Coordination compounds of 3d-metal phthalates with semicarbazide

Article abstract of DOI:10.1134/S1070363211030108

Complexes of cobalt(II), nickel(II), copper(II), and zinc phthalates with semicarbazide were synthesized. The obtained compounds were characterized by the methods of chemical analysis, IR spectroscopy, diffusion reflection spectroscopy, and thermogravimetry.

Full text of DOI:10.1134/S1070363211030108

ISSN 1070-3632, Russian Journal of General Chemistry, 2011, Vol. 81, No. 3, pp. 503–508. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © T.V. Koksharova, I.S. Gritsenko, 2011, published in Zhurnal Obshchei Khimii, 2011, Vol. 81, No. 3, pp. 407–412.
Coordination Compounds of 3d-Metal Phthalates
with Semicarbazide
T. V. Koksharova and I. S. Gritsenko
Mechnikov National University, ul. Dvoryanskaya 2, Odessa, 65026 Ukraine
e-mail: koksharova@farlep.net
Received May 21, 2009
Abstract—Complexes of cobalt(II), nickel(II), copper(II), and zinc phthalates with semicarbazide were
synthesized. The obtained compounds were characterized by the methods of chemical analysis, IR spec-
troscopy, diffusion reflection spectroscopy, and thermogravimetry.
DOI: 10.1134/S1070363211030108
Coordination compounds containing residues of
phthalic acid H2Pht are interesting from both theo-
retical and practical points of view. They are capable
to catalyze various reactions, whereas non-coordinated
carboxy group residues Pht2– and HPht– can be
important in various catalytic processes [1]. Earlier we
have prepared coordination compounds of phthalates
of 3d-metals with nicotinamide and have determined
structures of copper and cobalt compounds by the
XRD method [2, 3]. The copper(II) phthalate com-
plex with nicotinamide (NA) has the composition
[Cu(NA)2Pht(H2O)]·0.5H2O, the phthalate anion being
a bridging ligand. The composition of the cobalt(II)
phthalate coordination compound with nicotinamide
corresponds to the formula [Co(NA)2(H2O)4]Pht·2H2O,
the phthalate anion being in the outer sphere.
anions are present into the inner sphere, and in the blue
complex, in the outer sphere. In the 1:3 complex the
bond isomerism is added to the ionization isomerism:
in the pink isomer only bidentate semicarbazide
molecules enter into the inner sphere, whereas in the
blue isomer a tetrahedral coordination unit is formed
by three monodentate semicarbazides and one mono-
dentate benzoate anion [4].
The aim of the present work was to isolate products
of reactions of cobalt(II), nickel(II), copper(II), and
zinc(II) phthalates with semicarbazide in a solid state
and to study their structure and properties.
The complexes were prepared by the action of dry
phthalates of the corresponding 3d-metals on aqueous
solutions of preliminarily neutralized semicarbazide, in
the ratios metal–semicarbazide 1:2 and 1:4.
To study variations of the phthalate anion function
in coordination compounds upon replacement of one
molecular ligand by another, with a potentially greater
denticity, we have chosen semicarbazide NH2NHC·
(=O)NH2 (L) as such a ligand. Semicarbazide contains
the same donor atoms as nicotinamide (oxygen and
nitrogen), however nicotinamide in complexes is
preferably coordinated in a monodentate mode through
the nitrogen atom of the pyridine cycle, whereas
semicarbazide is capable to be both mono- and bi-
dentate. We have obtained blue and pink isomers of
the coordination compounds of cobalt(II) benzoate
with semicarbazide of the compositions 1:3 and 1:4. In
the 1:4 complex semicarbazide is monodentate and is
coordinated through oxygen, whereas the isomers are
of the ionization type: in the pink complex benzoate-
The chemical analysis (Table 1) shows that the
composition of isolated solid compounds is constant
irrespective of the taken ratio of reagents. Coordination
compounds of cobalt(II) and zinc(II) are similar in
composition: the metal–semicarbazide ratio 1:3, and
the phthalate anion is twice deprotonated. Copper(II)
and nickel(II) phthalates are monodeprotonated, and
the metal-semicarbazide ratio is 1:2 in the copper(II)
complex and 1:4 in the nickel(II) complex. The com-
parison with analogous data for nicotinamide com-
plexes of phthalates of 3d-metals [2, 3] shows that
semicarbazide increases the tendency to the phthalate
anion protonation: among the nicotinamide complexes
of phthalates, the anion HPht– was present only in the
nickel(II) complex, whereas in the copper complexes
503

504
KOKSHAROVA, GRITSENKO
Table 1. Elemental analysis data for the products I–IV of reactions of 3d-metals phthalates with semicarbazide
Found, %
Calculated, %
Comp.
no.
Color
Formula
M
N
M
N
Pink
13.4
28.3
C11H19CoN9O7 ([CoL3]Pht)
13.2
28.1
I
Colorless
Blue
14.7
8.6
28.1
24.2
C11H19N9O7Zn ([ZnL3]Pht)
14.3
8.6
27.8
24.4
II
C20H30N12NiO12 ([NiL4](HPht)2)
III
Dark brown
12.2
15.8
C18H20CuN6O10 ([CuL2](HPht)2)
11.8
15.4
IV
(1:2 and 1:4) the anion Pht2– was retained. The
majority of phthalate complexes with nicotinamide
includes bound water, whereas water is absent from
the analogous semicarbazide compounds. In the com-
plexes of all studied metals, except for copper(II), the
number of coordinated semicarbazide molecules is
greater than the number of coordinated nicotinamide
molecules.
frequency by 30–44 cm–1 and the decrease in the
frequency of δ(O=C–N) is even more essential, 50–
79 cm–1. The ν(C–N) band is shifted to the high-
frequency region, the value of this shift being about
40 cm–1 for complexes with М:L ratios of 1:2 [copper(II)
complex] and 1:3 [cobalt(II) and zinc(II) complexes],
whereas it does not exceed 30 cm–1 for the nickel(II)
complex, in which four coordinated ligands belong to
one metal atom. There are differences also in shifts of
the band ν(C–N) + δ(N–H) + δ(N–N): for the nickel
complex, despite of the equal direction of the shift (in
all cases to the low-frequency region), its value is
slightly less than for all the rest synthesized
compounds. Thus, taking into account a stoichiometry
of the complexes and certain differences in the values
of shifts of absorption bands in the IR spectra, we
should assume that semicarbazide is coordinated
variously: at the M:L ratios 1:2 (the copper complex)
and 1:3 (the cobalt and zinc complexes) it is bidentate
and coordinated to the metals through the oxygen atom
and the nitrogen atom of the hydrazine fragment to
form a five-membered chelate cycle, whereas in the
nickel complex (1:4) it is monodentate and is
coordinated only through the oxygen atom.
If we compare these products with complexes of
the same metals with semicarbazide synthesized
earlier, in which valerate and benzoate were taken as
anions of a salt, it is possible to assume that the
phthalate anion allows only one complex with the most
stable inner sphere to be isolated. So, for cobalt(II)
valerate the compounds 1:2 and 1:3 with semi-
carbazide were isolated, and analogous compounds
were isolated for cobalt(II) benzoate (1:3 and 1:4), i.e.
the complex with the metal–L ratio of 1:3 is
characteristic for both anions [4]. This is the ratio,
which is also realized in the semicarbazide complex of
cobalt(II) phthalate. For other studied complex-
forming agents the composition of the complexes of
phthalates with semicarbazide was the same as in the
complexes of valerates and benzoates.
Comparative analysis of the positions and shapes of
absorption bands in the IR spectra of synthesized
coordination compounds shows that the spectra of
CoL3Pht and ZnL3Pht are very similar, in some regions
these spectra are almost identical (Table 2). The
spectra of copper and nickel compounds are more
specific. It holds true for vibrational frequencies of
both semicarbazide and phthalate anions.
The assignment of bands in the IR spectra of
semicarbazide hydrochloride and of semicarbazide
complexes of 3d-metals phthalates based on the data
[5–7] is given in Table 2. Initial semicarbazide hydro-
chloride contains a protonated amino group, and its IR
spectrum includes the νs and νas(NH3+) bands at 2911,
2670, 1946 cm–1, which are absent from the IR spectra
of the synthesized complexes. As a result of the
complex formation the difference between frequencies
of the symmetric and antisymmetric stretching
vibrations of the amino group substantially increases
(from 54 up to 74–113 cm–1).
To make a diagnosis of a coordination model of
carboxylate groups, a value of Δν(νas – νs), i.e. the
distance between νas and νs is often used [8]. We think
that the value of ΔΔν(COO–), i.e. the difference of
Δν(COO–) values for a mix-ligand complex and the
initial carboxylate, but not Δν(νas – νs), is more
convenient for the interpretation of the IR spectra of
Frequencies of the absorption bands involving
contributions of CO groups vibrations decrease as a
result of the complex formation: ν(C=O) reduces its
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COORDINATION COMPOUNDS OF 3d-METAL PHTHALATES
505
Table 2. IR spectra of semicarbazide (L), phthalates of 3d-metals, and products I–IV of their reactions
Absorption bands (cm–1) of COO– group
Compound
L·HCl
Absorption bands (cm–1) of semicarbazide and phthalate anion
νas(COO–) νs(COO–) Δν(COO–) ΔΔν(COO–)
3425 [ν(NH)], 3314 [νas(NH2)], 3260 [νs(NH2)], 2911, 2670, 1946
[νs, νas (NH3+)], 1687 [ν(C=O)], 1585 [ν(CO) + δ(NH2)], 1524 [ν(C–N)],
1478 [ν(C–N) + δ(NH) + δ(N–N)], 1385 [ν(C–N) + δ(NH2)], 1213,
1182, 1090 [δ(NH2)], 935 [δ(O=C–N)], 770 [π(O=C–N2)], 721 [w(NH2)
or r(NH2)], 562, 512 [ν(C–N) + δ(HNN) + δ(NNC) + δ(OCN) +
δ(NCN)]
CоPht·2H2O
1558
1563a
1398
1383
160
180
3451 [ν(NH)], 3286 [νas(NH2)], 3212 [νs(NH2)], 1645 [ν(C=O)], 1563a
[ν(C–N)], 1444 [ν(C–N) + δ(N–H) + δ(N–N)], 1312 [ν(C–N) + δ(NH2)],
1124, 1154, 1117, 1087, 964 [δ(NH2)], 876 [δ(O=C–N)], 763 [π(O=C–N2)],
722 [w(NH2) or r(NH2)], 529 [ν(C–N) + δ(HNN) + δ(NNC) + δ(OCN) +
δ(NCN)]
–20
–42
I
ZnPht·2H2O
1616
1563a
1394
1383
222
180
3453 [ν(N–H)], 3285 [νas(NH2)], 3192 [νs(NH2)], 1647 [ν(C=O)], 1563a
[ν(C–N)], 1445 [ν(C–N) + δ(N–H) + δ(N–N)], 1312 [ν(C–N) + δ(NH2)],
1123, 1153, 1117, 1087, 1038, 964 [δ(NH2)], 885 [δ(O=C–N)], 771
[π(O=C–N2)], 721 [w(NH2) or r(NH2)], 514 [ν(CN) + δ(HNN) +
δ(NNC) + δ(OCN) + δ(NCN)]
II
NiPht·2H2O
1560
1582
1405
1403
155
179
3402 [ν(N–H)], 3275 [νas(NH2)], 3162 [νs(NH2)], 1643a [ν(C=O)], 1553
[ν(C–N)], 1452 [ν(C–N) + δ(N–H) + δ(N–N)], 1300 [ν(C–N) + δ(NH2)],
1222, 1124, 1025, 965 [δ(NH2)], 856 [δ(O=C–N)], 756 [π(O=C–N2)],
722 [w(NH2) or r(NH2)], 554 [ν(C–N) + δ(HNN) + δ(NNC) + δ(OCN) +
δ(NCN)]
24
III
CuPht·H2O
1530
1594
1410, 1350 120, 180
1391 203
3400 [ν(N–H)], 3290 [νas(NH2)], 3204 [νs(NH2)], 1657 [ν(C=O)], 1565
[ν(C–N)], 1444 [ν(C–N) + δ(N–H) + δ(N–N)], 1300 [ν(C–N) + δ(NH2)],
1214, 1150, 1123, 1087, 1000 [δ(NH2)], 864 [δ(O=C–N)], 762 [π(O=C–N2)],
704 [w(NH2) or r(NH2)], 565 [ν(C–N) + δ(HNN) + δ(NNC) + δ(OCN) +
δ(NCN)]
83, 23
IV
a Both semicarbazide and the phthalate anion make contributions to the absorption band.
the carboxylate complexes. The values of ΔΔν(COO–)
for the synthesized CoL3Pht and ZnL3Pht compounds
have appeared negative, i.e. the difference between
frequencies of antisymmetric and symmetric vibrations
has decreased as a result of the complex formation.
Obviously, it is connected with a certain equalization
of bonds in the phthalate anion. The most probable
reason for such changes can be the displacement of the
phthalate anion into the outer sphere of the complexes.
The negative ΔΔν(COO–) value was observed also in
the IR spectrum of cobalt(II) phthalate with nicotin-
amide, for which outer-sphere position of the phthalate
anion was confirmed by the XRSA method [3].
The IR spectra of copper(II) and nickel(II) com-
plexes confirm the presence of the monoprotonated
outer-sphere phthalate anion. Coordination compounds
of nickel(II), cobalt(II), copper(II), and zinc(II)
phthalates with 1-methyl-imidazole were studied by
the XRSA and IRS methods [1]. In the IR spectra of
the complexes [M(1-MeIm)6](HPht)2·2H2O (M = Co, Ni)
ν(COOH) absorption bands at 1634 cm–1 are present.
In the spectra of the CuL2(HPht)2 and NiL4(HPht)2
complexes similar bands were also recorded: in the
copper(II) spectrum a separate absorption band at
1640 cm–1 is observed, whereas in the case of the
nickel compound NiL4(HPht)2 the ν(COOH) absorp-
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KOKSHAROVA, GRITSENKO
Table 3. Diffusion reflection spectra of semicarbazide com-
plexes of 3d-metals phthalates I, III, IV
To determine the geometry of coordination units,
we have fulfilled the study of the synthesized com-
plexes by the diffusion reflection spectroscopy (Table 3).
The examination of bands positions suggests that the
cobalt(II) complex has the octahedral structure, the
nickel(II) complex, the tetrahedral structure, and the
copper (II), the pseudo-tetrahedral structure [10].
Comp. no.
λmax, nm
495
Assignment
4T1g(F) → 4T1g(P)
4T1g(F) → 4T2g
3T1 → 3T1(P)
3T1 → 1E
I
1188
580
III
IV
895
3T1 → 3A2
The results of the thermogravimetric study of the
synthesized compounds (Table 4) have shown that the
thermal stability of the synthesized semicarbazide
complexes of phthalates of various 3d-metals de-
creases in the sequence: Zn2+ > Ni2+ > Co2+ > Cu2+.
2067
1665
2153
tion band is imposed on the ν(C=O) band of semi-
carbazide at 1643 cm–1, therefore its intensity is
increased and this band becomes the most intensive in
the whole spectrum, whereas it is weaker than other
absorption bands in the spectra of the other
compounds: for CoL3Pht and ZnL3Pht the band at
1563 cm–1 has the greatest intensity and for
CuL2(HPht)2 it is the band at 1391 cm–1. For the
copper(II) compound ΔΔν(COO–) has two values due
to differently bound groups in the initial complex
CuPht·H2O, which was confirmed by the XRD data [9].
For cobalt(II), nickel(II), and copper(II) compounds
the first two effects in the thermograms are endo-
thermic, a similar pattern was observed also for
semicarbazide complexes of these metals with the
valerate anion [4]. For the zinc compound the first
three effects are endothermic. All effects at higher
temperatures are exothermic. Obviously, the endo-
effects correspond to the destruction of chemical bonds
of metals with semicarbazide and acido ligands, and
exoeffects, to burning-out organic fragments.
Table 4. Thermogravimetric data on the thermal stability of semicarbazide complexes of 3d-metals phthalates I–IV
Endoeffects
Exoeffects
Total weight
loss, %
Comp. no.
t, °C
Δm, %
t, °C
Δm, %
92–155 (118)
177–237 (195)
8.2
255–300 (290)
300–350 (340)
350–408 (390)
408–460 (450)
460–500 (490)
320–350 (335)
350–400 (390)
400–450 (435)
450–500 (470)
283–340 (330)
340–400 (360)
216–270 (252)
270–320 (300)
320–350 (340)
350–438 (400)
438–460 (450)
6.6
70.0
I
8.2
8.2
16.7
10.5
7.9
122–202 (152)
220–281 (260)
281–320 (300)
12.2
11.0
3.8
8.7
77.1
II
13.3
8.4
5.3
110–183 (133)
210–270 (225)
90–110 (103)
110–190 (150)
6.2
21.5
8.0
17.1
10.5
24.7
10.6
8.5
56.2
74.2
III
IV
5.5
8.0
7.5
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COORDINATION COMPOUNDS OF 3d-METAL PHTHALATES
507
The data obtained allow us to assign the following
structure to the synthesized compounds of 3d-metals
phthalates with semicarbazide.
KBr. Diffusion reflection spectra (DRS) were recorded
on a Perkin–Elmer Lambda-9 spectrophotometer with
MgO (βMgO 100%) as a standard. The thermogra-
vigrams were taken on a Paulik-Paulik-Erdey derivato-
graph in air at a heating rate of 10 deg min–1.
H
H2N
N
NH2
M
Analytical-grade cobalt(II), nickel(II), copper(II),
and zinc chlorides, phthalic acid, and semicarbazide
hydrochloride were used in the work.
O
NH2
O
C6H4(COO)2
NH
N
H2N
HN
Content of metals in the isolated compounds was
determined by the chelatometry method [11] and those
of nitrogen by the Dumas method [12].
H2
O
H2N
Neutralization of semicarbazide hydrochloride
[13]. A weighted sample of semicarbazide hydro-
chloride L·HCl was dissolved in a minimal quantity of
distilled water. The solution was neutralized by adding
one after the other granules of dry KОН. After addition
of each granule рН was checked by means of the
universal indicator. As soon as рН exceeded seven, the
addition of KОН was stopped. The resulting solution
was evaporated to dryness on a water bath, and hot
anhydrous ethanol was added in portions to the solid
residue. The precipitate of potassium chloride was
separated by filtering off the alcohol solution of
semicarbazide.
I, IV
M = Co (I), Zn (II).
H
H2N
NH2
N
NH2
O
Ni
O
HN
NH2
[C6H4(COO)(COOH)]2
O
O
H2N
NH
H2N
NH2
H2N
N
H
III
Complexes (I, II, IV). The alcohol solution
obtained after neutralization of 0.56 g of semicarbazide
hydrochloride was evaporated to a volume of
1.5 ml, 10 ml of water was added, and 0.0025 mol of a
dry 3d-metal phthalate was added in portions with
stirring. The mixture was stirred up to the formation of
a precipitate, which was filtered off, washed by a
minimal quantity of water, and dried in an desiccator
above СаСl2 to a constant weight.
H2N
NH
NH2
O
[C6H4(COO)(COOH)]2
Cu
O
H2N
HN
NH2
Complex (III). An initial solution of semicarbazide
hydrochloride (0.56 g) was neutralized, the base being
prepared similarly. Dry nickel(II) phthalate (0.0025 mol)
was added to the resulting solution in portions with
stirring and heated up to the full dissolution. A blue
solution was transferred to a porcelain cup and
evaporated at room temperature till the formation of a
precipitate, which was washed out by a minimal
quantity of water, and dried in an desiccator above
СаСl2 to a constant weight.
IV
Thus, the replacement of monodentate nicotinamide
by potentially bidentate semicarbazide in the
complexes of phthalates of 3d-metals increases the
tendency of the phthalate anion to protonation and
decreases its ability to take a position in the inner
sphere of a complex.
EXPERIMENTAL
Complexes with the molar ratio semicarbazide–3d-
metal phthalate of 0.01:0.0025 were obtained
similarly.
The IR spectra were taken on a Perkin–Elmer
SPECTRUM BX II FT-IR instrument in tablets with
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KOKSHAROVA, GRITSENKO
6. Murzubraimov, B. and Shtrempler, G.I., Zh. Neorg.
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