Structural, spectral and thermal studies of substituted N-(2-pyridyl)-N′-phenylthioureas

Article abstract of DOI:10.1016/S0022-2860(01)00934-6

N-2-(3-picolyl)-N′-phenylthiourea, 3PicTuPh, monoclinic, P2₁/n, a = 7.617(2) b = 7.197(5), c = 22.889(5) ?, β = 94.63(4)°, V = 1250.7(1) ?³ and Z = 4; N-2-(4-picolyl)-N′-phenylthiourea, 4PicTuPh, triclinic, P-1, a = 7.3960(5), b = 7.

Full text of DOI:10.1016/S0022-2860(01)00934-6

Journal of Molecular Structure 608 ꢀ2002) 77±87
www.elsevier.com/locate/molstruc
Structural, spectral and thermal studies of substituted
N-ꢀ2-pyridyl)-N0-phenylthioureas
a
Jesus Valdes-Martõnez , Simon Hernandez-Ortega , Georgina Espinosa-Perez ,
a
a
Â
Â
Â
Â
Â
Â
Carmina A. Prestob, Anne K. Hermetetb, Kristin D. Haslowb, Lily J. Ackermanb,
Lisa F. Szczepurab, Karen I. Goldbergc, Werner Kaminskyc, Douglas X. Westc,
*
a
   Â
Instituto de Quõmica, Universidad Nacional Autonoma de Mexico, Circuito Exterior, Ciudad Universitaria, Coyoacan 04510,
Mexico City, Mexico
bDepartment of Chemistry, Illinois State University, Normal, IL 61790-4160, USA
cDepartment of Chemistry, University of Washington, Box 351700, Seattle, WA 98195-1700, USA
Received 5 February 2001; revised 29 October 2001; accepted 29 October 2001
Abstract
N-2-ꢀ3-picolyl)-N0-phenylthiourea, 3PicTuPh, monoclinic, P21/n, a ˆ 7:617ꢀ2† b ˆ 7:197ꢀ5†; c ˆ 22:889ꢀ5† A,
Ê
0
Ê 3
b ˆ 94:63ꢀ4†8, V ˆ 1250:7ꢀ1† A and Z ˆ 4; N-2-ꢀ4-picolyl)-N -phenylthiourea, 4PicTuPh, triclinic, P-1, a ˆ 7:3960ꢀ5†; b ˆ
Ê
Ê 3
7:9660ꢀ12†; c ˆ 21:600ꢀ3† A, a ˆ 86:401ꢀ4†; b ˆ 84:899ꢀ8†; g ˆ 77:769ꢀ8†8, V ˆ 1237:5ꢀ3† A and Z ˆ 4; N-2-ꢀ5-picolyl)-
N0-phenylthiourea, 5PicTuPh, monoclinic, P21/c, a ˆ 14:201ꢀ1†; b ˆ 4:905ꢀ3†; c ˆ 17:689ꢀ3† A, b ˆ 91:38ꢀ1†8,
Ê
V ˆ 1231:8ꢀ7† A and Z ˆ 4; N-2-ꢀ6-picolyl)-N0-phenylthiourea, 6PicTuPh, monoclinic, C2/c2, a ˆ 14:713ꢀ1†; b ˆ
Ê 3
0
Ê
Ê 3
9:367ꢀ1†; c ˆ 18:227ꢀ1† A, b ˆ 92:88ꢀ1†8, V ˆ 2515:5ꢀ1† A and Z ˆ 8 and N-2-ꢀ4,6-lutidyl)-N -phenylthiourea, 4,6LutTuPh,
Ê
Ê 3
monoclinic, C2/c, a ˆ 11:107ꢀ2†; b ˆ 11:793ꢀ2†; c ˆ 20:084ꢀ4† A, b ˆ 96:10ꢀ3†8, V ˆ 2616ꢀ1† A and Z ˆ 8: Intramolecular
hydrogen bonding between N0H and the pyridyl nitrogen and intermolecular hydrogen bonding involving the thione sulfur are
affected by substitution of the pyridine ring, as is the planarity of the molecule. H NMR studies in CDCl3 show the NH0
hydrogen resonance considerably down®eld from other resonances in the spectrum for each thiourea. q 2002 Elsevier Science
B.V. All rights reserved.
1
Keywords: 2-Pyridyl thioureas; Crystal structures; Hydrogen bonding; Plane deviation
1. Introduction
including N-benzoylthioureas, show intramolecular
hydrogen bonding between N0H and the benzoyl,
alkyl or acyl oxygen [3±10]. There is also an inter-
molecular NH hydrogen bond with a sulfur of a neigh-
boring molecule to form a two-dimensional network
in these latter thioureas. In addition, crystal structures
of substituted thioureas with intermolecular N±H´´´S
bonding, but without intramolecular hydrogen
bonding, have been reported [11±15]. More recent
structural studies of substituted N-0ꢀ2-pyridyl)-N0-
arylthioureas include N-ꢀ2-pyridyl)-N -tolylthioureas
The structure of N-ꢀ2-pyridyl)-N0-phenylthiourea
1
[1] has been reported following a H NMR study of
the intramolecular hydrogen bonding between the
pyridyl nitrogen and N0H for N-ꢀ2-pyridyl)thioureas
[2]. Studies of a number of substituted thioureas,
* Corresponding author. Tel.: 11-206-616-4213; fax: 11-206-
685-8665.
E-mail address: westdx@chem.washington.edu ꢀD.X. West).
0022-2860/02/$ - see front matter q 2002 Elsevier Science B.V. All rights reserved.
PII: S0022-2860ꢀ01)00934-6

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J. Valdes-Martõnez et al. / Journal of Molecular Structure 608 :2002) 77±87
78
evaporating the reactant mixture ꢀ35 8C), the thioureas
crystallized from solution. The solids were ®ltered,
washed with cold isopropanol, dried on a warm
plate and then stored until required for spectral char-
acterization. The yields are ca. 75% for each of the
thioureas and the melting points are as follows:
3PicTuPh, 122±4 8C; 4PicTuPh, 160±161 8C;
5PicTuPh, 179±180 8C; 6PicTuPh, 187±188 8C; and
4,6LutTuPh, 216±217 8C. Their 1H NMR spectra
were recorded in CDCl3 with a Varian Gemini 2000
300 MHz spectrometer. Infrared and ultraviolet
spectra were recorded with Perkin±Elmer 783 and
Hewlett Packard 8452 A Diode Array spectrophot-
ometers, respectively.
Fig. 1. Representations of N-picolyl- and N-4,6-lutidyl-N0-
phenylthioureas with expected intramolecular hydrogen bonding.
[16], the three N-2-ꢀ4,6-lutidyl)-N0-tolylthioureas
[17], N-ꢀ5-bromo-2-pyridyl)-N0-2-ꢀ2,5-dimethoxy-
phenylethyl)thiourea [18] and four thioureas with
p-substituted aryl groups, N-ꢀ2-pyridyl)-N0-4-bromo-
phenyl-, 0N-ꢀ2-pyridyl)-N0-4-chlorophenyl-, N-ꢀ2-
pyridyl)-N -4-mehoxyphenyl-and N-ꢀ2-pyridyl)-N0-
4-nitrophenylthioureas [19]. The aforementioned
2-pyridyl thioureas, like N-benzoyl-N0-thioureas
[3±10], feature both intramolecular and intermole-
cular hydrogen bonding, but ring substituents affect
the distances and angles of both types of hydrogen
bonds. A recent communication showed that some
members of a series of N-ꢀ2-pyridyl)-N0-2-methoxy-
phenylthioureas possess bifurcated intramolecular
hydrogen bonding to the pyridyl nitrogen and
methoxy oxygen [20]. We prepared and acquired
crystals of the N-2-ꢀpicolyl)-N0-phenylthioureas and
N-ꢀ4,6-lutidyl)-N0-phenylthiourea in order to deter-
mine whether methyl groups at various positions on
the pyridyl ring alter the nature or strength of the
hydrogen bonding interactions, as well as the overall
planarity of the molecule. The 1H and 13C NMR
spectra have been recorded for each of the thioureas,
which are represented in Fig. 1.
Crystals of the ®ve thioureas were grown by slow
evaporation of 1:1 by volume acetone±anhydrous
ethanolic mixtures at room temperature. The colorless
thiourea crystals were mounted in random orientation
on a glass ®ber on a Nonius MACH3 Four Circle
Diffractometer ꢀ3PicTuPh), Nonius Kappa CCD
Diffractometer ꢀ4PicTuPh, 5PicTuPh), Siemens P4
ꢀ6PicTuPh) and Siemens P3/F ꢀ4,6LutTuPh) Four
Circle Diffractometers. The structures were solved
by direct methods and missing atoms were found by
difference-Fourier synthesis. The non-hydrogen
atoms were re®ned with anisotropic displacement
parameters and all hydrogens were found on a differ-
ence Fourier map. For all the thioureas except
4PicTuPh and the pyridine ring of 5PicTuPh the
hydrogens attached to carbons were allowed to ride
on their carbons and assigned ®xed isotropic displace-
Ê 2
ment parameters, U ˆ 0:05 A . For 4PicTuPh, the
methyl hydrogens were allowed to ride in a disordered
model, but the other hydrogens were re®ned isotropi-
cally as were the hydrogens on the pyridine ring of
5PicTuPh. The coordinates of the H atoms attached to
nitrogen in each of the thioureas were re®ned isotro-
pically. The two phenyl ring positions in 5PicTuPh
are ca. 608 from each other with equal occupancy.
For 3PicTuPh, scattering factors are from Wassmaier
and Kirfel [21], calculations were done by maXus,
version 2.0 [22,23], and graphics are platon for
Windows [24]. For 4PicTuPh and 5PicTuPh
DENZO[25] was used for data reduction, scattering
factors are from Wassmaier and Kirfel [21], structure
re®nement by shelxl-97 and graphics are zortep
[26]. For 6PicTuPh and 4,6LutTuPh scattering factors
were taken from International Tables for X-ray
2. Experimental
2-amino-3-picoline, 2-amino-4-picoline, 2-amino-
5-picoline, 2-amino-6-picoline and 2-amino-4,6-luti-
dine were purchased from Aldrich and used as
received. Phenyl isothiocyanate ꢀAldrich) was mixed
in a 1:1 molar ratio with the desired substituted pyri-
dine in 95% ethanol and the mixture stirred with
warming for a minimum of 1 h. On cooling and slowly

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J. Valdes-Martõnez et al. / Journal of Molecular Structure 608 :2002) 77±87
79
s
s
s
s
s
C
a
b
g
u

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J. Valdes-Martõnez et al. / Journal of Molecular Structure 608 :2002) 77±87
80
Fig. 2. Thermal ellipsoid plot showing 3PicTuPh with atom numbering scheme and displacement ellipsoids at 50% probability level.
Crystallography ꢀ1974, Vol. IV) [27] and calculations
were done with the shelxtl pce program package
[28]. Table 1 summarizes the crystal data, collection
information and re®nement statistics for these
thioureas.
®ve thioureas of this study, are shown in Figs. 2±7.
3PicTuPh, 5PicTuPh, 6PicTuPh and 4,6LutTuPh
crystallize with one unique molecule in the cell, but
4PicTuPh has two crystallographic unique molecules
per unit cell. These thioureas, like other pyridyl
thioureas [1,16±20], are found in a conformation
resulting from intramolecular hydrogen bonding of
N3HꢀN0H) to the pyridine is nitrogen, N1, in a manner
similar to the benzoyl and acyl thioureas [3±10] and
cis±cis like N-phenyl-N0-phenylthiourea [11]. The
®ve thioureas have similar bond distances and angles,
Table 2, and the only notable difference is the C2±
N1±C6 angle, which may be due to different positions
of the methyl groups and/or differences in hydrogen
3. Results and discussion
3.1. Structural studies
The ORTEP diagrams of 3PicTuPh, 4PicTuPh,
5PicTuPh, 6PicTuPh and 4,6LutTuPh, as well as a
packing diagram of 4,6LutTuPh, representing the
Fig. 3. Thermal ellipsoid plot showing the two unique molecules of 4PicTuPh with atom numbering scheme and displacement ellipsoids at 50%
probability level.

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J. Valdes-Martõnez et al. / Journal of Molecular Structure 608 :2002) 77±87
81
Fig. 4. Thermal ellipsoid plot of 5PicTuPh with atom numbering scheme and displacement ellipsoids at 50% probability level.
bonding interactions. The variation in the bond
distances and angles in the crystallographically
different molecules of 4PicTuPh is about the same
as between the ®ve thioureas.
Table 3 shows a comparison of the thiourea moiety
bond distances and angles for the present thioureas
with previously reported thioureas having an oxygen
able to accommodate a hydrogen bond ꢀi.e. BzOTup-
NO2Ph and BzOThpMeOPh) [6,7], N-ꢀ2-pyridyl)-N0-
phenylthiourea, PyTuPh [1], and N,N0-substituted
thioureas that do not have intramolecular hydrogen
bonding, PhTuPh and ChTuP0h, N,N0-diphe-
nylthiourea and N-cyclohexyl-N -phenylthiourea,
respectively [10,13]. The differences between the
pyridyl thioureas and those with oxygen involved in
the intramolecular hydrogen bond are: ꢀ1) N2±C7
bond is shorter ꢀi.e. ca. three times the combined
e.s.d.'s) and ꢀ2) S1±C7 bond is marginally longer
Fig. 5. Thermal ellipsoid plot showing 6PicTuPh with atom numbering scheme and displacement ellipsoids at 50% probability level.

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J. Valdes-Martõnez et al. / Journal of Molecular Structure 608 :2002) 77±87
82
Fig. 6. Thermal ellipsoid plot showing 4,6LutTuPh with atom numbering scheme and displacement ellipsoids at 50% probability level.
ꢀi.e. ca. two times their combined e.s.d.'s). There is
essentially no difference in the N3±C7 bond as would
be expected since both groups of thioureas have
aromatic rings attached to N3. These 2-picolyl and
2-lutidyl thioureas do not have the electron with-
drawing carbonyl group attached to N2, which allows
the N2±C7 bond to have slightly more double bond
character, but this bond is generally longer than found
for thioureas without intramolecular hydrogen bonds
[10,13]. There is no signi®cant difference in the N2±
C7±N3 bond angles between the two groups of intra-
molecularly hydrogen bonding thioureas, but both
angles involving S1 show some difference. The N2±
C7±S1 angle for the 2-picolyl and 2-lutidyl thioureas
is smaller while the N3±C7±S1 angle is slightly
larger compared to N-benzoyl thioureas [6,7]. N-
cyclohexyl- and N-phenyl-N0-phenylthiourea ꢀi.e.
ChTuPh and PhTuPh, respectively) have a longer
S1±C7 bond, and the present pyridyl thioureas, as
well as N-pyridyl-N0-phenylthiourea, PyTuPh [1],
have smaller N2±C7±S1 bond angles.
The N3±H3´´´N1 intramolecular interactions ꢀTable
4) have similar N3´´´N1 distances indicating that posi-
tion or extent of substitution on the pyridyl ring does not
affect the strength of this interaction. However, the N±
H´´´N angle does vary with the position of substitution
in the order 3PicTuPh , 4PicTuPh , 5PicTuPh ù 6
PicTuPh ù 4,6LutTuPh. Like these thioureas, PyTuPh
[1] has a N3±H´´´Nꢀpy) non-bonding distance of
Fig. 7. Depiction of intramolecular and intermolecular hydrogen
bonding in 4,6LutTuPh.
Ê
2.646ꢀ4) A. However, the angle for this N±H´´´N

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J. Valdes-Martõnez et al. / Journal of Molecular Structure 608 :2002) 77±87
83
Table 2
Selected bond distances ꢀA) and angles ꢀ8) for 3PicTuPh, 4PicTuPh, 5PicTuPh, 6PicTuPh and 4,6LutTuPh
Ê
3PicTuPh
4PicTuPha
5PicTuPh
6PicTuPh
4,6LutTuPh
Bond
S1±C7
N1±C2
N1±C6
N2±C2
N2±C7
N3±C7
N3±C8
C2±C3
1.684ꢀ2)
1.329ꢀ3)
1.349ꢀ3)
1.407ꢀ3)
1.377ꢀ3)
1.330ꢀ3)
1.418ꢀ3)
1.409ꢀ3)
1.676ꢀ3) 1.679ꢀ3)
1.320ꢀ4) 1.339ꢀ3)
1.348ꢀ5) 1.352ꢀ4)
1.411ꢀ4) 1.404ꢀ4)
1.367ꢀ4) 1.366ꢀ4)
1.330ꢀ4) 1.341ꢀ3)
1.420ꢀ4) 1.413ꢀ4)
1.397ꢀ4) 1.375ꢀ4)
1.672ꢀ3)
1.324ꢀ3)
1.349ꢀ4)
1.405ꢀ3)
1.369ꢀ3)
1.340ꢀ3)
1.416ꢀ3)
1.389ꢀ4)
1.678ꢀ3)
1.330ꢀ4)
1.346ꢀ4)
1.399ꢀ4)
1.372ꢀ4)
1.335ꢀ4)
1.415ꢀ4)
1.397ꢀ4)
1.687ꢀ3)
1.335ꢀ4)
1.346ꢀ4)
1.408ꢀ4)
1.367ꢀ4)
1.339ꢀ4)
1.418ꢀ4)
1.387ꢀ4)
Angle
C2±N1±C6
C2±N2±C7
C7±N3±C8
N1±C2±N2
N1±C2±C3
N2±C2±C3
S1±C7±N2
S1±C7±N3
N2±C7±N3
N3±C8±C9
N3±C8±C13
118.1ꢀ2)
131.3ꢀ2)
132.2ꢀ2)
117.8ꢀ1)
123.7ꢀ2)
118.5ꢀ2)
116.8ꢀ2)
127.8ꢀ2)
115.4ꢀ2)
114.9ꢀ2)
125.4ꢀ2)
115.8ꢀ4) 115.8ꢀ3)
130.6ꢀ3) 131.0ꢀ3)
133.1ꢀ4) 129.5ꢀ3)
118.2ꢀ4) 117.5ꢀ3)
123.9ꢀ3) 123.2ꢀ3)
117.9ꢀ4) 119.3ꢀ4)
118.1ꢀ3) 118.6ꢀ2)
126.7ꢀ3) 125.7ꢀ3)
115.1ꢀ3) 115.8ꢀ3)
114.9ꢀ4) 116.2ꢀ3)
126.8ꢀ4) 123.6ꢀ3)
116.7ꢀ3)
130.7ꢀ3)
130.2ꢀ3)
119.4ꢀ3)
122.2ꢀ3)
118.4ꢀ3)
118.5ꢀ2)
126.2ꢀ2)
115.3ꢀ3)
116.6ꢀ3)b
123.8ꢀ3)b
118.9ꢀ3)
130.8ꢀ2)
132.1ꢀ3)
118.8ꢀ2)
122.5ꢀ3)
118.6ꢀ3)
117.5ꢀ2)
126.7ꢀ2)
115.8ꢀ3)
115.1ꢀ3)
125.9ꢀ3)
118.4ꢀ2)
130.8ꢀ2)
132.6ꢀ3)
118.3ꢀ2)
122.9ꢀ3)
118.8ꢀ2)
117.7ꢀ2)
126.9ꢀ2)
115.4ꢀ2)
114.9ꢀ3)
126.1ꢀ3)
a
Second numbers refer to the second molecule of the two crystallographically unique molecules for 4PicTuPh, S1 and S2.
The N3±C8±C21 and N3±C8±C25 angles are 114.3ꢀ3) and 127.4ꢀ3), respectively, for the disordered phenyl ring.
b
Table 3
Ê
Selected bond distances ꢀA) and bond angles ꢀ8) for substituted thioureas
Ê
Bond distances ꢀA)
Compound
Bond angles ꢀ8)
N2±C7
S1±C7
N3±C7
N2±C7±N3
N2±C7±S1
N3±C7±S1
References
BzOTupNO2Pha
BzOTupMeOPhb
PhTuPhc
1.393ꢀ3)
1.392ꢀ4)
1.349ꢀ4)
1.332ꢀ2)
1.374ꢀ4)
1.377ꢀ3)
1.367ꢀ4)
1.366ꢀ4)
1.369ꢀ3)
1.372ꢀ4)
1.367ꢀ4)
1.658ꢀ2)
1.659ꢀ3)
1.681ꢀ5)
1.696ꢀ2)
1.682ꢀ3)
1.684ꢀ2)
1.676ꢀ3)
1.679ꢀ3)
1.672ꢀ3)
1.678ꢀ3)
1.687ꢀ3)
1.344ꢀ3)
1.329ꢀ4)
1.349ꢀ4)
1.347ꢀ2)
1.335ꢀ4)
1.330ꢀ3)
1.330ꢀ4)
1.341ꢀ3)
1.340ꢀ3)
1.335ꢀ4)
1.339ꢀ4)
115.0ꢀ2)
115.4ꢀ3)
113.9ꢀ4)
117.3ꢀ2)
116.8ꢀ5)
115.4ꢀ2)
115.1ꢀ3)
115.8ꢀ3)
115.3ꢀ3)
115.8ꢀ3)
115.4ꢀ2)
118.3ꢀ2)
119.2ꢀ2)
123.0ꢀ2)
123.6ꢀ1)
118.6ꢀ4)
116.8ꢀ2)
118.1ꢀ3)
118.6ꢀ2)
118.5ꢀ2)
117.5ꢀ2)
117.7ꢀ2)
126.6ꢀ2)
125.4ꢀ2)
123.0ꢀ2)
119.1ꢀ1)
124.6ꢀ4)
127.8ꢀ2)
126.7ꢀ3)
125.7ꢀ3)
126.2ꢀ2)
126.7ꢀ2)
126.9ꢀ2)
[6]
[7]
[10]
[13]
[1]
ChTuPhd
PyTuPhe
f
3PicTuPh
±
f
4PicTuPh
±
f
5PicTuPh
6PicTuPh
4,6LutTuPh
±
f
±
f
±
N-benzoyl-N0-ꢀ4-nitrophenyl)thiourea.
N-benzoyl-N0-ꢀ4-methoxyphenyl)thiourea.
N,N0-diphenylthiourea.
N-cyclohexyl-N0-phenyllthiourea.
N-ꢀ2-pyridyl)-N0-phenyllthiourea.
This work.
a
b
c
d
e
f

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J. Valdes-Martõnez et al. / Journal of Molecular Structure 608 :2002) 77±87
84
Table 4
Intramolecular and intermolecular hydrogen bond distances ꢀA) and angles ꢀ8) for the various N-ꢀ2-pyridyl)-N -ꢀ4-substituted phenyl)thioureas
0
Ê
Intramolecular
Ê
H´´´A ꢀA)
Ê
D±H´´´A ꢀA)
Thiourea
3PicTuPh
4PicTuPh
D
A
D±H
/ꢀD±H´´´A) ꢀ8)
145ꢀ2)
N3
N3
N6
N3
N3
N3
N1
N1
N4
N1
N1
N1
0.84ꢀ2)
0.99ꢀ3)
0.93ꢀ3)
0.83ꢀ3)
0.83ꢀ4)
0.87ꢀ3)
1.92ꢀ2)
1.75ꢀ4)
1.78ꢀ3)
1.95ꢀ3)
1.91ꢀ4)
1.83ꢀ4)
2.649ꢀ3)
2.617ꢀ4)
2.627ꢀ4)
2.648ꢀ4)
2.647ꢀ3)
2.633ꢀ4)
144ꢀ3)
149ꢀ2)
5PicTuPh
6PicTuPh
4,6LutTuPh
141ꢀ3)
146ꢀ3)
152ꢀ3)
Intermolecular
3PicTuPha
N2
C14
C13
N2
C3
S1#1
S1#1
S1#2
S1#1
S1#1
S2#2
S2#2
S2#1
S2#1
S1#1
S1#1
S1#1
S1#1
0.84ꢀ2)
0.96
3.15ꢀ3)
2.95
3.756ꢀ4)
3.896ꢀ3)
3.766ꢀ4)
3.413ꢀ3)
3.747ꢀ4)
3.397ꢀ3)
3.715ꢀ3)
3.440ꢀ3)
3.636ꢀ4)
3.387ꢀ3)
3.707ꢀ3)
3.462ꢀ3)
3.660ꢀ3)
145ꢀ2)
170.6
139.0
160ꢀ3)
143ꢀ2)
158ꢀ3)
132ꢀ2)
165ꢀ3)
144ꢀ3)
167ꢀ3)
144
0.96
2.98
4PicTuPhb
1.01ꢀ4)
0.96ꢀ3)
0.80ꢀ3)
0.95ꢀ2)
0.86ꢀ3)
0.91ꢀ3)
0.87ꢀ4)
0.93
2.44ꢀ4)
2.93ꢀ3)
2.62ꢀ3)
3.01ꢀ2)
2.60ꢀ3)
2.85ꢀ3)
2.53ꢀ4)
2.91
N5
C23
N2
C3
5PicTuPhc,d
6PicTuPhe
4,6LutTuPhf
N2
C3
N2
C3
0.82ꢀ4)
0.93
2.66ꢀ4)
2.88
165ꢀ3)
142
a
Symmetry transformations used to generate equivalent atoms: #1: 1 2 x; 2y, 2z; #2: 21 1 x; y, z.
Symmetry transformations used to generate equivalent atoms: #1: 1 2 x, 2y, 2z; #2: 1 2 x, 2y, 1 2 z.
b
c
d
e
f
Angle between the mean planes of the pyridine rings: S1=S2 ˆ 59:64ꢀ0:12†8.
#1: 2x, 2 2 y, 1 2 z.
#1: 2 2 x, 2y, 1 2 z.
#1: 2x, 1 2 y, 2z.
interaction is 132.8ꢀ2.1)8, which is smaller than found
for any compounds in this study.
diethyl-N0-o-tolylthiourea [12] 0 and the largest
Ê
3.563ꢀ1) A for N-cyclohexyl-N -cyclohexylthiourea
[11]. The present compounds have an average N´´´S
As was found for N-benzoyl-N0-ꢀ4-methoxyphe-
nyl)thiourea [7], NH is involved in intermolecular
hydrogen bonding with a sulfur from a neighboring
molecule. Using the non-bonding N´´´S distance as a
measure of the strength of this interaction, the order of
strength is as follows: 6PicTuPh . 4PicTuPh ꢀboth
molecules) . 5PicTuPh . 4,6LutTuPh q 3PicTuPh.
The comparatively long distance found for 3PicTuPh
is indicative of the steric effect of the methyl group in
this position. The next longest is 4,6-LutTuPh, and the
two methyl groups may also exert a steric effect; the
weaker dimer formation is probably due to packing of
the layers of dimers since greater volume is required
by the additional methyl group. The non-bonding
Ê
distance of 3.488ꢀ7) A, which is within the above
range. The intermolecular N±H´´´S bond angle for
3PicTuPh, an average of 145ꢀ2)8, is much smaller
than the other thioureas of this study, which average
more than 1608. This latter angle falls in the range
between 140ꢀ3)8 ꢀN-dimethyl-N0-o-tolylthiourea)
[12] and 170ꢀ1)8 ꢀN-ethyl-N0-ethylthiourea) [14].
Therefore, 3PicTuPh has the weakest intermolecular
N±H´´´S interaction among N-ꢀ2-pyridyl)thioureas
[1,16±20] reported to date, which is consistent with
it having the lowest melting point, 122±124 8C. Fig. 7
shows that C3H of 4,6LutTuPh, absent in 3PicTuPh,
is positioned to interact with a neighboring molecule's
S1 in conjunction with N2H when the pyridyl ring and
thiourea moiety are approximately coplanar. The
distances and angles for this interaction is included
in Table 4. The thiourea with molecules having
0
Ê
N´´´S distance is 3.592ꢀ2) A for N-benzoyl-N -ꢀ4-
methoxyphenyl)thiourea, while other N-substituted
0
Ê
and N,N -substituted thioureas average 3.46 A [10±
Ê
14], the smallest distance being 3.363ꢀ1) A for N-

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J. Valdes-Martõnez et al. / Journal of Molecular Structure 608 :2002) 77±87
85
Table 5
Mean plane data and angles between planes for 3PicTuPh, 4PicTuPh, 5PicTuPh, 6PicTuPh and 4,6LutTuPh
Compound Plane # Plane
Mean plane deviation Atom with greatest deviation Plane/plane Angle
3PicTuPh
1
2
3
1
2
3
4
5
6
1
2
3
4
1
2
3
1
2
3
N1±C2±C3±C4±C5±C6
N2±C7±S1±N3
0.0026
0.0039
0.0040
0.0003
0.0001
0.0001
C3, 0.0043ꢀ0.0015)
C7, 0.0068ꢀ0.0017)
C8, 0.0057ꢀ0.0016)
C3, 0.0053ꢀ0.0030)
C7, 0.0011ꢀ0.0030)
C8, 0.0031ꢀ0.0030)
C23, 0.0062ꢀ0.0032)
C7, 0.0033ꢀ0.0031)
C9, 0.0125ꢀ0.0039)
C5, 0.0127ꢀ0.0020)
C7, 0.0003ꢀ0.0021)
C11, 0.0655ꢀ0.0046)
C21, 0.0123ꢀ0.0040)
C5, 0.0048ꢀ0.0023)
C7, 0.0003ꢀ0.0024)
C9, 0.0030ꢀ0.0023)
C3, 0.0056ꢀ0.0019)
C7, 0.0001ꢀ0.0022)
C8, 0.0084ꢀ0.0021)
1/2
2/3
1/3
1/2
2/3
1/3
4/5
5/6
4/6
1/2
2/3
1/3
3/4
1/2
2/3
1/3
1/2
2/3
1/3
8.05ꢀ0.10)
15.69ꢀ0.11)
9.07ꢀ0.12)
3.46ꢀ0.14)
8.77ꢀ0.30)
5.95ꢀ0.24)
6.95ꢀ0.28)
43.55ꢀ1.46)
42.45ꢀ1.76)
4.55ꢀ0.14)
33.26ꢀ0.21)
34.89ꢀ0.20)
59.84ꢀ0.22)
3.96ꢀ0.21)
11.11ꢀ0.10)
11.07ꢀ0.21)
4.65ꢀ0.17)
13.13ꢀ0.17)
13.91ꢀ0.17)
C8±C9±C10±C11±C12±C13
N1±C2±C3±C4±C5±C6
N2±C7±S1±N3
4PicTuPh
C8±C9±C10±C11±C12±C13
N4±C22±C23±C24±C25±C26 0.0004
N5±C27±S2±N6 0.0004
C28±C29±C30±C31±C32±C33 0.0007
5PicTuPh
N1±C2±C3±C4±C5±C6
N2±C7±S1±N3
0.0084
0.0002
0.0401
0.0079
0.0034
0.0002
0.0019
0.0037
0.0000
0.0052
C8±C9±C10±C11±C12±C13
C8±C21±C22±C11±C24±C25
N1±C2±C3±C4±C5±C6
N2±C7±S1±N3
6PicTuPh
C8±C9±C10±C11±C12±C13
N1±C2±C3±C4±C5±C6
N2±C7±S1±N3
4,6LutTuPh
C8±C9±C10±C11±C12±C13
crystallographic differences, 4PicTuPh, could inter-
molecularly hydrogen bond between either crystallo-
graphically identical or different molecules; 4PicTuPh
forms hydrogen bonds between crystallographically
identical molecules.
The angles between planes often provide informa-
tion about the molecules' geometry with the angle
between the pyridyl and aryl mean planes being a
convenient measure for the present compounds,
Table 5. This angle is very different between the
two crystallographic unique molecules of 4PicTuPh,
5.95ꢀ0.24) and 42.45ꢀ1.76)8. The other thioureas of
this study, except for 5PicTuPh, have an angle ranging
from 9 to 148 between the pyridine and aryl mean
planes. It should be noted that substitution on the
aryl ring causes this angle to be much larger; the
angle between the pyridine ring and aryl ring for N-
ꢀ2-pyridyl)-N0-2-tolyl-, N-ꢀ2-pyridyl)-N0-3-tolyl-and
N-ꢀ2-pyridyl)-N0-4-tolylthiourea is 67.4ꢀ1)8, averages
79.4ꢀ1)8 ꢀtwo unique molecules) and 58.7ꢀ1)8 ꢀtwo
unique molecules), respectively [16]. The angle
between the mean planes of the pyridine ring and
thiourea moiety is larger for 3PicTuPh, ca. 88, than
the other thioureas of this study, ca. 48. The larger
angle for 3PicTuPh results in greater distance between
the 3-methyl group hydrogens and the hydrogen
attached to N2 and results in weaker intermolecular
N2±H´´´S1 hydrogen bonding as discussed earlier.
3.2. Thermal studies
Table 6
1H NMR and ultraviolet spectral data for PhTu, 3PicTuPh,
4PicTuPh, 5PicTuPh, 6PicTuPh and 4,6LutTuPh
The DSC plots of these thioureas show a sharp peak
due to melting followed immediately by a broader
peak representing decomposition. Representative
enthalpies of fusion are as follows: PyTuPh, 41.0;
6PicTuPh, 43.5 and 4,6LutTuPh, 50.9 kJ mol21. The
TGA experiments show loss of 100% of their mass at
temperatures beginning within 108 of their melting
points and ending approximately 208 above their
melting points with no mass loss preceding this one
step process.
Compound
N0H
NH
n ! pp
PhTu
13.865
13.930
13.739
13.648
14.103
14.119
10.903
8.268
9.027
9.559
9.205
8.311
32 900ꢀ4.429)a
32 680ꢀ4.350)
33 220ꢀ4.462)
32 680ꢀ4.317)
32 470ꢀ4.468)
32 680ꢀ4.443)
3PicTuPh
4PicTuPh
5PicTuPh
6PicTuPh
4,6LutTuPh
a
log 1:

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J. Valdes-Martõnez et al. / Journal of Molecular Structure 608 :2002) 77±87
86
3.3. Spectral studies
Acknowledgements
Acknowledgement is made to the Donors of the
Petroleum Research Fund, administered by the Amer-
ican Chemical Society, the National Science Founda-
tion and the Universidad Nacional Autonoma de
Mexico PAPIIT Program ꢀIN1038393) and Consejo
Nacional de Ciencia y Tecnologia ꢀ3920-E) for the
partial support of this research. In addition, we
thank the referees for comments that have signi®-
cantly improved this contribution.
The UV spectra ꢀCHCl3) show two strong bands
which we assign to a combination of p ! pp transi-
tions from both rings and an n ! pp ꢀTable 6) of the
heterocyclic ring. The former band appears at
37 000 cm21 in these thioureas and is somewhat
weaker than the latter band, which has a molar absorp-
tivity of ca. 2:8 £ 104: Based on the spectra of thiose-
micarbazones, which show a band associated with the
thioamide part of the molecule in the 25 000 cm21
region, n ! pp transitions involving sulfur non-
bonding electrons are observed as shoulders in the
spectra of some of these thioureas at ca.
28 000 cm21. In the infrared spectra of these thioureas
ꢀnꢀNH) is an absorption of medium intensity at ca.
3200 cm21 and nꢀCS) appears between 820 and
860 cm21 region.
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Crystallographic data ꢀexcluding structure
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have been deposited with the Cambridge Crystal-
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