Ligational behaviour of (E)-2-amino-N′-[1-(2-hydroxyphenyl) ethylidene]benzohydrazide towards later 3d metal ions: X-ray crystal structure of nickel(IV) complex

Article abstract of DOI:10.1016/j.molstruc.2014.03.001

Ligational behaviour of (E)-2-amino-N′-[1-(2-hydroxyphenyl) ethylidene]benzohydrazide (Aheb) towards later 3d metal ions[copper(II), cobalt(II), manganese(II), zinc(II), cadmium(II) and nickel(IV)] has been studied. Their structures have been elucidated o

Full text of DOI:10.1016/j.molstruc.2014.03.001

Journal of Molecular Structure 1065-1066 (2014) 179–185
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Ligational behaviour of (E)-2-amino-N0-[1-(2-hydroxyphenyl)
ethylidene]benzohydrazide towards later 3d metal ions: X-ray crystal
structure of nickel(IV) complex
a
a
b
Kalagouda B. Gudasi a, , Siddappa A. Patil , Raghavendra P. Bakale , Munirathinum Nethaji
⇑
a P.G. Department of Chemistry, Karnatak University, Dharwad 580 003, India
b Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, India
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
ꢀ
Hydrazone ligand (Aheb) and its
metal complexes were synthesized
and characterized.
ꢀ
ꢀ
Oxidation of Ni(II) to Ni(IV).
Comparative study of crystal
structure of ligand and its
Ni(IV)complex.
a r t i c l e i n f o
a b s t r a c t
Ligational behaviour of (E)-2-amino-N0-[1-(2-hydroxyphenyl)ethylidene]benzohydrazide (Aheb) towards
later 3d metal ions[copper(II), cobalt(II), manganese(II), zinc(II), cadmium(II) and nickel(IV)] has been
studied. Their structures have been elucidated on the basis of spectral (IR, 1H NMR, UV–Vis, EPR and
FAB-mass), elemental analyses, conductance measurements, magnetic moments, and thermal studies.
During complexation Ni(II) ion has got oxidized to Ni(IV). The changes in the bond parameters of the
ligand on complexation has been discussed by comparing the crystal structure of the ligand with that
of its Ni(IV) complex. The X-ray single crystal analysis of [Ni(aheb)2]Cl2ꢁ4H2O has confirmed an octahe-
dral geometry around the metal ion. EPR spectra of the Cu(II) complex in polycrystalline state at room
(300 K) and liquid nitrogen temperature (77 K) were recorded and their salient features are reported.
Ó 2014 Elsevier B.V. All rights reserved.
Article history:
Received 25 January 2014
Received in revised form 1 March 2014
Accepted 3 March 2014
Available online 11 March 2014
Keywords:
Ni(IV) complex
Spectral study
Thermal behaviour
X-ray structure
1. Introduction
catalysis as well. The active pharmacophore (NHAN@CHA) of
hydrazones is mainly responsible for the significant biological
Hydrazones merit special attention due to their varied structural
features. The possibility of tautomerism in this class of compounds
has drawn additional attraction. In addition, hydrazones constitute
an important class of compounds for new drug development and
activities. Some of the more effective anti-tuberculosis drugs like
isoniazide, isocarboxazide and iproniazide [1], antinociceptive/
antiinflammatory agent like Safrole [2], anti-platelet agent like
benzylidene 10H-phenothiazine-1-carbohydrazide [3] contain
hydrazide/hydrazone moiety. Besides being biologically active,
metal complexes of hydrazones play an important role in catalysis
[4–7].
⇑
Corresponding author. Tel.: +91 0836 2460129 (R)/2215286 (O); fax: +91 0836
2771275.
E-mail address: kbgudasi@rediffmail.com (K.B. Gudasi).
http://dx.doi.org/10.1016/j.molstruc.2014.03.001
0022-2860/Ó 2014 Elsevier B.V. All rights reserved.

180
K.B. Gudasi et al. / Journal of Molecular Structure 1065-1066 (2014) 179–185
Encouraged by these reports and in continuation of our studies
Argon/Xenon (6 kV, 10 mA) as the FAB gas. The accelerating volt-
age was 10 kV and spectra were recorded at room temperature.
The magnetic susceptibility measurements were carried out on a
Faraday balance using Hg[Co(NCS)4] as the calibrant and diamag-
netic corrections were made by direct weighing of the ligand for dia-
magnetic pull. Conductance measurements were recorded in DMSO
using Elico conductivity bridge type CM-82, provided with a dip
type conductivity cell fitted with platinum electrodes. EPR spectra
were recorded on Varian E-4 X-band spectrometer using tetracyano-
ethylene (TCNE) as ‘g’ (g = 2.0027) marker at room temperature and
also at liquid nitrogen temperature. Thermal stabilities of the com-
plexes were studied in the temperature range 25–1000 °C using a
TGA7 analyzer, Perkin Elmer at a heating rate of 10 °C per min in
a N2 atmosphere. A suitable crystal of the Ni(IV) complex was
mounted on a Bruker SMART APEX II CCD diffractometer. Reflection
on the synthesis and characterization of hydrazones and their liga-
tional behaviour towards late 3d metal ions [8,9], we undertook
the study of transition metal complexes of (E)-2-amino-N0-[1-(2-
hydroxyphenyl)ethylidene]benzohydrazide (Aheb) containing
˜C@O, ˜C@NA and AOH groups as potential coordinating sites.
On complexation, ligand (Aheb) act as a tridentate ligand, coordi-
nating through carbonyl oxygen, azomethine nitrogen and pheno-
lic oxygen via deprotonation. During complexation Ni(II) ion has
got oxidized to Ni(IV) as evidenced by single crystal X-ray analysis
and magnetic moment value.
2. Experimental
2.1. Materials and methods
data were measured at 293(2)
K using Mo Ka radiation
(k = 0.71073 Å) with a graphite monochromator empirical absorp-
tion correction was carried out by using SADABS program [11].
The structure of the complex was solved by heavy atom method
and refined by least square on F2 using the SHELX-97 software pack-
age [12]. All non H atoms were anisotropically refined. The hydro-
gen atoms were generated geometrically and allowed to ride on
their respective parent atoms. The final conventional R(F) = 0.0672
All the solvents used in the present investigation are of analyt-
ical grade and were used without further purification. Methyl
anthranilate, hydrazine hydrate, o-hydroxyacetophenone, and hy-
drated metal salts were obtained from S.D. Fine chemical company,
India. 2-Aminobenzoylhydrazide was prepared by known method
[10]. The metal content of the complexes was determined volu-
metrically using EDTA after decomposition with a mixture of HCl
and HClO4. The chloride content of the complexes was determined
gravimetrically as AgCl. The carbon, hydrogen and nitrogen
contents in each sample were determined using Heraus C H N
rapid analyzer. IR spectra in the 4000–400 cmꢂ1 range were mea-
sured on Thermo Nicolet 320 FT-IR spectrometer using KBr discs.
1H NMR spectra were recorded in DMSO-d6 as the solvent at
400 MHz on a BRUKER AMX 400 spectrometer using tetramethyl-
silane (TMS) as an internal reference. Electronic spectra of the com-
and wR(F2) = 0.1519 for I > 2
2(F2) + (0.0848P + 0.0000P], where P = (F2 + 2Fc2)/3.
r(I) with weighting scheme, w = 1/
[r
2.2. Synthesis
2.2.1. Synthesis of the (E)-2-amino-N0-(1-(2-hydroxyphenyl)
ethylidene)benzohydrazide ligand
The (E)-2-amino-N0-[1-(2-hydroxyphenyl)ethylidene]benzohyd-
razide was prepared according the literature method [13] with a
slight modification: A mixture of o-aminobenzoylhydrazide (7.60 g;
50.33 mmol) and o-hydroxyacetophenone (6.80 g; 50 mmol) in
ethanol (25 cm3) was stirred (Scheme 1) for 2 h at room temperature.
plexes were recorded on
a Varian CARY 50 Bio UV–Visible
spectrometer. EI mass spectrum was recorded on a M.I Ver. 14
on UIC 002002. FAB mass spectrum of the complex was recorded
on a JEOL SX 102/DA-6000 mass spectrometer/data system using
Scheme 1. Synthesis of (E)-2-amino-N0-[1-(2-hydroxyphenyl)ethylidene]benzohydrazide ligand and its metal complexes, M = copper(II), cobalt(II), manganese(II), zinc(II)
cadmium(II) [X = Nill, Y = 3] and nickel(IV) [X = 2Cl, Y = 4].

K.B. Gudasi et al. / Journal of Molecular Structure 1065-1066 (2014) 179–185
181
The resulting yellowish compound that precipitated was filtered,
washed and recrystallised from ethanol.
Yield 80%, M.P.:170–171 °C (literature reported: 170 °C).
2.2.2. Synthesis of the transition metal complexes
Metal(II) chlorides (1 mmol) were treated with Aheb
(0.02 mmol; 0.5386 g) in 1:2 ratio in alcoholic medium and refluxed
for about 2 h. Sodium acetate (2 g) was added to the reaction
mixture and refluxing was continued for another hour (Scheme 1).
The complexes precipitated were filtered, washed with alcohol and
finally air dried. All the isolated complexes are insoluble in most of
the organic solvents but soluble in DMF and DMSO.
Yield: 85–90%.
3. Results and discussion
3.1. General characterization
The analytical data along with some physical properties of the
complexes are summarized in Table 1. The elemental analyses
show 1:2 (metal:ligand) stoichiometry for all the complexes. The
complexes can be represented by the formulae [M(aheb)2]ꢁ3H2O
for copper(II), cobalt(II), manganese(II), zinc(II), and cadmium(II)
complexes and [Ni(aheb)2]Cl2ꢁ4H2O for nickel(IV) complex. The ob-
served molar conductance values indicate its 1:2 electrolytic nature
for Ni(IV) complex while non-electrolytic nature for copper(II),
cobalt(II), manganese(II), zinc(II), and cadmium(II) complexes.
Fig. 1a. ORTEP diagram of [Ni(aheb)2]Cl2ꢁ4H2O.
tions across the bonds C(9)AC(10)AC(11)AN(3), O(2)AC(9)AC
(10)AC(11), C(24)AC(25)AC(30)AN(6) and O(4)AC(24)AC(25)AC
(30) indicate the +synperiplanar arrangement and their torsional
angles are +5.8(7), +9.1(6), +4.3(7) and +10.4(6)° respectively.
The CAC bond distances in aromatic rings are in the normal
range of 1.35–1.49 Å, which are characteristic of delocalised aro-
matic rings. The bond distances Ni(1)AN(4) 2.045(3), Ni(1)AN(1)
2.049(3), Ni(1)AO(1) 2.062(3), Ni(1)AO(3) 2.067(4), Ni(1)AO(4)
2.080(3) and Ni(1)AO(2) 2.092(3) Å are in good agreement with
the bond distances found in similar distorted octahedral Ni(IV)
complexes [14–16]. The bond distances for the bonds
O(4)AC(24), O(2)AC(9), O(3)AC(16), O(1)AC(1), N(3)AC(11), and
N(6)AC(30) are 1.254(5), 1.257(5), 1.451(5), 1.445(5), 1.357(6)
and 1.350(6) Å respectively. The bond distances N(1)AC(7)
1.278(5) and N(4)AC(22) 1.286(5) Å are indicative of double bonds.
The Ni(IV) complex is coplanar and lies in five planes with plane I
[C(1), C(2), C(3), C(4), C(5), C(6)] forms a dihedral angle of 4.39(1)°
with plane II [C(16), C(17), C(18), C(19), C(20), C(21) ], 56.23(1)° with
plane III [C(25), C(26), C(27), C(28), C(29), C(30)], 55.58(1)° with plane
IV [C(10), C(11), C(12), C(13), C(14), C(15)], 70.99(1)° with plane V
[O(1), O(2), O(3), O(4), Ni(1)]. Plane II form dihedral angles 55.
54(1)°, 56.04(1)°, 71.11(1)° with planes III, IV and V respectively.
Plane III forms a dihedral angle of 12.49(1)°, 53.60(1)° with planes
IV and V respectively. Further plane IV forms a dihedral angle of
53.60(1)° with plane V.
3.2. Crystallographic study of Ni(IV) complex
The crystal structure consists of a discrete [Ni(aheb)2]2+ cation
and two uncoordinated chloride anions and four water molecules.
The ORTEP view of the complex with atom labelling is shown in
Fig. 1a. The experimental crystallographic details are given in Ta-
ble 2. The selected bond lengths and angles, torsional angles,
hydrogen bonds and equations for the main least square planes
in the structure are given in Tables 3–5 respectively. The coordina-
tion geometry of the Ni(IV) can be described as a distorted octahe-
dral geometry. The Ni(IV) ion is bonded to two carbonyl oxygens
[O(2) and O(4)], two azomethine nitrogens [N(1) and N(4)] and
two deprotonated phenolic oxygens [O(1) and O(3)] of the triden-
tate ligands. Four oxygen atoms [O(2), O(4), O(1) and O(3)] occupy
the equatorial belt and two nitrogen atoms [N(1) and N(4)] occupy
the axial position of the octahedron.
The angles O(3)ANi(1)AO(2), O(1)ANi(1)AO(4), O(4)ANi(1)AO
(2) and O(1)ANi(1)AO(3) measures 91.58(13), 91.94(13), 79.91
(12) and 101.23(13)°, respectively which deviates from a perfect
octahedral geometry (90°). The [N(1)ANi(1)AN(4)] angle measures
166.76(12)° and deviates from 180° expected for
a perfect
The molecular packing diagrams of the [Ni(aheb)2]Cl2ꢁ4H2O in
octahedral geometry. The CACAC bond angles in aromatic rings
are around 120° with the variation being less than 3°, tallying
closely with sp2-hybridized carbons. The conformational designa-
the unit cell is illustrated in Fig. 1b. Molecular packing is mainly
dictated by
a
three-dimensional hydrogen-bonding network
Table 1
Analytical and physicochemical data of aheb and its metal complexes.
a
Compound
Empirical formula
Elemental analyses found (calculated) (%)
leff (B.M.) KM
kmax in cmꢂ1
C
H
N
M
–
Cl
Aheb
C15H14N3O2
66.95 (66.90) 5.59 (5.61) 15.55 (15.58)
–
–
–
27777
[Cu(aheb)2]ꢁ3H2O
[Cu(C15H14N3O2)2]ꢁ3H2O
55.00 (55.08) 5.25 (5.23) 12.85 (12.84) 9.70 (9.71)
55.45 (55.47) 5.20 (5.27) 12.95 (12.93) 9.00 (9.07)
–
–
1.79
4.85
10.08 28169, 14705
9.57 14513, 18832
12.75 28571
11.73 28409
14.55 28985
13.56 347
[Co(aheb)2]ꢁ3H2O
[Co(C15H14N3O2)2]ꢁ3H2O
[Ni(aheb)2]Cl2ꢁ4H2O [Ni(C15H14N3O2)2]Cl2ꢁ4H2O 48.79 (48.80) 4.89 (4.91) 11.37 (11.38) 7. 92 (7.94)
9.59 (9.60)
[Mn(aheb)2]ꢁ3H2O
[Zn(aheb)2]ꢁ3H2O
[Cd(aheb)2]ꢁ3H2O
[Mn(C15H14N3O2)2]ꢁ3H2O
[Zn(C15H14N3O2)2]ꢁ3H2O
[Cd(C15H14N3O2)2]ꢁ3H2O
55.78 (55.81) 5.29 (5.30) 13.00 (13.01) 8.55 (8.50)
54.90 (54.92) 5.20 (5.22) 12.80 (12.81) 9.95 (9.96)
51.22 (51.25) 4.85 (4.87) 11.90 (11.95) 15.95 (15.98)
–
–
–
5.75
Dia
Dia
a
X
ꢂ1 cm2 molꢂ1
.

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K.B. Gudasi et al. / Journal of Molecular Structure 1065-1066 (2014) 179–185
Table 2
Table 4
Crystal data and structural refinement for nickel(IV) complex.
Hydrogen bonds (Å) and angles (°) for nickel(IV) complex (symmetry transformations
used to generate equivalent atoms: (i) x, y, z and (ii) x + 1/2, ꢂy + 1/2 + 1, +z.
Compound
C30H36Cl2N6NiO8
DAHꢁ ꢁ ꢁA
DAH
Hꢁ ꢁ ꢁA
Dꢁ ꢁ ꢁA
<DAHꢁ ꢁ ꢁA
CCDC no.
Molecular weight
Colour/shape
Temp.
Crystal system
Space group
288644
738.26
Brownish black
293(2) K
Triclinic
O(2)AH(2)00ꢁ ꢁ ꢁN(3)i
N(1)AH(1A)ꢁ ꢁ ꢁO(1)i
N(2)AH(2)0ꢁ ꢁ ꢁO(1)ii
C(5)AH(5)ꢁ ꢁ ꢁO(1)ii
0.921(3)
0.798(3)
0.855(2)
0.963(2)
1.731(3)
2.039(3)
2.063(2)
2.623(2)
2.522(3)
2.664(3)
2.905(3)
3.320(3)
142.09(2.42)
134.91(2.54)
168.24(2.13)
129.59(1.60)
P-1
V
a
b
c
a
b
c
Z
1692.1(11) Å3
12.564(5) Å
13.201(5) Å
13.191(5) Å
61.508(5)°
65.938(5)°
65.881(6)°
2
Previously we reported the crystal structure of the (E)-2-amino-
N0-(1-(2-hydroxyphenyl) ethylidene)benzohydrazide ligand [17].
The changes observed in the ligand on coordination are summa-
rized as follows: The C@O [C(7)AO(1) bond length [1.241(2) Å] in
ligand has increased in Ni(IV) complex [C(9)AO(2) 1.257(5) and
C(24)AO(4) 1.254(5) Å] as a result of decrease in bond order upon
complexation. The C@N [C(8)AN(3) 1.287 Å] bond distance in the
ligand has decreased in Ni(IV) complex [C(7)AN(1) 1.278(2) and
C(22)AN(4) 1.286(5) Å]. The reason for such a bond contraction
may be attributed to electron delocalisation in the coordinated
ligand [18]. On the other hand, the CAOH [C(14)AO(2)] bond
distance which was 1.349(3) Å in the ligand has increased to
[C(1)AO(1) 1.445(5) and C(16)AO(3) 1.451(5) Å] in Ni(IV)complex.
In the ligand, the two planes C(1), C(2), C(3), C(4), C(5), C(6) and
C(9), C(10), C(11), C(12), C(13), C(14) were almost planar with a
deviation of 5.47(7)°, on complexation this deviation has increased.
All the remaining bond lengths and bond angles do not show much
change upon complexation.
Dcalcd
Index ranges
1.449 mg mꢂ3
ꢂ16 6 h 6 16
ꢂ17 6 k 6 16
ꢂ17 6 l 6 17
768
F (000)
Absorption coefficient
Radiation
0.788 mmꢂ1
Mo K
a
Wavelength
0.71073 Å
14149
7569 [R(int) = 0.1050]
0.8183, 0.7726
0.34 ꢃ 0.33 ꢃ 0.27 mm
568
Reflection collected
Independent reflections
Tmax and Tmin
Crystal size
No. parameters
Goodness-of-fit (GOF)
0.963
Final R indices [I > 2
r(I)]
R1 = 0.0672, wR2 = 0.1519
R1 = 0.1195, wR2 = 0.1747
1.144, ꢂ0.491 e Aꢂ3
Largest diff. peak and hole
3.3. Spectroscopic studies
involving cations, anions and water molecules. The complex shows
intramolecular and intermolecular hydrogen bonding (Table 4).
These hydrogen bonding stabilize the crystal-packing pattern.
The diagnostic IR bands of the ligand and the respective com-
plexes are shown in Table 6. The bands at 3477 and 3365 cmꢂ1
in the infrared spectrum of the ligand may be assigned to the
mas(HNH) and
ms(HNH) vibrations of NH2 groups and the band at
Table 3
Selected bond lengths (Å) and angles along with the torsion angles (°) of Ni(IV) complex.
Bonds
Lengths
1.361(3)
Bonds
Lengths
C(1)AN(1)
C(1)AC(2)
C(1)AC(6)
C(2)AC(3)
C(3)AC(4)
C(4)AC(5)
C(5)AC(6)
C(6)AC(7)
C(7)AO(1)
C(7)AN(2)
C(8)AN(3)
C(8)AC(9)
1.475(3)
1.492(3)
1.399(3)
1.410(3)
1.376(4)
1.370(5)
1.376(4)
1.390(3)
1.349(3)
1.380(2)
1.404(3)
1.417(3)
1.378(3)
1.385(3)
1.377(3
1.396(3)
1.484(3)
1.241(2)
1.361(2)
1.287(2)
C(8)AC(15)
C(9)AC(10)
C(9)AC(14)
C(10)AC(11)
C(11)AC(12)
C(12)AC(13)
C(13)AC(14)
C(14)AO(2)
N(2)AN(3)
Bonds
Angles
Bonds
Angles
N(1)AC(1)AC(2)
N(1)AC(1)AC(6)
C(2)AC(1)AC(6)
C(3)AC(2)AC(1)
C(2)AC(3)AC(4)
C(5)AC(4)AC(3)
C(4)AC(5)AC(6)
C(5)AC(6)AC(1)
C(5)AC(6)AC(7)
C(1)AC(6)AC(7)
O(1)AC(7)A N(2)
O(1)AC(7)AC(6)
N(2)AC(7)AC(6)
N(3)AC(8)AC(9)
118.87(19)
123.19(19)
117.94(17)
121.54(19
120.5(2)
N(3)AC(8)AC(15)
C(9)AC(8)AC(15)
C(10)AC(9)AC(14)
C(10)AC(9)AC(8)
C(14)AC(9)AC(8)
C(11)AC(10)AC(9)
C(12)AC(11)AC(10)
C(11)AC(12)AC(13)
C(12)AC(13)AC(14)
O(2)AC(14)AC(13)
O(2)AC(14)AC(9)
C(13)AC(14)AC(9)
C(7)AN(2)AN(3)
C(8)AN(3)AN(2)
124.42(18)
120.82(16)
117.7(2)
120.37(18)
121.91(17)
121.2(3)
120.4(3
120.3(2)
120.3(3)
116.9(2)
118.8(2)
122.24(17)
118.89(17)
121.75(16)
119.32(16)
119.94(16)
122.32(15)
117.73(14)
114.76(15)
122.95(19)
120.1(2)
115.37(14)
120.89(15)
Bonds
Torsion angles
179.08(19)
161.12(18)
5.56(25)
Bonds
C(15)AC(8)AN(3)AN(2)
C(8)AC(9)AC(14)AO(2)
Torsion angles
3.28(27)
1.23(31)
N(1)AC(1)AC(6)AC(5)
C(5)AC(6)AC(7)AO(1)
O(1)AC(7)AN(2)AN(3)

K.B. Gudasi et al. / Journal of Molecular Structure 1065-1066 (2014) 179–185
183
Table 5
Least square planes through the mentioned atoms of Ni(IV) complex. Equation of the plane: m1x + m2y + m3z = D.
Planes
m1
m2
m3
D
I. C(9), C(10), C(11), C(12), C(13), C(14)
II. C(1), C(2), C(3), C(4), C(5), C(6)
ꢂ0.76422
ꢂ0.77154
0.56545
0.50650
ꢂ0.31022
ꢂ0.38495
ꢂ1.91616
ꢂ2.28689
Plane–plane
Angle
I
II
5.47
Dihedral angles (°) formed by LSQ-planes.
vibrations respectively. The shift of the amide-I [
m
(C@O)] band to
lower wave number compared to 2-aminobenzoylhydrazone of
butane-2,3-dione [10] suggest the involvement of oxygen in
hydrogen bonding which was also confirmed by crystallographic
studies. A shift to lower frequency (10–20 cmꢂ1) of amide-I
[m(C@O)] band in all the complexes is indicative of the coordinated
C@O group. A shift to the lower wave number (10–40 cmꢂ1) in the
amide II and to the slightly higher wave number (10–30 cmꢂ1) in
the amide III bands in the complexes also confirm the C@O coordi-
nation [22]. The azomethine
m(C@N) stretching observed at
1610 cmꢂ1 in the ligand spectrum has shifted to lower wave num-
ber (ꢄ1597–1585 cmꢂ1) in all the complexes, indicating coordina-
tion of azomethine nitrogen with the metal ions [23].
The numbering system followed for NMR assignments of ligand
is given in Scheme 1. The chemical shift values d (in ppm) are given
in Table 7. The spectrum of the ligand exhibits three singlets at
13.43, 10.92 and 2.47 ppm, assignable to phenolic AOH group
(D2O exchangeable), NH (D2O exchangeable) and methyl protons
respectively. Two doublets at 6.80, 7.30 and two triplets at 7.24
and 6.61 ppm are assigned to aromatic protons C(2)H C(5)H and
C(4)H, C(11)H respectively. A doublet expected of C(5)H and an-
other doublet of C(10)H have merged to give a multiplet at
7.64 ppm, integrating for two protons. One triplet of C(12)H and
another doublet of C(13)H have merged to give a multiplet at
6.61 ppm, which corresponds to two protons.
In the spectra of zinc(II), and cadmium(II) complexes, the
resonance due to N(2)H has appeared at the same position as in
the ligand (10.92 ppm) indicating the non-involvement of N(2)H
in coordination. The singlet at 13.43 ppm in the ligand spectrum
ascribed to phenolic AOH group is not observed in zinc(II), and
cadmium(II) complexes. This confirms the involvement of phenolic
oxygen in coordination with the metal via deprotonation. The
other signals [C(15)H, C(2)H, C(5)H, C(4)H, C(11)H, C(5)H, C(10)H,
C(12)H and C(13)H] in zinc(II), and cadmium(II) complexes did
not show any considerable shift. The signal due to free NH2
[N(1)H] was not observed in zinc(II) as well as cadmium(II)
complexes.
Fig. 1b. Molecular packing diagram of [Ni(aheb)2]Cl2ꢁ4H2O (intra-and inter-
molecular hydrogen bonds are omitted for clarity).
3213 cmꢂ1 to
metal complexes the bands of
m
(NH) group of the ligand. In the spectra of all the
m
as(HNH) and s(HNH) vibrations
m
of NH2 were not observed and might have been obscured by the
broad band at 3500 cmꢂ1, due to the lattice-held water molecules
where as the band corresponding to m(NH) group remains the same
as in the ligand [19,20]. Infrared spectrum of the ligand shows a
broad weak band in the region 3052–2925 cmꢂ1 due to the intra-
molecular hydrogen bonded OH with azomethine nitrogen moiety
as also confirmed by crystallographic studies. The absence of this
band in all the complexes, suggests the coordination of phenolic
oxygen of the ligand to the metal via deprotonation as also
confirmed by 1H NMR spectra. The
m(CAO) of phenolic moiety
observed at 1292 cmꢂ1 in the ligand shows a positive shift of
10–40 cmꢂ1, confirming the involvement of deprotonated phenolic
oxygen on complexation [21].
The UV–VIS spectrum of the ligand shows only one broad band
at 27777 cmꢂ1, which is assigned to n ? pꢅ of the C@N chromo-
phore. On complexation this band has shifted to lower energy,
suggesting the coordination of azomethine nitrogen. The spectrum
of the copper(II) complex exhibited only one broad d–d transition
The bands at 1625, 1547 and 1257 cmꢂ1 are assigned to amide-I
[mC@O], amide-II [m(CN) + d(NH) and amide-III [d(NH) + m(CN)]
Table 6
IR spectral bands (cmꢂ1) and their assignments in aheb and its metal complexes.
Compound
m
(NH)
m
(OH) phenolic
Amide bands
I
m
(C@N)
m(CAO) Phenolic
II
II
Aheb
3213(m)
3213(m)
3215(m)
3214(m)
3215(m)
3212(m)
3213(m)
2925(b)
1625(s)
1613(s)
1605(s)
1611(s)
1613(s)
1612(s)
1615(s)
1547(s)
1257(m)
1298(m)
1276(m)
1290(m)
1295(m)
1275(m)
1305(m)
1610(s)
1585(s)
1592(s)
1594(s)
1597(s)
1593(s)
1595(s)
1292
1332
1336
1322
1314
1300
1315
[Cu(aheb)2]ꢁ3H2O
[Ni(aheb)2]Cl2ꢁ4H2O
[Co(aheb)2]ꢁ3H2O
[Mn(aheb)2]ꢁ3H2O
[Zn(aheb)2]ꢁ3H2O
[Cd(aheb)2]ꢁ3H2O
–
–
–
–
–
–
1518(m)
1541(m)
1508(m)
1536(m)
1511(m)
1540(m)

184
K.B. Gudasi et al. / Journal of Molecular Structure 1065-1066 (2014) 179–185
Table 7
1H NMR spectral data of aheb and its zinc(II) and cadmium(II) complexes.
Protons
Aheb
Zinc(II) complex
Cadmium(II) complex
Chemical Shifts in d (ppm)
O(2)H
13.43 (s, 1H)
–
–
N(2)H
C(2)H
C(5)H and C(10)H
C(11)H
C(12)H and C(13)H
C(15)H
10.92 (s, 1H)
6.80 (d, 1H, J = 8.1 Hz)
7.64 (m, 2H)
6.61 (t, 1H, J = 7.4 Hz)
6.91 (m, 2H)
2.47 (s, 3H)
10.92 (s, 1H)
6.79 (d, 1H, J = 8.2)
7.63 (m, 2H)
6.61 (t, 1H, J = 7.4 Hz)
6.91 (m, 2H)
2.47 (s, 3H)
10.92 (s, 1H)
6.79 (d, 1H, J = 8.1)
7.63 (m, 2H)
6.61 (t, 1H, J = 7.4 Hz)
6.91 (m, 2H)
2.47 (s, 3H)
at 14285 cmꢂ1 assigned to 2Eg ? 2T2g transition, which is in confor-
mity with octahedral configuration around the copper ion [23,24].
upfield and has merged with the aromatic proton resonances. It
was further supported by the single crystal structure of the ligand
and its Ni(IV) complex as well. A lengthening of C@O bond, of Aheb
on coordination suggest a decrease in bond order in case of C@O.
The bond shortening in case of C@N, may be attributed to electron
delocalizations in the coordinated ligand. Magnetic and electronic
spectral data suggest distorted octahedral geometries around the
metal centres and was further confirmed by single crystal X-ray
diffraction studies in case of Ni(IV) complex. FAB mass spectral
analysis reveals the monomeric nature of Mn(II) complex. Thermal
studies suggest the presence of lattice held water in the complexes
reported.
The two d–d bands in the spectrum of cobalt(II) complex at 14492
4
and 18867 cmꢂ1 are attributed to 4T1g ? 4A2g
(m2
)
and T1g
(F) ? 4T1g (P) (
m3) transitions. These assignments are in good
agreement with literature values for octahedral geometry of cobal-
t(II) complex [24]. No absorptions were observed for the manga-
nese(II) complex indicating it to be
a high-spin octahedral
complex [25]. The nickel(IV), zinc(II) and cadmium(II) complexes
did not show any d–d transitions.
EPR spectrum of copper(II) complex recorded at room tempera-
ture and also at liquid nitrogen temperature. The g and g\ values
are 2.24 and 2.04 respectively. The gave was calculated to be 2.10.
The greater value of g as compared to g\ indicated the presence
Acknowledgments
of unpaired electron in dx2
orbital [26,27].
ꢂy2
Mass spectrum of the ligand shows the molecular ion peak at
m/z = 269, which correspond to the molecular mass of the ligand.
The FAB-mass spectrum of the [Mn(aheb)2]ꢁ3H2O complex was
recorded which show a molecular ion peak (M+) at m/z = 654, is
indicative of monomeric nature of the complex.
The authors thank the CCD-X-Ray facility under DST IRPHA pro-
gram, Department of Inorganic and Physical Chemistry and Sophis-
ticated Instrumentation Facility, Indian Institute of Science,
Bangalore, India, for the X-ray data collection and 1H NMR spectra.
Thanks are also due to University Sophisticated Instrumentation
Center, Karnatak University Dharwad and Sophisticated Analytical
Instrument Facility CDRI, Lucknow for carring out elemental anal-
yses and providing mass spectra. One of the authors (Dr. Siddappa
A. Patil) is grateful to Karnatak University, Dharwad for award of
University Research fellowship.
3.4. Magnetic studies
The room temperature effective magnetic moments of 1.79,
4.85, 5.75 BM for copper(II), cobalt(II) and manganese(II) com-
plexes suggest an octahedral geometry around the metal ion centre
[28]. Nickel(IV), zinc(II) and cadmium(II) complexes are diamag-
netic in nature.
Appendix A. Supplementary material
The 1HNMR spectrum of ligand, electronic spectra of cobalt(II)
and copper(II) complex, EPR spectrum of copper(II) complex and
FAB mass spectra of manganese(II) complex are given in supple-
mentary material. Crystallographic data, bond lengths and bond
angles of structure have been deposited with the Cambridge crys-
tallographic Data center, with the deposition number: CCDC
288644. Copies of this information are available free of charge from
the Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (Fax:
+44 1223 336 033; e-mail: deposit@ccdc.cam.ac.uk or http://
www.ccdc.cam.ac.uk). Supplementary data associated with this
article can be found, in the online version, at http://dx.doi.org/
10.1016/j.molstruc.2014.03.001.
3.5. Thermal studies
The copper(II) and cobalt(II) complexes decompose in two
stages. The first step 25–100 °C results in a mass loss of 8.20%
(Calcd. 8.25%) and 8.32% (Calcd. 8.31%) respectively, corresponding
to the loss of three lattice held water molecules. The temperature
range rules out the possibility of coordinated water molecules. In
the second step the mass loss of 82.43% (Calcd. 82.33%) and
83.02% (Calcd. 82.92%) in the temperature range 100–456 °C and
100–524 °C corresponds to the loss of ligand molecule in copper(II)
and cobalt(II) complexes. A plateau was obtained after heating
above 500 °C, which corresponds to the formation of stable CuO
and CoO. The weights of CuO and CoO correspond to 9.21% and
8.66% respectively and tallies with the metal analysis.
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