Download IJCA 41A(8) 1629-1633

Indian Journal of Chemistry
Vol. 41A August 2002, pp. 1629-1633
Synthesis and spectral studies on copper(II)
and cobalt(II) complexes of macrocyclic
ligand containing thiosemicarbazone moiety
complexes obtained from 3,4,9, 10-tetraphenyl1,2,5,6,8, 11-hexaazacycldodeca-7, 12-dithione2,4,8, I O-tetraene(H 2 L 2 ) structure I .
Experimental
Sulekh Chandra* & Sangeetika
Department of Chemistry, Zakir Husai n College
(University of Delhi) New Delhi 110 002, India
E-Mail : am it 1984@ mantraonline
Received 28 September 2001; revised 15 February 2002
All the chemicals used were of AnalaR grade.
Solvents were purified according to standared
procedures before use.
Preparation of ligand
1
New copper(II) and cobalt(II) complexes of macrocyclic
Schiff base ligand containing thiosemicarbazone moiety have
been prepared with a general composition [M(H 2L 2)X 2] [where
M = Cu(II) or Co(ll); H2L2 = 3,4,9,10-tetraphenyl-1,2,5,6,8,11hexaazacycldodeca-7, 12-dithione-2,4,8, 10-tetraene; X = Cr, N0 3,
'12 SO/, and ML2 [where salt used is copper acetate and cobalt
thiocyanate]. When the mesocycle 6-ethoxy-1,6-diphenyl-4-thio2,3,5-triazine (H 2L 1) in ethanol react with metal salt (chromium
chloride) acting as template using high dilution technique, the
macrocyclic ligand H2 L was formed. The complexes have been
characterized on the basis of elemental analysis, molar
1
conductance, magnetic susceptibility, IR, electronic H NMR,
Mass and EPR spectral studies. The complexes from H2L2 show
different characteristics stoichiometry ratio with a variable grade
of deprotonation in the ligand, depending upon the salt used
[CI", No 3·, '12SO/, CH 3Coo· or SCN"] and working conditions.
I
Schiff base macrocyclic ligands derived from
thiosemicarbazone are of significant interest not only
for their pharmacological properties as antibacterial,
anticancer, antiviral and antifungal agents 1'2 but also
for their capacity for chemical recognition of anions
and
metals
of
biochemical,
medical
and
environmental importance3·5 . They can yield mono- or
polynuclear complexes, some of which are
biologically relevant 6•7 . In particular, first row of
transition metal complexes with such ligands
containing thiosemicarbazone moieties have a wide
range of biological properties 8·9 . The number and
relative proportion of donor atoms and the cavity size
in the macrocyclic compounds gave special reactivity
to these molecules. The most important factors in the
condensation 10 reactions [1+1], [1+2] or [2+2] are
nature of relative proportions of reactants; chain
length and presence of heteroatoms in the precursor
molecules, type of condensation; experimental
conditions such as solvent, pH and temperature.
In the present paper we report the synthesis and
characterization of a series of copper(II) and cobalt(II)
Synthesis of ligand H2L
An
ethanolic
(50
mL)
solution
of
thiosemicarbazide(O.Ol mol, 0.92 gm) was added to
an ethanolic (50 mL) solution of benzil (0.01 mol, 2.1
gm) in the presence of 25 mL of 2M HCI. All the
reagents were added alternatively dropwise with
stirring. After addition of all the reagents, the mixture
was heated with stirring for 7-8 h. On keeping it
overnight, a yellow coloured crystalline solid was
formed, which was filtered, washed with ethanol and
dried in vacuo over P40 10 (yield 70 %, m.pt. 190°C).
structure I
2
Synthesis of macrocyclic ligand H2L
An ethanolic (50 mL) solution of chromium(III)
chloride hydrated (0.001 mol, 0.26 gm) was added to
1
an ethanolic (50 mL) solution of H2L (0.001 mol,
0.31 gm). The mixture was stirred at room
temperature until the cream solid H 2L 2 formed, which
was filtered, washed with ethanol and dried in vacuo
over P40 10 (yield 68 %, m.pt. 170°C) structure I.
PhKPh
NH-N
N-NH
S:C-)-(-C:SI
I
INDIAN J CHEM, SEC A, AUGUST 2002
1630
Preparation of complexes
A warm ethanolic (10 mL) solution of
corresponding metal salt (0.00 l mol) was added to a
warm ethanolic (10 mL) suspension of H2 L 2 (0.001
mol, 0.539 gm). The mixture was heated under reflux
with stirri ng for 2 h. On cooling a coloured complex
precipitated out, which was filtered, washed with
ethanol and dried in vacuo over P4 0 10 (yield 60-70%,
m.pt.- 200°C).
Microanalysis (C, H and N) of these complexes
were carried out on a Carlo-Erba 1106 elemental
analyzer. IR spectra were recorded on a Perkin Elmer
137 instrument as nujol mulls/KBr pellets. Electronic
spectra were recorded in DMSO solution on a
Shimadzu UV mini- 1240 spectrophotometer. Molar
conductance is measured on an ELICO Conductivity
Bridge (Type C M 82 T). Magnetic susceptibility
measurements were made on Gouy Balance at room
temperature using CuS0 4 .5H2 0 as calibrant. Electron
Impact Mass spectra were recorded on JEOL, JMS,
DX-303 mass spectrometer. 1H NMR spectra were
recorded on Hitachi FT-NMR, Model R-600
spectrometer using CDCI 3 as solvent. Chemical shifts
are given in ppm relative to tetramethylsilane. EPR
spectra of the complexes were recorded as powder
samples at room temperature on an E-4 EPR
spectrometer using DPPH as the g- marker. Molecular
weight of the complexes were determined in benzene
(freezing point) .
Results and discussion
The reaction of a H2 L 1 with chromium chloride in
ethanol at room temperature yield a cream solid H2L2
i.e a macrocyclic ligand. The analytical data confirms
the [l+l] and [2+2] condensation of benzil and
thiosemicarbazide (Table l ).
The reaction of mesocycle H2L 1 with chromium
chloride under the described conditions, is the first
direct procedure to isolate a free macrocycle H2 L2
containing
thiosemicarbazone
mOieties.
The
complexes are stable in air and moisture. The
analytical data of the complexes are consistent with
the proposed stoichiometries which are summarized
in Table l .
The mass spectrum of H2L 1 confirms the proposed
formula showing a peak at 311 amu corresponding to
the molecular ion 11 [C 17 H 17 N 30S t . It also shows
series of peaks corresponding to loss of ethanol i.e at
266 amu (M-C 2 H5 0Ht and various fragments. These
data suggests the l + l cyclization of benzil and
thiosemicarbazide.
H2L
1
H2L2
M+
M-OC 2H5+
311
266
530
M- H2L 1+
H2L
H2L
1
2
311
CsHsN3S+
2M++I
178
530
178
Table (-Characterization data of ligands and their complexes
Compound/Molecular
Formula
BM
M
c
H
N
9.25
(9.55)
8.43
(8 .84)
8.98
(9.21)
10.52
( 10.73)
8.66
(8.93)
7.98
(8.26)
8.24
(8.59)
10.15
(10.03)
65.25
(65.57)
67.65
(67.90)
53.98
(54. 17)
50.35
(50.16)
52. 10
(52.20)
60.72
(60.85)
54.35
(54.55)
50.32
(50.49)
52.45
(52.55)
61.48
(61.33)
5.25
(5.51)
3.99
(4.18)
3.12
(3.34)
3.12
(3.08)
2.97
(3.22)
3.58
(3.41)
3.2 1
(3.36)
2.98
(3 . 11)
2.98
(3.24)
3.58
(3.43)
13.24
(13.49)
15.65
(15.84)
12.45
(12.64)
15.32
(15 .61)
11.96
(12.17)
14.29
(14.19)
12.45
( 12.73)
15.42
(15 .71)
11.98
( 12.26)
14.08
(14.30)
1
H2L
CnHnNJOS
2
H2L
C3oH22N6S2
2
[CuH2L Cl2l
CuC3oH22N6S2CI2
2
[CuH2L (N03)2l
CuC3oHn NsS206
2
[CuH2L S04)
CuC3oH22 N6S304
[CuL2)
CuC3oH2oN6S2
2
[CoH2L CI2l
CoC30H22N6S2CI2
2
[CoH 2L (N0Jhl
CoC3oH22NsS20 6
[CoH 2L2S04)
CoC3oH22N6S304
[CoL 2)
CoC3oH2oN6S 2
llerr
Found (Calc.) %
1.92
1.90
2.01
2.04
4.94
4.98
1.94
1.94
NOTES
The mass spectrum of H2L 2 show a peak at 530
amu
corresponding
to
macrocyclic
species
[C 30H22N6S2t- It also shows series of peaks
corresponding to various fragments. Their intensity
gives the idea of stability of fragments.
As reference 12, 1H NMR spectral data of H 2L 1 in
CDC1 3 confirms the absence of terminal amine group
and presence of ethanol inserted, as well as two
signals assigned to the NH group. It exhibit signals in
ppm as : 10. l s(NH), 10.9s(NH), 7.2-7.37m(Ph),
3.6q(CH 2) and 1.5t(CH 3).
The NMR spectrum of H 2 L2 confirms the absence
of ethanol inserted or as a crystallization molecule. It
exihibit signals in ppm as: 10.5s(NH), 8.0-7.1 m(Ph).
The 1H NMR spectra of aceta to complex of copper
and thiocynate complex of cobalt indicates the
deprotonation of the ligands.
The infrared spectra of the ligands and their
complexes give important information regarding the
coordination to the metal ion. The absence of bands in
the region 2600-2800 cm· 1 and its metal complexes
suggest the absence of any thiol tautomer in the solid
state 13- 14.
The IR spectrum of H2L2 shows several bands
between 3398 and 3098 cm· 1 corresponding to N-H
stretching vibrations, which indicates that ligand is
present in neutral form according to the analytical
data. The most significant bands of H 2L2 in KBr are :
3252, 3149 cm· 1 (NH), 1609 cm- 1(CN), 1464
cm- 1(thioamide 1) and 767 cm-1(thioamide 2).
I
The spectra of copper(II) and cobalt(II) complexes
show that the C=N band slightly shifting to higher
frequency indicates that the ligand is bonded to the
metal ion through four imine nitrogen atoms. The
band assigned to thioamide 1 remains at the same
position as in the free ligand which indicates that this
group is not involved in coordination 15 .The IR spectra
of nitrato complexes of Cu(II) and Co(ll) display
multiple bands in the region 1475-1002 cm· 1. So it is
difficult to assign the coordination behaviour of
nitrato group 15. However, there is no broad absorption
band at 1390 em·' which corresponds to
uncoordinated nitrate group. The IR spectra of
sulphato complexes of Cu(II) and Co(ll) show two
bands at 1170 and 1104 em·' (v 3) and 765 and 695
cm- 1(v4) corresponding to unidentate sulphate group.
The sulphato complex posseses C4v symmetry
showing penta-coordination. The IR spectra of
complexes obtained by using copper(II) acetate and
1631
cobalt(II) thiocynate confirm the deprotonation of
ligands.
Copper ( //) complexes
The magnetic moment of all the Cu(II) complexes
at room temperature lie in the range 1.90-2.04 B.M .
(Table I) corresponding to one unpaired electron
which are higher than spin-only value of 1.73 BM for
one unpaired electron. This reveals that these
complexes are monomeric in nature and also shows
the absence of metal-metal interaction along the axial
positions.
Electronic spectra of six-coordinate Cu(Il)
complexes have either D4h or C4v symmetry, and eg
and t 2g level of 2D free ion term will split into 8 lg. A lg·
8 2g and Eg level respectively. Thus the three spin
allowed transitions are expected in the visible and
16
near IR region. But only few complexes are known
in which such bands are resolved. either by Gaussian
Analysis or single crystal polarisation studies. These
bands may be assigned to following transitions, 28 ,8
2
2
2
2
--7 A 1g(d/ -/ --7 dl ) , 8, g--7 8 2g (d/-/--7 dxy ) and 81 8
. order o f .mcreasmg
. en~rgy.
--7 2Eg (dx 2 - y2--7 d xz· d yz ) m
The electronic spectra of the complexes [Cu(H2L )X2l
(X= cr. N0- 3) display two characterstics bands in the
region 20080-22471cm· 1 and 10319-10330 cm· 1.
2
2
2
2
These may be assigned to 8 1g --7 £ 8 and 81 8 --7 A1 8
transitions respectively . The third band assigned to
28 --7 28 transition band is usually not observed as
18
28
a separate band in the tetragonal field . Sulphato
complex of copper display two d-d transition bands at
21276 and 16300 cm· 1 corresponding to transitions
2
2
2
2
2
8 1--7 A 1 and 8 1--7 £ 1. The complex Cu(L ) display
broad band at 17482 em·' and 22471 cm· 1
2
28
2
..
Ig --7 A Ig an d 8 Ig --7
correspon d.mg to transitiOns
2Eg which suggests the square planar geometry 16.
The EPR spectra recorded as polycrystalline
sample posseses a characterstic spectrum having one
asymetric band with two 8 values. The 811 and 8.1
values were computed from the spectrum using DPPH
free radical as '8 ' marker. The '8 ' values and spin
Hamiltonian parameters are summarized in Table 2.
17
Kivelson and Neiman have reported the 811 value <
2.3 for covalent character of the metal-ligand bond
and > 2.3 for ionic character. Applying this criteria,
the covalent character of the metal-ligand bond in the
complexes under study can be predicted. The trend
811> 8.1> 8e(2.0023) observed for these complexes
shows that the unpaired electron is localized in dx\ 2
orbital of the Cu(II) ions and the spectral features are
INDIAN J CHEM, SEC A, AUGUST 2002
1632
Table 2 Complexes
[CuH 2L2CI 2]
2
[CuH 2L (N03hl
2
[CuL ]
[CoH 2L2CI 2]
2
[CoH2L (N0 3h]
2
[CoL ]
[CuH 2L2S0 4]
[CoH 2L2S04)
EPR spectral data of Cu(II) complexes in DMSO and Co(II) complexes at LNT
en
gj_
Cav
G
An
Aj_
Aav
ci
2.069
2.103
2.093
4.813
4.987
4.572
(g3)
2.045
4.987
2.033
2.056
2.050
2.047
2.213
2.017
(g2)
2.032
2.385
2.045
2.072
2.060
2.969
3.137
2.87
(g,)
2.029
2.248
2.091
1.839
1.860
60
60
100
35
35
30
43.34
43.34
53.34
0.286
0.331
0.429
(R)
0.230
0.227
gav = g + 2 gj_/3
characteristic of axial symmetry 18 • The complex under
study may have six-coordinate tetragonal geometry.
In addition, there is exchange coupling interaction
between two copper centres explained
by
19 20
Hathaway • expression G=(8u-2)/(8.L-2). According
to Hathaway, if the value of G is greater than four, the
exchange interaction is negligible, whereas when the
value of G is less than four, a considerable interaction
is indicated in solid complex. The calculated G values
are given in Table 2.
The fraction a 2which is taken as a measure of
2
covalency, is evaluated by the expression. a = (Au/P)
+ (811- 2.0023) + 317(8.L- 2.0023) + 0.04
where A 11 is the parallel coupling constant expressed
in cm· 1 value of P=0.036 . The a 2 values for the
present copper complexes lie in the range 0.286-0.567
supporting the covalent nature of these complexes
(Table 2).
For the EPR spectra of sulphato complex 83 > 82 >
21
8 1 the ratio of (8r8 1)/8 3 -8 2 ) called the parameter R is
very useful. If the ground state is predominantly d//,
the value of R is less than one. On the other hand if
the ground state predominantly d/ the value of R is
greater than one. The complex under study shows the
value of R less than one, thus indicating d// ground
state and may have five coordinate square pyramidal
geometry.
Cobalt( II) complexes
The magnetic moment of cobaJt(II) complexes lie
in the range of 4.95-5.08 BM corresponding to three
unpaired electrons due to contribution of orbital
angular momentum. Whereas, the complex [CoL2]
prepared using thiocyanate salt show magnetic
moment 1.94 BM indicates the low-spin square planar
geometry for cobalt(II) complex (Tablel).
The electronic spectra of [Co(H 2 L2 )X 2 ] (X = Cr,
N0-3) show spin-allowed bands at 10131-11261 cm-1,
22471-23419 cm· 1 along with shoulder at 1447514800 cm- 1 which is not observed in all the
complexes. These transitions may be assigned to 4T 1g
4
4
4
4
4
~ T2g(F), T 18 ~ A2g(F) and T, 8 ~ T,g(P)
respectively. The position of bands indicates that
these complexes have distorted octahedral geometry 16
and might posseses D 411 symmetry. The electronic
spectrum of sulphato complex of cobalt displays three
bands at 10131(v 1) , 11261(v3) and 21000(v4) cm· 1
corresponding to five-coordinate distorted square
pyramidal geometry 24 and might possess C4.,
symmetry . Cobalt(II) complex, Co(L2) di splays
narrow band near 10132 cm· 1 and broader band near
22400 cm· 1 which suggests that the complex has low
spin Co(ll) complex possessing square planar
2
geometr/ .
The various ligand field parameters were calculated
for the cobalt(II) complexes . The value of Dq has
been calculated from transition energy diagrams using
the v 3/v 1 ratio. The value of Dq lies in the range 1144
-1375 cm- 1• Our results corresponds to respective
positions of anions in the spectrochemical series. The
nephelauxetic parameters 13 is readily obtained using
the relation;
13 = B(complex)/B (free ion)
where B(free ion) is 1120 cm· 1• The value of 13 lies
in the range 0.464 - 0.682 . The value of 13 indicates
that the covalent character of metal ligand cr bond is
low. Ligand field stabilization energy calculated for
chloro and nitrato complexes are 109.34, 131.40
respectively.
The EPR spectra of Co(ll) complexes were
recorded as polycrystalline samples. No EPR signal
'
NOTES
1633
7
Belicchi F M, Bisceglie F & Pelosi G, J inorg Biochem,
83(2001)169.
Jouad E M, Riou A, Allian M, Khan M A & Bouet G M,
Polyhedron, 20(2001)67.
Xinde Z, Wang C, Lu Z & Dang Y, Trans met Chern,
22( 1997) 13.
Dietrich 8, Viout P & Lehn J M, Ma crocylic
chemistry(VCH, Weinheim) 1993.
Franco E, Torres E L, Mendiola M A & Sevilla M T,
Polyhedron, 19(2000)441.
Souza P, Mendiola M A, Arquero A, Fernandej V, Gutierrez
P E & Ruiz-Valero C R, Z Naturforch Teil, 849( 1994)263.
Geary W J, Coord chem Rev, 7( 1971 )81.
Fenton 0 E & Cook 0 H, J chem Soc, chem Commun,
(1977)724.
Nakamoto K, lrifrared and Raman spectra of coordination
compounds#(Wiley lnterscience, New York) 1970.
Lever A 8 P, Inorganic electronic spectroscopy, 2"d Edn,
(Elsevier, Amsterdam) 1984.
Kivelson 0 & Neiman R, J chem Phys, 35(1961)149.
was observed at room temperature because the rapid
spin lattice relaxation of Co(ll) broadens the lines at
higher temperature. All the complexes show a very
broad signal at liquid nitrogen temperature. The 'g'
values are given in Table 2. The deviation of 'g'
values from the free electron value (2.0023) may be
due to angular momentum contribution in the
complexes.
8
9
10
II
12
Acknowledgement
We are thankful to the Principal, Zakir Husain
College for providing laboratory facilities and the
DST, New Delhi for financial assistance and liT,
Bombay for recording EPR spectra.
13
14
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