Complexes of some 3d-metal salts with N,N-dimethylhydrazide of 4-nitrobenzoic acid

Article abstract of DOI:10.1023/B:RUCO.0000043902.12955.5e

The [M(HL)₂(H₂O)₂]X₂ complexes were synthesized (M = Mn(II), Co(II), Ni(II), Cu(II), Zn; X = CH ₃COO^-, Cl^-, BF₄^-) that incorporate bidentately coordinated molecules of N,N-dimethylhydrazide of 4-nitrobenzoic acid (HL). The latter molecules chelate the metal atom through the carbonyl O atom and the N atom of dimethylamino group. The square-planar complexes of Cu and Ni with deprotonated form of a ligand with composition ML₂ were also isolated. The synthesized complexes were studied by IR, electronic and EPR spectroscopies, and by cyclic voltammetry.

Full text of DOI:10.1023/B:RUCO.0000043902.12955.5e

Russian Journal of Coordination Chemistry, Vol. 30, No. 10, 2004, pp. 747–751. Translated from Koordinatsionnaya Khimiya, Vol. 30, No. 10, 2004, pp. 792–797.
Original Russian Text Copyright © 2004 by Zub, Bugaeva, Strizhakova, Maletin.
Complexes of Some 3d-Metal Salts with N,N-Dimethylhydrazide
of 4-Nitrobenzoic Acid
V. Ya. Zub*, P. V. Bugaeva*, N. G. Strizhakova**, and Yu. A. Maletin**
*Shevchenko National University, ul. Vladimirskaya 64, Kiev, 01033 Ukraine
**National Technical University, pr. Pobedy 37, Kiev, 03056 Ukraine
Received August 4, 2003
Abstract—The [M(HL)2(H2O)2]ï2 complexes were synthesized (M = Mn(II), Co(II), Ni(II), Cu(II), Zn; X =
CH3COO–, Cl–, BF–4 ) that incorporate bidentately coordinated molecules of N,N-dimethylhydrazide of
4-nitrobenzoic acid (HL). The latter molecules chelate the metal atom through the carbonyl O atom and the N
atom of dimethylamino group. The square-planar complexes of Cu and Ni with deprotonated form of a ligand
with composition åL2 were also isolated. The synthesized complexes were studied by IR, electronic and EPR
spectroscopies, and by cyclic voltammetry.
The problem of recovery of extremely toxic 1,1- can affect the prototropic conversions in hydrazides of
dimethylhydrazine stimulated an interest in the studies acids. The organic radicals that exhibit a strong nega-
of the processes that can be used to convert it into eco- tive induction effect bring about the redistribution of
logically friendly products. One of these processes con- electronic density in the hydrazide molecule:
sists in its transformation into hydrazides of carboxylic
O
acids and their metal complexes, which are well known
a
as the biologically active compounds [1, 2]. The coor-
dination chemistry of hydrazide complexes has been
considered in many publications, but the majority of
studies in this field deal with the unsubstituted
hydrazide complexes containing a terminal primary becomes ionized, which is necessary for the intermo-
amino group [3–8]. However, the derivatives of non- lecular tautomeric conversion [7].
asymmetric N,N-dimethylhydrazine as ligands in the
coordination compounds are poorly studied.
R
C–N–NH2
b
c
H
As the result, the mobile H atom of the NH group
In our further studies of complexation processes, we
synthesized N,N-dimethylhydrazide of 4-nitrobenzoic
Previously, we described the synthesis and study of acid (HL) containing organic radical with the negative
the metal complexes with N,N-dimethylhydrazides of induction effect.
2,4-dichlorophenoxyacetic and α-(2-methyl-4-chlo-
rophenoxy)propionic acids that have pronounced herbi-
cide properties. It was shown that in the reactions with
EXPERIMENTAL
the metal salts, these hydrazides form complexes only
with a neutral amide form of the ligand (I). As the result
of the steric effect of methyl groups at the donor N
atom, these complexes have rather low stability [9].
Attempts to produce stable complexes with the
deprotonated imido form (II) of these hydrazides by
increasing the solution pH led, as a rule, to the hydrol-
ysis of the metal salts.
N,N-dimethylhydrazide of 4-nitrobenzoic acid was
obtained by condensation of nonasymmetric dimethyl-
hydrazine with para-nitrobenzoyl chloride:
O
O2N
C
+ H2N–N(CH3)2
Cl
O
O2N
C
+ HCl
NH N(CH3)2
R–C=O
HN–NR2
(I)
R–C–O
N–NR2
MXn
M
For C9H11O3N3
anal. calcd. (%):
Found (%):
C, 51.67; N, 20.09; H, 5.26.
C, 51.25; N, 20.30; H, 5.00.
(II)
R = H, Alk; X = Hal–, NO–3, NCS–
The capability of hydrazides to give different com-
The 1H NMR spectrum of HL (δ, ppm): 2.59 (6H,
pounds is known to depend on many factors. An impor- −ëH3); 7.98 (2H, H1); 8.28 (2H, H2); 9.71 (1H, NH–),
tant role is played by the nature of organic radical R that mp 151–152°C.
1070-3284/04/3010-0747 © 2004 åÄIä “Nauka /Interperiodica”

748
ZUB et al.
Table 1. Results of elemental analysis of the synthesized hydrazide metal complexes
Content (found/calcd), %
N
Compound
Color
Yellow
M
Cl
[Mn(HL)2(H2O)2]Ac2
[Ni(HL)2(H2O)2]Ac2
[Ni(HL)2(H2O)2]Cl2
[Ni(HL)2(H2O)2](BF4)2
[Co(HL)2(H2O)2]Ac2
[Co(HL)2(H2O)2]Cl2
[Zn(HL)2(H2O)2]Ac2
[Zn(HL)2Cl2]
8.63/8.76
9.38/9.30
13.65/13.40
13.57/13.32
14.49/14.39
12.32/12.24
13.50/13.31
14.43/14.39
13.11/13.18
15.42/15.15
17.38/17.51
17.83/17.69
Green
Green
Light blue
Pink
10.10/10.05
8.67/8.55
12.30/12.14
9.27/9.33
Pink
10.17/10.09
10.13/10.25
11.67/11.79
13.11/13.24
12.15/12.36
12.03/12.13
12.60/12.78
White
White
Red
[CuL2]
[NiL2]
Yellow
The metal complexes were prepared by pouring liminarily dried in vacuum at 100°ë in order to remove
together the alcohol solution of hydrazide (2 mmol) and moisture, and then acetonitrile that was purified and
a hot alcohol (or water–alcohol) solution of a metal salt dried beforehand was added in a stream of argon. The
(1 mmol). The metal salts used included the chlorides, potential sweep was controlled with a PI 50.1 poten-
acetates, and tetrafluoroborates of Mn, Co, Ni, Cu, and tiostat, the current was measured with a high-resistance
Zn. The reaction mixture was heated at constant stirring V 7-45 voltmeter, and voltammograms were recorded
for 10 min on a water bath and was allowed to stand for on a XY Recorder A3.
a day. The obtained crystals were filtered off.
The composition and structure of the synthesized
RESULTS AND DISCUSSION
complexes with the HL derivatives were established by
Hydrazides dissociate according to the acid mecha-
nism as follows:
the chemical analysis (Table 1) and by the electronic,
IR, and EPR spectroscopies. The electronic absorption
and the diffuse reflection spectra were recorded on a
Specord M40 spectrophotometer in the range of 400–
900 nm. IR spectra were taken on a Specord M80 spec-
trophotometer in the range of 400–4000 cm–1 (with
KBr pellets). The EPR spectra were recorded on a mini
PS 100.X EPR spectrometer (ADANI) at 293 and 77 K
and 9480 MHz.
O
O–
+ H+.
R
R
NH N(CH3)2
N
N(CH3)2
The pH-metric study of this process for HL and for
the previously described hydrazides gave the following
values of dissociation constants
The acid–base equilibrium in the solutions of N,N-
dimethylhydrazides were studied by pH-metric titra-
tion using automated MOLSPIN titration system with a
combined glass–calomel microelectrode calibrated
against the HNO3 solutions at 25°ë. The concentration
of hydrazide was 3 × 10–3 mol/l. All calculations were
performed with SUPERQUAD program.
Electrochemical measurements were carried out
with a three-electrode cell with a platinum working
microelectrode (10 µM in diameter), a platinum plate
auxiliary electrode (with 1 cm2 surface area), and sil-
ver-chloride reference electrode connected to the solu-
tion under consideration through an electrolytic bridge
containing a supporting electrolyte. The ferroce-
nium/ferrocene (Fc+/Fc) redox couple (with the redox
potential 0.47 V relative to the reference electrode
used) served as an internal standard. All potentials pre-
sented below are given with respect to the Fc+/Fc couple.
Hydrazide
O NH N(CH3)2
pKa
Cl
Cl
12.58
Cl
O
12.60
O
NH N(CH3)2
O
O
12.29
11.7
C
O
NH N(CH3)2
O
C
O2N
(HL)
NH N(CH3)2
A solution of tetraethylammonium tetrafluoroborate
in acetonitrile (with the salt concentrationa 0.1 mol/l)
The comparison of the obtained values shows that
was used as a supporting electrolyte. The salt was pre- hydrazide of 4-nitrobenzoic acid has the lowest K‡
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 30 No. 10 2004

COMPLEXES OF SOME 3d-METAL SALTS
749
Transmittance
value and is therefore expected to form most readily the
complexes with deprotonated imido form of a ligand.
Indeed, the reactions of Cu and Ni acetates with the
given hydrazide in water–alcohol solutions yield,
respectively, red and yellow complexes, whose analysis
indicates the formation of neutral ML2 complexes
(Table 1).
c
In IR spectra of åL2, the bands due to the stretching
vibrations ν(Nç) and ν(ë=é) typical of a free ligand
are lacking, but the bands from the ν(ë–é) and ν(ë=N)
vibrations appear at 1340 and 1560 cm–1, respectively,
which suggests the formation of complexes with the
deprotonated imido form of the ligand (Fig. 1b).
b
a
The nickel complex NiL2 is diamagnetic, which
confirms its square-planar structure. The diffuse reflec-
tion spectrum of this complex contains one band at
455 nm, while that of CuL2 has two resolved bands at
450 and 550 nm, which is typical of the square-planar
Cu(II) complexes. Both complexes are poorly soluble
in water, alcohols, and in the most of organic solvents.
3600 3200 2800 1800 1500 1200 900 700 600
ν, cm–1
Fig. 1. IR spectra of (a) N,N-dimethylhydrazide of 4-
nitrobenzoic acid (HL), (b) CuL , and (c) Ni(HL) (BF )
2
2
4 2
In the case of Cu, the imido complexes are formed
even in the acidic solutions, when the salts of the strong
acids (sulfates, chlorides, etc.) are used in the synthesis:
complexes.
The diffuse reflection spectra of the Co complexes
contain one band in the region of 550 nm, while those
of the Ni acetate complex with a neutral form of the
CuSO4 + 2HL = CuL2 + H2SO4.
This makes it possible to conclude that the metal
ions shift the equilibrium toward the formation of the
imido form. This occurs due to the fact that the neutral
åL2 complexes, particularly those of copper and
nickel, have significantly higher stability constants, as
compared to the å(HL)2X2 complexes (where X is an
anion of monobasic acid). However, in the case of
another metals, such as Mn, Co, Zn, no imido com-
plexes were produced by monitoring pH of the solu-
tions, since their synthesis was complicated by the
hydrolysis of the metal salts, whereas in the case with
Co, the oxidation of Co2+ to Co3+ was also observed
with the typical electronic absorption spectrum. There-
fore, these metals gave only complexes with neutral
hydrazide molecules. The results of the chemical anal-
ysis of the synthesized complexes are presented in
Table 1.
3
ligand exhibit the resolved bands due to the A2g
3T1g(P) transition (near 370 nm) and the A2g
3
3T1g(F) transition (near 640 nm) of the Ni2+ cation in the
distorted octahedral surrounding.
When the [Co(HL)2(H2O)2]Cl2 complex is dissolved
in an alcohol, the solution color changes from pink to
violet, while the electronic absorption spectrum of the
solution contains the bands due to the octahedral and
tetrahedral forms of the complex. In order to establish
the changes in the composition and structure of the
complex that occur during its dissolution and to deter-
mine the composition of the complexes in the solution,
we performed spectrophotometric study of the com-
plexation processes in the CoCl2–HL–isopropanol and
NiCl2–HL–isopropanol systems.
The composition of the complexes was determined
by the molar ratio method with the hydrated metal chlo-
rides used as the starting compounds. A series of solu-
tions was prepared with a constant metal concentration
and a variable ligand concentration (from zero to a five-
fold excess of L with respect to the metal ions).
Table 2 contains the main vibration frequencies for
the metal hydrazide complexes of amide type that allow
one to determine the coordination mode for the
hydrazide ligands [7–9]. IR spectra of the complexes
contain the absorption band due to the stretching vibra-
tions ν(ë=é) at 1630–1650 cm–1 (amide I band), the
absorption bands from the stretching vibrations ν(Nç)
As a result of dissolution of the starting CoCl2 in iso-
in the region of 3200 cm–1, and an intense band typical propanol, Co(II) has the coordination surrounding in
of hydrazides of acids (amide II band) in the range of the form of a distorted tetrahedron (λ = 653 nm). The
1530–1540 cm–1, which is a combined stretching- complex formation proceeds in steps, which is con-
deformation vibration with a considerable contribution firmed by the absence of the isosbestic point (Fig. 2a).
of the stretching vibrations ν(ë–N). In addition, in this The oxidation state of Co remains unchanged during
spectrum, one can identify the bands that correspond to complex formation. It was found that the addition of the
the nitro group vibrations: νas(Né2) at 1520 cm–1 and first hydrazide molecule to the Co2+ ion in a solution
νs(Né2) at ~1350 cm–1.
gives the tetrahedral complex [Co(HL)Cl2]. When the
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 30 No. 10 2004

750
ZUB et al.
D
D
0.7
0.6
0.5
0.4
(a)
0.5
(a)
1
2
0.4
0.3
0.2
0.1
3
0.3
0.2
4
5
0.1
0
0
1
2
3
4
5
6
6
c
HL/cCo
25 24 23 22 21 20 19 18 17 16 15 14 13
∆D
0.08
∆D
0.30
0.25
0.20
0.15
(b)
0.07
(b)
5
0.06
0.05
0.04
4
3
2
0.03
0.02
0.01
0.10
0.05
0
1
30 28 26 24 22 20 18 16 14 12
0
1
2
3
4
5
ν, cm–1 × 103
cHL/cNi
Fig. 2. The electronic absorption spectra of solutions con-
taining (a) CoCl (c = 0.01 mol/l) and HL (c = (1) 0, (2)
Fig. 3. The plot of optical density vs. the ratio of the com-
2
å
HL
ponent concentrations in the MCl –HL–isopropanol sys-
0.01, (3) 0.015, (4) 0.02, (5) 0.05 mol/l; (b) NiCl (c
=
2
2
å
tems at (a) λ
M = Ni.
= 654 nm, M = Co and (b) λ
= 668 nm,
0.01 mol/l) and HL (c = (1) 0.005, (2) 0.01, (3) 0.015, (4)
max
max
HL
0.02, (5) 0.04 mol/l).
were insignificant, we recorded the differential absorp-
tion spectra of this system (Fig. 2b). For this reason, the
spectrophotometric cell was filled not with a solvent but
with the initial solution of nickel chloride in isopro-
panol. The composition of the complexes was found
from the relationship between the change in the optical
density (∆D) at λ = 668 nm and the ratio cHL : cM. It was
shown that, as in the case with Co, only the complexes
with the ratio Ni : HL = 1 : 2 are formed in the solution
(Fig. 3b), as distinct from the Ni complexes with the
unsubstituted hydrazides, which give complexes with
three bidentate ligand molecules. This distinctive fea-
ture of hydrazide complexes, i.e., the 1,1-dimethylhy-
drazine derivatives, is explained by the steric effect of
two methyl groups at the donor nitrogen atom.
second hydrazide molecule is added, the geometry of
the Co surrounding changes to the distorted octahedron
(λ = 540 nm), which can be explained by the formation
of the [Co(HL)2(H2O)2]2+ complex.
One can see from Fig. 3a that even with a fivefold
ligand excess, the complex formed in the system has the
ratio Co : HL = 1 : 2. The results obtained make it pos-
sible to conclude that the change in the electronic
absorption spectrum of crystalline Co chloride complex
Co(HL)2Cl2(H2O)2 on dissolution occurs due to its par-
tial dissociation with the formation of tetrahedral com-
plex containing one molecule of hydrazide ligand. The
specific behavior of the chloride complex is explained
by a sufficiently high coordinating ability of the chlo-
ride anion. The dissolution of the Co2+ acetate complex
does not bring about any noticeable changes in the elec-
tronic absorption spectrum.
The cyclic voltammogram of HL contains in the
anode region the oxidation wave, whose half-wave
Since the spectral changes for the NiCl2–HL–iso- potential is E1/2 = 0.57 V. The slope of this wave ∆E =
propanol system as distinct from the system with Co2+, E3/4 – E1/4 equal to 110 mV and the lacking wave of
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 30 No. 10 2004

COMPLEXES OF SOME 3d-METAL SALTS
751
Table 2. Selected vibration frequencies (cm–1) in IR spectra of the synthesized metal complexes with N,N-dimethylhy-
drazide of 4-nitrobenzoic acid
Compound
ν(NH) Amide I, ν(C=O) Amide II, ν(C–N) ν(NN), ν(HNN) ν(MO), ν(MN) Anion band
HL
3200
3200
1655
1637
1530
1545
1168
1190
[Mn(HL)2(H2O)2]Ac2
475, 550
480, 555
1580 (Ac–)
1410
[Ni(HL)2(H2O)2]Ac2
3190
1630
1545
1195
1590 (Ac–)
1410
1080 (BF4– )
[Ni(HL)2(H2O)2](BF4)2
3190
1628
1540
1190
480, 560
[Ni(HL)2(H2O)2]Cl2
[Co(HL)2(H2O)2]Ac2
3190
3190
1632
1635
1540
1540
1200
1190
475, 565
475, 570
1595 (Ac–)
1415
[Co(HL)2(H2O)2]Cl2
[Zn(HL)2(H2O)2]Ac2
3185
3195
1640
1645
1530
1528
1190
1192
475, 560
470, 555
1580 (Ac–)
1410
reduction at the reverse potential sweep suggest that complexes with the deprotonated form of a ligand.
this oxidation is the electrochemically irreversible pro- Unlike complexes with a neutral form of a ligand, the
cess followed by the chemical stage of decomposition synthesized complexes are stable with respect to water
of the oxidation product. Since this wave is also and common organic solvents and have the higher
observed for the other investigated hydrazides, it can be redox stability.
assigned to the oxidation of the –NH–N(CH3)2 group.
During complexation, this oxidation wave shifts to the
anode region, while in the case of the Ni and Co salts,
REFERENCES
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2. Grekov, A.P. and Veselov, V.Ya., Fizicheskaya khimiya
gidrazina (Physical Chemistry of Hydrazine), Kiev:
Naukova Dumka, 1979.
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study. This can indicate the structural changes in
hydrazide, in particular, the transformation of the
ligand to the imido form, which contains no groups that
can be oxidized.
The cathode region of voltammograms of these
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the NO2 group with the slope of ≈60 mV, which points
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during complexation and hence, by an increase in
hydrazide stability toward the reduction processes.
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RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 30 No. 10 2004