Synthesis, spectral and structural studies of a novel semicarbazone synthesized from quinoline-2-carboxaldehyde and n4-phenyl-3- semicarbazide

Article abstract of DOI:10.1007/s10870-010-9765-z

A new semicarbazone, HL has been synthesized from quinoline-2- carboxaldehyde and N⁴-phenyl-3-semicarbazide and structurally and spectrochemically characterized. ¹H NMR, ¹³C NMR, IR and electronic spectra of the compound are studied. The existence of keto form in the solid state is supported by the crystal structure and IR data. The compound crystallizes into an orthorhombic space group P2₁2₁2 ₁. Intra and intermolecular hydrogen bonding interactions facilitates unit cell packing in the crystal lattice. Index Abstract: A new semicarbazone, HL has been synthesized from quinoline-2-carboxaldehyde and N4-phenyl-3- semicarbazide and it crystallizes into an orthorhombic with a space group P2₁2₁2₁. Unit cell parameters a = 6.4662(3) A, b = 10.3994(5) A, c = 21.0315(11) A, α = 90°, β = 90° and γ = 90°. ¹H NMR, ¹³C NMR, IR and electronic spectra of the compound were studied. The existence of keto form in the solid state is supported by the crystal structure and IR data. Intra and intermolecular hydrogen bonding interactions facilitates unit cell packing in the crystal lattice.[Figure not available: see fulltext.]

Full text of DOI:10.1007/s10870-010-9765-z

J Chem Crystallogr (2010) 40:927–932
DOI 10.1007/s10870-010-9765-z
ORIGINAL PAPER
Synthesis, Spectral and Structural Studies of a Novel
Semicarbazone Synthesized from Quinoline-2-Carboxaldehyde
and N4-Phenyl-3-Semicarbazide
•
T. A. Reena M. R. Prathapachandra Kurup
Received: 21 October 2008 / Accepted: 7 May 2010 / Published online: 30 May 2010
Ó Springer Science+Business Media, LLC 2010
Abstract A new semicarbazone, HL has been synthe-
sized from quinoline-2-carboxaldehyde and N4-phenyl-3-
semicarbazide and structurally and spectrochemically
characterized. 1H NMR, 13C NMR, IR and electronic
spectra of the compound are studied. The existence of keto
form in the solid state is supported by the crystal structure
and IR data. The compound crystallizes into an ortho-
rhombic space group P212121. Intra and intermolecular
hydrogen bonding interactions facilitates unit cell packing
in the crystal lattice.
subject of chemical and structural studies [5]. Semicarba-
zones have been known as anti-cancer and anti-viral agents
for many years [6]. Semicarbazones exist in two tautomeric
forms, keto (A) and enol (B) forms (Scheme 1). The keto
form functions as bidentate neutral ligand and the enol
form can deprotonate and act as anionic ligand. Here we
report the structural and spectral perspectives of a new
compound, quinoline-2-carboxaldehyde N4-phenylsemic-
arbazone, HL (Figure 1).
Keywords Crystal structure Á IR spectra Á
Quinoline-2-carboxaldehyde Á Semicarbazone
Experimental
Synthesis of Quinoline-2-Carboxaldehyde-N4-
Phenylsemicarbazone (HL)
Introduction
The synthesis of HL is given in Scheme 2. A methanolic
solution of quinoline-2-carboxaldehyde (0.157 g, 1 mmol)
was mixed with N4-phenylsemicarbazide (0.151 g, 1 mmol)
in methanol and 3 drops of glacial acetic acid. The reaction
mixture was refluxed for 2 h. On slow evaporation, colorless
crystalline compound formed was filtered, washed with
ether and dried over P4O10 in vacuo. Single crystals of HL
suitable for X-ray analysis were obtained from its solution in
1:1 (v/v) mixture of methanol and DMF. Yield: *0.5 g.
Elemental analysis, found (calculated): C 70.13 (70.33); H
4.99 (4.86); N 19.22 (19.30). IR (cm-1): 3380 va(N–H),
1702 v(C=O), 1592 v(C=N).
Semicarbazones are compounds with versatile structural
features and can coordinate to the metal either as a neutral
or a deprotonated anion. The coordinating ability of
semicarbazones is attributed to the extended delocalization
of electron density over the NH–C(O)–NH–N= system,
which is enhanced by the substitution at the N4 position [1].
The biological applications of these compounds are due to
their ability to form metal complexes [2]. It was reported
that aryl semicarbazones were devoid of sedative hypnotic
activity and exhibited anticonvulsant activity with less
neurotoxicity [3]. Semicarbazones are also used as pro-
tected carbonyl compounds in synthesis [4]. Several
semicarbazones and its metal complexes have been the
Materials and Physical Measurements
T. A. Reena Á M. R. P. Kurup (&)
Commercial reagents, quinoline-2-carboxaldehyde (Aldrich)
and N4-phenylsemicarbazide (Aldrich) were used as received.
Elemental analyses were carried out using a Vario EL III
Department of Applied Chemistry, Cochin University of Science
and Technology, Kochi 682 022, Kerala, India
e-mail: mrp@cusat.ac.in
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J Chem Crystallogr (2010) 40:927–932
O
Table 1 Crystal data and structure refinement parameters of HL
OH
R
N
R
CCDC no.
689742
17H14N4O
R
N
R
N
H
N
R
Empirical formula
Formula weight
Temperature
C
N
R
N
290.32
R
R
150(2) K
Keto (A)
Enol (B)
˚
Wavelength
0.71073 A
Orthorhombic
P212121
Crystal system
Space group
Scheme 1
˚
a = 6.4662(3) A
Unit cell dimensions
˚
b = 10.3994(5) A
˚
c = 21.0315(11) A
HN
a = 90°
N
b = 90°
c = 908
N
NH
O
3
˚
1414.25(12) A
Fig. 1 Quinoline-2-carboxaldehyde-N4-phenyl-3-semicarbazone, HL
Volume
Z
4
Density (calculated)
Absorption coefficient
F(000)
1.364 Mg/m3
0.089 mm-1
608
0.36 9 0.23 9 0.21 mm3
3.30°–25.00°
12679
CHNS analyzer at SAIF, Kochi, India. Infrared spectra
were recorded on a JASCO FT-IR-5300 spectrometer
in 4000–400 cm-1 range using KBr pellets. Electronic
spectra were recorded on a Cary 5000 Version 1.09
UV-VIS-NIR spectrophotometer using solution in DMF.
Crystal size
h range for data collection
Reflections collected
Independent reflections
1
The H and 13C NMR spectra were recorded using Bruker
-7 B h B 7, -12 B k B 12,
-25 B l B 21
Full-matrix least-squares on F2
DRX 500 with CDCl3 as solvent and TMS as standard at
the Sophisticated Instruments Facility, Indian Institute of
Science, Bangalore, India.
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I [ 2r(I)]
R indices (all data)
2488/0/207
1.019
R1 = 0.0427, wR2 = 0.0754
R1 = 0.0628, wR2 = 0.0834
X-ray Crystallography
R1 = R||Fo| - |Fc||/R|Fo|, wR2 = [Rw(F2o - F2c)2/Rw(Fo2)2]1/2
The crystallographic data and structure refinement parameters
of compound HL are given in Table 1. A crystal with
approximate dimensions 0.36 9 0.23 9 0.21 mm3 was
selected and was found to be orthorhombic with a space group
P212121. X-ray diffraction measurements were carried out on
CRYSALIS CCD diffractometer with graphite monochro-
0,withsmallstandarduncertainty,theabsolutestructuregiven
by the structure refinement is likely correct [8]. The molecular
graphics employed were DIAMOND version 3.1d [9] and
PLATON [10]. The final refinement cycle was based on all
2488 independent reflections and 207 variables with
R1 = 0.0628 and wR2 = 0.0834.
˚
mated Mo Ka (k = 0.71073 A) radiation. The program
CRYSALIS RED was used for data reduction and cell
refinement. The structure was solved by direct methods and
refined by least-square on F20 using SHELXL-97 [7]. All non-
hydrogen atoms were refined anisotropically. All hydrogen
atoms except those attached to nitrogens were geometrically
fixed at calculated positions. Those on nitrogen atoms were
refined from Fourier maps. Refinement of F2 was done against
all reflections. All esds, expect the esd in the dihedral angle
between two least square planes, are estimated using the full
Covariance matrix. Flack x parameter is 0(2). As this value is
Results and Discussion
Crystal Structure
The molecular structure of HL along with the atom num-
bering scheme is given in Fig. 2 and selected bond lengths
Scheme 2
MeOH
O
HN
HN
N
H2N
+
N
H
NH
O
N
NH
O
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929
Fig. 2 Molecular structure of HL
˚
Table 2 Selected bond lengths (A) and bond angles (8) of HL
Bond lengths
Bond angles
C(1)–N(1) 1.422(3)
C(7)–O(1) 1.222(3)
C(7)–N(1) 1.353(3)
C(7)–N(2) 1.376(3)
C(8)–N(3) 1.282(3)
C(8)–C(9) 1.469(3)
N(2)–N(3) 1.378(3)
O(1)–C(7)–N(1) 125.4(2)
O(1)–C(7)–N(2) 119.5(2)
N(1)–C(7)–N(2) 115.0(2)
N(3)–C(8)–C(9) 121.1(2)
C(7)–N(2)–N(3) 121.2(2)
C(8)–N(3)–N(2) 114.3(2)
C(9)–N(4)–C(17) 118.1(2)
Fig. 3 Molecular packing diagram of HL, the unit cell is viewed
down the c axis
Table 3 Interaction parameters of the compound HL
˚
Cg–Cg (A)
Cg(I)_Cg(J)
a°
b°
pÁÁÁp interactionsA
Cg(1)_Cg(2)a
Cg(2)_Cg(1)b
and angles are given in Table 2. The compound crystallizes
into an orthorhombic space group P212121. The molecule is
almost planar and exists in the E configuration with respect
to C8=N3 bond. A torsion angle value of 179.5(2)° cor-
responding to O(1)–C(7)–N(2)–N(3) moiety confirms the
trans configuration of the O(1) atom with respect to
hydrazine nitrogen atom N(3). The C(8)–N(3) bond dis-
4.5426
4.5426
14.60
14.60
51.04
37.25
˚
˚
XH(I)_Cg(J)
H_Cg (A) X–H_Cg (°) X_Cg (A)
CHÁÁÁp interactionsB
C(14)–H(14)_Cg(3)c 2.67
146
˚
3.498
˚
tance [1.282(3) A] is appreciably close to that of C=N
˚
double bond [1.28 A], [11] confirming the azomethine
˚
˚
D–HÁÁÁA
Hydrogen-bondingC
DÁÁÁH (A) HÁÁÁA (A) DÁÁÁA (A) D–HÁÁÁA (°)
bond formation. The existence of semicarbazone in the
keto form in the solid state is evidenced by the C(7)–O(1)
˚
bond distance of 1.222(3) A, which is very close to a for-
N(1)–H(1)ÁÁÁN(3) 0.860(3) 2.280(3) 2.662(3) 107(2)
C(6)–H(6)ÁÁÁO(1) 0.950
2.230
2.848(3) 122
N(2)–H(2)ÁÁÁN(4)d 1.04(3)
1.99(3)
3.028(3) 173(2)
˚
mal C=O bond length [1.21 A]. However, the N(3)–N(2)
[1.379(3)] and N(2)–C(7) [1.376(3)] bond distances are
intermediate between the ideal values of corresponding
single [N–N; 1.45 and C–N; 1.47] and double bonds [N=N;
1.25 and C=N; 1.28], which is in support of an extended p
delocalization along the semicarbazone chain [12, 13].
Figure 3 shows the packing diagram of HL. The
assemblage of molecules in the respective manner in the
unit cell is resulted by the p–p, C–HÁÁÁp and hydrogen
bonding interactions. The centroid Cg(1) is involved in p–p
interaction with Cg(2) of the neighbouring molecule at a
A
Equivalent position code: a = 1 ? x, y, z; b = -1 ? x, y, z.
Cg(1) = N(4), C(9), C(10), C(11), C(12), C(17); Cg(2) = C(1), C(2),
C(3), C(4), C(5), C(6). a = Dihedral angle between planes 1 and 2(°).
b = Angle Cg(1) –[ Cg(2) or Cg(1) –[ Me vector and normal to
plane 1 (°)
B
Equivalent position code: c = 1/2 ? x, 1/2-y, 1 - z. Cg(3) =
C(12), C(13), C(14), C(15), C(16), C(17)
C
D = donor, A = acceptor, Equivalent position code: d = -1/2 ? x,
-1/2-y, 1 - z
˚
distance of 4.5426 A and a C–HÁÁÁp interaction, C(14)–
and C(6)–H(6)ÁÁÁO(1) led to the formation of one-five-
membered ring and one-six-membered ring comprising of
atoms N(3), N(2), C(7), N(1), H(1)N and O(1), C(7), N(1),
C(1), C(6), H(6)C respectively [14, 15]. An intermolecular
hydrogen-bonding, N(2)–H(2)ÁÁÁN(4) at a N(2)–N(4) dis-
˚
H(14) ? Cg(3) at a distance of 2.67 A contribute stability
to the unit cell packing. The unit cell comprises of four
molecules. The crystal structure is stabilized by intra and
intermolecular hydrogen-bonding and the molecules are
arranged in opposite manner. Two prominent intramolec-
ular hydrogen-bonding interactions, viz. N(1)–H(1)ÁÁÁN(3)
˚
tance of 3.028(3) A also supports the present conformation
of the semicarbazones (Table 3; Fig. 4).
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2
1
d = 11.187 and 9.141 ppm are assigned to NH and NH
protons respectively. These protons are shifted downfield
because they are attached to hetero atoms and so are easily
subjected to hydrogen bonding and are decoupled by the
2
electrical quadrupole effects. The protons attached to N
and 1N appear as singlets as expected since these NH
protons are decoupled from the nitrogen atoms and the
protons from the adjacent atoms. Absence of any cou-
pling interactions by C(8)H proton due to availability of
protons on neighbouring atoms render singlet peak at
d = 8.157 ppm. Two doublets at d = 8.537 and 8.423 ppm
are assigned to the C(11)H and C(10)H protons. At
d = 8.007, we got a quartet which is assigned to be a merged
form of one triplet and a doublet corresponding to C(15)H
and C(13)H protons. Another triplet at d = 7.998 ppm is
assigned to C(14)H proton. The resonances for the C6H5-
group appear as a doublet at d = 7.685 ppm (ortho) and as
triplets at d = 7.334 and 7.060 ppm corresponding to meta
and para phenyl protons. All the assignments made above
are in good agreement with previous reports [16, 17]
(Fig. 5).
13C NMR spectrum of ligand HL was recorded in
CDCl3. The proton decoupled 13C spectrum of the com-
pound contains 15 peaks corresponding to the 15 magnet-
ically unique carbon atoms. The signals from 13C spectrum
are much weaker than that of the corresponding proton
Fig. 4 Intermolecular hydrogen bonding interaction
Spectral Studies
1
The H NMR spectrum of the compound along with the
spectral assignments is given in Fig. 5. The signals at
Fig. 5 1H NMR spectrum
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J Chem Crystallogr (2010) 40:927–932
931
has a band at 1150 cm-1is due to m(N–N). The bands at
1225 and 1113 cm-1 correspond to the in-plane vibrations
of the quinoline ring while the out-of-plane vibrations are
observed at 749 and 689 cm-1 [20, 21].
Electronic spectrum of the ligand in DMF shows bands
at 31400 and 29900 cm-1 which are assigned to the n-p*
of azomethine and carbonyl groups of semicarbazone
moiety respectively. The band observed at 36900 cm-1 is
attributed to intraligand p–p* transition of the imine
function of the semicarbazone moiety [22].
Supplementary Material
Crystallographic data for the structural analysis has been
deposited with the Cambridge Crystallographic Data cen-
ter, CCDC 689742 for compound HL. Copies of this
information may be obtained free of charge at http://
www.ccdc.cam.ac.uk/conts/retrieving.html [or from Cam-
bridge Crystallographic Data Centre (CCDC), 12 Union
Road, Cambridge, CB2, IEZ, UK; Fax: ?44(0)1223-
336033; e-mail: deposit@ccdc.cam.ac.uk
Fig. 6 13C NMR spectrum
NMR spectrum. Assignment of different resonant peaks to
respective carbon atoms is presented in Fig. 6. The peaks at
152.863, 147.314 and 141.422 ppm correspond to the C(8),
C(9) and C(17) carbon atoms respectively. The carbon
atom at para position to the heteroatom viz. C(11) resonate
at lower field value when compared to the meta positioned
carbon atom C(10). The non-protonated carbon C(7) is
showing more downfield shift due to increased electron
density resulting from the presence of electronegative
oxygen and conjugative effect of the N(3)–N(2)–C(O)–N(1)–
semicarbazone skeleton. The 13C peaks are assigned as
follows. C(1), 138.857 ppm; C(2), 122.810 ppm; C(3),
120.326 ppm; C(4), 118.205 ppm; C(5), 120.326 ppm; C(6),
122.810 ppm; C(7), 153.900 ppm; C(8), 152.863 ppm;
C(9), 147.314 ppm; C(10), 129.895 ppm; C(11), 136.245
ppm; C(12), 128.751 ppm; C(13), 127.763 ppm; C(14),
126.989 ppm; C(15), 128.458 ppm; C(16), 127.924 ppm;
C(17), 141.422 ppm. The downfield shift of C(8) carbon is
due to the p electron delocalization on the C(8)=N(3) bond
[18] (Fig. 6).
Acknowledgements M.R.P. Kurup is thankful to the Council of
Scientific & Industrial Research, New Delhi, India for the financial
assistance. The authors are thankful to the National Single Crystal
X-ray diffraction Facility, IIT, Bombay, India for providing single
crystal XRD data.
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