
41.4(4)
� 104.8(4)
� 132.7(4)
18.9(5)
� 143.6(3)
� 28.2(4)
� 154.1(3)
2.2(6)
0
0
0
0
O1 C1 C2 C3
C2 C3 C13 C23
0
0
0
0
0
C2 C3 C13 C23
C2 C1 C11 C21
0
0
0
C2 C1 C11 C21
C1 C2 C3 C13
0
0
0
0
C1 C2 C3 C13
3.4(5)
˚
Note. Distances are given in A, and angles in deg.
whereas S C2 C3 is slightly narrowed (Table 5).
The overall conformations are very different as
in 1, lacking short intramolecular C O���O C
contacts and intramolecular face-to-face stacking
interactions of the aromatic groups (Figs. 1(b)
and 1(c)). Furthermore, both sulfones crystal-
lize on general positions, and their conforma-
tions have no internal symmetries. Neverthe-
less, the bond lengths in the propene group
clearly verify the structure assignment shown in
Scheme 2.
Apart from the covalent geometry, the in-
termolecular interactions deserve a look too. The
molecules carry no conventional hydrogen bond
donors, so that the C O acceptors must be ex-
pected to accept weak C H���O hydrogen bonds
as a resort.1
0,11
Indeed, numerous such interac-
tions are formed. In 1, for example, O1 is involved

9
2
Gnanadeepam, Selvaraj, Schreurs, Kroon, Steiner, and Perumal
thank UGC for a special assistance program.
M. Gnanadeepam thanks the management, Fatima Col-
lege, Madurai, for facilities. T. Steiner has performed
part of his work during a stay at the Weizmann-Institute
of Science, Rehovot (Israel), supported by the Minerva
Foundation (Munich).
References
1
2
3
. Selvaraj, S.; Dhanabalan, A.; Arumugam, N. Sulfur Lett. 1993,
5, 233.
. Renuga, S.; Selvaraj, S.; Perumal, S.; Sivakolunthu, S. Indian
J. Heterocycl. Chem. 1998, 8, 81.
. Gnanadeepam, M.; Renuga, S.; Selvaraj, S.; Perumal, S.
Hewlins, M.J.E. Phosphorus, Sulfur Silicon 1998, 134/135,
1
Fig. 2. Compound 1 drawn in a projection on the plane of the
p-chlorophenyl group to show the intramolecular �-stacking
interaction.
171.
4
5
. Gnanadeepam, M.; Selvaraj, S.; Perumal, S.; Hewlins, M.J.E.;
Lycka, A. Phosphorus, Sulfur Silicon 1999, 155, 167.
. Renuga, S.; Selvaraj, S.; Perumal, S.; Hewlins, M.J.E.;
Tetrahedron, 55 (1999) 9309.
in an interaction C63 H���O1 C1 (x, 1 + y, z)
˚
with H���O = 2.40, C���O = 3.42 A, C H���O =
�
6. Boulton, A.J.; McKillop, A. Comprehensive Heterocyclic
Chemistry; Pergamon Press: Oxford, 1984, Vol. 3, p. 885.
˚
1
57 (for C H = 1.08 A) which is a very good ge-
ometry for a hydrogen bond of this kind. In 2 and
, related interactions are formed too, but need not
7
8
9
. Gnanadeepam, M. PhD Thesis, Madurai Kamaraj University,
Madurai, 1999.
3
. Sheldrick, G.M. SHELXS-86, Program for the Solution of Crys-
tal Structures; University of G o¨ ttingen: Germany, 1986.
. Sheldrick, G.M. SHELXS-93, Program for the Refinement
of Crystal Structures; University of G u¨ ttingen: Germany,
1993.
be discussed here in greater detail.
Acknowledgments
1
1
0. Steiner, T. Chem. Commun. 1997, 727.
1. Desiraju, G.R.; Steiner, T. The Weak Hydrogen Bond in Struc-
tural Chemistry and Biology; Oxford University Press: Oxford,
1999.
S. Perumal thanks the CSIR, New Delhi, for
a major research project. S. Selvaraj and S. Perumal