Cobalt(III) complexes of some aromatic thiohydrazides - Synthesis, characterization and structure

Article abstract of DOI:10.1016/j.ica.2010.01.011

[Co(NH₃)₅Cl]Cl₂ forms neutral 1:3 complex by reaction with aromatic thiohydrazides, i.e. thiobenzhydrazide, o-hydroxythiobenzhydrazide, thiophen-2-thiohydrazide and furan-2-thiohydrazide. All these complexes are diamagneti

Full text of DOI:10.1016/j.ica.2010.01.011

Inorganica Chimica Acta 363 (2010) 1495–1499
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Cobalt(III) complexes of some aromatic thiohydrazides – Synthesis,
characterization and structure
a
b
a
Prodyut Basak a, Snigdha Gangopadhyay a, , Sudipta De , M.G.B. Drew , Pijush Kanti Gangopadhyay
*
a Department of Chemistry, Presidency College, Kolkata 700073, India
b University of Reading, Whitenights, Reading, Berkshire RG6 6AH, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 1 October 2009
Received in revised form 3 January 2010
Accepted 9 January 2010
Available online 15 January 2010
[Co(NH3)5Cl]Cl2 forms neutral 1:3 complex by reaction with aromatic thiohydrazides, i.e. thiobenzhyd-
razide, o-hydroxythiobenzhydrazide, thiophen-2-thiohydrazide and furan-2-thiohydrazide. All these
complexes are diamagnetic and have been characterized by elemental analysis and combination of spec-
troscopic methods. Cyclic voltammometry of the complexes shows irreversible metal centered and ligand
centered electron transfer reactions. One complex, tris-o-hydroxythiobenzhydrazidocobalt(III), has been
crystallized from DMSO solution to produce solvated crystals and its structure has been established by
X-ray crystallography. Cobalt(III) ion is linked through three hydrazinic nitrogen and three sulfur atoms
of three identical deprotonated ligand molecules in a distorted octahedral environment. Involvement of
–OH group in intramolecular and intermolecular hydrogen bonding is crucial for crystal formation.
Ó 2010 Elsevier B.V. All rights reserved.
Keywords:
Cobalt(III)
Thiohydrazides
Synthesis
X-ray crystallography
Intermolecular hydrogen bonding
1. Introduction
2. Experimental
Transition metal ions form a large number of complexes with
ligands having N and S as donor site. Thiourea binds to such me-
tal ions through thioketo group [1–3] while thiosemicarbazides
and thiosemicarbazones may offer various modes of coordina-
tion [4,5]. Moreover, these ligands constitute an important class
of nitrogen–sulfur donor ligands, because of their highly inter-
esting chemical [6–8] and biological properties [9]. The ligands
and their metal complexes have gained special attention due
to their activity against protozoa [10], influenza [11], small pox
viruses [12], fungi [13] and cancer [14]. Thiohydrazides are li-
gands closely related to thiosemicarbazides and may be repre-
Pentaamminechlorocobalt(III)choloride (99.99%) was purchased
from Aldrich Chemicals and was used as a source of cobalt(III). All
solvents used were purified according to standard methods. All
other chemicals were of reagent grade and used without further
purification.
2.1. Preparations
2.1.1. Synthesis of thiobenzhydrazide (Htbh) [15]
Carboxymethyldithiobenzoate (2.12 g) was dissolved in 15 ml
1 M NaOH and cooled in ice. An ice-cold mixture of 1 ml (80%) of
hydrazine hydrate and 10 ml 1 M NaOH was added slowly to this.
The mixture was allowed to stand on an ice bath for 2 h. It was
then neutralized with ice-cold dilute HCl to pH 6. Thiobenzhydraz-
ide separated on cooling the mixture in an ice bath for one hour. It
was collected by filtration, washed with ice-cold water, crystal-
lized from tepid water and dried in vacuum. Yield: 0.80 g. Anal.
Calc. for C7H8N2S: C, 55.26; H, 5.26; N, 18.43; S, 21.05. Found: C,
55.11; H, 5.20; N, 18.38; S, 20.97%.
sented as RC(S)NHNH2 [where R = an alkyl or aryl or
a
heterocyclic group]. These ligands are simpler than thiosemicar-
bazides in the sense that N4 NH2 group is absent here. In the
present communication synthesis of cobalt(III) complexes of thi-
obenzhydrazide (Htbh), o-hydroxythiobenzhydrazide (Hhtbh),
thiophen-2-thiohydrazide (Htth) and furan-2-thiohydrazide
(Hfth) and their characterization by combined spectroscopic
method have been described. The structure of DMSO-solvated
cobalt(III) complex of Hhtbh has been established by the single
crystal X-ray diffraction.
2.1.2. Synthesis of o-hydroxythiobenzhydrazide (Hhtbh) [16]
Freshly distilled salicylaldehyde (10 ml) was dissolved in 30 ml
of ethanol and heated to about 60 °C. To this was added 44 ml of
ammonium polysulfide dropwise with vigorous shaking. The solu-
tion was refluxed for 10 min, cooled to room temperature and fil-
tered. The filtrate was transferred to a separatory funnel, covered
* Corresponding author.
E-mail address: snigdhagangopadhyay@yahoo.com (S. Gangopadhyay).
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.01.011

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P. Basak et al. / Inorganica Chimica Acta 363 (2010) 1495–1499
with ether and acidified with ice-cold 1:1 HCl. The o-hydroxydi-
thiobenzoic acid formed was then extracted with ether. The dark
brown ether layer was washed thoroughly with brine and then
back extracted with several small portions of 10% hydrazine hy-
drate solution. Because of high solubility of the compound, the vol-
ume of combined extract is kept within 50 ml. After keeping the
whole solution for about 40 min at room temperature, it was just
acidified with glacial acetic acid and extracted with ether. o-Hydro-
xy-thiobenzhydrazide obtained on evaporation of ether was
recrystallized from tepid water to afford light yellow crystals.
Yield: 1.8 g. Anal. Calc. for C7H8N2OS: C, 50.00; H, 4.76; N, 16.67;
S, 19.05. Found: C, 49.85; H, 4.69; N, 16.57; S, 18.98%.
NH4OH solution. The resulting solution was then digested on a
boiling water bath for 3–4 h. Brown precipitate was collected by
filtration through a previously weighed sintered glass frit (G-4),
washed with hot water to remove excess reagent and dried to
110 °C. Yield: 98%. Anal. Calc. for Co(C7H7N2OS)3: C, 45.01; H,
3.75; N, 15.00; S, 17.15. Found: C, 44.88; H, 3.52; N, 14.85; S,
16.96%.
2.1.7. Synthesis of Co(tth)3
To the aqueous solution of 25 mg (0.1 mmol) [Co(NH3)5Cl]Cl2,
8–10 drops of concentrated HCl was added with stirring. Calcu-
lated amount of thiophen-2-thiohydrazize (760 mg, 4.5 mmol) dis-
solved in ethanol was added to the stirred solution. 1:1 NH4OH was
added drop wise to maintain the pH near about 6.5–6.7. After the
digestion for 3–4 h the solution afforded brown precipitate which
was collected by filtration through a sintered glass frit (G-4) previ-
ously weighed, washed with hot water and dried to 110 °C. Anal.
Calc. for Co(C5H5N2S2)3: C, 33.97; H, 2.83; N, 15.85; S, 36.23. Found:
C, 33.75; H, 2.69; N, 15.65; S, 36.07%.
2.1.3. Synthesis of thiophen-2-thiohydrazide (Htth) [17]
Freshly distilled thiophen-2-aldehyde (10 ml) was dissolved in
30 ml of ethanol and heated to about 60 °C. To this 44 ml of ammo-
nium polysulfide was added very slowly with continuous shaking.
The solution was boiled for 10 min, cooled to room temperature
and filtered. The filtrate was transferred to a separatory funnel,
covered with ether and acidified with ice-cold 1:1 HCl. The free
acid formed was then extracted with ether. The dark brown ether
layer was washed several times with ice-cold brine and then back
extracted with several 5 ml portions of 10% hydrazine hydrate
solution. The aqueous layer was collected, allowed to stand for
30–40 min at room temperature. It was then neutralized with gla-
cial acetic acid and crystallized from hot water to afford light yel-
low crystals. Yield: 3.0 g. Anal. Calc. for C5H6N2S2: C, 37.97; H, 3.80;
N, 17.72; S, 40.51. Found: C, 38.22; H, 3.67; N, 17.80; S, 40.49%.
2.1.8. Synthesis of Co(fth)3
To the aqueous solution of 25 mg (0.1 mmol) [Co(NH3)5Cl]Cl2,
8–10 drops of concentrated HCl was added with stirring. The solu-
tion was heated nearly to boiling and calculated amount of furan-
2-thiohydrazide dissolved in ethanol was added. The pH of the
solution adjusted to between 6.5 and 6.9 by adding drop wise
1:1 NH4OH solution. The resulting solution was digested on a boil-
ing water bath for 3–4 h. Brown precipitate was collected by filtra-
tion through a sintered glass frit (G-4) previously weighed, washed
with hot water and dried to 110 °C. Yield: 98%. Anal. Calc. for
Co(C5H5N2OS)3: C, 37.35; H, 3.11; N, 17.43; S, 19.92. Found: C,
36.93; H, 2.95; N, 17.17; S, 19.86%.
2.1.4. Synthesis of furan-2-thiohydrazide (Hfth) [17]
Freshly distilled furfural (10 ml) was dissolved in 30 ml of eth-
anol and heated to about 60 °C. Ammonium polysulfide (44 ml)
was added to this with vigorous shaking. The solution was refluxed
for 10 min, cooled to room temperature and filtered. The filtrate
was transferred to a separatory funnel, covered with ether and
acidified with ice-cold 1:1 HCl. The free acid thus formed was ex-
tracted with ether. The dark brown ether layer was washed thor-
oughly with brine and then back extracted with several small
portions of 10% hydrazine hydrate solution. The aqueous layer
was collected, allowed to stand for 40 min at room temperature.
It was then neutralized with glacial acetic acid and the separated
brown solid was collected by filtration. It was then crystallized
from hot water to afford light brown crystals. Yield: 2.5 g. Anal.
Calc. for C5H6N2OS: C, 42.25; H, 4.23; N, 19.72; S, 22.54. Found:
C, 42.00; H, 4.44; N, 19.61; S, 22.45%.
2.2. Physical measurements
Microanalyses (C, H, N, S) were done in IACS, Kolkata using 2400
series II Perkin Elmer, CHNS analyzer. Electronic spectra were re-
corded on a Hitachi 3210 UV–vis spectrophotometer. IR spectra
were obtained on a Unicam 300S spectrometer (4000–300 cmꢀ1
)
with samples prepared as KBr pellets. 1H NMR spectra in d6-DMSO
solutions were obtained on a Brucker DRX 500 spectrometer using
TMS as the internal standard. Cyclic Voltammometric measure-
ments were made with a EG&G Potentiostat model 263A instru-
ment using
a platinum working electrode, a platinum wire
auxiliary electrode and an Ag/AgCl (saturated KCl) as reference
electrode. All cyclic voltammometric experiments were performed
under a nitrogen atmosphere in distilled DMSO solution (0.1 M
TBAP). Cyclic voltammometric data were collected at 298 K and
are uncorrected for junction potential.
2.1.5. Synthesis of Co(tbh)3
An aqueous solution of 25 mg (0.1 mmol) of [Co(NH3)5Cl]Cl2
was acidified with 8–10 drops of concentrated HCl. The solution
was heated nearly to boiling and calculated amount of ligand
(670 mg, 4.5 mmol) dissolved in ethanol was added. The pH of
the solution was adjusted between 6.4 and 6.6 by drop wise addi-
tion of 1:1 NH4OH solution. The resulting solution was digested on
a boiling water bath for 3–4 h. Brown precipitate was collected by
filtration through a sintered glass frit (G-4) previously weighed,
washed with hot water and dried to 110 °C. Yield: 98%. Anal. Calc.
for Co(C7H7N2S)3: C, 49.27; H, 4.10; N, 16.41; S, 18.75. Found: C,
48.92; H, 3.93; N, 16.27; S, 18.42%.
2.3. X-ray crystallography
Deep red flaky crystals of suitable for X-ray crystallography
were obtained from a saturated solution of Co(htbh)3 complex in
DMSO. The crystalline compound was found to have the composi-
tion [Co(htbh)3].3(CH3)2SO. Anal. Calc.: C, 31.74; H, 2.65; N, 10.58;
S, 24.18. Found: C, 31.38; H, 2.34; N, 10.37; S, 23.95%.
Crystallographic data were collected with Mo K
a (k = 0.71073)
radiation at 150 K using the Oxford Diffraction X-Caliber CCD sys-
tem. The crystal was positioned at 50 mm from the CCD. Frames of
321 were measured with a counting time of 10 s. Data analysis was
carried out with the CrysAlis program [18]. The structure was
solved using direct methods with SHELXS97 [19]. The non-hydrogen
atoms were refined with anisotropic thermal parameters. The
hydrogen atoms bonded to carbon and nitrogen were included in
geometric positions and given thermal parameters equivalent to
2.1.6. Synthesis of Co(htbh)3
To an aqueous solution of [Co(NH3)5Cl]Cl2 (25 mg, 0.1 mmol) 8–
10 drops of concentrated HCl were added with constant stirring
and the solution was heated nearly to boiling. Calculated amount
of o-hydroxythiobenzhydrazide (760 mg, 4.5 mmol) dissolved in
ethanol was added to the nearly boiling solution. The pH of the
solution adjusted between 6.4 and 6.8 by adding drop wise 1:1

P. Basak et al. / Inorganica Chimica Acta 363 (2010) 1495–1499
1497
Table 2
1.2 times those of the atom to which they were attached. An
Selected bond lengths (Å) and angles (°) in the metal coordination sphere.
absorption correction was carried out using the ABSPACK program
[20]. The structure was refined on F2 using SHELXL97 [19].
Bonds
Distance (Å)
Bonds
Distance(Å)
Co(1)–S(11)
Co(1)–S(21)
Co(1)–S(31)
Co(1)–N(14)
Co(1)–N(24)
Co(1)–N(34)
N(13)–N(14)
N(33)–N(34)
2.234(1)
2.214(1)
2.217(1)
1.965(3)
1.969(3)
1.963(3)
1.443(4)
1.449(3)
C(12)–S(11)
C(22)–S(21)
C(32)–S(31)
C(12)–N(13)
C(22)–N(23)
C(32)–N(33)
N(23)–N(24)
1.736(3)
1.744(3)
1.741(3)
1.294(4)
1.293(4)
1.290(4)
1.451(3)
3. Results and discussion
3.1. Description of the structure of [Co(htbh)3]ꢁ3(CH3)2SO complex
The crystal data, together with the data collection and structure
refinement parameters are presented in Table 1. The selected bond
lengths and angles were summarized in Table 2. The ORTEP dia-
gram along with the numbering scheme of the compound is pre-
sented in Fig. 1.
The crystal structure of [Co(C7H7N2OS)3]ꢁ3(CH3)2SO contains
discrete Co(C7H7N2OS)3 entities and three DMSO molecules. The
cobalt(III) ions are hexacoordinated with three nitrogen and three
sulfur atoms from three identical ligands forming a facial structure.
The structure shows the cobalt atom in a distorted octahedral
environment being bonded to three bidentate ligands through N
Bonds
Angles (°)
Bonds
Angles (°)
N(34)–Co(1)–N(14)
N(34)–Co(1)–N(24)
N(34)–Co(1)–S(21)
N(14)–Co(1)–S(21)
N(14)–Co(1)–S(31)
S(21)–Co(1)–S(31)
N(14)–Co(1)–S(11)
S(21)–Co(1)–S(11)
90.17(11)
92.94(11)
90.94(8)
85.11(8)
93.28(8)
89.41(3)
84.98(8)
94.12(3)
N(14)–Co(1)–N(24)
N(14)–Co(1)–S(21)
N(14)–Co(1)–S(31)
N(24)–Co(1)–S(31)
N(34)–Co(1)–S(11)
N(24)–Co(1)–S(11)
S(31)–Co(1)–S(11)
92.22(11)
177.16(8)
85.73(8)
174.34(8)
173.25(8)
91.94(8)
89.85(3)
and S. The bond lengths of Co(1)–S(11), Co(1)–S(21) and Co(1)–
0
S(31) are 2.234(1), 2.214(1) and 2.217(1) ÅA respectively while
those of Co(1)–N(14), Co(1)–N(24) and Co(1)–N(34) are 1.965(3),
0
1.969(3) and 1.963(3) ÅA respectively. These bond lengths are simi-
lar to those found in cobalt complexes with methylated isatin and
ferrocene containing thiosemicarbazones [21,22].
The C–S bond lengths in the ligands of 1.736(3), 1.744(3) and
0
1.741(3) ÅA are within the normal range of C–S single bonds, indi-
cating that the thiohydrazide moieties adopt the thiol tautomeric
form [23]. In the ligands, the C–N distances are 1.294(4),
0
1.293(4) and 1.290(4) ÅA while the N–N bond lengths are
0
1.443(4), 1.451(3), 1.449(3) ÅA. Both sets of distances are intermedi-
ate between formal single bond and double bonds, but with the C–
N distances closer to a double bond and the N–N distances closer to
a single bond, thus pointing to an extensive electron delocalization
over the molecular skeleton.
Furthermore, the bond angles in o-hydroxythiobenzhydrazide
ligand of approximately around 117° are also compatible with
the electron delocalization [24].
Table 1
Crystal data and refinement details of the Co(htbh)3ꢁ3(CH3)2SO complex.
Empirical formula
Formula weight
Crystal system
C27H39N6CoO6S6
794.93
Triclinic
ꢀ
Space group
P1
Fig. 1. The structure of Co(htbh)3ꢁ3(CH3)2SO together with the atomic numbering
0
Unit cell dimensions
scheme. Ellipsoids at 50% probability. Hydrogen bonds are shown as dotted lines.
a = 10.7535(17) ÅA
0
b = 12.0000(13) ÅA
0
c = 16.0388(15) ÅA
Table 3
0
a
= 69.933(9)°
Hydrogen bond lengths (AÅ) and angles (°).
b = 85.116(10)°
c
= 66.705(12)°
Donor (D)
Acceptor (A)
Hꢁ ꢁ ꢁA
D–Hꢁ ꢁ ꢁA
Dꢁ ꢁ ꢁA
0
Cell volume
1782.49 ÅA3
2
1.481
0.881
828
O(20)–H(20)
O(30)–H(30)
O(40)–H(40)
N(14)–H(14A)
N(14)–H(14B)
N(14)–H(14B)
N(24)–H(24A)
N(24)–H(24B)
N(34)–H(34A)
N(34)–H(34B)
N(13)
N(23)
N(33)
O(20)a
O(74)
O(64)
O(74)
O(54)
O(54)
O(64)
1.78
1.92
1.78
2.09
2.06
2.53
2.15
2.09
2.07
2.06
147
145
156
169
152
116
141
142
145
150
2.514
2.634
2.579
2.977
2.879
3.033
2.902
2.854
2.861
2.872
Z
Calculated density
Absorption coefficient
F(0 0 0)
Theta range for data collection
Reflections collected/unique [Rint = 0.0282]
Crystal size (mm)
2.30°–30.00°
9933
0.22 ꢂ 0.03 ꢂ 0.03
Completeness to theta
95.6°
Data [I > 2
r
(I)]/parameters
6360/426
0.913
Goodness-of-fit (GOF) on F2
a
Final R indices [I > 2
R indices (all data)
r(I)]
R1 = 0.0563
wR2 = 0.1486
R1 = 0.0880
wR2 = 0.1583
2.249 and ꢀ1.579
Symmetry element ꢀx, 1 ꢀ y, 1 ꢀ z.
0
There is an extensive set of hydrogen bonds in the structure
which are detailed in Table 3. In the three ligands the O–H bonds
Largest differential peak and hole (e ÅAꢀ3
)

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P. Basak et al. / Inorganica Chimica Acta 363 (2010) 1495–1499
Table 5
form hydrogen bonds to the nitrogen atoms, thus O(20)–Hꢁ ꢁ ꢁN(13),
Characteristic infrared absorption data for cobalt(III) thiohydrazide complexes (in
O(30)–Hꢁ ꢁ ꢁN(23) and O(40)–Hꢁ ꢁ ꢁN(33) show Oꢁ ꢁ ꢁN distances of
cmꢀ1).
0
2.514, 2.634 and 2.579 ÅA respectively.
m
H)
(N–
m(C–S)
m
N)
(C–
m
N)
(M–
m
S)
(M–
m
(S–H)
bNH2
In addition the three DMSO molecules, each form two bifur-
cated hydrogen bonds, O(54) to N(24)–H(24B) and N(34)–H(34A)
0
H(tbh)
3280,
3200
3340
1180, 1070
1565,
1450
–
–
2515vw 1595
1590
2590vw 1608
1690
2530vw 1607
1610
at 2.864 and 2.861 ÅA respectively, O(64) to N(34)–H(34B) and
0
N(14)–H(14B) at 2.872, 3.033 0AÅ and O(74) to N(14)–H(14B) and
N(24)–H(24A) at 2.879, 2.902 ÅA. Five of these bonds are relatively
strong with N–Hꢁ ꢁ ꢁO angles in the range 141–152°. However
N(14)–H(14B)ꢁ ꢁ ꢁO(64) is much weaker with a N–Hꢁ ꢁ ꢁO angle of
116°. The reason for this is readily apparent as O(64) is hydrogen
bonded to H(14B) not H(14A) as might be expected. Instead
N(14)–H(14A) forms a strong hydrogen bond to O(20) (ꢀx, 1 ꢀ y,
1 ꢀ z) thus forming a centrosymmetric dimer held together by
two hydrogen bonds.
These hydrogen bonds in between the –OH group of the ben-
zene ring and the hydrazinic nitrogen is important for the success-
ful crystallization. It well may be for that reason that the crystals of
the other cobalt(III)–thiohydrazide complexes are not obtained
since they do not possess the –OH group in ligand moiety. Also
the inclusion of three solvent molecules with their hydrogen bonds
to the complex may also have facilitated the crystallization.
Co(tbh)3
H(htbh)
1160, 1120, 1615,
1070, 760 1480
1175, 1105, 1580,
870
1160, 1100,
820
1295, 1160, 1535,
755 1500
1248, 1150, 1590,
730 1530
1255, 1150, 1585,
820 1545
1241, 1125, 1600,
785 1575
540
–
420
–
–
3300,
3220
1465
1610,
1480
Co(htbh)3 3350
530
–
430
–
–
H(tth)
3280,
3200
3330
Co(tth)3
H(fth)
510
–
420
–
3230
3290
2510vw 1584
1590
Co(fth)3
550
440
plex did not change significantly from those in the free ligands,
these are not recorded. Board bands between 3300 and
3200 cmꢀ1 in the ligands are due to (N–H) stretching of NH2 and
NH groups. The number of bands in the complexes is usually great-
3.2. Electronic spectra
er than those in the ligands. The m(C–N) band (amide II) [27] is ob-
served in the region 1580–1530 cmꢀ1 in the ligands. Their shifts to
higher frequency on complex formation [28] suggest partial double
bond character of C–N bond in the cobalt(III) complexes.
Absorption maxima in the electronic spectra of the cobalt(III)–
thiohydrazide complexes in ethanol and their assignments are
listed in Table 4.
Bands involving
nation of sulfur induces changes in positions and intensities of
bands other than pure C–S stretching frequencies. The (C–S) band
is not found at a particular frequency. Because of coupled vibra-
tions it may occur near (C–N), aromatic (C–C) and dNH2 modes.
In thiosemicarbazide,
(C–S) has been assigned [30] at 803 cmꢀ1
and is reported to have more than 50% contribution from the (C–
S) stretching mode. The intensity ratio
1.38 to 1.5 [31] enables assignment of
and their cobalt(III) complexes. Bands having contributions from
(C–S) are given in Table 5. A very weak band observed around
2510–2590 cmꢀ1 is assigned to
(S–H), attributed to the presence
m(C–S) are often difficult to assign [29]. Coordi-
The electronic spectra of the ethanolic solutions of complexes
exhibit two bands in the region of 252–270 nm (log
4.362) and 310–330 nm (log
= 4.112–4.1085 dm3 cmꢀ1 molꢀ1
attributed to intraligand charge transfer bands and
n ? *, respectively) [25]. The spectra also show peaks in the re-
gion of 420–432 nm (log
= 2.996–3.663 dm3 cmꢀ1 molꢀ1). These
e = 4.185–
m
e
)
(p ? p*
m
m
p
m
e
may arise due to S ? cobalt(III) charge transfer (LMCT) bands.
The d–d transition bands could not be observed because those
were obscured by strong charge transfer bands [26].
m
m
(C@O)/
(C–S) bands in the ligands
m(C@S) ranges from
m
3.3. Infrared spectra
m
of keto-enol tautomerism in the ligand. The weakness of the band
is most probably due to the following equilibrium lying to the left
hand side
The characteristic IR bands (4000–200 cmꢀ1) for the ligands
when compared with those of its cobalt(III) complexes provided
meaningful information regarding the bonding sites of the primary
ligand molecule. Significant bands observed in the IR spectra of the
ligands and the corresponding complexes with their probable
—Cð@SÞ—NH—NH2 $ —CðSHÞ@N—NH2:
The absence of m(S–H) in the complex indicates coordination to
occur through S atom and thioenolisation takes place before com-
assignments are listed in Table 5. Other peaks [
the benzene ring, out of plane(C–H), in plane(C–H) bending,
m
(C–C),
m
(C–H) of
(N–
m
plex formation [31].
N), and b(C–N–N) vibrations] were of course observed in both
reagent and corresponding complex. As their positions in the com-
Metal–nitrogen
frequencies have also been assigned. The
be tentatively assigned [32] at around 510–550 cmꢀ1. In several
m(M–N) and metal–sulfur
m(M–S) stretching
m
(M–N) vibrations may
coordination compounds the m(M–S) band has been assigned at
Table 4
around 380–450 cmꢀ1 [33]. In complexes under study, the bands
observed in the region 420–440 cmꢀ1 may therefore be assigned
to the (M–S) stretch.
Electronic absorption data of the complexes kmax (nm) in ethanol.
Complex
Co(tbh)3
Absorption
Assignment
257.6
310.4
420.4
p ? p*
The bending mode of vibration for –NH2 (bNH2) is observed near
1600 cmꢀ1 in free ligands and these sharp bands suffer a shift to-
wards higher frequency in the complexes indicating complexation
occurs through hydrazinic –NH2 group [34].
n ?
p*
LMCT
Co(htbh)3
Co(tth)3
Co(fth)3
252.8
316.6
420.4
p
?
p*
n ?
p*
LMCT
258.4
318.4
415.2
p
?
p*
3.4. Proton NMR spectra
n ?
p*
LMCT
Table 6 presents chemical shift data for 1H NMR spectra of the
ligands and their cobalt(III) complexes.
270.8
330.8
432.0
p
?
p*
n ?
p*
From the 1H NMR data of all the free ligands and its complexes
it is suggested that position of protons i.e., aromatic and –OH
LMCT

P. Basak et al. / Inorganica Chimica Acta 363 (2010) 1495–1499
1499
Table 6
for providing electrochemistry instrumental facility. Financial
assistance received from the Higher Education Department, Gov-
ernment of West Bengal is gratefully acknowledged.
1H NMR data for ligands and complexes. Chemical shifts (d) are given in ppm, relative
to TMS. Spectra were recorded in d6-DMSO as solvent.
Compound/ligand
Hydrazinic proton
Amidic proton
H(tbh)
6.2
10.80
–
11.75
–
8.2
–
8.25
–
Appendix A. Supplementary material
Co(tbh)3
H(htbh)
Co(htbh)3
H(tth)
Co(tth)3
H(fth)
7.26
5.75
7.008
6.2
7.06
5.24
7.105
CCDC 737525 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif. Supplementary data associated with this article
can be found, in the online version, at doi:10.1016/j.ica.2010.
01.011.
Co(fth)3
protons for H(htbh) remain almost unaltered on complexation and
hence are not recorded in the table. Amidic proton resonance sig-
nals observed in the region d = 8.20–11.75 in the ligands are absent
in the complexes. It signifies involvement of deprotonated ligands
in complexation. The NMR signal of hydrazinic proton underwent a
downfield shift by more than 0.8 ppm in the complexes compared
to the corresponding ligand. The fact suggests that coordination oc-
curs through hydrazinic nitrogen atom [35–37].
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The present study shows that cobalt(III) ion forms sufficiently
stable, diamagnetic, innermetallic, 1:3 complexes with thiohydra-
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From the crystal structure of the Co(htbh)3ꢁ3(CH3)2SO it is evident
that inter and intra molecular hydrogen bonding involving –OH
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complexes cannot be crystallized may be due to the absence of
the –OH group in the ligand moiety. The electronic, IR and proton
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Acknowledgement
The authors thank Dr. P.C. Mondal, Saha Institute of Nuclear
Physics, Kolkata and Dr. Saurav Das, Jadavpur University, Kolkata