I.C. Mendes et al. / Journal of Molecular Structure 559 (2001) 355–360
357
Table 2
small difference in the two series; the average C7–
N2 bond is 1.279(2) and 1.287(3) A for the formyl-
˚
Selected bond distances (A) and angles (Њ) for H4Fo4DH,
H3Fo4DH, H4Ac4DH and H3Ac4DH
˚
pyridine and acetylpyridine derivatives, respectively.
˚
The average N2–N3 bond is 1.369(2) A for the
Bond
H4Fo4DH H3Fo4DH H4Ac4DH H3Ac4DH
˚
formylpyridine thiosemicarbazones and 1.386(3) A
C8–S
1.677(3)
1.279(2)
1.371(2)
1.358(2)
1.323(2)
1.693(2)
1.278(2)
1.367(2)
1.357(3)
1.311(3)
1.697(2)
1.290(2)
1.390(2)
1.372(2)
1.330(2)
1.697(2)
1.284(3)
1.384(3)
1.354(3)
1.311(3)
for the acetylpyridine thiosemicarbazones. The small
differences are attributable to the different electronic
effects of the aldehyde hydrogen and ketone methyl
group.
C7–N2
N2–N3
N3–C8
C8–N4
The formylpyridine thiosemicarbazones have
higher melting points compared to the corresponding
acetyl analogues, probably due to the fact that the
angle between the mean plane of the pyridine ring
and the plane involving C(7)–N(2)–N(3)–C(8) is
much smaller in the formylpyridine thiosemicarba-
zones (H3Fo4DH, 9.34(9)Њ; H4Fo4DH, 18.36(8)Њ)
than in the corresponding acetylpyridine thiosemi-
carbazones (H3Ac4DH, 46.3(1)Њ; H4Ac4DH,
50.04(8)Њ). The smaller angle favors molecular
stacking leading to higher density and melting point.
In fact, the calculated densities (H3Fo4DH, 1.358 g/
cm3; H4Fo4DH, 1.407 g/cm3; H3Ac4DH, 1.320 g/
cm3 and H4Ac4DH, 1.336 g/cm3) are in agreement
with closer packing for the formylpyridine thiosemi-
carbazones.
Angle
C7–N2–N3 116.6(1)
N2–N3–C8 118.6(1)
N3–C8–N4 117.0(1)
N3–C8–S
N4–C8–S
116.5(2)
119.4(2)
117.0(2)
119.1(2)
123.9(2)
116.5(5)
118.6(1)
117.5(2)
119.1(1)
123.4(1)
118.2(2)
117.9(2)
117.9(2)
119.2(2)
122.9(2)
119.5(1)
123.5(1)
by direct methods [9] and subsequent difference
Fourier maps, which revealed the position of all
non-hydrogen atoms, and refined on F2 by a full-
matrix least-squares procedure using anisotropic
displacement parameters [10]. Hydrogens on nitro-
gens were located by difference Fourier maps and
refined isotropically and hydrogens attached to
carbons were located in their calculated positions
˚
(C–H 0.93–0.97 A) and refined using a riding
model. Atomic scattering factors were taken from
the International Table for X-ray Crystallography
[11].
Table 3 contains the distances and angles for the
hydrogen bonding of the four thiosemicarbazones.
Three intermolecular hydrogen bonds are observed
for H3Fo4DH, H4Ac4DH and H3Ac4DH and only
two for H4Fo4DH. Taking into consideration the
intermolecular hydrogen bonding, H3Fo4DH,
H4Ac4DH and H3Ac4DH present each a N3–
H3N…S bond and H4FoDH presents no such a
bond, indicating that the melting points are not
much affected by the presence of those interactions.
Of note is the different mode of hydrogen bonding by
the N4H2 function in H3Fo4DH, which is the most
planar of these four thiosemicarbazones.
3. Results and discussion
3.1. Structural characterization
Table 1 has summaries of crystal data and X-ray
data collection, data reduction and structure refine-
ment results for H4Fo4DH, H3Fo4DH, H4Ac4DH
and H3Ac4DH. Selected bond distances and angles
for the four thiosemicarbazones are listed in Table
2. Perspective views for H4Fo4DH, H3Fo4DH,
H4Ac4DH and H3Ac4DH are shown in Fig. 2a–d.
Intramolecular and intermolecular hydrogen bonding
parameters are presented in Table 3 and the mean
plane data are compiled in Table 4.
3.2. Spectral characterization
1
The H NMR spectra, reported previously [7,8],
showed two signals for N4H2 due to one hydrogen
interacting with N2 in each of the compounds. N3H
is found in the 11.65 region for the formylpyridine
thiosemicarbazones, but at ca. d 10:35 for the acet-
ylpyridine thiosemicarbazones, which is consistent
with hydrogen bonding to DMSO [12] in both cases.
As would be expected, there are not large differ-
ences in the bond distances of the thiosemicarbazone
moieties. However, the imine C7–N2 and, possibly
the N2–N3 bonds, would be expected to show a