Synthesis, characterization and quantum chemical studies of some Co(II) and Cu(II) complexes of acetoacetic acid hydrazide

Article abstract of DOI:10.14233/ajchem.2013.14669

New complexes of cobalt(II) and copper(II) acetoacetic acid hydrazides have been synthesized and characterized by elemental analysis, infrared and electronic reflectance spectra and room temperature magnetic susceptibility measurements. The infrared spectra of the complexes revealed the coordination to the metal ion occurs at the carbonyl oxygen and the amino nitrogen of the hydrazide moiety. This was supported by theoretical calculations. The conjoint of the electronic spectra and magnetic susceptibility measurements suggests plausible octahedral geometry for the cobalt(II) complexes while the copper(II) complexes adopt a square planar geometry. The stereochemistry of the modeled structures calculated by semi-empirical (PM³) and density functional theory (DFT) methods are also consistent with those experimentally deduced.

Full text of DOI:10.14233/ajchem.2013.14669

Asian Journal of Chemistry; Vol. 25, No. 13 (2013), 7371-7376
http://dx.doi.org/10.14233/ajchem.2013.14669
Synthesis, Characterization and Quantum Chemical Studies of
Some Co(II) and Cu(II) Complexes of Acetoacetic Acid Hydrazide
*
F.A.O. ADEKUNLE , B. SEMIRE and O.A. ODUNOLA
Department of Pure and Applied Chemistry, Ladoke Akintola University of Technology, Ogbomoso, Nigeria
*Corresponding author: Tel: +234 8035821847; E-mail: fnnmy2001@yahoo.com
(Received: 11 October 2012;
Accepted: 28 June 2013)
AJC-13710
New complexes of cobalt(II) and copper(II) acetoacetic acid hydrazides have been synthesized and characterized by elemental analysis,
infrared and electronic reflectance spectra and room temperature magnetic susceptibility measurements. The infrared spectra of the
complexes revealed the coordination to the metal ion occurs at the carbonyl oxygen and the amino nitrogen of the hydrazide moiety. This
was supported by theoretical calculations. The conjoint of the electronic spectra and magnetic susceptibility measurements suggests
plausible octahedral geometry for the cobalt(II) complexes while the copper(II) complexes adopt a square planar geometry. The
stereochemistry of the modeled structures calculated by semi-empirical (PM3) and density functional theory (DFT) methods are also
consistent with those experimentally deduced.
Key Words: Synthesis, Infrared, Hydrazides, DFT, Electronic spectra.
Preparation of acetoacetic acid hydrazide: Ethylaceto
acetate (51 mL, 0.04 mol) was added dropwisely to hydrazine
hydrate (19.4 mL 0.04 mol) in quick fit conical flask fitted
with a reflux condenser. The orange coloured suspension
obtained was refluxed for 15 min and on addition of 170 mL
of ethanol a clear yellow solution was obtained. The resultant
solution was refluxed for an additional 4 h after which the
ethanol was distilled off. The remaining solution was trans-
ferred to a 250 mL beaker and left overnight at room temperature.
The precipitate was filtered by suction, washed with deionized
water and dried in a desiccator over calcium chloride (yield
17.2 g; 63 %).
Synthesis of [Cu(AAAH)2](OAc)2: Acetoacetic acid
hydrazide (3.48 g, 0.003 mol) dissolved in 10 mL methanol
was added dropwisely to Cu(OAc)2·4H2O (2.99 g, 0.0015 mol)
dissolved in methanol (30 mL, 40 %) with stirring on a magnetic
stirrer.Ammonia was added to raise the pH to 9 to aid precipi-
tation. The resulting mixture was left to stir for 1 h after which
it was filtered by suction, washed with 40 % methanol and
deionized water and dried over calcium chloride (yield 3.4 g
55 %). The other complexes of Co(II) and Cu(II) were similarly
prepared.
INTRODUCTION
Transition metal complexes of hydrazides have been
intensely investigated by coordination chemists because of
their interesting structural properties and their wide ranging
applications1-5. Aliphatic carboxylic acid hydrazides among
many other uses are employed as metal ion removal from waste
waters6, aromatic hydrazides are used as stabilizers for rigid
PVC against therm-oxidative degradation7. Hydrazides are also
used for the extraction of non-ferrous metals and rare earth
from aqueous solutions8-10,11. The coordinating ability of
hydrazides to a variety of elements particularly transition
metals afford the study of the metals in such systems.
In continuation of our studies on alkyl acetoacetate
hydrazides12,13 we present the results of our investigations on
the synthesis, spectral and the theoretical studies of Co(II) and
Cu(II) complexes of acetoacetic acid hydrazide. The complexes
are new and represent the first systematic study of acetoacetic
acid hydrazide series.
EXPERIMENTAL
Reagents grade cobalt(II) acetate tetrahydrate, cobalt(II)
chloride hexahydrate, cobalt(II) sulphate heptahydrate,
copper(II) acetate monohydrate, copper(II) chloride dihydrate,
copper(II) sulphate pentahydrate, copper(II) nitrate penta-
hydrate, ethylacetoacetate, hydrazine hydrate, methanol were
available from BDH.
Physical measurements: Microanalysis for carbon,
hydrogen and nitrogen for the ligand and complexes were
determined using a Perkin-Elmer 240C elemental analyzer.
The percentage metal was determined using complexometric
method14. Infrared spectra were recorded on a Nicolet Avatar

7372 Adekunle et al.
Asian J. Chem.
330 FT-IR spectrophotometer in nujol. Electronic reflectance
spectra of the ligand and complexes in nujol were recorded
using Genesys 10 scanning spectrophotometer (Thermo Electron
Corporation).
The reaction of the metal salts and the ligand to form
complexes can be represented as:
MX2·xH2O + 2CH3COCH2CONHNH2 → M[CH3COCH2-
CONHNH2]2 + xH2O
Computational details: The Co(II) and Cu(II) complexes
were modeled based on the spectroscopic interpretations which
involved the O2 and N2 atoms (Fig. 1) forming coordinate
bonds with metal ions using Spartan program (Spartan 06)
implemented on an Intel Pentium M 2.0 GHz computer. Other
possibilities involving O1 and N2 in ligand-metal bonds were
considered. Three copper(II) complex ions and two cobalt(II)
complex ions were modeled to determine their thermodynamic
stability as shown in Fig. 1. The optimization and frequency
calculation of both the Cu(II) complexes and Co(II) complexes
were performed using both semi-empirical method (PM3) and
DFT (B3LYP/6-31G*) DFT levels of calculations based on
the preliminary stability study. Semi-emperical method (PM3)
was considered along with DFT since PM3 have been success-
fully used either alone or with other theoretical methods for
structural analysis of Cu(II) complexes15-20. Density functional
theory (DFT) calculations were performed with the hybrid B3LYP
exchange and correlation functional21,22 and 6-31G(d) basis set.
All calculations carried out both at PM3 and DFT levels are
without symmetry restriction.
M = Co
MX2·xH2O + 2CH3COCH2CONHNH2 → M[CH3COCH2-
CONHNH2]2 + xH2O
M = Cu
The analytical data for the ligand and complexes are
presented in Table-1. The complexes were obtained in different
shades of colours ranging from purple to green. The complexes
obtained as solids display very poor solubility in protic and
non-coordinating solvents; hence the single crystals X-ray
diffraction studies of any of the compounds could not be studied.
Infrared spectra of ligand and complexes: The infrared
spectra bands (Table-2) were assigned by critically comparing
the spectra of the free ligand with those of the complexes.
There are three major vibrations that have been used success-
fully to infer coordination of ligands to the metal in the spectra
of complexes of hydrazides. These are the carbonyl stretching
frequency [νs(C=O)] or the 'amide 1', the in-plane bending
deformation and stretching frequency for cyanate [δ(N-H) +
νs(C-N)] or the 'amide II' and the amino stretching vibrations
νs(NH2). In the spectra of the acetoacetic acid hydrazide the
absorption band observed at 1612 cm-1 is assigned to the
ν(C=O), the carbonyl stretching mode called "amide 1". The
band was also observed at 1614 and 1704 cm-1 from DFT and
PM3 quantum mechanical calculations. These vibrations
experienced a bathochromic shift on coordination to the Co(II)
metal to 1570-1566 cm-1. In the modeled Cobalt(II) complex
ion the 'amide 1' band was observed between 1672-1600 and
1598-1552 cm-1 for PM3 and DFT calculations, respectively.
The similar band for the Cu(II) complexes were experimentally
observed between 1566-1563 cm-1; 1645-1642 cm-1 for PM3
and 1584-1545 cm-1 for DFT calculations.
Ligand
A
The "amide II" band was observed at 1544 cm-1 in the
acetoacetic hydrazide ligand. This band was found at 1620
cm-1 for PM3 and 1540 cm-1 for DFT calculations, respectively.
This band also experienced bathochromic shift on coordination
to the metal between 1556-1507 and 1542-1507 cm-1 for the
Co(II) and Cu(II) complexes studied, respectively23-26. The
calculated 'amide II' for both the Co(II) and Cu(II) complexes
were at 1608-1598 cm-1 for PM3 and 1535-1525 cm-1 for DFT,
respectively.
B
C
This ν(N-H) stretching frequency of the amino observed
at 3539 cm-1 on coordination was lowered to between 3345-
3199 cm-1 for the Co(II) complexes while for the Cu(II)
complexes the bands were observed between 3357-3278 cm-1.
The observed values are consistent with previous studies23-26
.
D
E
Fig. 1. Optimized structures of the ligand and complex ions: (A) = Cu(II)
complex ion (square planar), (B) = Cu(II) complex ion (trans-), (C)
= Cu(II) complex ion (cis-), (D) = Co(II) complex ion (octahedral)
and (E) = Co(II) complex ion (bend octahedral)
The calculated values of ν(N-H) for the Co(II) and Cu(II) co
mplexes appear at 3383-3196 and 3427-3264 cm-1 for PM3
and 3456-3257 and 3498-3321 cm-1 for DFT, respectively.
Although the vibrational frequencies calculated at DFT are
closer to the experimentally determined values especially for
amide I and amide II, the PM3 calculated IR followed quanti-
tatively the same trend as the experimentally observed ones
(Table-2). In addition, only the IR data calculated for Cu(II)
and Co(II) complex ions involving the O2 and N2 atoms of
RESULTS AND DISCUSSION
The formation of acetoacetic acid hydrazide proceeded gene-
rally in appreciable yields as shown in the following equations:
CH3COCH2COOR' + H2NNH2 → CH3COCH2CONHNH2
+ R'OH

Vol. 25, No. 13 (2013)
Compound
Synthesis, Characterization and Quantum Chemical Studies of Some Co(II) and Cu(II) Complexes 7373
TABLE-1
ANALYTICAL DATA OF LIGAND AND Co(II) AND Cu(II) COMPLEXES
Metal observed (calcd.) (%)
Yield
(%)
Colour
µeff (BM)
m.p. (ºC)
M
C
H
N
AAAH
White
Purple
Purple
Purple
Purple
63
61
76
60
60
55
75
68
53
–
217-219
194
162
192
210
146
154
142
178
–
41.22 (41.37)
36.42 (36.58)
30.62 (30.13)
28.88 (28.63)
27.33 (27.13)
34.62 (34.83)
26.49 (26.20)
24.23 (24.53)
22.69 (22.89)
6.86 (6.94)
5.68 (5.76)
4.89 (5.06)
4.80 (4.81)
4.55 (4.55)
4.57 (5.36)
4.69 (4.40)
4.28 (4.12)
3.74 (3.84)
23.68 (24.13)
16.22 (16.00)
17.55 (17.57)
16.50 (16.70)
21.00 (21.09)
13.65 (13.54)
15.41 (15.28)
13.95 (14.30)
20.00 (20.02)
Co[AAAH]3(OAc)2
Co[AAAH]3Cl2
Co[AAAH]3SO4
Co[AAAH]3(NO3)2
5.24
5.23
5.17
5.54
1.54
1.76
1.79
1.77
11.07 (11.22)
12.39 (12.32)
11.37 (11.71)
11.05 (11.09)
15.00 (15.35)
17.61 (17.32)
15.93 (16.22)
15.33 (15.14)
Cu[AAAH]2(OAc)2 Dirty-green
Cu[AAAH]2Cl2
Cu[AAAH]2SO4
Cu[AAAH]2(NO3)2
Dirty-green
Dirty-green
Dirty-green
TABLE-2
RELEVANT EXPERIMENTAL AND CALCULATED INFRARED SPECTRAL
BANDS (cm–1) OF LIGAND AND Co(II) AND Cu(II) COMPLEXES (cm-1)
Compound
Amide I
Amide II
ν(N-H)
ν(C=O)
ν(C-H)
AAAH
1612(m)
1570(s)
1570(s)
1544(w)
1514(w)
1514(w)
1556(w)
1507(w)
1542(s)
1542(w)
–
3539(w)
3333(w)
3290(w)
3199(w)
3345(w)
3247(m)
3357(w)
3278(w)
3345(w)
1782(m)
1724(s)
1708(m)
1712(s)
1700(s)
1697(m)
1731(m)
1703(m)
1700(w)
1964
2939(w)
2913(w)
2919(w)
2925(w)
2900(w)
2913(w)
2913(w)
2960(w)
–
Co(AAAH)3Cl2
Co(AAAH)3(OAc)2
Co(AAAH)3SO4
Co(AAAH)3(NO3)2
Cu(AAAH)2Cl2
Cu(AAAH)2(OAc)2
Cu(AAAH)2SO4
Cu(AAAH)2(NO3)2
1570(s)
1566(m)
1563(m)
1563(m)
1563(m)
1566(m)
1704
1507(m)
1620
1540
PM3
DFT
PM3
3385, 3350, 3350
3467, 3365, 3235
3089, 3080, 2944
3256, 3167, 3051
AAAH
1614
1672, 1610, 1600
1778
1608, 1601, 1598
3383, 3377, 3326, 3312, 1960, 1939, 1931 3063, 3013, 3008, 2933,
Co(AAAH)32+
3196
2931
DFT
PM3
1598, 1557, 1552
1642, 1645
1535, 1532, 1525
1586, 1508
3456, 3426, 3367, 3257
3427, 3422, 3264
1742, 1740, 1732
1959, 1932
3256, 3241, 3172, 2998
3070, 3069, 3065, 2913,
2964, 2913
Cu(AAAH)22+
DFT
1584, 1560
1532, 1523
3498, 3364, 3321
1739, 1736
3257, 3232, 2968, 2962
the ligand formed coordinate bonds with the metal ions (i.e.,
complexA and complex D) which, are also in agreement with
the experimental observations.
The structural parameters calculated at semi-empirical
(PM3) were quite different from those obtained at DFT. For
instance, Cu-O1 (Cu-N1) bond lengths are 1.830 Å (1.847 Å)
and 1.842 Å (1.845 Å) for PM3 and DFT, respectively. The
Co-O1 (Co-N1) bond lengths are 1.915 Å (1.926 Å) and 1.860
Å (1.857 Å) for PM3 and DFT, respectively. Also, the bond
angles calculated at PM3 are slightly different from those
calculated at DFT level (Table-4). Generally, both PM3 and
DFT methods showed that M-O and M-N calculated for Cu(II)
complex ion are shorter than that of Co(II) complex ion. How-
ever, based on the infrared data that showed close correlation
between experimentally observed values and DFT calculations,
the structural data calculated at DFT are expected to be closer
to the experimental values than that of PM3.
Structural features: The formation of both Cu(II) and
Co(II) complex ions involving the O2 and N2 atoms of the
ligand are thermodynamically and energetically favoured in
forming coordinate bonds with the metal ions (i.e., complexes
A and D) over those involving O1 and N2 atoms of the ligand
(i.e., complexes B, C and E) as shown in Table-3. This is also
in agreement with the experimentally predicted structures from
spectroscopic data. Therefore, the selected geometric para-
meters of the most thermodynamically stable Cu(II) and Co(II)
complex ions calculated at both semi-empirical (PM3) and
DFT levels are displayed in Table-4.
TABLE-3
CALCULATED RELATIVE ENERGIES (REL. E), HOMO, LUMO AND DIPOLE
MOMENT AT SEMI-EMPIRICAL (PM3) AND B3LYP/6-31G* LEVELS
Cu(II) complex ions
Trans
Co(II) complex ions
Sq-planar
0.00 (0.00)*
-12.80 (-16.06)
-7.57 (-9.13)
5.23 (6.93)
Cis
Nor. Octah.
0.00 (0.00)
Bend Octah.
179.02 (270.77)
-12.53 (-15.06)
-7.56 (-9.76)
4.97 (5.30)
Rel. E
H (eV)
L (eV)
122.06 (165.54)
-12.82 (-16.10)
-7.68 (-9.53)
5.14 (6.57)
87.34 (114.20)
-12.31 (-16.82)
-7.09 (-8.83)
5.22 (7.99)
-12.46 (-15.98)
-7.44 (-9.58)
5.02 (6.40)
∆(H-L) eV
D.M (debye)
3.54 (4.98)
6.67 (9.24)
3.21 (3.65)
3.55 (4.97)
7.32 (10.19)
*PM3 values in bracket. Relative energies (Rel. E), HOMO (H), LUMO (L) and dipole moment (DM).

7374 Adekunle et al.
Asian J. Chem.
TABLE-4
SELECTED GEOMETRICAL PARAMETERS OF MOST STABLE Cu(II)
AND Co(II) COMPLEX IONS CALCULATED AT PM3 AND B3LYP/6-31G* LEVELS
Cu(II) complex ion
Co(II) complex ion
Bond length (Å)
Cu-O1
PM3
1.830
1.851
1.847
1.840
DFT
1.842
1.855
1.845
1.843
Bond length (Å)
Co-O1
PM3
1.915
1.922
1.917
1.860
1.852
1.820
DFT
1.926
1.967
1.922
1.857
1.865
1.821
Cu-O2
Cu-N1
Cu-N2
Co-O2
Co-O3
Co-N1
Co-N2
Bond angle (Å)
175.75
89.84
O1-Cu-O2
O1-Cu-N1
O1-Cu-N2
O2-Cu-N1
O2-Cu-N2
176.80
86.07
92.34
90.89
89.65
Co-N3
Bond angle (Å)
88.09
90.88
91.22
88.50
173.91
O1-Co-O2
O1-Co-O3
O1-Co-N1
O1-Co-N2
O1-Co-N3
O2-Co-N1
O2-Co-N2
O2-Co-N3
O3-Co-N1
O3-Co-N2
O3-Co-N3
N1-Co-N2
N1-Co-N3
N2-Co-N3
89.98
177.35
87.05
89.22
92.95
86.11
82.90
177.66
91.26
90.65
89.03
170.42
92.09
100.22
179.66
86.97
88.08
93.27
83.78
83.56
178.47
93.14
91.74
87.04
N1-Cu-N2
172.87
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
166.55
95.59
97.70
The Frontier molecular orbitals for the complex (A) and
(D) computed at the DFT level are shown in Fig. 2. The HOMO
and the LUMO of Cu(AAAH)22+ ion are mainly localized on
carbonyl and amide II regions of the ligand, respectively, while
both the HOMO and LUMO of the Co(AAAH)32+ ion localized
around the central metal ions (Fig. 2). The Mulliken atomic
charges for copper, cobalt, oxygen and nitrogen atoms are
displayed in Table-5. The Mulliken charges of copper and
cobalt atoms are -0.429 and -0.226, respectively. In both
2+
2+
Cu(AAAH)2 and Co(AAAH)3 ions, lower values of
Mulliken charges on nitrogen and oxygen atoms that are
directly bonded to the central metal ion was observed. This
was an evident that charges are transferred from ligand to the
central metal ion during complex formation.
HOMO
HOMO
LUMO
(D)
Fig. 2. Frontier molecular orbital: HOMO and LUMO of the Cu(AAAH)22+
LUMO
(A)
(A) and Co(AAAH)32+ (D) ions

Vol. 25, No. 13 (2013)
Synthesis, Characterization and Quantum Chemical Studies of Some Co(II) and Cu(II) Complexes 7375
TABLE-5
observed magnetic moments around 4.8-5.2 BM at room
temperature29, which favourably compare with those of the
acetoacetate complexes studied. The copper(II) complexes
display the effective magnetic moments (µeff) in the range 1.76-
1.79 BM except Cu[AAAH]2(OAc)2 with 1.54 BM. Most of
the copper(II) complexes agrees with the spin-only value (µs.o)
of 1.73 BM. In the Cu[AAAH]2(OAc)2 complex, a reduction
in the (µeff) to 1.54 BM from the spin-only value of 1.73 BM
observed can be attributed to strong Cu-Cu interactions in the
crystal lattice of the compound29.
MULLIKEN CHARGES OF THE COMPLEX A AND D IONS
Atom
Complex A
Complex D
N1
*N2
N3
*N4
N5
*N6
*O1
*O2
*O3
a O4
aO5
aO6
M
0.246
0.029
0240
0.150
–
0.024
0.156
0.146
0.042
0.171
0.131
-0.235
-0.257
-0.139
-0.385
-0.310
-0.345
-0.226
–
-0.004
-0.069
–
-0.348
-0.371
–
The experimental data thus obtained are consistent with
the following structures of the complexes (Fig. 3).
-0.429
*Atoms bonded to metal ion, acarbonyl oxygen atom.
N
O
O
N
O
Co
Electronic spectra: The electronic reflectance spectra of
the ligand and complexes are presented in Table-6. In the
ultraviolet spectra of the acetoacetic acid hydrazide, the n→π*
transition observed at 51,282 cm-1 attributed to the excitation
of a nitrogen lone pair of electron to the antibonding σ*
orbital of the amino group was shifted to 48,077-51,020 cm-1
in the spectra of the complexes. The π→π* transition in the
carbonyl group observed at 37,175 cm-1 in the ligand also
experienced bathochromic shifts to ca. 36,496 cm-1 upon comp-
lexation in all the compounds. An additional band observed
in the ultraviolet spectra of the complexes between 31,646-
33,223 cm-1 was attributed to π→π* transition. The charge
transfer transitions were observed at 23,256-29,497 cm-1 in
Cu
N
N
O
O
N
= CH3COCH2CONHNH2; X = CH3COO, Cl2, NO3 or 0.5SO4
Fig. 3. Suggested structures for the complexes
Conclusion
The elemental and spectroscopic studies revealed that the
cobalt(II) ions are in an octahedral environment while the
copper(II) metal complexes adopt a square planar geometry.
This is further supported by the room temperature magnetic
susceptibility measurements and the quantum chemical studies
employed using semi-empirical PM3 and density functional
theory (DFT) methods. The DFT method appears to compare
favourably well with spectra interpretations obtained from the
experimental work while the PM3 though slightly different
also point to the same trend observed with DFT in both the
spectral and structural features obtained.
the complexes12,13,23-26
.
In the visible spectra of octahedral cobalt(II) complexes,
three electronic transitions; 4T1g → 4T2g, 4T1g → 4A2g and 4T1g
→ 4T1g(P) which is represented by ν1, ν2 and ν3, respectively27.
The experimentally observed transitions are Co[AAAH]3(OAc)2
with transitions at 9,434 and 20,284 cm-1 was assigned to 4T1g
→ 4T2g and 4T1g → 4T1g(P), respectively. The Co[AAAH]3Cl2,
Co[AAAH]3(NO3)2 and Co[AAAH]3SO4 complexes had only
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TABLE-6
ELECTRONIC SPECTRAL TRANSITIONS FOR THE LIGAND AND COMPLEXES (cm-1)
Compound
d-d
CT
Intra ligand transitions
AAAH
Co(AAAH)3(OAc)2
Co(AAAH)3Cl2
–
20,284; 9,434
17,241
–
51,282; 37,175
50,251; 47,393; 36,496; 31,646
–
29,497; 27,855
–
Co(AAAH)3SO4
Co(AAAH)3(NO3)2
Cu(AAAH)2(OAc)2
Cu(AAAH)2Cl2
Cu(AAAH)2SO4
Cu(AAAH)2(NO3)2
20,408
18,767
15,060
13,699
14,286
16,155
–
51,020; 47,393; 31,646
48,077; 45,455; 31,646
48,077; 38,168; 36,496
–
28,653
–
–
–
–
23,256
50,251; 36,496; 33,223

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