Synthesis, spectral and structural studies of zinc(II) complexes of salicylaldehyde N(4)-phenylthiosemicarbazone

Article abstract of DOI:10.1016/j.saa.2007.05.025

Five Zn(II) complexes of salicylaldehyde N(4)-phenylthiosemicarbazone (H₂L) have been synthesized and physicochemically characterized. Out of the five Zn(II) complexes, one is binuclear {[(ZnL)₂]·3C₂H₅OH (1)} an

Full text of DOI:10.1016/j.saa.2007.05.025

Available online at www.sciencedirect.com
Spectrochimica Acta Part A 69 (2008) 726–732
Synthesis, spectral and structural studies of zinc(II) complexes of
salicylaldehyde N(4)-phenylthiosemicarbazone
∗
E.B. Seena, M.R. Prathapachandra Kurup
Department of Applied Chemistry, Cochin University of Science and Technology, Kochi 682022, Kerala, India
Received 27 March 2007; accepted 10 May 2007
Abstract
Five Zn(II) complexes of salicylaldehyde N(4)-phenylthiosemicarbazone (H
2
L) have been synthesized and physicochemically characterized.
OH (2),
Out of the five Zn(II) complexes, one is binuclear {[(ZnL)
2
]·3C
2
H
5
OH (1)} and the other four are mononuclear {[Zn(HL)
2
]·C
2 5
H
[
ZnLbipy]·1/2H
2
O (3), [ZnLphen]·H
2
O (4) and [ZnLdmbipy] (5)} in nature. In complex 2, IR band due to ν(Zn–O) is absent and also the
1
–
OH signal due to the phenolic –OH group appears at δ = 11.38 ppm obtained from the H NMR spectrum supports the existence of free –OH
group. Complexes 3–5 are heterocyclic base adducts and their IR spectra display bands characteristic of coordinated heterocyclic bases. The
molecular structure of one of the complex 3 is resolved by single crystal X-ray diffraction studies. The complex 3 is orthorhombic with a space
group P2
pyramid (TBDSBP).
2007 Elsevier B.V. All rights reserved.
1
cn. The Zn(II) in 3 is five coordinated and is having an approximately trigonal bipyramidal geometry with distortion from square based
©
ꢀ
ꢀ
ꢀ
Keywords: Salicylaldehyde; Thiosemicarbazone; Zn(II) complex; 2,2 -Bipyridine; 1,10-Phenanthroline; 4,4 -Dimethyl 2,2 -bipyridine; Crystal structure
1
. Introduction
The zinc(II) ion is known to have a high affinity towards
nitrogen and sulfur donor ligands. Dowling and Perkin inves-
tigated Zn(II) complexes with mixed N, O and S coordination
to understand the reactivity of the pseudotetrahedral zinc center
in proteins [6]. Complexes of group 12 metals, mainly zinc,
can provide an interesting range of stoichiometries depend-
ing on the preparative salt. Here, we report the synthesis
and characterization of five Zn(II) complexes of salicylalde-
hyde N(4)-phenylthiosemicarbazone using infrared, electronic
and H NMR studies. It also describes the single crystal X-
ray diffraction studies of the first heterocyclic base adduct of
Zn(II)thiosemicarbazonecomplexwithfivecoordinatedgeome-
try.
Thiosemicarbazones and their metal complexes show signif-
icant biological activity [1] and possess medicinal properties
2], which are dependent upon the chemical nature of the
[
moiety attached to the C S carbon atom. The biological
activity of Zn(II) complexes of thiosemicarbazones mainly 2-
pyridylketone thiosemicarbazone and p-isopropylbenzaldehyde
thiosemicarbazone were reported earlier [3,4]. Zinc atom has
eitherastructuraloranalyticalroleinseveralproteins. Ithasbeen
recognized as an important cofactor in biological molecules,
either as a structural template in protein folding or as a Lewis
acid catalyst that can readily adopt 4-, 5- or 6- coordination [5].
Zinc is able to play a catalytic role in the activation of thiols
as nucleophiles at physiological pH. Mononuclear zinc com-
plexes may serve as model compounds for zinc enzymes such as
phospholipase C, bovine lens leucine aminopeptidase, ATPases,
carbonic anhydrases and peptide deformylase. Binuclear cores
are versatile at active sites of many metalloenzymes and play
essential role in biological systems.
1
2. Experimental
2.1. Materials
All compounds used for the synthesis of salicylaldehyde
N(4)-phenylthiosemicarbazone (H L) and their metal com-
2
plexes were purified by standard methods and solvents were
purified by distillation. Zn(OAc)2·2H2O (S.D.Fine chemicals),
ꢀ
2,2 -bipyridine(bipy)(Centraldrughouse), 1,10-phenanthroline
∗
Corresponding author. Tel.: +91 484 2575804; fax: +91 484 2577595.
E-mail addresses: mrp@cusat.ac.in, mrp k@yahoo.com (M.R.P. Kurup).
ꢀ ꢀ
(phen) (Ranboxy fine chemicals) and 4,4 -dimethyl 2,2 -
1
386-1425/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2007.05.025

E.B. Seena, M.R.P. Kurup / Spectrochimica Acta Part A 69 (2008) 726–732
727
Scheme 1.
bipyridine (dmbipy) (E-Merck) were used. The reagents used
were of analar grade and used without further purification.
when yellow compound began to separate. This was filtered,
washed with ethanol and ether and dried in vacuo over P4O10.
2.3. Physical measurements
2
.2. Synthesis of the ligand and their Zn(II) complexes
Elemental analyses were performed on a Vario ELIII ele-
Synthesis of the ligand H2L (Scheme 1) was carried out by
mental analyzer at SAIF, Cochin University of Science and
Technology, Kochi-22, India. The FT-IR spectra were recorded
on a Thermo Nicolet AVATAR 370 DTGS FTIR spectrome-
adapting the procedure of Klayman et al. and also by us [7,8].
2
.2.1. [(ZnL)2]·3C2H5OH (1)
−1
ter using KBr pellets in the range 4000–400 cm at SAIF,
Cochin University of Science and Technology, Kochi-22, India.
To a solution of H2L (1 mmol, 0.271 g) in hot ethanol
was added an ethanolic solution of Zn(OAc)2·2H2O (1 mmol,
TM
Electronic spectra were recorded on a GENESYS 10 series
0
.219 g) with constant stirring. The stirring was continued for
1
spectrophotometer in DMF solution. The H NMR spectra were
about an hour when yellow compound separated was filtered,
recorded on a Brucker DRX 500 MHz instrument using CDCl3
as the solvent and TMS as the internal reference at Sophisticated
Instruments Facility, Indian Institute of Science, Bangalore. Sin-
gle crystal X-ray crystallographic study of one of the compounds
was carried out using the Argus (Nonius, MACH3 software) at
National Single Crystal X-Ray Diffraction Facility, IIT, Bom-
bay, India.
washed with ethanol and ether and dried in vacuo over P4O10.
2
.2.2. [Zn(HL)2]·C2H5OH (2)
A solution of Zn(OAc)2·2H2O (1 mmol, 0.219 g) in ethanol
and a solution of H2L (2 mmol, 0.542 g) in hot ethanol were
mixed and refluxed for 4 h. On cooling, yellow solid separated
was filtered, washed with ethanol and ether and dried in vacuo
over P4O10.
2.4. X-ray crystallography
2
.2.3. [ZnLbipy]·1/2H2O (3)
A yellow block crystal of the compound [ZnLbipy] having
To a solution of H2L (1 mmol, 0.271 g) in hot ethanol
approximate dimensions 0.40 mm × 0.35 mm × 0.20 mm was
sealed in a glass capillary and intensity data were measured
at 293(2) K. The data acquisition and cell refinement were done
using the Argus (Nonius, MACH3 software) [9]. The Maxus
was added an ethanolic solution of Zn(OAc)2·2H2O (1 mmol,
0
.219 g) with constant stirring. This was followed by the addi-
ꢀ
tion of the base 2,2 -bipyridine (1 mmol, 0.156 g) in the solid
form. The stirring was continued for about an hour when yellow
crystalline compound formed was filtered, washed with ethanol
and ether and dried in vacuo over P4O10.
(
Nonius software) were used for data reduction [10]. The struc-
ture was solved by direct methods and full-matrix least-squares
refinement using SHELX97 [11] package. The positions of
all the non-hydrogen atoms were included in the full-matrix
least-squares refinement using SHELX97 program and all the
hydrogen atoms were fixed in calculated positions. The structure
of the compound 3 was plotted using the program Diamond Ver-
sion 3.0 [12] and PLATON [13]. The crystal data and structure
refinement parameters for [ZnLbipy] are given in Table 1.
2
.2.4. [ZnLphen]·H2O (4)
To a solution of H2L (1 mmol, 0.271 g) in hot ethanol
was added an ethanolic solution of Zn(OAc)2·2H2O (1 mmol,
0
.219 g) with constant stirring. This was followed by the addi-
tion of the base 1,10-phenanthroline (1 mmol, 0.198 g) in the
solid form. The stirring was continued for about an hour when
yellow compound began to separate. This was filtered, washed
with ethanol and ether and dried in vacuo over P4O10.
3
. Results and discussion
3.1. Synthesis
2
.2.5. [ZnLdmbipy] (5)
To a solution of H2L (1 mmol, 0.271 g) in hot ethanol
The colors, partial elemental analyses and magnetic moments
was added an ethanolic solution of Zn(OAc)2·2H2O (1 mmol,
of the complexes are presented in Table 2. The elemental anal-
yses data are consistent with the general composition (ML)2,
M(HL)2 and MLB, where M is the zinc atom, L is the doubly
deprotonated thiosemicarbazone ligand and B is the bidentate
0
.219 g) with constant stirring. This was followed by the addi-
ꢀ
ꢀ
tion of the base 4,4 -dimethyl 2,2 -bipyridine (1 mmol, 0.184 g)
in the solid form. The stirring was continued for about an hour

7
28
E.B. Seena, M.R.P. Kurup / Spectrochimica Acta Part A 69 (2008) 726–732
Table 1
Crystal data and structure refinement parameters for [ZnLbipy]
Empirical formula
Formula weight
Temperature
C24H19N5OSZn
490.87
293(2) K
Wavelength
0.71073 A˚
Crystal system
Space group
Unit cell dimensions
Orthorhombic
P21cn
a = 9.8250(16) A˚ , b = 10.5580(6) A˚ ,
c = 20.7990(12) A˚ , α = 90 , β = 90 , γ = 90
◦
◦
◦
2157.5(4) A˚
3
Volume
Z
4
3
Density (calculated)
Absorption coefficient
F(0 0 0)
1.511 Mg/m
1.263 mm
1008
−
1
Crystal size
θ range for data collection
Index ranges
Reflections collected
Independent reflections
Refinement method
Data/restraints/parameters
0.40 mm × 0.35 mm × 0.20 mm
◦
1.96–24.96
−11 ≤ h ≤ 0, −12 ≤ k ≤ 0, −24 ≤ l ≤ 0
2012
2012 [R(int) = 0.0000]
Full-matrix least-squares on F
2
2012/1/293
1.017
2
Fig. 1. Structure and labeling diagram of the compound 3.
Goodness-of-fit on F
Final R indices [I > 2σ(I)]
R indices (all data)
Largest diff. peak and hole
R1 = 0.0383, wR2 = 0.0681
R1 = 0.0923, wR2 = 0.0795
0.324 and −0.380 e A˚ −
3
equatorial positions are occupied by the S(1), O(1), N(2) and
the axial positions by N(1) and N(3) [Zn(1)–N(1), 2.164(5),
ꢀ
ꢀ
R1 =
||Fo| − |Fc||/
|Fo|, wR2 =
˚
ꢁ
ꢂ
Zn(1)–N(3), 2.098(5) A] with the N(3)–Zn(1)–N(1) angle of
1
/2
ꢀ
ꢀ
2
2
2
2
2
◦
◦
[
w(F − F ) / [w(F ) ]
.
177.5(2) being close to the ‘ideal’ value of 180 which is usual
for such systems [14]. In a five-coordinate system, the angular
structural parameter (τ) is used to propose an index of trigonal-
ity. The trigonality index τ of 0.53 {According to Addison et
o
c
o
heterocyclic bases viz. bipy, phen or dmbipy. All the zinc com-
plexes are yellow in color. Elemental analyses data shows both
compounds 1 and 2 having ethanol molecules and compounds
◦
al, τ = (β − α)/60, where β = N(3)–Zn(1)–N(1) = 177.5(2) and
◦
α = O(1)–Zn(1)–S(1) = 145.18(16) ; for perfect square pyrami-
3
and 4 having water molecules present as solvents of crystal-
dal and trigonal bipyramidal geometries the values of τ are
zero and unity, respectively [15]} indicates that the coordination
geometry around zinc is intermediate between trigonal bipyra-
midal and square pyramidal geometries and is better described as
trigonal bipyramidal distorted square based pyramid (TBDSBP)
lizations. In compound 5, there is neither ethanol nor water of
crystallization present in it. The complexes are insoluble in most
of the common polar and non-polar solvents. The complexes are
soluble in DMF, CHCl3 and DMSO.
˚
withzincdisplaced0.3225 AabovetheN(1), N(3), O(1)andS(1)
3
.2. Crystal structure of the compound [ZnLbipy]
coordination plane and towards the elongated apical N(2) atom
[
16].
One of the reasons for the deviation from an ideal stere-
ochemistry is the restricted bite angle imposed by both the
The molecular structure of the compound 3 along with the
atom numbering scheme is represented in Fig. 1 and selected
bond lengths and bond angles are summarized in Table 3. Suit-
able pale yellow crystals were obtained from a solution of 3 in a
mixture of CH3OH and CH3CN. The compound 3 is orthorhom-
bic with a space group P21cn. This complex is mononuclear and
five coordinated. In the complex [ZnLbipy], Zn(II) is located in
an approximately trigonal bipyramidal geometry in which the
2−
(L)
and bipy ligands. The bite angle around the metal
◦
viz. N(2)–Zn(1)–N(1) of 77.1(2) may be considered nor-
mal, when compared with an average value of 77 cited in
◦
the literature [17–19]. The variation in Zn–N bond distances,
Zn(1)–N(2), 2.097(5), Zn(1)–N(3), 2.098(5) and Zn(1)–N(1),
2.164(5) indicate differences in the strengths of the bonds
Table 2
Colors and partial elemental analyses data of Zn(II) complexes of H2L ligand
Compound
Color
Found (calculated) (%)
C
H
N
[(ZnL)2]·3C2H5OH (1)
[Zn(HL)2]·C2H5OH (2)
[ZnLbipy]·1/2H2O (3)
[ZnLphen]·H2O (4)
[ZnLdmbipy] (5)
Yellow
Yellow
Yellow
Yellow
Yellow
50.14 (50.56)
54.77 (55.25)
57.92 (57.66)
58.63 (58.60)
59.90 (60.18)
5.08 (4.99)
4.49 (4.64)
3.88 (4.03)
3.96 (3.97)
4.58 (4.47)
10.55 (10.41)
13.35 (12.89)
14.02 (14.01)
13.13 (13.14)
13.38 (13.50)

E.B. Seena, M.R.P. Kurup / Spectrochimica Acta Part A 69 (2008) 726–732
729
Table 3
Selected bond lengths ( A˚ ) and bond angles ( ) for [ZnLbipy]
◦
Bond lengths
Zn(1)–O(1)
Zn(1)–N(2)
Zn(1)–N(3)
Zn(1)–N(1)
Zn(1)–S(1)
S(1)–C(18)
O(1)–C(11)
N(3)–C(17)
N(3)–N(4)
N(4)–C(18)
N(5)–C(18)
N(5)–C(19)
N(5)–H(105)
1.958(5)
2.097(5)
2.098(5)
2.164(5)
2.3435(19)
1.738(7)
1.315(7)
1.276(7)
1.396(7)
1.308(7)
1.393(9)
1.414(9)
0.81(8)
Bond angles
O(1)–Zn(1)–N(2)
O(1)–Zn(1)–N(3)
N(2)–Zn(1)–N(3)
O(1)–Zn(1)–N(1)
N(2)–Zn(1)–N(1)
N(3)–Zn(1)–N(1)
O(1)–Zn(1)–S(1)
N(2)–Zn(1)–S(1)
N(3)–Zn(1)–S(1)
N(1)–Zn(1)–S(1)
C(18)–S(1)–Zn(1)
C(11)–O(1)–Zn(1)
C(5)–N(1)–Zn(1)
C(1)–N(1)–Zn(1)
C(6)–N(2)–Zn(1)
C(10)–N(2)–Zn(1)
C(17)–N(3)–N(4)
C(17)–N(3)–Zn(1)
N(4)–N(3)–Zn(1)
C(18)–N(4)–N(3)
C(18)–N(5)–C(19)
104.3(2)
89.19(19)
100.8(2)
92.68(19)
77.1(2)
177.5(2)
145.18(16)
110.34(15)
81.30(15)
98.10(14)
92.5(2)
129.0(4)
114.0(4)
126.9(4)
117.1(4)
125.0(5)
115.5(5)
126.2(5)
118.0(4)
110.9(5)
126.5(7)
Fig. 3. Hydrogen bonding interactions for the compound 3.
◦
by the least square plane Cg(5) and Cg(7) is 4.78 for the
compound 3.
Ring puckering analyses shows that the ring Cg(3) com-
prising of atoms Zn(1), O(1), C(11), C(16), C(17) and N(3)
˚
with puckering amplitude (QT) = 0.1714 A and the ring Cg(1)
comprising of atoms Zn(1), S(1), C(18), N(4) and N(3) with
˚
puckering amplitude (QT) = 0.3742 A [21]. The ring Cg(1)
adopts an envelope on Zn(1) {The pseudorotation parameters
◦
◦
P = 159.1 and τ = 28.1 for Zn(1)–S(1) [22]}.
Fig. 2 shows the contents of the unit cell along the a axis. The
assemblage of molecules in the respective manner in the unit
cell is resulted by the ␲–␲ and CH–␲ interactions as depicted in
Table 4. One intermolecular hydrogen bonding is observed, i.e.,
[
C(9)–H(9) and O(1)] (Fig. 3), but no classic hydrogen bonds
were found. The centroid Cg(4) is involved in ␲–␲ interac-
tions with pyridyl ring of the neighbouring unit at a distance
˚
of 3.8418 A and the centroid Cg(5) with phenyl ring at a dis-
formed by each of the coordinating nitrogen atoms. The Zn–N
bond lengths are shorter than those reported for mononuclear
zinc(II) complexes, while there is no significant variation in the
Zn–S bond lengths reported [20]. The dihedral angle formed
˚
tance of 3.7274 A, the CH–␲ interactions of the ring Cg(6) with
the neighbouring molecules also contribute stability to the unit
cell packing.
Fig. 2. Unit cell packing diagram of the compound 3 viewed along the a axis.

7
30
E.B. Seena, M.R.P. Kurup / Spectrochimica Acta Part A 69 (2008) 726–732
Table 4
Interaction parameters of the compound [ZnLbipy]
Cg(I)–Res(1)–Cg(J)
Cg–Cg ( A˚ )
α ( )
◦
β ( )
◦
␲
–␲ interactions
a
b
c
b
Cg(4)[1] → Cg(5)
Cg(5)[1] → Cg(4)
Cg(5)[1] → Cg(7)
Cg(7)[1] → Cg(5)
3.8418
3.8418
3.7274
3.7274
23.58
23.58
4.78
5.95
29.44
18.80
19.81
4.78
Eqivalent position codes: a = −1/2 + x, −y, −z, b = 1/2 + x, −y,
z, c = −1/2 + x, −1/2 + y, 1/2 − z, d = 1/2 + x, 1/2 + y, 1/2 − z
Cg(4) = N(1), C(1), C(2), C(3), C(4), C(5); Cg(5) = N(2), C(6), C(7),
C(8), C(9), C(10); Cg(7) = C(19), C(20), C(21), C(22), C(23), C(24)
−
XH(I)–Cg(J)
H· · ·Cg ( A˚ )
X–H· · ·Cg (◦)
X· · ·Cg (A)
˚
CH–␲ interactions
a
C(4)–H(4)[1] → Cg(6)
2.75
153
3.6078
Equivalent position codes: a = −1/2 + x, −y, −z
D· · ·H· · ·A
D–H ( A˚ )
H· · ·A ( A˚ )
D· · ·A ( A˚ )
3.2456
D–H· · ·A (◦)
H bonding
C(9)–H(9)–O(1)
0.93
2.41
149
D: donor, A: acceptor, Cg: centroid, α: dihedral angles between planes I and J, and β: angle Cg(I)–Cg(J).
3
.3. Infrared spectra
ν(N C) band. From this, it is clear that coordination via its
thiolato sulfur takes place. In all the five complexes, except
in 2, phenolic oxygen is coordinated to copper by loss of the
–OH proton. In complex 1, the phenolic oxygen, on loss of
the –OH proton, occupies the third and fourth (through bridg-
ing) coordination sites. This causes ν(C–O) to shift to higher
Table 5 lists the tentative assignments of main IR bands
−
1
of Zn(II) complexes for the ligand H2L in 4000–50 cm
region. The spectrum of free ligand exhibits a medium band
at 3146 cm , which is assigned to ν(N–H) vibration. The
absence of ν(N–H) band in the spectra of complexes provides
a strong evidence for the ligand coordination around Zn(II) ion
in its deprotonated form. On coordination of azomethine nitro-
gen, ν(C N) shifts to lower wavenumbers by 10–20 cm , as
the band shifts from 1613 cm in the uncomplexed thiosemi-
carbazone spectrum to ca.1598 cm
the five Zn(II) complexes. Coordination of azomethine nitro-
gen is confirmed with the presence of new bands in the
range 410–420 cm , assignable to ν(Zn–N) for these com-
plexes [23]. The ν(N–N) of the thiosemicarbazone is found
at 1149 cm . The increase in the frequency of this band in
the spectra of the complexes, due to the increase in the bond
strength, again confirms the coordination via the azomethine
nitrogen.
−1
−1
wavenumbers (lower frequency) by 50–60 cm from its posi-
−
1
tion at 1255 cm in the ligand spectra, which is consistent
with a bridging phenolic oxygen [24]. A new band in the range
−
1
−1
570–590 cm in the spectra of the complexes is assignable
−
1
to ν(Zn–O) [25]. In complex 2, the band due to ν(Zn–O) is
absent, which suggests that the phenolic –OH group is not coor-
dinated to the metal in this complex. The non-involvement of
the phenolic –OH group in a zinc(II) complex of a similar
thiosemicarbazone is established by single crystal X-ray diffrac-
tion study [26]. Tentative structure of the complex 2 is shown
in Fig. 4. The IR spectra of the complexes 3, 4 and 5 display
bands characteristic of coordinated heterocyclic bases [27,28].
In the spectrum of the thiosemicarbazone ligand, there is a sharp
−
1
in the spectra of all
−
1
−1
−
1
peak at 3336 cm , which may be due to the presence of phe-
The decrease in the stretching frequency of ν(CS) bond
nolic group. But, in the complexes 1–4, no sharp peaks were
−1
−1
−1
from 874 cm in the thiosemicarbazone by 10–50 cm upon
complexation indicates coordination via its thiolato sulfur. In
all the five Zn(II) complexes, another strong band is found at
observed at ∼3336 cm , but there were broad bands in the
3200–3500 region. This is because of the presence of either the
alcoholic group or the lattice water present in these complexes
[29].
−
1
ca.1530–1550 cm , which may be due to the newly formed
Table 5
Selected IR bands (cm 1) with tentative assignments of Zn(II) complexes with H2L ligand
−
Compound
ν(C N)
ν(N C)
ν(N–N)
ν(C–S)
ν(C–O)
ν(Zn–O)
ν(Zn–N)
Bands due to heterocyclic base
H2L
1613
1597
1596
1597
1604
1597
–
1548
1542
1534
1534
1541
1149
1154
1154
1175
1169
1169
1328, 874
1316, 824
1327, 864
1316, 824
1309, 852
1309, 837
1255
1200
1204
1245
1239
1239
–
573
–
587
588
583
–
417
421
411
420
416
–
–
–
[
[
[
[
[
(ZnL)2]·3C2H5OH
Zn(HL)2]·C2H5OH
ZnLbipy]·1/2H2O
ZnLphen]·H2O
1429, 758, 690
1426, 751, 693
1432, 752, 694
ZnLdmbipy]

E.B. Seena, M.R.P. Kurup / Spectrochimica Acta Part A 69 (2008) 726–732
731
Table 7
1
H NMR signals of H2L and their Zn(II) complexes (δ, ppm)
Compound
–CH N1
–4NH
Aromatic
H2L
8.37
–
8.72
8.7
8.74
8.67
7.26
7.26
7.26
7.26
7.26
7.26
6.84–7.60
–
6.85–7.9
6.5–7.6
6.5–7.9
6.5–7.9
[
[
[
[
[
(ZnL)2]·3C2H5OH
Zn(HL)2]·C2H5OH
ZnLbipy]·1/2H2O
ZnLphen]·H2O
ZnLdmbipy]
a bathochromic shift due to the donation of a lone pair of elec-
trons to the metal and hence the coordination of azomethine [30].
−1
The absorption band centered around 29,060 cm in the ligand
was assigned to n → ␲* of the thioamide chromophore, which
suffers a blue shift in the complexes due to thioenolization.
The moderately intense broad bands for the complexes in the
−
1
region 28,500–23,500 cm are assigned to Zn(II) → S metal to
ligand charge transfer transition (MLCT). The MLCT maxima
for the phenolato complexes show line broadening, with a tail
running into the visible part of the spectrum. This may result
from Zn(II) to phenolate MLCT band being superimposed on
the low energy side of Zn(II) → S MLCT [31]. Except this,
the complexes show no appreciable absorptions in the region
Fig. 4. Tentative structure of the compound 2.
Table 6
Electronic spectral assignments (cm 1) of the ligand H2L and their Zn(II)
−
complexes
−
1
below 22,000 cm in DMF solution, in accordance with the
Compound
H2L
␲–␲*
n–␲*
MLCT
10
d
electronic configuration of the Zn(II) ion.
32,250
33,670
33,330
33,110
33,440
33,440
29,060
–
.5. 1H NMR spectra
[
[
[
[
[
(ZnL)2]·3C2H5OH
Zn(HL)2]·C2H5OH
ZnLbipy]·1/2H2O
ZnLphen]·H2O
31,440, 30,300
31,540, 30,300
31,540, 30,300
31,940
27,240, 26,240
27,470, 26,240
27,390, 26,240
26,170, 25,640
27,390, 26,240
3
1
The H NMR signals of the ligand H2L and their Zn(II)
complexes recorded in CDCl3 are listed in Table 7. The lig-
ZnLdmbipy]
31,740, 30,300
and has signals at δ = 11.36, δ = 9.54 and δ = 8.37 ppm, which
2
1
are due to –OH, – NH and –CH N , respectively. In the Zn(II)
2
3
.4. Electronic spectra
complexes, signal due to– NH is absent supporting thioenoliza-
tion [32]. The low field position of – NH (δ = 7.26 ppm) could
4
The electronic absorption bands of the Zn(II) complexes,
recorded in DMF solution, are given in Table 6. The thiosemi-
be attributable to the deshielding caused by the phenyl group
and the adjacent –N C of the system –N C(SH)–NH–C H .
6
5
−
1
carbazone (H2L) has a ring ␲ → ␲* band at 32,250 cm and a
In all the complexes, except in the spectrum of the complex
−
1
band at 29,060 cm due to n → ␲* transition associated with
[Zn(HL)2]·C2H OH (2), the–OH proton signals are absent. But
5
the azomethine linkage. This band in the complexes have shown
in complex 2, the –OH signal appears at δ = 11.38 ppm, which
Fig. 5. 1H NMR spectra of the compounds 2 and 4.

7
32
E.B. Seena, M.R.P. Kurup / Spectrochimica Acta Part A 69 (2008) 726–732
supports for the existence of the phenolic –OH group in this
complex. Considerable shift of characteristic signals occurs on
complexation [33,34]. Representative spectra of the complexes
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[
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2
and 4 are presented in Fig. 5.
[
[
10] G.M. Sheldrick, Acta Cryst. A 46 (1990) 467.
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many, 1997.
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Soc., Dalton Trans. (1984) 1349.
4
. Supplimentary data
[
[
[
Crystallographic data for the structural analysis has been
deposited with the Cambridge Crystallographic Data center,
CCDC 283005 for compound [ZnLbipy]. Copies of this infor-
mation may be obtained free of charge at http://www.ccdc.
cam.ac.uk/conts/retrieving.html [or from Cambridge Crystal-
lographic Data Centre (CCDC), 12 Union Road, Cambridge,
CB2, IEZ, UK; fax: +44 1223 336033; e-mail: deposit@ccdc.
cam.ac.uk].
[
16] D. Chakrabarthy, H. Nagase, M. Kamijo, T. Endo, H. Ueda, Anal. Sci. 21
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[
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Acknowledgements
[19] R.P. John, A. Sreekanth, V. Rajakannan, T.A. Ajith, M.R.P. Kurup, Poly-
hedron 23 (2004) 2549.
[
[
[
[
20] C. Zhang, C. Janiak, J. Chem. Cryst. 31 (2001) 29.
The authors are indebted to SAIF, Cochin University of
Science and Technology, Kochi, Kerala, India for elemental
analyses and IR spectral analysis. We are thankful to National
Single Crystal X-ray diffraction studies, IIT, Bombay, India for
providing single crystal XRD results. The financial support by
DST, New Delhi, India (No. SR/SI/IC-31/2002) is greatfully
acknowledged.
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