Spectral and thermal studies of divalent transition metal complexes with indole-2-carboxylic acid and 4-substituted hydrazinethiocarbamide

Article abstract of DOI:10.1016/j.saa.2005.05.028

Ternary complexes of Co(II), Ni(II) and Cu(II) with indole-2-carboxylic acid (A) and 4-substituted hydrazinethiocarbamide (L) [4-phenylhydrazinethiocarbamide (L¹), 4-benzylhydrazinethiocarbamide (L²) and 4-(2-propenyl)hydrazinethiocarbamide (L³)] were prepared. The structures of the complexes were proposed by molar conductance, electronic, IR, ¹H NMR, mass spectra as well as thermogravimetric (TG) studies. An octahedral structure is suggested for Co(II), Ni(II) and Cu(II) ternary complexes.

Full text of DOI:10.1016/j.saa.2005.05.028

Spectrochimica Acta Part A 63 (2006) 416–422
Spectral and thermal studies of divalent transition metal complexes with
indole-2-carboxylic acid and 4-substituted hydrazinethiocarbamide
Iman T. Ahmed∗
Chemistry Department, Faculty of Science, El-Minia University, El-Minia 61519, Egypt
Received 10 February 2005; received in revised form 14 May 2005; accepted 18 May 2005
Abstract
Ternary complexes of Co(II), Ni(II) and Cu(II) with indole-2-carboxylic acid (A) and 4-substituted hydrazinethiocarbamide (L) [4-
phenylhydrazinethiocarbamide (L1), 4-benzylhydrazinethiocarbamide (L2) and 4-(2-propenyl)hydrazinethiocarbamide (L3)] were prepared.
The structures of the complexes were proposed by molar conductance, electronic, IR, 1H NMR, mass spectra as well as thermogravimetric
(TG) studies. An octahedral structure is suggested for Co(II), Ni(II) and Cu(II) ternary complexes.
© 2005 Elsevier B.V. All rights reserved.
Keywords: Indole-2-carboxylate transition metal complexes; Hydrazinethiocarbamide complexes; Electronic spectra; IR spectra; Mass spectra
1. Introduction
fore, as a part of our program of the synthesis of several
ternary complexes, we have recently reported the ternary
complexes of divalent transition metal ions with the bio-
logically active N-(2-acetamido)iminodiacetic acid [16–22],
8-hydroxyquinoline [23,24], creatinine [25], mercaptobenza-
zoles [26] and thiosemicarbazide as well as dithiocarbazate
derivatives [21]. The present investigation deals with syn-
thesis and spectral characterization of ternary metal com-
plexes M(II)-4-substituted hydrazinethiocarbamides-indole-
2-caboxylic acid. It is hoped that such study may give further
insight into the type of coordination of these ligands with
Co(II), Ni(II) and Cu(II).
Thiourea and hydrazinethiocarbamide derivatives have
long history as ligands in coordination to a metal via either
sulphur or nitrogen [1]. Hydrazinethiocarbamide is an inter-
esting ligand, not only for the structural chemistry of its mul-
tifunction coordination modes, but also for the formation of
complexeswithantifungal, antimicrobialandantitumorprop-
erties [2–4]. Although metal complexes of hydrazinethio-
carbamide derivatives have been reported either in enol or
keto form [5–13], there are no reports available in the lit-
erature on synthesis or spectral studies of their mixed lig-
and complexes with the polyfunctional donating indole-2-
carboxylic acid. Singh and Parkash [14,15] have been iso-
lated and characterized the complexes of Fe(III), Cu(II),
Hg(II), Pb(II) and Ag(I) with indole-2-carboxylic acid. The
analytical studies for complexes isolated showed the sto-
ichiometry 1:3, 1:2, 1:2, 1:2 and 1:1 (metal:ligand) for
the Fe(III), Cu(II), Hg(II), Pb(II) and Ag(I) complexes,
respectively [14,15]. It seems that the reaction of transi-
tion metals with substituted hydrazinethiocarbamides and
indole-2-carboxylic acid is rather complicated and reac-
tion products depend on the type of ligand used. There-
2. Experimental
2.1. Materials and reagents
The metal salts cobalt(II) chloride, nickel(II) chloride
and copper(II) chloride as well as indole-2-carboxylic
acid were analytical grade (Aldrich) products of a high
purity. 4-Substitutedhydrazinethiocarbamideswere prepared
according to literature 4-phenyhydrazinethiocarbamide
(L1) [27,28], 4-benzylhydrazinethiocarbamide (L2) [28,29]
and 4-(2-propenyl)hydrazinthiocarbamide (L3) [29,30],
the purity of these compounds was verified by thin
layer chromatography (TLC). Spectroscopic grade DMSO
∗
Tel.: +20 862340945; fax: +20 862342601.
E-mail address: h imanth124@yahoo.com.
1386-1425/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2005.05.028

I.T. Ahmed / Spectrochimica Acta Part A 63 (2006) 416–422
417
purchased from Aldrich was used for electronic spectral
measurements.
2.2. Synthesis of ternary metal complexes
In a round bottomed flask an ethanolic solution (10 ml)
containing 5 mmol (0.806 g) of ligand A was added
to an ethanolic solution (10 ml) containing 5 mmol of
each of the following metal salts: CoCl2·6H2O (1.190 g);
NiCl2·6H2O (1.189 g); or CuCl2·2H2O (0.852 g). To
each mixture an ethanolic solution (10 ml) containing
5 mmol of the following 4-substituted hydrazinethiocar-
bamides: 4-phenylhydrazinethiocarbamide (L1) (0.836 g),
4-benzylhydrazinethiocarbamide (L2) (0.906 g) or 4-(2-
propenyl)hydrazinethiocarbamide (L3) (0.656 g) were added
slowly with stirring. The ternary mixture was refluxed for
5 h and then evaporated to half of its volume and left to
cool. The ternary complexes precipitated out, were filtered
and washed thoroughly with distilled H2O and EtOH and
dried in vacuo over P4O10. The microanalytical data of the
isolated chelates along with their decomposition temperature
are listed in Table 1.
2.3. Physical measurements
Melting points have been determined in open glass cap-
illaries on Gallen Kamp melting point apparatus and are
uncorrected. However, all synthesized complexes are decom-
posed at a high temperature (>300 ◦C). The C, H, N, S and
Cl contents of the prepared ternary complexes were deter-
mined by the Microanalytical Unit at Cairo University. Molar
conductance of DMSO solutions of the synthesized ternary
complexes were measured at 25 ◦C using a model 31 YSI
conductivity bridge with conductivity cell constant = 0.10 M.
Thermogravimetric (TG) analysis was performed automati-
cally using a Dupont 9000 thermal analyzer at a heating rate
of 10 ◦C min−1 in a dynamic air atmosphere. Infrared spectra
were recorded in the 4000–200 cm−1 range on FT-IR 1650
(Perkin Elmer) spectrophotometer using KBr disk technique.
A Bruker WM 300 instrument has been used to determine 1H
NMR (300.1 MHz). Mass spectra have been obtained with a
JEOL JMS 600 instrument. Electronic spectra of freshly pre-
pared solutions of the complexes in DMSO were monitored at
25 ◦C in 200–1000 nm range by an Unicam Scanning UV–vis
spectrophotometer model UVA 1000E with an accuracy of
1 nm using matched silica cells of 1.0 cm path length. The
spectrophotometer and its accessories were controlled by
software under Windows to provide advanced operational
facilities.
3. Results and discussion
3.1. Characterization of the ternary metal complexes
The analytical data listed in Table 1 clearly suggested two
formulae [M(A)(L)Cl·H2O]H2O for the Co(II) and Ni(II)

418
I.T. Ahmed / Spectrochimica Acta Part A 63 (2006) 416–422
Table 2
Tentative assignment of the most important IR frequencies (cm−1) of the various synthesized ternary complexes
[M(II)-L1-A
M(II)-L2-A
M(II)-L3-A
Assignment of IR bands
Co(II)
3520
Ni(II)
3525
Cu(II)
–
Co(II)
3510
Ni(II)
3520
Cu(II)
–
Co(II)
3500
Ni(II)
3495
Cu(II)
–
ν(OH) of hydrated and
coordinated H2O
3360
3355
3330
3370
3330
3360
3360
3370
3350
ν(NH) asymm. stretching of
indole-2-carboxylic acid
3280–3200 3265–3210 3280–3190 3260–3200 3245–3170 3270–3190 3280–3140 3275–3160 3280–3150 ν(NH and NH2) of
hydrazinethiocarbamides
ν(COO−) asymm. of
1595
1550
1510
1410
1330
1000
870
1610
1545
1520
1400
1325
1000
890
1600
1550
1500
1390
1330
1000
–
1605
1555
1500
1400
1335
995
1590
1545
1505
1390
1330
1010
865
1610
1550
1510
1400
1340
1000
–
1605
1545
1515
1400
1325
1010
890
1615
1560
1510
1410
1335
1000
885
1610
1550
1510
1400
1330
1000
–
indole-2-carboxylic acid
ν(C C) of indole and aryl
rings
ν(C N) of
hydrazinethiocarbamides
ν(COO−) symm. stretching
of indole-2-carboxylic acid
ν(C S) of
hydrazinethiocarbamides
ν(N N)
hydrazinethiocarbamides
ρr of rocking mode of
coordinated H2O
875
770
765
770
750
770
765
755
750
755
ν(C S) of
hydrazinethiocarbamides
ν(M N) stretching of
475
480
470
490
470
475
480
485
470
indole-NH
M
370
355
370
375
360
355
350
355
350
ν(M S) stretching of
hydrazinethiocarbamides – M
ν(M Cl)
235
212
218
220
230
220
232
235
230
ternary metal complexes and H[M(A)(L)Cl2] for Cu(II)
ternary metal complexes.
complexes do not display noticeable weight losses up to
the relatively high temperature (≈200 ◦C). This behaviour
reveals that such complexes do not contain hydration or coor-
dination water. This is in accordance with the results of the
microanalyses (Table 1) as well as with the infrared spectra
(Table 2). However, at high temperature (>300 ◦C) a weight
loss step is observed containing a rapid decomposition of the
ternary complexes (see Fig. 1).
The TG with the corresponding DTG of Co(II)-indole-
2-carboxylic acid-phenylhydrazinethiocarbamide is shown
in Fig. 2. The TG curve indicates that the complex under
investigation shows a remarkable stability up to ≈200 ◦C.
Above this temperature the complex starts to decompose and
the thermogram exhibits two main distinct steps, which are
maximized at 274 and 478 ◦C on DTG curve. Finally, one
can observe that we have a plateau above 550 ◦C. This cor-
responds to the formation of the metal oxide (CoO) with
The prepared ternary complexes were found to be insol-
uble in water as well as in most common organic sol-
vents. However, they are slightly soluble in DMF and
DMSO. The measured molar conductance values (Λmax) of
10−3 mol dm−3 DMSO solutions of Co(II) and Ni(II) ternary
complexes are in the range 12–19 ꢀ−1 cm2 mol−1 indicating
the non-electrolytic nature of these complexes [31]. On the
otherhand, themolarconductancevaluesoftheternaryCu(II)
complexes found to be in the range 92–112 ꢀ−1 cm2 mol−1
is consistent with a 1:1 electrolyte [31]. The (Λmax) values
obtained are in a good agreement with the values reported for
various complexes measured in DMSO [31]. However, the
non-zero values for the non-electrolyte and relatively high
values for the 1:1 electrolyte complexes could be attributed
to high polarity of solvent.
3.1.1. TG analysis
Thermogravimetric analysis of the various prepared
ternary complexes have been carried out to obtain diagnostic
structural evidence of the suggested molecular formula. Gen-
erally, the TG curves of Co(II) and Ni(II) ternary complexes
indicate the removal of two water molecules in the temper-
ature range up to 200 ◦C. These water molecules may be
removed due to water of hydration and coordination. On the
other hand, the TG curves of the synthesized Cu(II) ternary
Fig. 1. The structure of the ligands.

I.T. Ahmed / Spectrochimica Acta Part A 63 (2006) 416–422
419
structure in admixture with spin-forbidden transition to
doublet states [32]. Accordingly, an octahedral structure
could be suggested for these complexes. The spectra of the
Ni(II) complexes showed a main broad absorption band
in the range 590–610 nm (ε = 5.30–8.60 cm−1 mol−1 L),
depending on the nature of the hydrazinecarbothioamide
derivative ligands. An additional weak absorption band is
also observed around 890 nm (ε = 1.25–1.45 cm−1 mol−1 L).
Six-coordinated and octahedral Ni(II) complexes exhibit
an absorption spectrum involving three allowed transitions
in the ranges 1428–770, 909–500 and 526–370 nm of
comparatively low intensity [32]. Accordingly, an octahedral
structure is suggested for the Ni(II) complexes, where the
observed band in the range 590–610 nm is assigned to
3
3
the A2g (F) → T1g (F) transitions. The weak absorption
3
2
around 890 nm is attributed to the A2g → Eg transition
Fig. 2. TG and DTG curves of the [Co(A)(L1)Cl(H2O)]H2O ternary com-
plex.
[19].
The spectra of the Cu(II) complexes showed a broad band
with λmax at 700–630 nm followed by a broad band into
the near infrared region. It was reported previously that the
majority of six-coordinate Cu(II) complexes have a tetrago-
nal distorted structure giving rise to an absorption band near
630 nm. Therefore, a tetragonal distorted structure is sug-
gested for these complexes. Accordingly, the observed band
the deposition of three moles of carbon giving 24% (calcd.
24.36%).
3.1.2. Electronic spectra
The electronic absorption spectroscopic data of
10−3 mol dm−3 DMSO solutions of the various pre-
pared ternary complexes (for example, Fig. 3) are listed in
Table 1. All the spectra of the ternary complexes showed
a band with λmax at 306–271 nm, may be ascribed to
intermolecular charge-transfer transition from the ligand
molecules to the vacant orbital localized on the metal
ion (L-MCT-transition) [32]. In addition to the above
transitions, the electronic spectra of reddish-brown coloured
Co(III) complexes demonstrate a well-defined absorption
band around 512 nm (ε = 5–40 cm−1 mol−1 L) (Table 1).
It was previously reported that the electronic spectra of
six-coordinated cobalt complexes exhibit a broad absorption
band near 500 nm (ε = 23.24–32.54 cm−1 mol−1 L), which
is assigned to a combination of 2B1g → A1g, 2B1g → B2g
2
2
2
and 2B1g → E1g transitions.
3.1.3. Infrared spectra
Relevant IR bands, which provide conclusive structural
evidence for the ternary complexes prepared, are listed in
Table 2.
Generally, the IR spectra of ligands were compared
with the spectra of the metal complexes. The IR spectra
of the ternary complexes display the broad bands in the
range 3525–3495 cm−1, which could be attributed to the
OH-stretching vibration of hydrated and coordinated water
[33]. The stretching-NH vibration is observed at 3395 cm−1
in indole-2-carboxylic acid [34] shifts to the lower fre-
quencies in the region 3370–3330 cm−1. The lowering of
these frequencies may be attributed to the formation of
nitrogen–metal bond. Furthermore, the sharp band appearing
in the range 1410–1390 cm−1 in the spectra of all synthe-
sized ternary complexes could be attributed to symm. COO−
of indole-2-carboxylic acid. The IR spectra of 4-substituted
hydrazinethiocarbamides show strong bands in the region
3460–3100 cm−1, which may be assigned to NH and NH2
groups. These bands are shifted towards lower wavenumber
in all the complexes (Table 2), suggesting that the NH2 and
hydrazinethiocarbamide-4NH groups are taking part in com-
plex formation [35].
4
is assigned to the 4T1g → T1g(p) transition of an octahedral
The stretching modes of C S of free substituted
hydrazinethiocarbamides observed at 1360 cm−1 [36] is
shifted to lower frequency at 1340–1325 cm−1 range in the
IR spectra of the complexes, revealing the participation of
thione group coordinated with the metal ion. Also, bands
at 770–750 cm−1 are assigned to free ν(C S) [37]. The
Fig. 3. UV–vis electronic absorption spectra of Co(III), Ni(II), and
Cu(II) ternary complexes containing indole-2-carboxylic acid and 4-
phyenylhydrazinethiocarbamide as ligands: (a) [Co(A)(L1)Cl(H2O)]H2O;
(b) [Ni(A)(L1)Cl(H2O)]H2O; (c) H[Cu(A)(L1)Cl2].

420
I.T. Ahmed / Spectrochimica Acta Part A 63 (2006) 416–422
Fig. 4. 1H NMR spectrum of [Co(A)(L1)Cl(H2O)]H2O ternary complex in
DMSO-d6.
Fig. 5. Mass spectrum of [Co(A)(L1)Cl(H2O)]H2O ternary complex.
bands at 1485 cm−1 assigned to ν(C N) are shifted to higher
wavenumbers (1520–1500 cm−1) which is an additional evi-
dence for the contribution of the thione group [38]. The
positive shift in the ν(N N) mode in the spectra of the com-
plexes, indicates the involvement of only one of the hydrazine
nitrogen [39] in coordination.
3.1.4. 1H NMR spectrum of [Co(A)(L1)Cl(H2O)]H2O
The 1H NMR spectrum of [Co(A)(L1)Cl(H2O)]H2O
ternary complex in DMSO-d6 (Fig. 4), in addition to aro-
matic and indole-CH protons shows four broad signals at
6.40, 8.82, 9.42 and 9.87 ppm in 1:1:1:1 ratio, which are down
field from TMS and disappear upon adding D2O. These sig-
nals are attributed to the protons of hydrazinethiocarbamide-
4NH, hydrazinethiocarbamide-2NH[44], indole-NH[45]and
New bands around 490–470, 375–350 and 235–212 cm−1
seemed to be the spectra of complexes which are assigned to
ν(M N) [40], ν(M S) [41,42] and ν(M Cl) [40,43], respec-
tively.
Fig. 6. Representative examples of the structures for the synthesized ternary metal complexes (R = phenyl, benzyl and allyl).

I.T. Ahmed / Spectrochimica Acta Part A 63 (2006) 416–422
421
hydrazinethiocarbamide-1NH [44], respectively. The pres-
ence of the previous signals in the 1H NMR spectrum
of [Co(A)(L1)Cl(H2O)]H2O ternary complex indicates that
substituted hydrazinecarbothioamides act as bidentate lig-
ands via a contribution of hydrazinethiocarbamide-4NH as
well as C S groups in coordination. On the other hand, the
disappearance of carboxylic proton in indole ring indicates
the involvement of carboxylic group in complex formation.
The [CoIII(A)(L1)Cl(H2O)]H2O ternary complexes are dia-
magnetic implying that their preparation proceeds via oxi-
dation of cobalt(II) ions and only cobalt(III) chelates were
isolated. A similar rapid oxidation was reported with many
ligands [46].
ions. Indole-2-carboxylic acid behaves as a mononega-
tive bidentate ligand via indole-NH and COOH groups
(in accordance with the results of 1H NMR and IR spec-
tra) with the displacement of hydrogen atom from the
latter group, forming two five-membered rings as shown
in Fig. 6.
(iv) Theanalyticaldataoftheternarycomplexesunderinves-
tigation would also match for other alternative structures
and could be ruled out on the basis of the above thermal
and spectroscopic data.
(v) Further, the molecular mechanics PM3 program [48]
for the structure of H[Cu(A)(L1)Cl2] complex (Fig. 6),
as examples suggest that the coordination by both the
thiocarbonyl and the NH2 groups towards Cu metal is
more stable (steric energy = 125 kcal/mol) with respect
to the other structure which involved coordination by the
R NH and NH2 groups (steric energy = 248 kcal/mol)
towards the same metal. Moreover, the coordination via
the C S group is more favorable compared with the
RNH group.
3.1.5. Mass spectrum of [Co(A)(L1)Cl(H2O)]H2O
For the complex [Co(A)(L1)Cl(H2O)]H2O, the gross for-
mula C16H18CoClN4SO4, was confirmed by the mass spec-
trometry (Fig. 5). Besides the molecular ion at m/z = 457/459,
the characteristic fragment ion pattern of monohalo com-
pounds was observed [47].
(vi) The metal complexes are insoluble in ethanol, methanol,
acetonitrile and various solvents, but soluble in DMSO.
All attempts to prepare single crystals of the compounds
failed. Thus, no definite structure can be described, but
the analytical and spectroscopic data enable us to predict
the possible structures as shown in Fig. 6.
The mass spectrum shows fragments at 361 (8), 268 (17),
150 (11), 117 (100), 103 (21), and 93 (46). The fragments at
m/z 135 (representing Ph N C S residue), 117 (representing
indole residue), 103 (representing Ph N C residue), and 93
(representing aniline residue) resulting from the cleavage of
Co N and Co S bonds.
The mass spectral fragmentation of the ternary metal
complex [Co(A)(L1)Cl(H2O)]H2O, however, is in agreement
with structure in Fig. 6.
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(i) All complexes are stable on heating up to 200 ◦C, the
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