Structural and spectral perspectives of a novel thiosemicarbazone synthesized from di-2-pyridyl ketone and 4-phenyl-3-thiosemicarbazide

Article abstract of DOI:10.1016/j.saa.2005.05.001

A new thiosemicarbazone, HL is synthesized from di-2-pyridyl ketone and 4-phenyl-3-thiosemicarbazide and structurally and spectrochemically characterized. ¹H NMR, ¹³C NMR, COSY, HMQC and IR spectra of the compound are studied and the proton magnetic resonance spectrum reveals some unprecedented observations. The thione form is predominant in the solid state, as supported by the crystal structure and IR data, while a thiol-thione equilibrium is proposed in the solution state by NMR studies. The compound crystallizes into a monoclinic lattice with space group C2/c and the ZE conformation is exhibited by the thiosemicarbazone. Intra- and intermolecular hydrogen-bonding interactions give rise to a two-dimensional packing in the crystal lattice.

Full text of DOI:10.1016/j.saa.2005.05.001

Spectrochimica Acta Part A 63 (2006) 174–181
Structural and spectral perspectives of a novel thiosemicarbazone
synthesized from di-2-pyridyl ketone and
4-phenyl-3-thiosemicarbazide
a
a,∗
b
V. Suni , M.R. Prathapachandra Kurup , Munirathinam Nethaji
a
Department of Applied Chemistry, Cochin University of Science and Technology,
Kochi 682022, Kerala, India
Department of Inorganic and Physical Chemistry, Indian Institute of Science,
b
Bangalore 560012, India
Received 18 January 2005; received in revised form 30 April 2005; accepted 2 May 2005
Abstract
A new thiosemicarbazone, HL is synthesized from di-2-pyridyl ketone and 4-phenyl-3-thiosemicarbazide and structurally and spectro-
1
13
chemically characterized. H NMR, C NMR, COSY, HMQC and IR spectra of the compound are studied and the proton magnetic resonance
spectrum reveals some unprecedented observations. The thione form is predominant in the solid state, as supported by the crystal structure
and IR data, while a thiol–thione equilibrium is proposed in the solution state by NMR studies. The compound crystallizes into a monoclinic
lattice with space group C2/c and the ZE conformation is exhibited by the thiosemicarbazone. Intra- and intermolecular hydrogen-bonding
interactions give rise to a two-dimensional packing in the crystal lattice.
©
2005 Elsevier B.V. All rights reserved.
Keywords: Di-2-pyridyl ketone; Thiosemicarbazone; HMQC; COSY; Crystal structure
1
. Introduction
ketone, offer much more coordination possibilities for the
thiosemicarbazone ligand.
For the past three decades, thiosemicarbazones with the
Interestingly, di-2-pyridyl ketone (dpk), as such can
function as a ligand construction unit, chelating with
metal ions and forming promising clusters and cubanes
with excellent ferromagnetic characteristics [14–16]. The
hydrolysed derivative of dpk, commonly referred to as the
gem-diol form of di-2-pyridyl ketone coordinate to metals
either in the monoanionic or dianionic form, giving rise to
infinite arrays. Hence, incorporation of di-2-pyridyl ketone
into an N(4)-substituted thiosemicarbazone chain offer
a variety of binding modes with possible extension into
polymeric structures. However, the coordination chemistry
of substituted or unsubstituted thiosemicarbazones of di-2-
pyridyl ketone is quite unexplored with few previous reports
[17–21]. This prompted our study into the synthesis and
characterization of di-2-pyridyl ketone thiosemicarbazones
and their metal complexes [22–24], and here we report the
structural and spectral perspectives of a new compound,
1
2 3
general formula (R )NH–C(S)–NH–N(R R ) has remained
an important ligand construction unit in both the neutral
and anionic forms [1–13]. These organic molecules with
potential donor atoms in their structural skeleton fascinate
coordination chemists with their versatile chelating behav-
ior. The coordinating ability of thiosemicarbazides to both
transition and main group metallic cations is attributed to
the extended delocalization of electron density over the
NH C(S) NH N system, which is enhanced by substitu-
tion at the N(4) position. Condensation of thiosemicarbazides
with aromatic aldehydes or ketones extend the electron delo-
calization along the azomethine bond. Presence of additional
donor sites in the ketonic part as in the case of di-2-pyridyl
∗
Corresponding author. Tel.: +91 484 2575804; fax: +91 484 2577595.
E-mail address: mrp@cusat.ac.in (M.R. Prathapachandra Kurup).
1
386-1425/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2005.05.001

V. Suni et al. / Spectrochimica Acta Part A 63 (2006) 174–181
175
Table 1
Crystal data and structural refinement for HL
Parameters
HL
Empirical formula
Formula weight, M
Crystal system
Space group
C18H15N5S
333.41
Monoclinic
C2/c
Lattice constants
a ( A˚ )
22.073(19)
9.740(8)
16.380(14)
90.00
104.766(13)
90.00(9)
3405(5)
b ( A˚ )
c ( A˚ )
◦
α ( )
◦
β ( )
◦
γ ( )
3
Fig. 1. Structure of compound HL.
Volume V ( A˚ )
Z
8
−
3
Calculated density, ρ (Mg m
Absorption coefficient, µ (mm 1)
)
1.301
0.199
di-2-pyridyl ketone N(4)-phenylthiosemicarbazone, HL
−
(Fig. 1).
F(0 0 0)
1392
Crystal size (mm)
θ Range for data collection
Limiting indices
0.80 × 0.64 × 0.61
1.91–27.32
−28 ≤ h ≤ 25,
−11 ≤ k ≤ 12,
2
. Experimental
−
20 ≤ l ≤ 20
Reflections collected
Unique reflections
Completeness to θ
12701
3534 [Rint = 0.0184]
27.32 (91.8%)
2
.1. Materials
Commercial reagents, phenyl isothiocyanate (Fluka),
hydrazine hydrate (Lancaster) and di-2-pyridyl ketone
Aldrich) were used as received. Elemental analyses were
Absorption correction
Refinement method
Data/restraints/parameters
Goodness-of-fit on F
Final R indices [I > 2σ (I)]
R indices (all data)
None
Full-matrix least-squares on F2
3534/0/278
(
2
1.057
carried out at CDRI, Lucknow, India, with Heraeus Ele-
mental Analyser. Infrared spectra were recorded on ABB
Bomem FTIR instrument using KBr pellets in the range of
R1 = 0.0521, wR2 = 0.1525
R = 0.0599, wR = 0.1621
1
2
Largest difference peak and hole
0.814 and −0.234
(e A˚
−
3
−
1
)
4
000–500 cm . Electronic spectrum in the solid state was
recorded on Ocean Optics, SD2000 Fibre Optic Spectrome-
1
13
ter. The H NMR, C NMR, COSY and HMQC spectra were
recorded using Bruker DRX 500, with CDCl3 as solvent and
TMS as standard at Sophisticated Instruments Facility, Indian
Institute of Science, Bangalore, India.
ketone (0.921 g, 5 mmol) continuously for 4 h after adding
one drop of acetic acid. Light yellow crystals of the thiosemi-
carbazone were separated upon cooling, which were filtered
and washed with methanol. The compound was recrystalized
from ethanol and dried over P4O10 in vacuo.
2
.2. Synthesis of HL
2.3. X ray data collection, structure solution and
Preparation of compound HL was carried out as in
refinement
Scheme 1, adapting a reported procedure [25]. A solu-
tion of phenyl isothiocyanate (0.675 g, 5 mmol) in 20 ml of
ethanol was continuously stirred with an ethanolic solution
of hydrazine hydrate (0.250 g, 5 mmol) for 1 h. The white
product of N(4)-phenylthiosemicarbazide thus formed was
washed, dried and recrystalized from ethanol. A ethanolic
solution of N(4)-phenyl thiosemicarbazide (0.836 g, 5 mmol)
was then refluxed with methanolic solution of di-2-pyridyl
The crystallographic data and structure refinement param-
eters of compound HL are given in Table 1. A light yellow
rectangular single crystal of HL with approximate dimen-
sions 0.08 mm × 0.64 mm × 0.61 mm was used for data col-
lection. Measurement of X-ray diffraction data was done at
˚
293(2) K using Mo K␣ radiation of wavelength 0.71073 A
with Bruker SMART APEX CCD diffractometer equipped
Scheme 1.

1
76
V. Suni et al. / Spectrochimica Acta Part A 63 (2006) 174–181
with a fine focus sealed tube X-ray source. The structure was
interactions with adjacent nitrogen atoms N(1) and N(3).
Hydrogen-bonding decreases the electron density around the
proton, and thus moves the proton absorption to a lower field
[29]. Absence of any coupling interactions by N(4)H and
N(5)H protons due to the lack of availability of protons on
neighboring atoms render singlet peaks for the imine pro-
tons. Two doublets at δ = 8.84 and 8.675 ppm are assigned to
the C(1)H and C(11)H protons, respectively. These signals
are shifted to lower field due to electronic effect of the adja-
centelectronegativepyridylnitrogensandthemoredownfield
shift of C(1)H can be attributed to the increased charge den-
sity on N(1) resulted by its hydrogen-bonding to N(4)H.
Coupling of these protons with the C(2) and C(10) protons
splits their signals into doublets. The proton resonances of the
two pyridyl rings also appear separately in the NMR spec-
trum, due to the intramolecular hydrogen-bonding. There are
two multiplets at δ = 7.815 and 7.855 ppm corresponding to
similar protons on C(3) and C(9) of the two pyridyl rings,
while the C(2)H and C(10)H resonances appear overlapped
in the multiplet at δ = 7.40 ppm. A doublet at δ = 7.57 ppm
ideally correspond to C(4)H and C(8)H protons. However,
the C(4)H protons are found to have experienced a greater
downfield shift into the multiplet at δ = 7.815, as evident
2
solved by direct methods and refined by least-square on F0
2
using SHELXL-97 [26]. Refinement of F was done against
all reflections. All esds, except the esd in the dihedral angle
between two least square planes, are estimated using the full
covariance matrix. The SMART software was used for data
acquisition and the SAINT software for data extraction [27].
The graphics tool was DIAMOND [28]. All non-hydrogen
atoms were refined anisotropically, while the hydrogen
atoms were treated with a mixture of independent and con-
strained refinement and used for structure factor calculation
only.
3
. Results and discussion
3
.1. Synthesis of HL
The compound is obtained as crystalline product from
the condensation of di-2-pyridyl ketone with 4-phenyl-3-
thiosemicarbazone and the single crystals suitable for X-
ray analysis were grown by slow evaporation of a dilute
solution in methanol. Elemental analyses, found (calcd.):
◦
C 64.79(64.84); H 4.53(4.46); N 21.11(21.01), mp 135 C,
from the HMQC spectrum. The resonances for the C H –
6 5
yield 62%.
group appear as a doublet at δ 7.705 ppm (ortho), and as
multiplets at δ 7.40 and 7.24 ppm corresponding to meta and
para phenyl protons. All the assignments made above are
observed to be in general agreement with previous reports on
di-2-pyridyl ketone thiosemicarbazones [16,17]. However,
3
.2. 1H NMR
Proton magnetic resonance spectroscopy is a helpful tool
for the identification of organic compounds in conjunction
with other spectrometric informations. The H NMR spec-
trum of the compound along with the spectral assignments
is given in Fig. 2. A sharp singlet, which integrates as one
hydrogen at δ = 14.55 ppm is assigned to the proton attached
to the nitrogen atom N(4), while another similar singlet at
δ = 9.55 ppm is assigned to the N(5)H proton. The downfield
shifts of these protons are assigned to their hydrogen-bonding
1
interestingly, the H NMR spectrum of the present com-
1
pound reveals some more singlet peaks in the higher field
region beyond δ = 2.2 ppm. A comparatively weak signal at
δ = 2.18 ppm together with a sharp peak at δ = 1.60 ppm can
be assigned to an –SH peak attributable to the possible pres-
ence of the thiol tautomer in solution. Thiosemicarbazones
are believed to exhibit a thione–thiol equilibrium in the solu-
tion state. However, in all the previous reports mentioned
Fig. 2. 1H NMR spectrum.

V. Suni et al. / Spectrochimica Acta Part A 63 (2006) 174–181
177
above, such an –SH signal was absent and the compounds
were established to retain their structure in solution. Another
interesting singlet at δ 1.25 ppm, which integrates as two pro-
tons, is typical of the present compound and it is assigned
to be of the protons on the hetero atoms N(4) and N(5),
which are subjected to hydrogen-bonding in CdCl3 solvent
bons on the substituted phenyl ring are clearly distinguishable
inthe13CNMRspectrum. Thepeakcorrespondingtothepara
positioned carbon atom C(16) is observed rather upfield when
compared to its ortho [C(14) and C(18)] and meta [C(15) and
C(17)] counterparts. The phenyl resonances are: C(14) and
C(18), 124.819 ppm; C(15) and C(17), 129.449 ppm; C(16),
126.691 ppm.
[29]. To the best of our knowledge, such a typical evidence
for the intramolecular hydrogen-bonding in N(4)-substituted
thiosemicarbazones has never been previously obtained from
the H NMR spectrum.
.4. 1H– H COSY
1
3
1
1
1
The COSY spectrum reveals the H– H coupling interac-
3
.3. 13C NMR
tions in a molecule. It is usually plotted as three-dimensional
contours, where the conventional spectrum is represented
along the diagonal (Fig. 4). The cross-peaks along both the
sides of the diagonal identify the nuclei that are coupled
to each other. On the contrary, the protons that are decou-
pled from the adjacent ones due to the lack of ␣-protons
will show no correlation in the spectrum. For instance, in the
COSYspectrum of the present compound, absence ofany off-
diagonal peaks extending from δ = 14.55 and 9.55 ppm con-
firm their assignment to N(4)H and N(5)H protons, respec-
tively. However, extending horizontal and vertical lines from
δ = 8.84 ppm [C(1)H] and 8.675 ppm [C(11)H] encounter
cross-peaks at δ 7.40 ppm, where the C(2)H and C(10)H reso-
nances are merged into multiplets along with the phenyl ring
proton resonances. The comparatively weaker coupling inter-
actions of C(1)H and C(11)H with the β-positioned C(3)H
and C(9)H protons are shown by the poorly resolved cross
peaks at δ 7.815 and 7.855 ppm. This also helps to accurately
assign C(3)H (δ 7.815 ppm) and C(9)H (δ 7.855 ppm) protons
to their respective values, which is contrary to the expected
more downfield shift of C(3)H proton of the hydrogen bonded
pyridine ring. COSY spectrum also turns out very helpful in
the accurate assignment of proton resonances in the aromatic
region. The multiplets of the C(3)H and C(9)H protons show
coupling interactions with the doublet at δ 7.57 ppm [C(4)H
and C(8)H] and with the multiplet at δ 7.40 ppm [C(2)H
and C(10)H]. However, the C(3) and C(9) protons show no
The 13C NMR spectrum provides direct information about
the carbon skeleton of the molecule. Assignment of differ-
ent resonant peaks to respective carbon atoms are presented
in Fig. 3. Considering the two pyridyl rings non-equivalent,
resulting from the hydrogen-bonding interaction, there are
1
6 unique carbon atoms in the molecule, which give a total
13
of 16 different peaks in the C NMR spectrum. In both the
pyridyl rings, the C(1) and C(11) carbon atoms adjacent to
the more electronegative nitrogen atoms N(1) and N(2) are
shifted further downfield when compared to the neighbor-
ing carbon atoms. Also, the carbon atoms at para position
to the hetero atoms, viz. C(3) and C(9) resonate at lower
field values when compared to the meta positioned carbons,
C(2), C(4), C(8) and C(10). However, the non-protonated car-
bons C(5) and C(7) are showing more downfield shift in the
pyridyl rings due to an increased electron density resulting
from the presence of electronegative nitrogen atom and ␲
electron delocalization in the magnetic environment. Hence,
1
3
the C peaks of the two pyridyl rings are assigned as follows:
C(1), 148.932 ppm; C(2), 124.429 ppm; C(3), 137.684 ppm;
C(4), 125.017 ppm; C(5), 155.033 ppm; C(7), 156.671 ppm;
C(8), 127.510 ppm; C(9), 137.804 ppm; C(10), 124.721 ppm;
C(11), 149.557 ppm. Thenon-protonatedcarbonatomatC(6)
is shifted farthest downfield in the spectrum (δ 177.422 ppm),
effected by the magnetic interaction of two bulky pyridyl
rings and the ␲ electron delocalization on the C(6) = N(3)
bond. Similarly, the C(12) carbon atom resonance is also
observed at a lower field of 152.349 ppm, resultant of the
conjugative effect of the –N(3)–N(4)–C(S)–N(5)– thiosemi-
carbazone skeleton. The three different types of aromatic car-
Fig. 3. 13C NMR assignments of HL.
Fig. 4. 1H– H COSY spectrum.
1

1
78
V. Suni et al. / Spectrochimica Acta Part A 63 (2006) 174–181
1
interactions with the doublet at δ 7.705 ppm, which helps
to assign the latter peak to the phenyl protons at the ortho
position, i.e., C(14)H and C(18)H. Coupling interactions of
these protons are observed at δ 7.40 ppm, thus assigning the
multiplet to the meta positioned phenyl protons C(15)H and
C(17)H also. Assignment of the multiplet at δ 7.24 ppm to
the para phenyl proton C(16)H is clearly evident from the
COSY, as its only correlation is observed with the multiplet
at δ 7.40 ppm, which is assigned to the neighboring C(15)H
and C(17)H.
at δ 7.40 ppm in the H NMR shows two different resul-
tant contour peaks around δ 124 and 129 ppm, which reveal
the presence of both the phenyl and pyridyl ring proton
resonances in the multiplet. With the help of these con-
tours, the carbon atoms at meta positions of the phenyl
ring are assigned to the 13C resonance at δ 129.449 ppm,
while the carbon atoms at meta positions to the nitrogen
atoms on the two pyridyl rings are assigned at δ 124.721
and 124.429 ppm.
3.6. IR spectrum of HL
13
3
.5. 1H– C HMQC
The thioamide function in the thiosemicarbazone skele-
1
13
ton usually exhibit free –NH stretching vibrations as mul-
The H– C heteronuclear multiple-quantum coherence
HMQC) spectrum provides information regarding the inter-
−
1
tiple bands near 3300–3060 cm . Multiple bands usually
result from the association of thioamide groups in differ-
ent molecules to form dimers or polymers [29]. However,
the samples in the solid state can give rise to a widened
(
actions between the protons and the carbon atoms to which
they are directly attached. Contrary to COSY spectrum, only
the resultant interactions are plotted as contour peaks in the
HMQC spectrum (Fig. 5). In the present compound, the
absence of any contours at δ = 155.033, 177.422, 156.671,
−
1
band near 3400 cm , as in the case of the present com-
−1
pound, HL. Absence of any bands at in the 2800–2550 cm
region points towards the lack of –SH stretching absorp-
tions in the molecule. It reveals the presence of only the
thione tautomer in the solid state. The azomethine stretch-
ing vibrations, characteristic of a Schiff base, are observed
1
52.349 and 141.217 ppm assign them to the C(5), C(6),
C(7), C(12) and C(13) carbon atoms, respectively. This is
because, they belong to the non-protonated carbon atoms
on the pyridyl rings, C(6) N(3); C(12) S(1) and on the
phenyl ring, respectively, all of which are unable to show any
direct H– C coupling interactions. The peaks observed at
δ 148.932 and 149.557 ppm are assigned to C(1) and C(11)
−
1
−1
at 1592 cm [30]. The band at 1529 cm is the resul-
tant of the interactions between N–H bending and C–N
stretching vibrations of the C–N–H group of the thioamide
1
13
−
1
1
function. A weak band at 1253 cm also results from the
N–H bending and C–N stretching interactions. The thio-
carbon atoms, respectively, due to their interactions with H
resonances at δ 8.84 and 8.675 ppm. The evidence for the
presence of protons attached to three different types of carbon
atoms in the multiplets at δ 7.855 and 7.815 ppm is obtained
−
1
carbonyl group shows absorptions at 1320 and 806 cm
,
−1
while additional bands in the broad region of 1400–700 cm
13
1
are due to vibrations involving interactions between C S
stretching and C–N stretching of the C S group attached
from the C– H HMQC spectrum, which gives three con-
tours at 13C signals δ 137.684 ppm [C(3)]; 137.804 ppm
−1
to a nitrogen atom. The bands at 1174 and 1110 cm
[
C(9)] and 124.429 ppm [C(4)]. The doublets at δ 7.705 and
.57 ppm and the quartet at δ 7.24 ppm show contours at
δ 124.81 ppm [C(14) and C(18)], 127.510 ppm [C(8)] and
correspond to the in-plane vibrations of the pyridyl ring,
while the out-of-plane vibrations are observed at 762 and
7
−
1
13
695 cm
.
1
26.691 ppm [C(16)], which help to distinguish these
C
resonances, which are close to each other. The multiplet
3.7. UV–visible spectrum of HL
In contrast to the infrared spectrum, the electronic spec-
trum is not used primarily for the identification of individual
functional groups, but rather to show the relationship between
functional groups, chiefly conjugation [31]. The UV–visible
spectra of organic compounds are associated with the elec-
tronic transitions between energy levels, and at wavelengths
above 200 nm, excitation of electrons from the ␲-orbitals
usually occurs giving rise to informative spectra [32]. Solid-
state reflectance spectrum of the present thiosemicarbazone
reveals the spectral bands in close proximity with similar
systems reported earlier (Fig. 6). The ␲ → ␲* transitions of
the pyridyl ring and the thiosemicarbazone imine function
−
1
are rather weak, observed at ca. 35300 cm . However, an
−
1
intense band at ca. 27900 cm is attributed to the ␲ → ␲*
transition of the C S group and the n → ␲* transition of the
pyridine ring [29].
Fig. 5. 1H–13C HMQC spectrum of HL.

V. Suni et al. / Spectrochimica Acta Part A 63 (2006) 174–181
179
Table 2
Selected bond lengths ( A˚ ) and bond angles ( ) of HL
◦
HL
C(6)–N(3)
N(3)–N(4)
N(4)–C(12)
C(12)–S(1)
N(3)–N(4)
C(12)–N(5)
N(5)–C(13)
C(6)–C(7)
C(5)–C(6)
1.2858(8)
1.3573(10)
1.3616(9)
1.6763(12)
1.3573(10)
1.3392(8)
1.4137(10)
1.4935(12)
1.4806(9)
C(7)–C(6)–C(5)
C(5)–C(6)–N(3)
C(6)–N(3)–N(4)
N(3)–N(4)–C(12)
N(4)–C(12)–S(1)
N(4)–C(12)–N(5)
C(12)–N(5)–C(13)
118.88(4)
127.81(6)
120.51(5)
120.03(4)
117.44(4)
114.27(6)
128.50(6)
Fig. 6. Electronic spectrum of HL.
3
.8. Crystal structure
The molecular structure of HL along with atomic number-
ing scheme is given in Fig. 7 and selected bond lengths and
angles are given in Table 1. The compound crystallizes into
a monoclinic lattice with space group C2/c. The molecule
exists in the ZE conformation of thiosemicarbazones since
Z and E configurations are perceived with respect to C6–N3
and C12–N4 bonds, respectively. A torsion angle value of
carbazone chain. Among the three aromatic rings, the pyridyl
ring Cg(1) with the N(1) nitrogen on it, suffers least devia-
tion from the thiosemicarbazone moiety at a dihedral angle of
◦
1
7.65(1) between the two corresponding planes. The pyridyl
ring Cg(2) and the phenyl ring Cg(3) make a dihedral angle
◦
of 60.81(2) between each other and they are deviated from
◦
1
71.58(5) corresponding to the S1–C12–N4–N3 moiety
confirms the trans configuration of the thiocarbonyl S1 atom
33]. The thiosemicarbazone skeleton comprising of atoms
◦
the central thiosemicarbazone moiety at angles 35.98(1)
and 57.34(2) , respectively. The largest deviation is observed
◦
[
between the planes of the two pyridyl rings positioned at a
dihedral angle of 67.66(2) between each other, which owes
mainly to the steric interactions of the bulky pyridyl groups.
Two prominent intramolecular hydrogen-bonding interac-
tions, viz. N(4)–H(4)N· · ·N(1) and N(5)–H(5)N· · ·N(3) lead
to the formation of one six-membered ring and one five-
membered ring comprising of atoms N(1), C(5), C(6),
N(3), N(4), H(4)N and N(3), N(4), C(12), N(5), H(5)N,
respectively. A short interatomic contact, C(8)–H(8)· · ·N(2),
N3, N4, C12, S1 and N5 is almost planar with a maxi-
˚
mum deviation of −0.0650(4) A from the mean plane. The
˚
C6–N3 bond distance (1.2858(8) A) is appreciably close to
˚
that of a C N double bond (1.28 A) [34], confirming the
azomethine bond formation. The existence of the thiosemi-
carbazone in the thione form in the solid state is evidenced by
˚
the C(12)–S(1) bond distance of 1.6763(12) A, which is very
˚
closetoaformalC Sbondlength(1.60 A)[35]. However, the
N(3)–N(4) (1.3573(10)) and N(4)–C(12) (1.3616(9)) bond
distances are observed intermediate between the ideal values
˚
at a C(8)–N(3) distance of 2.919(2) A also helps to sta-
bilize the present conformation of the thiosemicarbazone
Table 2.
˚
˚
of corresponding single [N–N; 1.45 A and C–N; 1.47 A] and
˚
˚
double bonds [N N; 1.25 A and C N; 1.28 A] [36], which is
The packing of the molecules of HL is shown in Fig. 8,
where the unit cell is viewed down the ‘c’ axis. The basic unit
of the crystal packing consists of a set of two molecules which
are held together by intermolecular hydrogen-bonding inter-
actions involving N(2) (acceptor) of one molecule and N(5)
insupport of anextended ␲ delocalization along the thiosemi-
(donor) of the adjacent molecule through H(5)N. Two adja-
cent sets are then aligned in an offset fashion, which forms
the repeating unit of the packing in the crystal lattice. It is
interesting to note that no intermolecular interactions are per-
ceived between these adjacent sets and the overall packing in
a two-dimensional manner is affected by the offset alignment
of neighboring sets in the unit cell. Some weak C–H· · ·␲ and
i
␲
–␲ interactions, viz. C(15)–H(15)· · ·[1]· · ·Cg(1) [Cg(1):
˚
= 3.5800 A;
N(1), C(1), C(2), C(3), C(4), C(5); d
C(15)· · ·Cg
ii
i = −x, 2 − y, 1 − z] and Cg(2)· · ·[1]· · ·Cg(2) ; [Cg(2): N(2),
˚
C(7), C(8), C(9), C(10), C(11); dCg· · ·Cg = 3.5809 A; ii = −x,
Fig. 7. Molecular structure of HL. Displacement ellipsoids are drawn at 50%
probability level.
y, 1/2 − z] are the shortest interactions observed of their

1
80
V. Suni et al. / Spectrochimica Acta Part A 63 (2006) 174–181
Fig. 8. Molecular packing diagram of HL, the unit cell is viewed down the ‘b’ axis.
type in the lattice of the present compound. However, the
two intra-molecular hydrogen-bonding interactions observed
are much effective, operating at appreciably short distances,
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iii
˚
viz. N(5)–H(5)N· · ·N(3) [dD· · ·A = 2.596(2) A; iii = x, y, z]
iii
˚
and N(4)–H(4)N· · ·N(1) [dD· · ·A = 2.670(2) A]. These intra-
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Suni acknowledges State Counsil for Science, Technology
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