Synthesis and characterization of metal complexes of N-methyl-and N-ethylacetoacetanilide semicarbazones

Article abstract of DOI:10.1081/SIM-100001931

Fourteen new metal complexes of N-methyl-(H₂L) and N -ethylacetoacetanilide (H₂L′) semicarbazones, having the general formulae [M(LH)₂], [ML/L′(H₂O)], [ML/L′(H₂O)₃], and [FeLCl (H₂

Full text of DOI:10.1081/SIM-100001931

Synthesis and Reactivity in Inorganic and Metal-Organic
Chemistry
ISSN: 0094-5714 (Print) 1532-2440 (Online) Journal homepage: http://www.tandfonline.com/loi/lsrt19
SYNTHESIS AND CHARACTERIZATION OF
METAL COMPLEXES OF N-METHYL- AND N-
ETHYLACETOACETANILIDE SEMICARBAZONES
Kallumpurath P. Deepa & Kuttamath Kunniyur Aravindakshan
To cite this article: Kallumpurath P. Deepa & Kuttamath Kunniyur Aravindakshan (2001)
SYNTHESIS AND CHARACTERIZATION OF METAL COMPLEXES OF N-METHYL- AND N-
ETHYLACETOACETANILIDE SEMICARBAZONES, Synthesis and Reactivity in Inorganic and
Metal-Organic Chemistry, 31:1, 43-56, DOI: 10.1081/SIM-100001931
To link to this article: http://dx.doi.org/10.1081/SIM-100001931
Published online: 20 Aug 2006.
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Date: 30 August 2017, At: 14:55

SYNTH. REACT. INORG. MET.-ORG. CHEM., 31(1), 43–56 (2001)
SYNTHESIS AND CHARACTERIZATION OF
METAL COMPLEXES OF N-METHYL- AND
N-ETHYLACETOACETANILIDE
SEMICARBAZONES
Kallumpurath P. Deepa and
Kuttamath Kunniyur Aravindakshan∗
Department of Chemistry, University of Calicut,
Kerala 673 635, India
ABSTRACT
Fourteen new metal complexes of N-methyl- (H2L) and N-
ethylacetoacetanilide (H2Lꢀ) semicarbazones, having the general
formulae [M(LH)2], [ML/Lꢀ(H2O)], [ML/Lꢀ(H2O)3], and [FeLCl
(H2O)]2, where M = Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II)
or Hg(II), LH = tridentate monoanion of H2L and L/Lꢀ = triden-
tate dianion of H2L or H2Lꢀ, were synthesized. Characterization
of these compounds was mainly done by chemical analyses, molar
conductance, magnetic susceptibility and electronic, infrared and
1H NMR spectral studies. Thermogravimetric studies of Mn(II),
Co(II), Ni(II), and Cu(II) complexes of N-methylacetoacetanilide
semicarbazone were also carried out.
KeyWords: N-methyl-and N-ethylacetoacetanilidesemicarbazones;
Synthesis; Characterization; Thermogravimetric studies
∗Corresponding author.
43
Copyright ꢁ 2001 by Marcel Dekker, Inc.
www.dekker.com
C

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DEEPA AND ARAVINDAKSHAN
R
NPh
O
N
C
C
CH2
CH3
O
C
NH
H2N
R = CH3 (H2L) or C2H5 (H2L′)
Figure 1. Suggested structure of the ligands.
INTRODUCTION
== –
Compounds having >C N N< groups were found to exhibit immense
physiological and analytical applications. Semicarbazones, typical members of
this class, can act as ligands towards various metal ions. They usually act as
chelating ligands towards transition metal ions by bonding through oxygen and
hydrazinic nitrogen atoms (1), although in a few cases they are reported to be-
have as monodentate ligands. In continuation of our investigations on the donor
properties of semicarbazones and thiosemicarbazones of β-ketoderivatives (2,3),
it was found to be worthwhile and interesting to synthesize and characterize metal
complexes of semicarbazones of N-substituted acetoacetanilides. We describe
here the synthesis and characterization of several typical transition metal com-
plexes of semicarbazones of N-methyl- (H2L) and N-ethylacetoacetanilide (H2Lꢀ)
(Fig. 1).
RESULTS AND DISCUSSION
The ligands of the present investigation exist mainly in the keto form. This
is established from the IR and 1H NMR spectral studies. The ligands show bands
in the regions 3400–3000, 1700–1640, and 1610–1590 cm−1, which are assigned,
–
==
==
respectively, to N H, C O and C N stretching vibrations. In the spectra of the
–
==
complexes, broadening of the bands in N H region is noticed. The C O band
either shifts to lower frequency or disappears during complex formation. The
==
C N stretching band is also found to be lowered in the spectra of the complexes.
1
The H NMR spectra of the ligands show peaks due to CH2 and NH protons,
eliminating the possibility of their enol structures.

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METAL COMPLEXES OF SEMICARBAZONES
Formulae and General Properties of the Complexes
45
Formation of the complexes can be represented by the following equations:
M(CH3COO)2nH2O + H2L/H2Lꢀ → [ML/Lꢀ(H2O)] + 2CH3COOH
+ (n−1) H2O
L = tridentate dianion of H2L, M = Zn(II)
Lꢀ = tridentate dianion of H2Lꢀ, M = Zn(II) or Cd(II)
M(CH3COO)2nH2O + H2L/H2Lꢀ → [M(L/Lꢀ) (H2O)3] + 2CH3COOH
+ (n − 3) H2O
M = Co(II) or Ni(II) for L
M = Mn(II), Co(II), Ni(II) or Cu(II) for Lꢀ
2FeCl3 + 2H2O + 2H2L → [FeLCl(H2O)]2 + 4HCl
M(CH3COO)2nH2O + 2H2L → [M(LH)2] + 2CH3COOH + nH2O
M = Mn(II), Cu(II) or Cd(II)
LH = tridentate monoanion of H2L
HgCl2 + 2H2L → [Hg(LH)2] + 2HCl
Except for the Fe(III) and Ni(II) complexes of N-methylacetoacetanilide
semicarbazone, all the others were found to be pale coloured, nonhygroscopic air-
and photostable. The Fe(III) and Ni(II) complexes of the N-methyl derivative were
found to be deliquescent. Generally, the complexes were found to be soluble in
ethanol, methanol, and DMSO. However, the solubility of the Zn(II) and Cd(II)
complexes are very poor. The electrical conductance of the complexes measured in
DMSO and the calculated molar conductance values indicate their nonelectrolytic
nature. The analytical data (Table 1) of the H2L complexes correspond to the
==
formulae [M(LH)2], where M Mn(II), Cu(II), Cd(II) or Hg(II); [ML(H2O)3],
==
where M Co(II) or Ni(II); ꢀ[ZnL(H2O)] and [FeLCl(H2O)]2. The complexes of
ꢀ
==
H2L have the formulae [ML (H2O)3], where M Mn(II), Co(II), Ni(II) or Cu(II)
and [MLꢀ(H2O)], where M = Zn(II) or Cd(II).
Magnetic Behaviour
The magnetic moment (Table 1) of [Mn(LH)2] (6.14 B.M.) which is close
to the spin-only value (5.92 B.M.) indicates its octahedral geometry (4). The low
value of the magnetic moment of [MnLꢀ(H2O)3] (4.54 B.M.) may be due to its
distorted octahedral geometry (5). The Fe(III) complex of H2L shows a magnetic
moment value of 4.96 B.M., which is found to be lower than the spin-only value

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METAL COMPLEXES OF SEMICARBAZONES
47
(5.90 B.M.). This may be due to its binuclear configuration, facilitating antifer-
romagnetic exchange interaction (6). The µeff values of 5.00 and 4.83 B.M. for
the Co(II) complexes together with their pale-pink colour indicate their octahedral
structure. The Ni(II) complexes, [NiL(H2O)3] and [NiLꢀ(H2O)3], register magnetic
moment values at 2.71 and 2.53 B.M., respectively. Their pale-green colour and the
magnetic moment values indicate octahedral geometry around the Ni(II) ion. The
Cu(II) complexes, [Cu(LH)2] and [CuLꢀ(H2O)3], register magnetic moments at
2.15 and 2.17 B.M., respectively, which indicate the absence of antiferromagnetic
exchange interaction in them.
Electronic Spectra
The important electronic spectral bands of the Mn(II), Fe(III), Co(II), Ni(II),
and Cu(II) complexes and their assignments are given in the Table 2. The Mn(II)
complex of H2L do not register any characteristic band in the visible region.
Table 2. Electronic Spectral Data of the Complexes and Assignmentsa
Compound
Bands (cm−1
)
Assignments
Geometry
4
[FeLCl(H2O)]2 26109
6A1g → T2g(D)
Octahedral binucleated
4
22026 br
22222
18181 br
9551 w
6A1g → T2g(G)
4
[CoL(H2O)3]
[NiL(H2O)3]
4T1g(F) → T1g(P) Distorted octahedral
4T1g(F) → A2g(F)
4
4T1g(F) → T2g(F)
4
3
25000
3A2g(F) → T1g(P) Distorted octahedral
3
15673 br
9756 w
3A2g(F) → T1g(F)
3A2g(F) → T2g(F)
3
2
[Cu(LH)2]
20876 br
11037 br
2B1g → Eg
Octahedral
Octahedral
4
2B1g → A1g
4
[Mn(LꢀH)2]
[CoLꢀ(H2O)3]
28818
22935
6A1g → T2g(D)
4
6A1g → T2g(G)
4
21598
4T1g(F) → T1g(P) Distorted octahedral
4
17889 br
9587 w
4T1g(F) → A2g(F)
4T1g(F) → T2g(F)
4
[NiLꢀ(H2O)3]
[CuLꢀ(H2O)3]
24691
16000 br
9881 w
3A2g(F) → T1g(P) Distorted octahedral
3
3A2g(F) → T1g(F)
3
3A2g(F) → T2g(F)
3
2
23529
2B1g → Eg
Distorted ocahedral
4
15600 br
2B1g → A1g
abr = broad, w = weak.

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DEEPA AND ARAVINDAKSHAN
Whereas, the Mn(II) complex of H2Lꢀ registers a series of weak bands stretch-
ing over the whole UV-Visible region of the spectrum. The most prominent ones
6
observed at 28,818 and 22,935 cm−1 may be assigned, respectively, to A1g
→
4T2g(D) and A1g → T2g(G) transitions which are characteristic of an octahe-
6
4
dral Mn(II) complex (7,8). The Fe(III) complex of H2L registers bands at 26,109
and 22,026 cm−1. These may be assigned, respectively, to A1g → T2g(D) and
6
4
6A1g → T2g(G) transitions of an Fe(III) ion in a spin-free d5 configuration. The
4
Co(II) complexes register a band ∼22,000, a broad one ∼18,000 and a weak one
∼9700 cm−1. These may be assigned, respectively, to 4T1g(F) → T1g(P), 4T1g(F)
4
→ A2g(F)and4T1g(F)→ T2g(F)transitionsofanoctahedrallycoordinatedCo(II)
4
4
ion. The complexes of Ni(II), viz., [NiL(H2O)3] and [NiLꢀ(H2O)3], register an in-
tense band at ∼25,000, a broad one at ∼16,000 and a weak one at ∼9800 cm−1
.
These may assigned, respectively, to 3A2g(F) → T1g(P), 3A2g(F) → T1g(F) and
3
3
3A2g(F) → T2g(F) transitions of 6-coordinated octahedral Ni(II) ion. [Cu(LH)2]
3
registers bands at 20,876 and 11,037 cm−1, whereas [CuLꢀ(H2O)3] registers bands
at 23,529 and 15,600 cm−1. These are characteristic of an octahedral or distorted
octahedral geometry around the Cu(II) ion.
Infrared Spectra
The important IR spectral bands and their tentative assignments are given in
Table 3. The bands around 3500 cm−1 in the spectra of the ligands may be assigned
to asymmetric and symmetric stretching modes of NH2 and NH groups. In the
spectra of the Fe(III), Co(II), and Ni(II) complexes of H2L and all the complexes
of H2Lꢀ, this region appears as broad and this may be due to the stretching modes
of coordinated water molecule (9).
−1
==
The ν(C O) (anilide) band appears at 1670 and 1692 cm in the spectra
of H2L and H2Lꢀ, respectively (10). In the spectra of the Mn(II), Cu(II), Cd(II),
and Hg(II) complexes of H2L, this band shifts to lower frequency by a few cm−1
,
indicating the participation of the anilide cabonyl oxygen in coordination. In the
spectra of all the other complexes i.e., those of Fe(III), Co(II), Ni(II), and Zn(II)
with H2L, and all the complexes of H2Lꢀ this band disappears and a new band is
observed at ∼1190 cm−1. This may be due to the enolization of CH2 C O to
–
– ==
–
== –
CH C OH and subsequent coordination through the deprotonated oxygen.
The ν(C=O) (semicarbazide) band appears at 1645 and 1651 cm−1 in the
spectra of H2L and H2Lꢀ, respectively. In the spectra of all the complexes this band
is absent and a new band appears in the 1110–1140 cm−1 region. This may be due
== – – ==
== – == –
to the enolization of N NH C O to N N C OH during complex formation.
The ν(C N) band appears at 1605 and 1593 cm−1 in the spectra of H2L and
==
H2Lꢀ, respectively. In the spectra of all the complexes, this band shifts to lower
frequency indicating the participation of the azomethine nitrogen in coordination.

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METAL COMPLEXES OF SEMICARBAZONES
49

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50
DEEPA AND ARAVINDAKSHAN
−1
The ν(N N) band of the free ligands (at 1010 and 1005 cm for H2L and H2Lꢀ,
respectively) undergoes a marked shift to higher frequency upon complex forma-
tion. This observation is also an indication of the participation of the azomethine
nitrogen in coordination. The broad bands at ∼3500 cm−1 together with medium
ones at ∼870–950 and ∼660 cm−1 in the spectra of the Fe(III), Co(II), Ni(II), and
Zn(II) complexes of H2L and all the complexes of H2Lꢀ may be assigned, respec-
tively, to stretching, rocking and wagging modes of coordinated water molecules.
–
–
–
The bands due to M N and M O stretching frequencies appear, respectively, at
∼530 and ∼450 cm−1 in the spectra of all the complexes.
1H NMR Spectra
H2L and Its Zn(II) Complex
The spectrum of the ligand, recorded in CDCl3 (Table 4) shows a singlet
at 7.92 and a doublet at 7.23–7.17 ppm. These may be assigned to NH and NH2
protons, respectively. The symmetrical multiplet observed at 7.48–7.31 ppm may
be assigned to aromatic protons. The singlets observed at 3.28, 3.08, and 1.83 ppm
–
–
–
may be assignd to N CH3, α CH2, and ω CH3 protons, respectively.
In the spectrum of the Zn(II) complex recorded in CDCl3, the NH proton
== – – ==
signal is not observed. It is a clear evidence for the enolization of N NH C O
== – == –
to N N C OH during complex formation. The peaks due to aromatic, NH2,
–
–
N CH3, coordinated water, and ω CH3 protons are observed at 7.48–7.33 (m),
7.23-7.17 (d), 3.29 (s), 3.00 (s), and 1.82 (s) ppm, respectively. The signal due to
–
α CH2 protons, which is observed as a singlet at 3.09 ppm in the ligand spectrum,
–
– ==
is shifted to 7.65 ppm. This may be due to the enolization of CH2 C O to
== –
–
CH C OH during complex formation.
H2Lꢀ and Its Zn(II) Complex
The ligand spectrum, recorded in CDCl3 shows a singlet at 7.95 and a doublet
at 7.20–7.16 ppm. These peaks may be due to NH and NH2 protons, respectively.
The symmetrical multiplet at 7.47–7.33 ppm may be assigned to aromatic protons.
The quartet at 3.79–3.72 and triplet at 1.15–1.10 ppm are due to N-ethyl CH2 and
N-ethyl CH3 protons, respectively. The singlets observed at 3.02 and 1.81 ppm
–
–
may be due to α CH2 and ω CH3 protons, respectivly.
In the spectrum of the Zn(II) complex recorded in DMSO, the absence
== – – ==
of a peak at 7.95 ppm is a clear evidence for the enolization of N NH C O
== – == –
to N N C OH during complex formation. A multiplet observed in the re-
gion 7.54–7.26, a doublet at 7.20–7.17, a quartet at 3.61–3.53, a singlet at 2.07,
and a triplet at 1.16–1.12 ppm may be assigned to aromatic, NH2, N-ethyl CH2,

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METAL COMPLEXES OF SEMICARBAZONES
51
Table 4. Significant 1H NMR Spectral Assignments of H2L and H2Lꢀ
and Their Zn(II) Complexesa
Compound
(H2L)
δ (ppm)
Proton
7.92 (1H, s)
7.48–7.31 (5H, m)
7.23–7.17 (2H, 6.78 Hz)
3.28 (3H, s)
NH
Aromatic
NH2
–
N CH3
–
3.08 (2H, s)
α CH2
–
1.83 (3H, s)
ω CH3
[ZnL(H2O)]
7.48–7.33 (5H, m)
7.23–7.17 (2H, 6.96 Hz)
7.65 (1H, s)
Aromatic
NH2
–
α CH
–
3.28 (3H, s)
N CH3
3.00 (2H, s)
1.82 (3H, s)
Coordinated water
–
α CH3
(H2Lꢀ)
7.95
NH
7.47–7.33 (5H, m)
Aromatic
7.20–7.16 (2H, d, 6.78 Hz) NH2
3.79–3.72 (2H, q, 7.14 Hz) N-ethyl CH2
–
3.02 (2H, s)
1.81 (3H, s)
α CH2
–
ω CH3
1.15–1.10 (3H, t, 7.14 Hz) N-ethyl CH3
[ZnLꢀ(H2O)]
11.18 (1H, s)
7.54–7.26 (5H, m)
Hydrogen bonded NH
Aromatic
7.20–7.17 (2H, d, 7.31 Hz) NH2
3.61–3.53 (2H, q, 6.96 Hz) N-ethyl CH2
2.69 (2H, s)
2.07 (3H, s)
Coordinated water
–
ω CH3
1.16–1.12 (3H, t, 6.96 Hz) N-ethyl CH3
as = singlet, m = multiplet, d = doublet, t = tripplet, q = quartet.
–
ω CH3, and N-ethyl CH3 protons, respectively. The new peaks observed at 5.54
–
and 2.69 ppm may be assigned to α CH, formed as a result of enolization of
– == == –
–
–
CH2 C O to CH C OH, and protons of coordinated water molecule,
respectively.
Thermal Decomposition Studies
The thermal analysis data of the complexes of H2L are summarized in
Table 5. The Mn(II) complex follows a two-step degradation pattern. In the first
step, loss of a ligand molecule takes place and the second stage of decomposition

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52
DEEPA AND ARAVINDAKSHAN

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METAL COMPLEXES OF SEMICARBAZONES
53
OH2
OH2
Fe
N
N
Cl
Cl
C
O
N
O C
H3C
CH3
CH
HC
Fe
C
N
C
CH3
H3C
O
O
N
N
C
C
NH2
NH2
Figure 2. Structure of Fe(III) complex of H2L.
leads to the formation of MnO2. The Co(II) complex follows a three-staged de-
composition pattern. In the first stage, the loss of 3 water molecules takes place
in the temperature range of 130–180◦C, indicating their coordinated nature. In the
second stage, the loss of half of the ligand molecule occurs. The third stage of
decomposition leads to the formation of Co3O4.
The Ni(II) complex follows a two-step decomposition. In the first step, the
loss of the three coordinated water molecules occurs in the temperature range of
110–175◦C. The second stage of decomposition leads to the formation of NiO.
In the case of the Cu(II) complex, only a single stage of decomposition occurs
leading to the formation of CuO.
The analytical and physico-chemical studies show that the Mn(II) and Cu(II)
complex of H2L has octahedral geometry. The Co(II) and Ni(II) complexes of
H2L and the Mn(II), Co(II), Ni(II), and Cu(II) complexes of H2Lꢀ are found to
have distorted-octahedral geometry. The Fe(III) complex of H2L is found to be
6-coordinate dimeric with a chloro bridged distorted octahedral structure (Fig. 2).
The Zn(II) complexes and the Cd(II) complex of H2Lꢀ are 4-coordinate, whereas
the Cd(II) and Hg(II) complexes of H2L are 6-coordinate.
EXPERIMENTAL
All the chemicals used in the present investigation were of BDH AnalaR
quality. TheN-substitutedacetoacetanilideswerepreparedbythereportedmethods
(11).

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DEEPA AND ARAVINDAKSHAN
Preparation of N-Substituted Acetoacetanilides
N-methyl- and N-ethylacetoacetanilides were obtained as their sodium
derivatives. N-alkylaniline (0.1 mol) and ethylacetoacetate (11.4 mL, 0.1 mol)
were taken in a round-bottomed flask and refluxed on a sand bath at the boiling
temperature for 15 min. The oily product was cooled and treated with 2N NaOH
(200 mL). The white product that formed was filtered, washed successively with
diethyl ether and petroleum ether (60–80◦C). The product was recrystallised from
ethanol and dried in a desiccator under reduced pressure over anhydrous calcium
chloride. Sodium N-methylacetoacetanilide: yield, 14.98 g (70%); m.p. 85◦C,
sodium N-ethylaceta- cetanilide: yield, 14.62 g (65%); m.p. 180◦C. These sodium
derivatives were used for the preparation of the ligands.
Preparation of the Ligands
The semicarbazide (0.55 g, 0.05 mol) in the minimum amount of water was
added to sodium N-methyl- or N-ethylacetoacet- anilide (0.05 mol) in ethanol-
water (2:1 in the case of N-methyl acetoacetanilide and 4:1 in the case of N-
ethylacetoacetanilide) (150 mL) with stirring. The reaction mixture was kept stir-
ring for 2 h and allowed to stand for one day at room temperature. The white
crystalline product formed was filtered, washed several times with water, and dried
in a desiccator over anhydrous calcium chloride. The product was recrystallised
from methanol.
Preparation of the Complexes
A methanolic solution (20 mL) of metal acetate (0.005 mol) was added to
an ethanolic solution (20 mL) of H2L or H2Lꢀ (0.005 mol) and the mixture was
refluxed for 2 h on a water bath. The solution was cooled and evaporated at room
temperature to reduce the volume to 20 mL. The solid complex that formed was
filtered off, washed several times with water and finally with methanol. It was
dried under reduced pressure over anhydrous calcium chloride. In the case of the
Mn(II), Cu(II), Cd(II), and Hg(II) complexes of H2L a 1:2 molar ratio of metal to
ligand was maintained for better yields.
Analytical Methods
The complexes were analysed for their metal contents by standard meth-
ods. Chlorine was determined by Volhard’s method after sodium carbonate fusion

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METAL COMPLEXES OF SEMICARBAZONES
55
and dissolving in dilute nitric acid (12). Carbon, hydrogen and nitrogen were
–
determined by microanalysis using a Hitachi CHN O rapid analyser. The mo-
lar conductances of the complexes were determined using 10−3 M solutions in
DMSO at 28 3◦C on a direct-reading 305 Systronic conductivity bridge and
a dip-type cell (cell constant = 1.083) calibrated with AnalaR potassium chlo-
ride. The magnetic susceptibilities were determined at room temperature by the
Gouy method using Hg[Co(CNS)4] as a calibrant and diamagnetic corrections
were made using Pascal constants (13). The electronic spectra of the compounds
were recorded on a Shimadzu UV-Vis-1601 spectrophotometer using the Nu-
jol mull technique (14). The IR spectra were recorded using KBr discs on a
1
8101 Shimadzu FTIR spectrophotometer. The H NMR spectra of the ligands
and the Zn(II) complexes were recorded in CDCl3 or DMSO-d6 on a Varian 300
NMR spectrometer. Thermal analyses were carried out on a TGS-I Perkin Elmer
thermobalance with the following operational characteristics: heating rate,
10◦ min−1; sample size, 2–10 mg; atmosphere, static air; crucible, platinum.
ACKNOWLEDGMENT
The authors thank Prof. Dr. T. D. Radhakrishnan Nair, Head of the De-
partment of Chemistry, Calicut University and the Heads, Regional Sophisticated
Instrumentation Centre, Central Drug Research Institute, Lucknow; Panjab Uni-
versity, Chandigarh and Regional Sophisticated Instrumentation Centre, Indian
Institute of Technology, Mumbai, for providing laboratory facilities. Thanks are
also due to the University Grant Commission, New Delhi for financial assistance.
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Received November 25, 1998
Accepted October 27, 2000
Referee I: G. L. Powell
Referee II: R. K. Musselman

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