Structural and spectral studies of N-(2-pyridyl)-N′-(4-substituted phenyl)thioureas

Article abstract of DOI:10.1016/S0022-2860(01)00811-0

The following molecules were found to have intramolecular hydrogen bonding between the N′H and the pyridine nitrogen and intermolecular hydrogen bonding between the NH and a thione sulfur of a second molecule to form dimers: N-(2-pyridyl)-N′-(4-methoxyphe

Full text of DOI:10.1016/S0022-2860(01)00811-0

Journal of Molecular Structure 607 (2002) 101±110
www.elsevier.com/locate/molstruc
Structural and spectral studies of N-(2-pyridyl)-N0-(4-substituted
phenyl)thioureas
*
Lisa F. Szczepura , Kristin K. Eilts, Ann K. Hermetet, Lily J. Ackerman,
John K. Swearingen, Douglas X. West
Department of Chemistry, Illinois State University, Normal, IL 61790-4160, USA
Received 5 March 2001; accepted 9 July 2001
Abstract
The following molecules were found to have intramolecular hydrogen bonding between the N0H and the pyridine nitrogen
and intermolecular hydrogen bonding between the NH and a thione sulfur of a second molecule to form dimers: N-(2-pyridyl)-
0
ꢀ
N -(4-methoxyphenyl)thiourea, PyTu4OMe, triclinic, P-1, a ˆ 7:158ꢀ4†; b ˆ 8:742ꢀ3†; c ˆ 10:833ꢀ4† A; a ˆ 70:53ꢀ3†; b ˆ
0
ꢀ3
74:38ꢀ3†; g ˆ 73:97ꢀ4†8; V ˆ 635:5ꢀ5† A and Z ˆ 2; N-(2-pyridyl)-N -(4-nitrophenyl)thiourea, PyTu4NO2, monoclinic, P21/
c, a ˆ 11:670ꢀ1†; b ˆ 5:9225ꢀ9†; c ˆ 18:792ꢀ4† A; b ˆ 107:99ꢀ1†8; V ˆ 1244:8ꢀ7† A and Z ˆ 4; N-(2-pyridyl)-N0-(4-
ꢀ
ꢀ3
ꢀ
chlorophenyl)thiourea, PyTu4Cl, triclinic, P-1, a ˆ 9:939ꢀ3†; b ˆ 11:399ꢀ4†; c ˆ 12:264ꢀ5† A; a ˆ 65:50ꢀ4†; b ˆ 87:46ꢀ3†;
g ˆ 76:63ꢀ3†8; V ˆ 1228:1ꢀ7† A and Z ˆ 4 and N-(2-pyridyl)-N0-(4-bromophenyl)thiourea, PyTu4Br, triclinic, P-1, a ˆ
ꢀ3
ꢀ
ꢀ3
10:020ꢀ2†; b ˆ 11:444ꢀ2†; c ˆ 12:353ꢀ5† A; a ˆ 64:76ꢀ2†; b ˆ 87:61ꢀ3†; g ˆ 77:88ꢀ2†8; V ˆ 1250:8ꢀ7† A and Z ˆ 4: The
methoxy and nitro moieties of PyTu4OMe and PyTu4NO2 also interact with N0H, and there is a weak intermolecular interaction
1
between one of the pyridine hydrogen atoms and the thione sulfur in PyTu4Br. Solution H NMR spectral studies (DMSO-d6)
show the N0H resonance considerably down®eld for each thiourea and its chemical shift, as well as that of NH, is affected by
substituents on the phenyl ring. q 2002 Elsevier Science B.V. All rights reserved.
Keywords: Heterocyclic thioureas; Intramolecular hydrogen bonding; Intermolecular hydrogen bonding; Crystal structures; 1H NMR spectroscopy
1. Introduction
intermolecular hydrogen bond with the NH and the
sulfur of a neighboring molecule to form a two-dimen-
sional network in these latter thioureas [3±8]. In addi-
tion, crystal structures of substituted thioureas with
intermolecular N±H´´´S0 bonding, but without intra-
molecular hydrogen bonding, have been reported
[10±14]. More recent studies of substituted N-(2-
pyridyl)-N0-(aryl)thioureas include N-2-(4,6-lutidyl)-
N0-(phenyl)thiourea, 4,6LuTuPh [15], the three N-(2-
pyridyl)-N0-(tolyl)thioureas [16], the three N-2-(4,6-
lutidyl)-N0-(tolyl)thioureas [17] and N-(5-bromo-2-
pyridyl)-N0-[2-(2,5-dimethoxyphenyl)ethyl]thiourea
[18]. The present thioureas, like the N-
(benzoyl)thioureas [3±8], feature both intramolecular
Arecent0structural study has been reported for N-(2-
1
pyridyl)-N -(phenyl)thiourea [1] after H NMR spec-
troscopy correctly predicted intramolecular hydrogen
bonding between the pyridine nitrogen and N0H for
N-(2-pyridyl)thioureas [2]. Studies of a number of
substituted thioureas, including N-(benzoyl)thioureas,
indicate intramolecular hydrogen bonding between
N0H and the benzoyl oxygen [3±9]. There is also an
* Corresponding author. Tel.: 11-309-438-2359; fax: 11-309-
438-5538.
E-mail address: lfs@xenon.che.ilstu.edu (L.F. Szczepura).
0022-2860/02/$ - see front matter q 2002 Elsevier Science B.V. All rights reserved.
PII: S0022-2860(01)00811-0

102
L.F. Szczepura et al. / Journal of Molecular Structure 607 (2002) 101±110
and intermolecular hydrogen bonding. Arecent
communication showed that some members of
series of N-(2-pyridyl)-N0-(2-methoxyphenyl)-
a
thioureas possess bifurcated intramolecular hydrogen
bonding to the pyridine nitrogen and methoxy oxygen
[19]. In order to determine whether functional groups
at other positions of the phenyl ring are involved in
1
hydrogen bonding, we prepared, recorded H NMR
spectra of, and obtained the crystal structures 0and
lattice arrangements for four N-(2-pyridyl)-N -(4-
substituted phenyl)thioureas, Fig. 1.
Fig. 1. Representations of N-(2-pyridyl)-N0-(4-substituted phenyl)
thioureas with expected intramolecular hydrogen bonding
(X ˆ OMe, Br, Cl, NO2).
2. Experimental
2-Aminopyridine and 4-methoxy-, 4-nitro-, 4-
chloro- and 4-bromophenyl isothiocyanates were
purchased from Aldrich and used as received. 2-Amino-
pyridine and a 4-substituted phenyl isothiocyanate
Table 1
Crystallographic data and methods of data collection, solution and re®nement for PyTu4OMe, PyTu4NO2, PyTu4Cl and PyTu4Br
Crystal data
PyTu4OMe
C13H13ON3S
Colorless, prism
0:30 £ 0:25 £ 0:15
Triclinic
P-1
PyTu4NO2
C12H10O2N4S
Yellow, prism
0:25 £ 0:20 £ 0:12
Monoclinic
P21/c
PyTu4Cl
C12H10ClN3S
Colorless, prism
0:32 £ 0:24 £ 0:14
Triclinic
PyTu4Br
C12H10BrN3S
Colorless, prism
0:30 £ 0:20 £ 0:12
Triclinic
Empirical formula
Crystal color, habit
Crystal size (mm)
Crystal system
Space group
P-1
P-1
Ê
a (A)
7.158(4)
8.742(3)
10.883(4)
70.53(3)
74.38(3)
73.97(4)
635.5(5)
2
11.670(1)
5.9225(9)
18.792(4)
90(0)
9.939(3)
10.020(2)
11.444(2)
12.353(5)
64.76(2)
Ê
b (A)
Ê
c (A)
11.399(4)
12.264(5)
65.50(4)
a (8)
b (8)
g (8)
107.99(1)
90(0)
87.46(3)
87.61(3)
76.63(3)
77.88(2)
Ê 3
Volume (A )
Z
1244.8(7)
4
1228.1(7)
4
1250.8(7)
4
Formula weight
Density (calcd.) (g/cm3)
259.3
274.3
263.8
309.2
1.355
1.464
1.427
1.642
Absorp. coeff. (mm21
F(000)
)
0.246
0.264
0.461
3.434
272
568
544
620
Index ranges
0 # h # 9
211 # k # 11
214 # l # 14
3227
0 # h # 15
0 # k # 7
224 # l # 24
3401
0 # h # 12
214 # k # 14
215 # l # 15
6215
0 # h # 13
214 # k # 14
216 # l # 16
6278
Re¯ections collected
Independent re¯ections
Observed re¯ections
3126
2858
5620
5723
1433 {I . 3:0sꢀI†}
None
2412 {I . 3:0sꢀI†}
3893 {I . 3:0sꢀI†}
3002 {I . 3:0sꢀI†}
Absorption correction
Max. and min. transmissions
c-scan
0.993 and 0.967
1.216
c-scan
1.000 and 0.942
1.324
c-scan
1.000 and 0.838
2.946
Goodness-of-Fit
Ê 23
0.474
Largest diff. peak (eA
Largest diff. hole (eA
R, wR
)
0.25
2 0.16
0.60
2 0.32
0.49
2 0.33
0.99
2 1.33
Ê 23
)
0.0332, 0.0329
0.2697, 0.2654
0.0485, 0.0688
0.0623, 0.0859
0.0484, 0.0733
0.0859, 0.1313
0.0637, 0.0922
0.1443, 0.1426
R, wR (all re¯ections)

L.F. Szczepura et al. / Journal of Molecular Structure 607 (2002) 101±110
103
Fig. 2. ORTEP diagram showing the two unique molecules of PyTu4OMe with atom numbering scheme and displacement ellipsoids at 50%
probability level.
were dissolved in a 1:1 molar ratio in 95% ethanol,
and the resulting mixture gently re¯uxed for a
minimum of 1 h. On cooling and slowly evaporating
(358C) the reactant mixture, the thioureas crystallized
from solution. The solids were ®ltered, washed with
cold isopropanol followed by anhydrous ether, dried
on a warm plate and then stored until required for
characterization. The yields are ca. 75% for each of
the thioureas and the melting points are as follows:
PyTu4OMe, 187±1908C; PyTu4NO2, 175±1788C;
PyTu4Cl, 190±1938C and PyTu4Br, 202±2048C.
volume) at room temperature. Crystals were mounted
on glass ®bers and used for data collection at 293 K on a
Nonius MACH3 automatic diffractometer, MoKa ꢀl ˆ
ꢀ
0:71073 A†: Cell constants and an orientation matrix for
data collections were obtained by least squares re®ne-
ments of the diffraction data from 25 re¯ections. The
structures were solved with direct methods and missing
atoms were found by difference-Fourier synthesis. All
non-hydrogen atoms were re®ned with anisotropic
temperature factors and hydrogens attached to nitrogens
were found on the difference-Fourier map. The H atoms
1
ꢀ
Their H NMR spectra were recorded in DMSO-d6
of CH were ®xed at d ˆ 0:96 A; allowed to ride on the
with a Varian Mercury 400 MHz spectrophotometer.
1H NMR data (DMSO-d6): PyTu4OMe 3.76 (s, 3H),
6.94 (d, 2H), 7.08 (dd, 1H), 7.24 (d, 1H), 7.51 (d, 2H),
7.82 (m, 1H), 8.29 (dd, 1H), 10.82 (s, 1H, NH), 13.58
(s, 1H, N0H). PyTu4Cl: 7.12 (dd, 1H), 7.25 (d, 1H),
7.44 (d, 2H), 7.74 (d, 2H), 7.84 (m,01H), 8.32 (dd, 1H),
10.99 (s, 1H, NH), 13.91 (s, 1H, N H). PyTu4Br: 7.11
(dd, 1H), 7.25 (d, 1H), 7.57 (d, 2H), 7.70 (d, 2H), 7.84
(m, 1H), 8.32 (dd, 1H), 10.99 (s, 1H, NH), 13.92 (s,
1H, N0H). PyTu4NO2: 7.15 (dd, 1H), 7.28 (d, 1H),
7.87 (m, 1H), 8.16 (d, 2H), 8.25 (d, 2H), 8.37 (dd,
1H), 11.20 (s, 1H, NH), 14.48 (s, 1H, N0H).
C atoms and assigned ®xed isotropic temperature factor,
ꢀ2
U ˆ 0:05 A : The coordinates of the H atoms attached
to N and N0 were re®ned isotropically. Re®nement of
the structures was made by full-matrix least-squares on
F. Scattering factors are from Wassmaire and Kirfel
[20], calculations were done by maxus, version 2.0
[21], and graphics are platon for Windows [22].
3. Results and discussion
3.1. Structural studies
Prismatic crystals of the thioureas were grown by
slow evaporation of acetone±ethanol solutions (1:1 by
The crystallographic data, as well as the solution

104
L.F. Szczepura et al. / Journal of Molecular Structure 607 (2002) 101±110
Fig. 3. ORTEP diagram showing PyTu4NO2 with atom numbering scheme and displacement ellipsoids at 50% probability level.
Fig. 4. ORTEP diagram showing the two unique molecules of PyTu4Cl with atom numbering scheme and displacement ellipsoids at 50%
probability level.

L.F. Szczepura et al. / Journal of Molecular Structure 607 (2002) 101±110
105
Fig. 5. Packing diagram of PyTu4Br showing intramolecular and intermolecular hydrogen bonding.
and re®nement information for these thioureas, are
shown in Table 1, and the atomic coordinates and
equivalent isotropic displacement coef®cients are
included in the deposited material (see Section 4), as
are a complete list of bond distances and angles.
The molecular structures are represented by the
ORTEP diagrams of PyTu4OMe, PyTu4NO2 and
PyTu4Cl shown in Figs. 2±4, respectively. Fig. 5
shows the packing diagram for PyTu4Br with the
intermolecular and intramolecular hydrogen bonding
indicated. These thioureas are in a conformation
resulting from intramolecular hydrogen bonding of
N0H to the pyridine nitrogen, in a manner similar to
th0e N-(benzoyl)thioureas [3±8] and the N-(2-pyridyl)-
N -(tolyl)thioureas [16]. Three of the reported
thioureas (all but PyTu4NO2) crystallize in the P-1
symmetry group with two crystallographically unique
molecules. Inspection of Table 2 shows that the bonds
of the two unique molecules of PyTu4OMe have a
number of signi®cantly different distances, but the
two molecules of PyTu4Cl and PyTu4Br have similar
bond distances. However, the average bond distances
for PyTu4OMe are in good agreement with the
distances for the other three thioureas of this study
Table 2
Ê
Selected bond distances (A) and angles (8) for PyTu4OMe, PyTu4NO2, PyTu4Cl and PyTu4Br. The second column represents the analogous
bonds in the S2 molecule of PyTu4OMe, PyTu4Cl and PyTu4Br
Ê
Distances (A)
S1±C7
PyTu4OMe
PyTu4NO2
1.681(4)
1.332(5)
1.349(6)
1.399(5)
1.370(5)
1.355(5)
1.406(5)
PyTu4Cl
1.688(5) 1.684(5)
PyTu4Br
1.68(2) 1.69(2)
1.72(2) 1.65(2)
1.28(2) 1.35(3)
1.39(3) 1.39(2)
1.35(2) 1.47(2)
1.32(2) 1.41(2)
1.29(2) 1.37(2)
1.45(3) 1.42(3)
N11±C2
N11±C6
N12±C2
N12±C7
N13±C7
N13±C8
1.338(7) 1.336(7)
1.348(7) 1.346(7)
1.404(6) 1.411(6)
1.372(7) 1.370(7)
1.337(7) 1.337(7)
1.435(8) 1.434(8)
1.34(2) 1.35(2)
1.35(2) 1.35(2)
1.42(2) 1.41(2)
1.35(2) 1.35(2)
1.36(2) 1.35(2)
1.44(2) 1.43(2)
Angles (8)
C2±N12±C7
C7±N13±C8
N11±C2±N12
N12±C2±C3
S1±C7±N12
S1±C7±N13
N12±C7±N13
N13±C8±C9
N13±C8±C13
128.9(13) 130.3(12)
128.0(12) 120.5(12)
124.4(14) 114.5(12)
116.9(14) 118.2(12)
122.1(10) 114.6(10)
119.3(10) 126.9(11)
118.6(11) 118.3(12)
122.5(14) 118.2(13)
122.3(15) 117.7(15)
130.7(4)
131.6(3)
119.1(4)
117.6(4)
117.3(3)
127.1(3)
115.2(4)
126.4(4)
114.2(4)
130.0(5) 129.9(5)
126.8(4) 124.7(4)
118.8(4) 119.0(5)
118.2(4) 118.2(4)
118.9(4) 118.5(4)
124.6(4) 123.8(4)
116.5(4) 117.7(5)
121.0(5) 120.8(5)
117.7(5) 118.0(5)
130.5(10) 130.0(10)
124.6(9) 127.5(9)
118.4(10) 118.4(10)
118.3(11) 118.1(10)
119.1(9) 119.1(9)
123.6(9) 123.6(9)
117.3(10) 117.3(10)
120.7(11) 120.2(11)
117.2(11) 118.4(11)

106
L.F. Szczepura et al. / Journal of Molecular Structure 607 (2002) 101±110
Table 3
Comparison of selected bond distances (A) and bond angles (8) for N-(2-pyridyl)-N -(phenyl)thiourea and N-(2-pyridyl)-N -(4-substituted
phenyl)thioureas
0
0
Ê
Ê
Bond distances, A
Bond angles, 8
N12±C7±N13
Compound
N12±C7
S1±C7
N13±C7
N12±C7±S1
N13±C7±S1
Ref
a
a
a
a
PyTu4OMe
PyTu4NO2
PyTu4Cl
PyTu4Br
PyTu4Tb
PyTuPhc
1.365(20)
1.370(5)
1.371(7)
1.35(2)
1.685(20)
1.681(4)
1.686(4)
1.685(20)
1.678(4)
1.682(3)
1.33(2)
118.4(12)
115.2(4)
116.3(4)
117.3(10)
116.2(7)
116.8(5)
118.4(10)
117.3(3)
117.5(3)
119.1(9)
118.8(6)
118.6(4)
123.1(11)
127.1(3)
126.1(3)
123.6(9)
125.0(6)
124.6(4)
1.355(5)
1.337(7)
1.355(20)
1.340(6)
1.335(4)
1.376(5)
1.374(4)
16
1
a
This work.
N-(2-pyridyl)-N0-(4-tolyl)thiourea.
N-(2-pyridyl)-N0-(phenyl)thiourea.
b
c
and are within three orders of magnitude of their
combined estimated standard deviations. The bond
angles of the two molecules of PyTu4OMe also
show some variation, however, as with the bond
lengths, the average bond angles of the two molecules
of PyTu4OMe are in good agreement with the other
three thioureas of this study. The greatest differences
in angles for the four thioureas occur for N13±C8±C9
and N13±C8±C13; the difference between these two
angles (i.e. /N13±C8±C9±/N13±C8±C13) is
largest for PyTu4NO2, 12.2(4)8 followed by PyTu4Br,
3.5(11)8, PyTu4Cl, 3.3(5)8, and PyTu4OMe has
essentially no difference.0 The previously reported
PyTu4T, N-(2-pyridyl)-N -(4-tolyl)thiourea, has a
value of 3.1(7)8 [16] for this difference. Thus, the
electronic effect of the 4-substituent attached to the
aryl ring affects the structural nature of these
thioureas. The C11(31)±X (X ˆ OMe, NO2, Cl, Br)
average bond distances are 1.39(3), 1.474(5), 1.751(6)
Ê
and 1.92(2) A for PyTu4OMe, PyTu4NO2, PyTu4Cl
Table 4
Angles between mean planes for PyTu4OMe, PyTu4NO2, PyTu4Cl and PyTu4Br. Plane A(D) ˆ mean plane of pyridine ring, plane
B(E) ˆ mean plane of the thiourea moiety, N±C(S)±N0, and plane C(F) ˆ mean plane of the phenyl ring
Compound Plane
Plane Mean plane deviation Atom with greatest deviation Plane/Plane Angle
PyTu4OMe N11±C2±C3±C4±C5±C6
N12±C7±S1±N13
A0.0006
C6, 0.0632(0.0166)
C7, 0.0167(0.0125)
/B
A
5.7(0.2)
B/C
B
0.0010
0.0051
0.0063
0.0083
0.0035
85.8(5.2)
86.9(3.0)
1.3(0.1)
C8±C9±C10±C11±C12±C13
N21±C22±C23±C24±C25±C26
N22±C27±S2±N23
C
C12, 0.0488(0.0147)
C26, 0.0952(0.0167)
S2,0.0413(0.000)
A/C
D/E
D
E
E/F
83.5(2.4)
83.5(2.8)
C28±C29±C30±C31±C32±C33
F
C31, 0.0374(0.0220)
F/D
PyTu4NO2
PyTu4Cl
N11±C2±C3±C4±C5±C6
N12±C7±S1±N13
A0.0001
B
C3, 0.0067(0.0042)
/B
A
A
11.2(0.4)
B/C
0.0003
0.0002
C7, 0.0030(0.0034)
C13, 0.0049(0.0038)
8.2(0.2)
C8±C9±C10±C11±C12±C13
N11±C2±C3±C4±C5±C6
N12±C7±S1±N13
C
A/C
19.4(0.6)
A0.0004
B
C6, 0.0088(0.0062)
/B
11.3(0.4)
B/C
0.0006
0.0001
0.0003
0.0001
0.0001
C7, 0.0061(0.0050)
C9, 0.0043(0.0052)
C26, 0.0114(0.0059)
C27, 0.0005(0.0051)
C33, 0.0063(0.0052)
57.9(1.8)
60.4(2.1)
1.9(0.1)
C8±C9±C10±C11±C12±C13
N21±C22±C23±C24±C25±C26
N22±C27±S2±N23
C
A/C
D
D/E
E
E/F
F/D
57.1(2.1)
58.7(1.6)
C28±C29±C30±C31±C32±C33
N11±C2±C3±C4±C5±C6
N12±C7±S1±N13
F
PyTu4Br
A0.0007
C6, 0.0173(0.0139)
/B
A
1.1(0.1)
B/C
B
C
D
E
F
0.0004
0.0001
0.0004
0.0003
0.0001
C7, 0.0073(0.0149)
C12, 0.0079(0.0125)
C26, 0.0073(0.0149)
C27, 0.0022(0.0124)
C32, 0.0092(0.0127)
55.7(1.6)
56.7(2.0)
10.8(0.2)
58.3(1.8)
60.0(1.8)
C8±C9±C10±C11±C12±C13
N21±C22±C23±C24±C25±C26
N22±C27±S2±N23
A/C
D/E
E/F
C28±C29±C30±C31±C32±C33
F/D

L.F. Szczepura et al. / Journal of Molecular Structure 607 (2002) 101±110
107
Table 5
0
Ê
Intramolecular and intermolecular hydrogen bond distances (A) and angles (8) for the various N-(2-pyridyl)-N -(4-substituted phenyl)thioureas
(D ˆ donor, A ˆ acceptor)
Intramolecular
Thiourea
D
AD±H
N11
N21
N11
N11
N21
N11
N21
H´´´AD±H´´´A
1.13(2)
1.16(2)
/(D±H´´´A)
136.8(8)
140.2(8)
144.7(3)
139.6(4)
142.2(3)
128.7(7)
137.1(7)
PyTu4OMe
N13
N23
N13
N13
N23
N13
N23
1.75(2)
1.70(2)
1.849(4)
2.012(4)
1.842(4)
1.94(1)
1.87(1)
2.68(2)
2.70(2)
2.655(5)
2.664(6)
2.673(6)
2.66(2)
2.66(2)
PyTu4NO2
PyTu4Cl
0.922(3)
0.812(4)
0.967(4)
0.974(9)
0.960(9)
PyTu4Br
Intermolecular
Thiourea
D
AD±H
S2
S1
H´´´AD±H´´´A
/(D±H´´´A)
141.6(7)
152.6(7)
116.0(7)
110.3(7)
163.6(3)
120.2(1)
154.2(3)
171.5(3)
168.9(6)
163.3(6)
151.6(7)
144.2(7)
PyTu4OMe
N12
N22
N13
N23
N12
N13
N12
N22
N12
N22
C3
1.12(2)
1.04(2)
1.13(2)
1.16(2)
0.865(4)
0.922(3)
0.948(5)
0.954(5)
0.96(1)
0.96(1)
0.98(2)
0.97(2)
2.473(0)
2.454(2)
3.19(1)
3.42(2)
3.41(1)
3.82(1)
3.62(1)
3.414(3)
3.333(5)
3.322(5)
3.504(5)
3.51(1)
3.32(1)
3.80(1)
3.51(1)
O2
O1
S1
3.05(2)
PyTu4NO2
PyTu4Cl
PyTu4Br
2.576(1)
3.247(4)
2.443(2)
2.557(2)
2.563(4)
2.391(4)
2.915(3)
2.681(4)
O1
S2
S1
S2
S1
S2
C23
S1
and PyTu4Br, respectively. The O±C14(34) bond
4)
consistent
with
N13H13´´´N11
(and
Ê
distance for PyTu4OMe is 1.42(3) A, the two N±O
bond distances of PyTu4NO2 are 1.224(5) and
Ê
1.229(6) A and the O±N±O bond angle is 124.2(4)8.
N23H23´´´N21) intramolecular hydrogen bonding
(vide infra). However, the angle between the mean
planes of the thiourea moiety and the phenyl ring is
larger for most of these thioureas (mean plane angles
B/C and E/F in Table 4). The average of the two
unique molecules is 84.7(5.2), 57.5(2.1) and
57.0(1.8)8 for PyTu4OMe, PyTu4Cl and PyTu4Br,
respectively. However, the angle between the mean
planes of the thiourea moiety of PyTu4NO2 and the
phenyl ring is much smaller, 8.2(0.2)8, and between
the pyridine and phenyl rings is 19.4(0.6)8 (mean
plane angles A/C and D/F in Table 4) showing that
this molecule is the most planar of the four thioureas
studied here.
The various modes of hydrogen bonding are shown
in Table 5. As found for the N-(2-pyridyl)thioureas
previously [2,15±17,19], intramolecular hydrogen
bonding between N13H13(N23H23) and N11(N21)
occurs with an N13´´´N11 (N23´´´N21) distance of
Ê
about 2.7 A and an N13±H13´´´N11 (N23±
H23´´´N21) angle of about 1408. The small angle
between the mean planes of the pyridine ring and
Acomparison of the bond distances and angles of
the thiourea moiety of the four complexes of this
study and N-(2-pyridyl)-N0-(phenyl)thiourea [1] and
N-(2-pyridyl)-N0-(4-tolyl)thiourea, PyTuPh and
PyTu4T [16], is shown in Table 3. There are no signif-
icant differences in the bond distances, but the two
NCS bond angles (N12±C7±S1 or N13±C7±S1)
show some variation. However, this variation does
not appear to be related to the electronic effects of
the functional groups on the aryl ring; the angles for
PyTu4NO2 and PyTu4Cl show the largest difference.
Listed in Table 4 are the mean plane deviations for
the pyridine ring, the thiourea moiety and the phenyl
ring along with the angles between planes and the
atom deviating to the greatest extent for each plane.
For the four thioureas and their crystallographically
unique molecules the angle between the pyridine ring
and the thiourea moiety ranges from 1.1(0.1) to
11.3(0.4)8 (mean plane angles A/B and D/E in Table

108
L.F. Szczepura et al. / Journal of Molecular Structure 607 (2002) 101±110
Fig. 6. Plot of the chemical shift of the N0H resonance vs the Hammett substituent constant for the series of PyTu4X (where X ˆ OMe, H, Cl,
Br, NO2).
the thiourea moiety is also consistent with the forma-
tion of the intramolecular hydrogen bond. This
hydrogen also interacts weakly with oxygens in
PyTu4OMe and PyTu4NO2. For PyTu4OMe the inter-
action is between crystallographically different mole-
cules and the N´´´O average non-bonding distance is
(tolyl)thioureas, PyTu2T (N-(2-pyridyl)-N00-(2-tolyl)
thiourea),
thiourea) and PyTu4T [16], have N´´´S non-bonding
PyTu3T
(N-(2-pyridyl)-N -(3-tolyl)
distances of 3.401(2), 3.387 and 3.410(2), and
Ê
3.352(4) and 3.523(4) A, respectively, which are
comparable to the thioureas of this study, Table 5.
Other parameters of the N±H´´´S hydrogen bonding
shown in Table 5 are comparable to thioureas
previously studied [10±14,16]. The N±H´´´S
hydrogen bonding interaction in the previously
studied complexes results in the formation of dimers,
which are often centrosymmetric [1]. When there are
two or more crystallographic unique molecules, and
the N±H´´´S interactions to form dimers are between
unlike molecules, centrosymmetry is lost. Inspection
of Table 5 shows that PyTu4OMe, PyTu4Cl and
PyTu4Br have different interaction distances and
angles for the two hydrogen bonds making up the
dimer. In addition to the N±H´´´S hydrogen bond, the
sulfur is also interacting with a pyridine hydrogen,
C3H3 in PyTu4Br, but not in the other three molecules.
This intermolecular hydrogen bonding interaction
Ê
approximately 3.7 A indicating this interaction to be
considerably weaker than the intramolecular N0 ±
H´´´N hydrogen bonding. Neither the chlorine or
bromine atoms in PyTu4Cl and PyTu4Br form a
signi®cant interaction with the H atom involved in
the intramolecular bond of the neighboring molecule.
Amore important intermolecular hydrogen
bonding interaction is between the thione sulfurs
and N12H12 (N22H22) of neighboring molecules.
The previously studied N-substituted and N,N0-substi-
tuted thioureas (i.e. thioureas without intramolecular
hydrogen bonding) have an average N´´´S non-
Ê
bonding distance of 3.46 A [10±14], the smallest
0
Ê
being 3.363(2) A for N,N-diethyl-N -(2-tolyl)thiourea
0
Ê
[12] and the largest 3.653(1) A for N-cyclohexyl-N0-
(cyclohexyl)thiourea [11]. The N-(2-pyridyl)-N -

L.F. Szczepura et al. / Journal of Molecular Structure 607 (2002) 101±110
109
results in the sulfur appearing to be positioned
between the two interacting molecules and is similar
to the N-(2-pyridyl)-N0-(tolyl)thioureas, PyTu2T,
PyTu3T and PyTu4T [16].
be obtained, free of charge, on application to the
Director, CCDC, 12 Union Road, Cambridge
CB21EZ, UK, (fax: 144-(0) 1223-336033 or e-mail:
deposit@ccdc.cam.ac.uk).
3.2. Spectral studies
Acknowledgements
1
The H NMR spectral data (provided in Section 2)
contains chemical shift evidence that the intramole-
cular hydrogen bonds observed in the reported solid
state structures are maintained in DMSO solution (at
room temperature). In general, intramolecular
hydrogen bonding interactions are known to cause
down®eld shifts in proton resonances. For example,
the previously reported N-(2-pyridyl)thioureas
display the non-hydrogen bonded (NH) resonance
around 9±10 ppm, and the intramolecularly hydrogen
bonded (N0H) resonance between 12±14 ppm [2]. In
addition, other organic and inorganic compounds with
intramolecular hydrogen bonding show similar shifts
[23,24]. By analogy, we have assigned the down®eld
Acknowledgement is made to the Donors of the
Petroleum Research Fund, administered by the
American Chemical Society. We also thank Werner
Kaminsky (University of Washington) for his help in
preparing Fig. 5
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4. Supplementary material
Crystallographic data (excluding structure factors)
for the structures reported in this paper have been
deposited with the Cambridge Crystallographic Data
Center as supplementary publication no. CCDC-
144804 for PyTu4OMe, CCDC-144805 for
PyTu4NO2, CCDC-144802 for PyTu4Cl and CCDC-
144803 for PyTu4Br. Copies of available material can
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