Zinc(II) complexes derived from di-2-pyridyl ketone N4-phenyl-3-semicarbazone: Crystal structures and spectral studies

Article abstract of DOI:10.1016/j.poly.2008.08.014

Six zinc(II) complexes, Zn(HL)Br₂ (1), Zn(HL)Cl₂ (2), ZnL(OAc) (3), ZnLN₃ (4), ZnL₂ (5) and ZnL₂ · H₂O (6), have been synthesized and characterized by different physicochemical techniques. Complex 1 is five coordinated and has a distorted square pyramidal geometry. Complexes 5 and 6 are six coordinated and have distorted octahedral geometries. In complexes 1 and 2, the ligand moieties are coordinated in the neutral form (HL), and in the other complexes they are monoanionic (L^-).

Full text of DOI:10.1016/j.poly.2008.08.014

Polyhedron 27 (2008) 3461–3466
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Polyhedron
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Zinc(II) complexes derived from di-2-pyridyl ketone
N4-phenyl-3-semicarbazone: Crystal structures and spectral studies
*
T.A. Reena, E.B. Seena, M.R. Prathapachandra Kurup
Department of Applied Chemistry, Cochin University of Science and Technology, Kochi 682 022, Kerala, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Six zinc(II) complexes, Zn(HL)Br2 (1), Zn(HL)Cl2 (2), ZnL(OAc) (3), ZnLN3 (4), ZnL2 (5) and ZnL2 ꢀ H2O (6),
have been synthesized and characterized by different physicochemical techniques. Complex 1 is five
coordinated and has a distorted square pyramidal geometry. Complexes 5 and 6 are six coordinated
and have distorted octahedral geometries. In complexes 1 and 2, the ligand moieties are coordinated
in the neutral form (HL), and in the other complexes they are monoanionic (Lꢁ).
Received 1 July 2008
Accepted 8 August 2008
Available online 6 October 2008
Keywords:
Crystal structures
IR spectra
Ó 2008 Elsevier Ltd. All rights reserved.
Zinc(II) complexes
Di-2-pyridyl ketone
Semicarbazone
1. Introduction
entate ligand, di-2-pyridyl ketone N4-phenyl-3-semicarbazone
(HL).
Semicarbazones are very versatile ligands in both the neutral
and anionic form. These compounds are have the formula
R2C@N–NH–(CO)–NH2. The coordination possibilities derived from
the many potential donor atoms in the semicarbazones are in-
creased if the substituents include additional donor atoms and
they can also be modified by placing substituents on the backbone
donor atoms. These classes of compounds usually react with
metallic cations giving complexes in which the semicarbazones be-
have as chelating ligands. Research on the coordination chemistry,
analytical applications and biological activities of these complexes
has increased steadily for many years [1]. It has also been reported
that many complexes of semicarbazones have antimicrobial and
antitumor activities [2].
Zinc shows a fairly high affinity towards the main coordinating
atoms such as sulfur, nitrogen and oxygen. This means high flexi-
bility in the structure, coordination mode and coordination num-
ber of the complexes produced [3]. We have recently reported
the synthesis, spectral characterization and structural studies of
cadmium(II) complexes of the present semicarbazone, with the
aim to correlate the structural features and chelating ability [4].
Di-2-pyridyl ketone N4-phenyl-3-semicarbazone tautomerizes into
keto and enol forms and as a result a small negative charge resides
on the nitrogen atom of the pyridine ring which enhances its bio-
logical activity [5–7]. This paper deals with the synthesis, spectral
and structural studies of zinc(II) complexes of a potential quadrid-
2. Experimental
2.1. Materials
Di-2-pyridyl ketone (Aldrich) and N4-phenylsemicarbazide (Al-
drich) were used as received. ZnBr2, ZnCl2, Zn(OAc)2 ꢀ 2H2O and
NaN3 were commercial products of higher grade (Aldrich) and sol-
vents were purified according to standard procedures. Elemental
analyses were carried out using a Vario EL III CHNS analyzer at
SAIF, Kochi, India. Infrared spectra were recorded on a JASCO FT-
IR-5300 spectrometer in the range 4000–400 cmꢁ1 using KBr pel-
lets. Electronic spectra were recorded on a Cary 5000, version
1.09 UV–Vis–NIR spectrophotometer using solutions in DMF.
2.2. Synthesis of di-2-pyridyl ketone-N4-phenyl-3-semicarbazone (HL)
Di-2-pyridyl ketone-N4-phenyl-3-semicarbazone (Fig. 1) was
prepared by the earlier reported method [4].
2.3. Synthesis of complexes
2.3.1. Synthesis of Zn(HL)Br2 (1), Zn(HL)Cl2 (2) and ZnL(OAc) (3)
A solution of the ligand HL (0.317 g, 1 mmol) in 20 ml of meth-
anol was treated with a methanolic solution of the appropriate zin-
c(II) salt (1 mmol). The solution was heated under reflux for 4 h.
The resulting solution was allowed to stand at room temperature
* Corresponding author. Tel.: + 91 484 2575804; fax: +91 484 2577595.
E-mail address: mrp@cusat.ac.in (M.R. Prathapachandra Kurup).
0277-5387/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2008.08.014

3462
T.A. Reena et al. / Polyhedron 27 (2008) 3461–3466
and after slow evaporation yellow crystals separated out, which
were collected, washed with ether and dried over P4O10 in vacuo.
Zn(HL)Br2 (1): Yield ꢂ0.35 g; found (calc): C, 40.16 (40.76); H,
2.79 (2.78); N, 12.91 (13.25); IR data (cmꢁ1): 3239, 1597, 1661,
1147, 407.
Zn(HL)Cl2 (2): Yield ꢂ0.28 g; found (calc): C, 47.66 (47.72); H,
3.33 (3.41); N, 15.44 (15.57); IR data (cmꢁ1): 3369, 1597, 1667,
1153, 404.
2.3.4. Synthesis of ZnL2 ꢀ H2O (6)
A solution of the ligand HL (0.317 g, 1 mmol) in methanol was
treated with a methanolic solution of Zn(OAc)2 ꢀ 2H2O (0.219 g,
1 mmol). The solution was heated under reflux and sodium azide
(0.065 g, 1 mmol) was added in portions to the solution and further
refluxed for 4 h. The resulting solution was allowed to stand at
room temperature and upon slow evaporation gave yellow crys-
tals. The crystals that separated out were collected, washed with
ether and dried over P4O10 in vacuo. Yield ꢂ0.16 g; found (calc):
C, 59.87 (60.38); H, 4.01 (4.22); N, 19.25 (19.56); IR data (cmꢁ1):
1597, 1515, 1229, 416, 520.
ZnL(OAc) (3): Yield ꢂ0.32 g; found (calc): C, 54.25 (53.73); H,
4.33 (4.30); N, 15.82 (15.71); IR data (cmꢁ1): 1597, 1521, 1156,
414, 516.
2.3.2. Synthesis of ZnLN3 (4)
2.4. X-ray crystallography
A solution of the ligand HL (0.317 g, 1 mmol) in methanol was
treated with
a
methanolic solution of Zn(OAc)2 ꢀ 2H2O
Single crystals of compound 1 suitable for X- ray diffraction
were obtained by slow evaporation of its solution in a 1:1:1 mix-
ture of CH3OH, CHCl3 and CH2Cl2. Single crystals of compound 5
were obtained by slow evaporation of its solution in a 1:1 mixture
of CH3OH and CH3CN, and of compound 6 by slow evaporation of
its solution in a 1:1:1:1 mixture of DMF, CHCl3, CH3CN and CH3OH.
X-ray diffraction measurements were carried out on a CRYSALIS CCD
(0.219 g,1 mmol). The solution was heated under reflux and so-
dium azide (0.130 g, 2 mmol) was added in portions to the solution
and further refluxed for 4 h. The resulting solution was allowed to
stand at room temperature and upon slow evaporation gave yellow
crystals. The crystals that separated out were collected, washed
with ether and dried over P4O10 in vacuo. Yield ꢂ0.25 g; found
(calc): C, 54.25 (53.73); H, 3.33 (3.27); N, 26.44 (26.56); IR data
(cmꢁ1): 1595, 1518, 1148, 404, 502.
diffractometer
with
graphite-monochromated
Mo
Ka
(k = 0.71073 Å) radiation. The program CRYSALIS RED was used for data
reduction and cell refinement [8]. The structure was solved by di-
rect methods using SHELXS [9] and refined by full-matrix least-
squares refinement on F2 using SHELXL [10]. The N–H hydrogen
atoms were located from difference Fourier maps and refined iso-
tropically. The remainder of the H-atoms were included in calcu-
lated positions and refined as riding atoms using default SHELXL
parameters. Compound 6 is non-centrosymmetric and its Flack x
parameter is 0.001(12). As this value is near 0, with small standard
uncertainty, the absolute structure given by the structure refine-
ment is likely correct [11]. The structures of the compounds were
2.3.3. Synthesis of ZnL2 (5)
A solution of the ligand HL (0.317 g, 1 mmol) in 20 ml of meth-
anol was treated with a methanolic solution of Zn(OAc)2 ꢀ 2H2O
(0.109 g, 0.5 mmol). The solution was heated under reflux for 2 h.
The resulting solution was allowed to stand at room temperature
and after slow evaporation yellow crystals were separated out,
which were collected, washed with ether and dried over P4O10 in
vacuo. Yield ꢂ0.20 g; found (calc): C, 61.53 (61.94); H, 3.96
(4.04); N, 20.01 (20.07); IR data (cmꢁ1): 1597, 1515, 1223, 420,
518.
Table 1
Crystal data and structure refinement parameters for [Zn(HL)Br2] (1), [ZnL2] (5) and [ZnL2] ꢀ 0.3H2O (6)
1
5
6
Empirical formula
Formula weight
Temperature, K
Wavelength, Å
Crystal system
Space group
Unit cell dimensions
a (Å)
C18H15Br2N5OZn
542.54
120(2)
0.71073
monoclinic
P21/n
C36H28N10O2Zn
698.05
120(2)
0.71073
monoclinic
P21/n
C36H28N10O2Zn ꢀ 0.3H2O
702.85
120(2)
0.71073
orthorhombic
P212121
7.3466(3)
11.0982(2)
8.5993(4)
b (Å)
14.5893(4)
16.6320(3)
17.0904(6)
c (Å)
18.5267(5)
17.8826(4)
22.3002(11)
a
(°)
90
90
90
b (°)
98.315(3)
98.690(2)
90
c
(°)
90
90
90
3277.4(3)
V (Å3)
1964.85(11)
3262.97(11)
Z
4
4
4
Dcalc (Mg/m3)
1.834
5.335
1064
1.421
0.803
1440
1.424
0.801
1450
Absorption coefficient (mmꢁ1
F(000)
)
Crystal size (mm3)
h range for data collection (°)
Index ranges
0.32 ꢃ 0.28 ꢃ 0.26
0.26 ꢃ 0.21 ꢃ 0.19
0.18 ꢃ 0.11 ꢃ 0.08
3.01–25.00
2.99–25.00
2.99–25.00
ꢁ8 6 h 6 8, ꢁ17 6 k 6 17,
ꢁ21 6 l 6 22
ꢁ13 6 h 6 12, ꢁ19 6 k 6 18,
ꢁ21 6 l 6 21
ꢁ10 6 h 6 10, ꢁ20 6 k 6 20,
ꢁ26 6 l 6 26
Reflections collected
Independent reflections
Refinement method
16909
30049
31407
3445 [R(int) = 0.0341]
full-matrix least-squares on F2
3445/0/252
5729 [R(int) = 0.0358]
full-matrix least-squares on F2
5729/0/450
5772 [R(int) = 0.1000]
full-matrix least-squares on F2
5772/0/454
Data/restraints/parameters
Goodness-of-fit on F2
1.058
1.073
1.010
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0273, wR2 = 0.0532
R1 = 0.0507, wR2 = 0.0632
0.362 and ꢁ0.262
R1 = 0.0306, wR2 = 0.0638
R1 = 0.0444, wR2 = 0.0711
0.272 and ꢁ0.290
R1 = 0.0500, wR2 = 0.0661
R1 = 0.0741, wR2 = 0.0734
0.608 and ꢁ0.415
Largest difference in peak and hole (e Aꢁ3
)
P
P
R1
=
kFoj ꢁ jFck/ jFoj.
P
P
2
2 1=2
wR2 ¼ ½ wðF2o ꢁ Fc2Þ = wðF2oÞ ꢄ
.

T.A. Reena et al. / Polyhedron 27 (2008) 3461–3466
3463
plotted using the program ORTEP [12]. The crystallographic data
along with the structural refinements are given in Table 1.
nitrogen (N2), pyridyl nitrogen (N1), ketoxy oxygen (O1) and two
bromide ions (Br1 and Br2). The bond distances to Zn are in the or-
der Zn–N(azo) < Zn–N(py) < Zn–O(ketoxy) < Zn–Br1 < Zn–Br2. The bond
lengths, Zn–N(py), 2.154(3) Å and Zn–N(azo), 2.130(3) Å are very
similar compared to other Zn complexes of thiosemicarbazones
[13–15]. The Zn–Br bond distances are 2.3561(5) and
2.4026(6) Å, but there is a difference of 0.0465 Å between the
Zn–Br bonds of [Zn(HL)Br2]. The basal plane could involve either
Br1 or Br2 with the semicarbazone moiety, but because Zn–Br1
is marginally shorter and it can be designated as the apical posi-
tion. The Zn atom is displaced by a distance of 0.8335 Å above
the basal plane and elongated towards Br1. Selected bond lengths
and bond angles are given in Table 2.
3. Results and discussion
3.1. Synthesis of complexes
Di-2-pyridyl ketone N4-phenyl-3-semicarbazone (HL) reacts
with zinc(II) halides in a 1:1 molar ratio to form 1 and 2, complexes
of the type Zn(HL)X2 where X = Br and Cl. Complexes 3 and 4 were
consistent with the general formula ZnLY where Y = OAc and N3
and for complexes 5 and 6, the composition ZnL2 was obtained.
For the preparation of complexes 3 and 5, Zn(OAc)2 ꢀ 2H2O and
HL were taken in 1:1 and 1:2 ratios, respectively, and for com-
plexes 4 and 6, Zn(OAc)2 ꢀ 2H2O, HL and NaN3 were taken in
1:1:2 and 1:1:1 ratios, respectively. In complex 6, however, the
azide added was not coordinated and ZnL2 ꢀ H2O was obtained acci-
dentally, though the yield was much lower. Although the molecu-
lar formulae of 5 and 6 are same, the crystallographic parameters
are different.
According to Addison et al., for five coordinated complexes, the
angular structural parameter (
trigonality. The value of is defined by an equation represented
by )/60, where b is the greatest basal angle and is the
= (b ꢁ
second greatest angle; is 0 for rectangular pyramidal forms and
s) is used to propose an index of
s
s
a
a
s
1 for trigonal bipyramidal forms [16,17]. However, in the case of
five-coordinate systems, the structures vary from near regular tri-
gonal bipyramidal (RTB) to near square based pyramidal (SBP). The
s
value for the compound 1 of 0.27 indicates that the coordination
3.2. Description of the crystal structures of Zn(HL)Br2 (1), ZnL2 (5) and
ZnL2 ꢀ 0.3H2O (6)
geometry around Zn(II) is best described as a distorted square
based pyramidal geometry [18].
The deviations from the least-square plane through the O1, N1,
N2 and Br2 atoms comprising the square plane are 0.3697, 0.5336,
ꢁ0.6794 and ꢁ0.0054 Å, respectively, and the Zn1 atom is deviated
by 0.8335 Å in the direction of the Br1 atom. Ring puckering anal-
ysis and least square plane calculations show that the rings Cg(1)
comprising of atoms Zn1, O1, C12, N3 and N2 and Cg(2) comprising
of atoms Zn1, N1, C5, C6 and N2 adopt a twisted conformation
[Cg(1) on N2–Zn1 and Cg(2) on C5–C6] [19]. In the crystal packing
four molecules are present and two of them are complementary to
The molecular structure of complex 1, along with the atom
numbering scheme, is presented in Fig. 2. The compound crystal-
lizes in the monoclinic crystal system with the space group P21/
n. In this compound, the Zn atom is coordinated by an azomethine
N
each other (Fig. 3). In the unit cell
p–p
, C–Hꢀ ꢀ ꢀ
p and hydrogen
NH
O
Table 2
Selected bond lengths (Å) and bond angles (°) for [Zn(HL)Br2] (1), [ZnL2] (5) and
[ZnL2] ꢀ 0.3H2O (6)
N
N
HN
1
5
6
Bond lengths
Zn1–N2 2.130(3)
Zn1–N1 2.154(3)
Zn1–O1 2.243(2)
Zn1–Br1 2.3561(5)
Zn1–Br2 2.4026(6)
O1–C12 1.233(3)
N1–C1 1.328(4)
N1–C5 1.345(4)
N2–C6 1.287(4)
N2–N3 1.355(4)
N3–C12 1.369(4)
Zn1–N7 2.0716(17)
Zn1–N2 2.0851(17)
Zn1–O1 2.0950(14)
Zn1–O2 2.1234(13)
Zn1–N1 2.1499(17)
Zn1–N6 2.2047(16)
O1–C12 1.257(2)
O2–C30 1.257(2)
N5–C12 1.363(3)
N5–C13 1.403(3)
N3–N2 1.352(2)
Zn1–N2 2.073(3)
Zn1–N7 2.077(3)
Zn1–O1 2.097(3)
Zn1–O2 2.099(3)
Zn1–N1 2.155(3)
Zn1–N6 2.221(3)
O1–C12 1.252(4)
O2–C30 1.256(4)
N1–C1 1.339(4)
N1–C5 1.352(5)
N2–C6 1.296(5)
N2–N3 1.347(4)
Fig. 1. Structure of HL.
Bond angles
N2–Zn1–N1 73.88(10)
N2–Zn1–O1 72.60(9)
N1–Zn1–O1 146.06(9)
N2–Zn1–Br1 129.81(8)
N1–Zn1–Br1 99.40(7)
O1–Zn1–Br1 97.86(6)
N2–Zn1–Br2 114.29(8)
N1–Zn1–Br2 101.82(8)
O1–Zn1–Br2 96.60(6)
Br1–Zn1–Br2 115.75(2)
C12–O1–Zn1 114.11(19)
N7–Zn1–N2 165.27(6)
N7–Zn1–O1 109.11(6)
N2–Zn1–O1 76.14(6)
N7–Zn1–O2 76.17(6)
N2–Zn1–O2 118.01(6)
O1–Zn1–O2 91.14(5)
N7–Zn1–N1 99.93(6)
N2–Zn1–N1 75.49(6)
O1–Zn1–N1 150.95(6)
O2–Zn1–N1 96.65(6)
N7–Zn1–N6 74.92(6)
N2–Zn1–N6 90.96(6)
O1–Zn1–N6 96.57(6)
O2–Zn1–N6 151.03(6)
N1–Zn1–N6 90.05(6)
C12–O1–Zn1 111.16(13)
N2–Zn1–N7 167.20(14)
N2–Zn1–O1 76.08(11)
N7–Zn1–O1 109.42(11)
N2–Zn1–O2 115.77(12)
N7–Zn1–O2 76.30(12)
O1–Zn1–O2 90.11(10)
N2–Zn1–N1 75.84(12)
N7–Zn1–N1 99.40(12)
O1–Zn1–N1 151.17(11)
O2–Zn1–N1 96.25(11)
N2–Zn1–N6 92.80(13)
N7–Zn1–N6 75.15(13)
O1–Zn1–N6 98.13(11)
O2–Zn1–N6 151.42(11)
N1–Zn1–N6 89.61(11)
C12–O1–Zn1 110.7(3)
Fig. 2. Molecular structure of Zn(HL)Br2.

3464
T.A. Reena et al. / Polyhedron 27 (2008) 3461–3466
Fig. 3. Partial unit cell packing diagram for compound 1 with intra- and intermolecular hydrogen bonding interactions shown as dotted lines.
bonding interactions were observed. The
ceived at 4.0873 Å for Cg(1)–Cg(1)a [Cg(1) = Zn1–O1–C12–N3–
interaction is shown
p–p interaction is per-
N2; a = 1 ꢁ x, 1 ꢁ y, 1 ꢁ z]. Only one C–Hꢀ ꢀ ꢀ
p
in the unit cell and that is between C(8)–H(8)ꢀ ꢀ ꢀCg(5)b
[Cg(5) = C(13)–C(14)–(15)–C(16)–C(17)–C(18); dH–Cg = 2.95 Å; b =
1 ꢁ x, 1 ꢁ y, 1 ꢁ z]. One intra- and one intermolecular hydrogen
bonding interaction were observed, ie, N3(H) and N4 of the same
molecule and N5(H) of one molecule with Br2 of the other mole-
cule [N(3)–H(3 N)ꢀ ꢀ ꢀN(4), D–H = 0.80(3) Å, Hꢀ ꢀ ꢀA = 2.04(3) Å,
Dꢀ ꢀ ꢀA = 2.669(4) Å, D–Hꢀ ꢀ ꢀA = 135(3)°; N(5)–(H5N)ꢀ ꢀ ꢀBr(2)c, D–
H = 0.70(3) Å, Hꢀ ꢀ ꢀA = 2.68(3) Å, Dꢀ ꢀ ꢀA = 3.374(3) Å, D–Hꢀ ꢀ ꢀA =
170(3)°, c = 1 ꢁ x, 1 ꢁ y, 1 ꢁ z].
Figs. 4 and 5 show the molecular structures of compounds 5 and
6 along with the atom numbering schemes. Compound 5 crystal-
lizes in the monoclinic crystal system with the space group P21/
n, while compound 6 in the orthorhombic crystal system with
the space group P212121. In both the compounds [ZnL2], the Zn
atom is six coordinate in which both ligands are coordinated in
their deprotonated enolate forms via the pyridine nitrogen, azome-
thine nitrogen and enolate oxygen atoms. The ligands with their
donor atoms are arranged around the zinc ion in a meridional fash-
ion and both compounds are polymorphic. In compound 5, atoms
O1, O2, N1 and N6 lie in the equatorial plane, and N2 and N7 occu-
py the axial positions, while in compound 6, atoms O1, O2, N1 and
N6 lie in the equatorial plane, and N2 and N7 occupy the axial posi-
tions of the distorted octahedron. In both compounds 5 and 6, the
atoms Zn1, O1, O2, N1, N6 do not deviate significantly from the
Fig. 5. Molecular structure of ZnL2 ꢀ 0.3H2O.
least square plane [0.0034 Å for 5 and 0.0015 Å for 6]. Each of
the semicarbazone fragments {(O1 and N1, O2 and N6 for 5); (O1
and N1, O2 and N6 for 6)} are coordinated to the Zn centre with
an angle of 150.95(6)°, 151.03(6)° and 151.17(11)°, 151.42(11)°,
respectively, for 5 and 6, having a large distortion from an ideal
octahedron (180°). The planes containing Zn1, O1, N1, N2, N7
(plane 1) and Zn1, O2, N2, N6, N7 (plane 2) are deviated from
the central metal atom (Zn1) by 0.0837 and 0.0248 Å, respectively,
in compound 5, similarly in compound 6, the planes containing
Zn1, O2, N7, N6, N2 (plane 3) and Zn1, O1, N2, N1, N7 (plane 4)
are deviated from the central metal atom (Zn1) by 0.0314 and
0.0610 Å, respectively. The dihedral angle formed by the planes 1
and 2 is 85.81(0.04)° for compound 5 and by the planes 3 and 4
in compound 6 is 85.69 (0.08)°, consistent with a nearly 90° octa-
hedral angle. Selected bond lengths and bond angles are given in
Table 2.
In compound 5, when viewed along a axis, the molecules are ar-
ranged in an opposite manner and are interconnected through
N5(H) and N3 of the same molecule with N8 and N10(H) of the
nearby molecule, respectively (Fig. 6) [D–Hꢀ ꢀ ꢀA, N(5)–
H(5)ꢀ ꢀ ꢀN(8)d;
D–H = 0.84(3) Å;
Hꢀ ꢀ ꢀA = 2.13(3) Å;
Dꢀ ꢀ ꢀA =
2.961(2) Å; D–Hꢀ ꢀ ꢀA = 170.(2)°; Symmetry code, d = 1/2 ꢁ x, 1/
2 + y, 3/2 ꢁ z; D–Hꢀ ꢀ ꢀA, N(10)–H(10)ꢀ ꢀ ꢀN(3)e; D–H = 0.83(2) Å;
Hꢀ ꢀ ꢀA = 2.21(2) Å; Dꢀ ꢀ ꢀA = 3.023(2) Å; D–Hꢀ ꢀ ꢀA = 170.(2)°; Symme-
try code, e = 1/2 ꢁ x, ꢁ1/2 + y, 3/2 ꢁ z]. Intramolecular hydrogen
bonding interactions were also observed i.e., C4(H) with N4 and
C8(H) with N3 and C14(H) with O1 [D–Hꢀ ꢀ ꢀA, C(4)–H(4)ꢀ ꢀ ꢀN(4);
D–H = 0.93 Å; Hꢀ ꢀ ꢀA = 2.42 Å; Dꢀ ꢀ ꢀA = 2.984(3) Å; D–Hꢀ ꢀ ꢀA = 119°;
Fig. 4. Molecular structure of ZnL2.

T.A. Reena et al. / Polyhedron 27 (2008) 3461–3466
3465
Table 3
Interaction parameters of the compounds [Zn(HL)Br2] (1), [Zn(L)2] (5) and
[Zn(L)2] ꢀ 0.3H2O (6)
Cg(I)–Res(1)ꢀ ꢀ ꢀCg(J)
ꢀ ꢀ ꢀ Interactions
Cg(1) [1] ? Cg(1)a
Cg–Cg(Å)
a
°
b °
p
p
4.0874
0.02
31.75
Equivalent position codes: a= 1 ꢁ x, 1 ꢁ y, 1 ꢁ z
Cg(1) = Zn(1), O(1), C(12), N(3), N(2)
XH(I)ꢀ ꢀ ꢀCg(J)
CHꢀ ꢀ ꢀ interactions
C(8)–H(8)[ 1] ? Cg(5)b
Hꢀ ꢀ ꢀCg (Å)
X–Hꢀ ꢀ ꢀCg (°)
Xꢀ ꢀ ꢀCg (Å)
p
2.95
118
3.447(4)
Equivalent position codes: b= 1 ꢁ x, 1 ꢁ y, 1 ꢁ z
Cg(1) = C(13), C(14), C(15), C(16), C(17), C(18)
D–Hꢀ ꢀ ꢀA
D–H
Hꢀ ꢀ ꢀA
Dꢀ ꢀ ꢀA
D–Hꢀ ꢀ ꢀA
H bonding
[Zn(HL)Br2] (1)
N(3)–H(3N)ꢀ ꢀ ꢀN(4)
N(5)–H(5N)ꢀ ꢀ ꢀBr(2)c
[Zn(L)2] (5)
0.80(3)
0.70(3)
2.04(3)
2.68(3)
2.669(4)
3.374(3)
135(3)
170(3)
N(5)–H(5N)ꢀ ꢀ ꢀN(8)d
N(10)–H(10N)ꢀ ꢀ ꢀN(3)e
C(4)–H(4)ꢀ ꢀ ꢀN(4)
C(8)–H(8)ꢀ ꢀ ꢀN(3)
C(14)–H(14)ꢀ ꢀ ꢀO(1)
[Zn(L)2]0.3H2O (6)
N(5)–H(5N)ꢀ ꢀ ꢀN(8)f
N(10)–H(10N)ꢀ ꢀ ꢀN(3)g
C(4)–H(4)ꢀ ꢀ ꢀN(4)
C(14)–H(14)ꢀ ꢀ ꢀO(1)
C(22)–H(22)ꢀ ꢀ ꢀN(9)
0.84(3)
0.83(2)
0.93
0.93
0.93
2.13(3)
2.21(2)
2.42
2.56
2.32
2.961(2)
3.023(2)
2.984(3)
2.940(3)
2.901(3)
170(2)
170(2)
119
105
120
Fig. 6. Partial unit cell packing diagram for compound 5 with intermolecular
hydrogen bonding interactions shown as dotted lines.
0.84(3)
0.84(3)
0.95
0.95
0.95
2.15(3)
2.18(3)
2.45
2.36
2.61
2.992(5)
3.018(5)
3.041(6)
2.921(5)
3.026(5)
179(5)
176(3)
120
118
107
D–Hꢀ ꢀ ꢀA,
C(8)–H(8)ꢀꢀN(3)i;
D–H = 0.93 Å;
Hꢀ ꢀ ꢀA = 2.56 Å;
Dꢀ ꢀ ꢀA = 2.940(3) Å; D–Hꢀ ꢀ ꢀA = 105°; D–Hꢀ ꢀ ꢀA, C(14)–H(14)ꢀ ꢀ ꢀO(1);
D–H = 0.93 Å; Hꢀ ꢀ ꢀA = 2.32 Å; Dꢀ ꢀ ꢀA = 2.901(3) Å; D–Hꢀ ꢀ ꢀA = 120°].
In compound 6, two intermolecular hydrogen bonding interactions
are observed i.e., N5(H) and N8 and with N10(H) and N3, which are
arranged in an opposite manner (Fig. 7) [D–Hꢀ ꢀ ꢀA, N(5)–
H(5)ꢀ ꢀ ꢀN(8)f; D–H = 0.84(3) Å; Hꢀ ꢀ ꢀA = 2.15(3) Å; Dꢀ ꢀ ꢀA =
2.992(5) Å; D–Hꢀ ꢀ ꢀA = 179(5)°; Symmetry code, f = 1 ꢁ x, 1/2 + y,
1/2 ꢁ z; D–Hꢀ ꢀ ꢀA, N(10)–H(10)ꢀ ꢀ ꢀN(3)g; D–H = 0.84(3) Å;
Hꢀ ꢀ ꢀA = 2.18(3) Å; Dꢀ ꢀ ꢀA = 3.018(5) Å; D–Hꢀ ꢀ ꢀA = 176(3)°; Symme-
try code, g = 1 ꢁ x, ꢁ1/2 + y, 1/2 lꢁ z]. Intramolecular hydrogen
bonding interactions were also observed i.e., C4(H) with N4 and
C14(H) with O1 and C22(H) with N9 [D–Hꢀ ꢀ ꢀA, C(4)–H(4)ꢀ ꢀ ꢀN(4);
D–H = 0.95 Å; Hꢀ ꢀ ꢀA = 2.45 Å; Dꢀ ꢀ ꢀA = 3.041(6) Å; D–Hꢀ ꢀ ꢀA = 120°;
Equivalent position codes: c= 1 ꢁ x, 1 ꢁ y, 1 ꢁ z.
d= 1/2 ꢁ x, 1/2 + y, 3/2 ꢁ z; e= 1/2 ꢁ x, ꢁ1/2 + y, 3/2 ꢁ z; f= 1 ꢁ x, 1/2 + y, 1/2 ꢁ z;
g = 1 ꢁ x, ꢁ1/2 + y, 1/2 ꢁ z.
(D = donor, A = acceptor, Cg = centroid,
a = dihedral angles between planes I and J,
b = angle Cg(1)–Cg(J).
D–Hꢀ ꢀ ꢀA, C(14)–H(14)ꢀ ꢀ ꢀO(1); D–H = 0.95 Å; Hꢀ ꢀ ꢀA = 2.36 Å;
Dꢀ ꢀ ꢀA = 2.921(5) Å; D–Hꢀ ꢀ ꢀA = 118°; D–Hꢀ ꢀ ꢀA, C(22)–H(22)ꢀ ꢀ ꢀN(9);
D–H = 0.95 Å; Hꢀ ꢀ ꢀA = 2.61 Å; Dꢀ ꢀ ꢀA = 3.026(5) Å; D–Hꢀ ꢀ ꢀA = 107°]
(Table 3).
3.3. Infrared and electronic spectral studies
The infrared spectral data of the zinc(II) complexes are given in
Table 4. The va(NH) vibrations of the imino group are observed at
ca. 3369 cmꢁ1 in the IR spectrum of HL. The lack of an N–H stretch-
ing vibration in the spectra of the complexes ZnL(OAc) and ZnLN3
endorses the ligand coordination to zinc(II) ion in the deprotonated
enolate form. However in the complexes Zn(HL)Br2 and Zn(HL)Cl2
the presence of bands at 3239 and 3369 cmꢁ1, corresponding to
m
(NH) vibrations, indicates that the semicarbazone is coordinated
in the neutral form. A strong band at 1591 cmꢁ1 in the IR spectrum
of HL corresponds to the (N3–C6) stretching, which suffers a po-
m
sitive shift on complexation. Coordination of the azomethine nitro-
gen atom is also consistent with the presence of a band in the
404–420 cmꢁ1 region, assignable to
m(Zn–N) for these complexes
Table 4
IR spectral assignments for the ligand and the zinc(II) complexes
Compound
HL
m
(NH)
m
(C@N)
m
(CO)
m
(N@C)
m
(N–N)
m
(Zn–N)
m(Zn–O)
3369
1591
1597
1597
1597
1595
1597
1597
1718
1661
1667
1129
1147
1153
1156
1148
1223
1229
Zn(HL)Br2 (1) 3239
407
404
414
404
420
416
Zn(HL)Cl2(2)
ZnL(OAc) (3)
ZnLN3(4)
ZnL2(5)
ZnL2 ꢀ H2O (6)
3369
1521
1518
1515
1515
516
502
518
520
Fig. 7. Intermolecular hydrogen bonding interactions of compound 6.

3466
T.A. Reena et al. / Polyhedron 27 (2008) 3461–3466
Table 5
The authors are thankful to the National Single Crystal X-ray dif-
fraction Facility, IIT, Bombay, India for providing single crystal
XRD results.
Electronic spectral assignments for the ligand and the zinc(II) complexes
compound
p–
p*
n–p*
MLCT
HL
40000
37630
37460
37410
37200
37280
37270
30770
31840
31450
31350
32250
32230
32240
Zn(HL)Br2 (1)
Zn(HL)Cl2 (2)
ZnL(OAc) (3)
ZnLN3 (4)
ZnL2 (5)
24220
24280
24280
24210
24230
24210
Appendix A. Supplementary data
CCDC 648484, 648485 and 648486 contain the supplementary
crystallographic data for 1, 5 and 6. These data can be obtained free
of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: de-
posit@ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at doi:10.1016/
j.poly.2008.08.014.
ZnL2 ꢀ H2O (6)
[20–22]. A band at 1718 cmꢁ1 in the ligand has significant contri-
bution from the C@O stretching vibration and it is shifted to
1667 cmꢁ1 in Zn(HL)Cl2 and 1661 cmꢁ1 in Zn(HL)Br2 confirming
the keto form of HL in these complexes. In complexes 3–6, the
(Zn–O), consistent with
oxygen coordination. The spectra of the complexes exhibit a sys-
tematic shift in the position of the (N–N) bands in the region
bands at 502–520 cmꢁ1 are assignable to
m
References
[1] J.S. Casas, M.S. Garcia-Tasende, J. Sordo, Coord. Chem. Rev. 209 (2000) 197.
[2] Q. Li, H. Tang, Y. Li, M. Wang, L. Wang, C. Xia, J. Inorg. Biochem. 78 (2000) 167.
[3] T. Matsukura, H. Tanaka, Biochemistry 65 (2000) 817.
[4] T.A. Reena, E.B. Seena, M.R.P. Kurup, Polyhedron 27 (2008) 1825.
[5] H. Cerecetto, M. González, Curr. Topics Med. Chem. 2 (2002) 1185.
[6] H. Cerecetto, R. Di Maio, G. Ibarruri, G. Seoane, A. Denicola, C. Quijano, G.
Pelluffo, M. Paulino, Farmaco 53 (1998) 89.
m
1129–1229 cmꢁ1. A medium band around 601 cmꢁ1, indicating
an out-of-plane pyridyl ring vibration in the uncomplexed ligand,
shifts to higher frequencies on complexation which confirms the
coordination of the ligand to the metal via the pyridine nitrogen
[23–26]. Compound ZnLN3 exhibits strong bands at 2076 and
1302 cmꢁ1 corresponding to the asymmetric and symmetric
stretching of the coordinating azido group. For the complex
ZnL(OAc) the asymmetric and symmetric stretching vibrations of
the acetate group appear at 1562 and 1433 cmꢁ1 respectively.
The presence of a band at 3440 cmꢁ1 for ZnL2 ꢀ H2O indicates the
presence of the H2O molecule.
[7] V. Martinez, H. Cerecetto, Bioorg. Med. Chem. 9 (2001) 1025.
[8] CRYSALIS CCD and CRYSALIS RED Versions 1.171.29.2
(CRYSALIS171. NET), Oxford
Diffraction Ltd, Abingdon, Oxfordshire, England, 2006.
[9] G.M. Sheldrick, Acta Crystallogr., Sect. A 46 (1990) 467.
[10] G.M. Sheldrick, SHELXL97 and SHELXS97, University of Göttingen, Germany, 1997.
[11] H.D. Flack, G. Bernardinelli, J. Appl. Crystallogr. 33 (2000) 1143.
[12] L.J. Farrugia, J. Appl. Crystallogr. 30 (1997) 565.
[13] K.A. Ketcham, J.K. Swearingen, A. Castineiras, I. Garcia, E. Bermejo, D.X. West,
Polyhedron 20 (2001) 3265.
[14] E. Bermejo, A. Castineiras, I. Garcia-Santos, D.X. West, Z. Anorg. Allg. Chem. 630
(2004) 1097.
[15] I. Garcia, E. Bermejo, A.K. El Sawaf, A. Castineiras, D.X. West, Polyhedron 21
(2002) 729.
[16] A.W. Addison, T.N. Rao, J. Reedijk, J. Van Rijn, G.C. Verschoor, J. Chem. Soc.,
Dalton Trans. (1984) 1349.
[17] G. Murphy, C.O. Sullivan, B. Murphy, B. Hathaway, Inorg. Chem. 37 (1998) 240.
[18] M. Vaidyanathan, R. Balamurugan, U. Sivagnanam, M. Palaniandavar, J. Chem.
Soc., Dalton Trans. (2001) 3498.
[19] D. Cremer, J.A. Pople, J. Am. Chem. Soc. 97 (1975) 1354.
[20] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination
compounds, fifth ed., Wiley, New York, 1997.
[21] D.F. Xiang, C.Y. Duan, X.S. Tan, Q.W. Hang, W.X. Tang, J. Chem. Soc., Dalton
Trans. (1998) 1201.
The electronic spectral data of the zinc(II) complexes are given
in Table 5. The ligand HL has an absorption at 40000 cmꢁ1 due to
the intra-ligand
function of the semicarbazone moiety. Another band at
30770 cmꢁ1 for HL corresponding to a n– * transition of the amide
p–
p* transitions of the pyridyl ring and imine
p
function, which undergoes a small blue shift on complexation,
indicating coordination via the pyridyl nitrogen with a reduction
in intensity [27]. The shift of the
p–
p* bands to the longer wave-
length region is the result of the C@O bond being weakened and
the conjugated system being enhanced after the formation of the
complexes. The metal–ligand CT bands are found around
[22] M.J.M. Campbell, Coord. Chem. Rev. 17 (1975) 279.
[23] E. Bayer, C.G. Witte, J. Coord. Chem. 7 (1997) 13.
[24] D.F. Little, C.J. Long, Inorg. Chem. 7 (1968) 3401.
[25] M. Canadas, E. Lopez-Torres, A. Martinez-Arias, M.A. Mendiola, M.T. Sevilla,
Polyhedron 19 (2000) 2059.
24200 cmꢁ1
.
Acknowledgement
[26] R.A. Bailey, S.L. Kozak, T.W. Michelsen, W.N. Mills, Coord. Chem. Rev. 6 (1971)
407.
[27] V. Philip, V. Suni, M.R.P. Kurup, M. Nethaji, Polyhedron 24 (2005) 1133.
M.R.P. Kurup is thankful to the Council of Scientific and Indus-
trial Research (CSIR), New Delhi, India for the financial assistance.