Spectroscopic characterization of tetradentate macrocyclic ligand: It's transition metal complexes

Article abstract of DOI:10.1016/j.saa.2004.01.015

Manganese(II), cobalt(II), nickel(II) and copper(II) complexes are synthesized with a novel tetradentate ligand viz. 1,3,9,11-tetraaza-4,8,12,16- tetraoxo-2,6,10,14-tetrathiacyclohexadecane (L) and characterized by the elemental analysis, molar conductance measurements, magnetic susceptibility measurements, electron impact mass, ¹H NMR, IR, electronic and EPR spectral studies. The molar conductance measurements of the complexes in DMSO correspond to be nonelectrolytic nature for Mn(II), Co(II) and Cu(II) while 1:2 electrolytes for Ni(II) complexes. Thus these complexes may be formulated as [M(L)X₂] and [Ni(L)]X₂ (where M: Mn(II), Co(II), and Cu(II) and X = Cl^- and NO₃^-). On the basis of IR, electronic and EPR spectral studies an octahedral geometry has been assigned for Mn(II) and Co(II) complexes, square-planar for Ni(II) whereas tetragonal for Cu(II) complexes. The ligand and its complexes were also evaluated against the growth of bacteria and pathogenic fungi in vitro.

Full text of DOI:10.1016/j.saa.2004.01.015

Spectrochimica Acta Part A 60 (2004) 2767–2774
Spectroscopic characterization of tetradentate macrocyclic
ligand: it’s transition metal complexes
Sulekh Chandra∗, Lokesh Kumar Gupta
Department of Chemistry, Zakir Husain College, University of Delhi, JLN-Marg, New Delhi 110 002, India
Received 15 December 2003; accepted 13 January 2004
Abstract
Manganese(II), cobalt(II), nickel(II) and copper(II) complexes are synthesized with a novel tetradentate ligand viz. 1,3,9,11-tetraaza-4,8,12,
16-tetraoxo-2,6,10,14-tetrathiacyclohexadecane (L) and characterized by the elemental analysis, molar conductance measurements, magnetic
susceptibility measurements, electron impact mass, 1H NMR, IR, electronic and EPR spectral studies. The molar conductance measurements
of the complexes in DMSO correspond to be nonelectrolytic nature for Mn(II), Co(II) and Cu(II) while 1:2 electrolytes for Ni(II) complexes.
Thus these complexes may be formulated as [M(L)X2] and [Ni(L)]X2 (where M: Mn(II), Co(II), and Cu(II) and X = Cl− and NO3−).
On the basis of IR, electronic and EPR spectral studies an octahedral geometry has been assigned for Mn(II) and Co(II) complexes,
square-planar for Ni(II) whereas tetragonal for Cu(II) complexes. The ligand and its complexes were also evaluated against the growth of
bacteria and pathogenic fungi in vitro.
© 2004 Elsevier B.V. All rights reserved.
Keywords: Macrocyclic; Thiodiglycolic acid; Thiourea and antimicrobial screening
1. Introduction
2. Experimental
The applications of macrocyclic ligands and their tran-
sition metal complexes depends upon the nature of reac-
tants and the corresponding metal ion. The macrocyclic
ligands are a growing class of compounds with varying
chemistry a wide range of different molecular topologies
and sets of donor atoms [1–3]. The chemical properties of
macrocyclic complexes can be tuned to force metal ions
to adopt unusual coordination geometry. Nature prefers
macrocyclic derivatives for many biological fundamen-
tal systems such as photosynthesis and transport of oxy-
gen in mammalian and other respiratory systems [4,5].
In view of the above in this paper we are reporting the
synthesis and spectroscopic characterization of macro-
cyclic Mn(II), Co(II), Ni(II), and Cu(II) complexes with a
novel macrocyclic tetradentate nitrogen donor [N4] ligand
(Fig. 1).
All the chemicals used were of AnalaR grade, and pro-
cured from Sigma–Aldrich. Metal salts were purchased from
E. Merck and were used as received.
2.1. Synthesis of ligand
The hot ethanolic solution (20 ml), of thiodiglycolic acid
(7.50 g, 0.05 mol), and a hot ethanolic solution (20 ml), of
thiourea (3.80 g, 0.05 mol) were mixed slowly with con-
stant stirring. This mixture was refluxed at ∼75 ◦C for 9 h
in the presence of few drops of concentrated hydrochlo-
ric acid. Cooling gave an off-white precipitate, which was
filtered, washed with cold EtOH, and dried under vacuum
over P4O10. Yield 69%, mp 267 ◦C. Elemental analysis
found %(found atomic mass 381 amu), C 31.50; H 3.09;
N 14.70. Calculated for C10H12N4O4S4 (calculated atomic
mass 380 amu), C 31.58; H 3.16 and N 14.74%.
2.2. Synthesis of complexes
∗
Corresponding author. Tel.: +91-11-22911-267;
fax: +91-11-23215-906.
The hot ethanolic (20 ml) solution of ligand (0.760 g,
0.002 mol) and hot ethanolic (20 ml) solution of
E-mail addresses: schandra 00@yahoo.com (S. Chandra),
lokesh kg@rediffmail.com (L.K. Gupta).
1386-1425/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2004.01.015

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S. Chandra, L.K. Gupta / Spectrochimica Acta Part A 60 (2004) 2767–2774
Fig. 1. Preparation and structure of the ligand.
corresponding metal salt (0.001 mol) were mixed together
with constant stirring. The mixture was refluxed for 4–9 h
at 55–80 ◦C. Cooling gives a colored complex. It was fil-
tered, washed with cold EtOH and dried under vacuum over
P4O10.
3. Results and discussion
3.1. Ligand
The electron impact mass spectrum of metal free ligand
confirms the proposed formula by showing a peak at 381 amu
corresponding to the macrocyclic moiety ((C10H12N4O4S4)
atomic mass 380 amu). The series of peaks in the range i.e.
74, 102, 116, 158, 218, 228, 278, 306 amu, etc., may be as-
signed to various fragments. Their intensity gives an idea
2.3. Physical measurements
The C, H and N were analyzed on a Carlo-Erba 1106
elemental analyzer. Molar conductance was measure on
the ELICO (CM82T) conductivity bridge. Magnetic sus-
ceptibility was measured at room temperature on a Gouy
balance using CuSO4·5H2O as a callibrant. Electron impact
mass spectrum was recorded on JEOL, JMS, DX-303 mass
spectrometer. 1H NMR spectrum was recorded on Hi-
tachi FT-NMR, model R-600 spectrometer using CDCl3
as solvent, chemical shifts are given in ppm relative to
tetramethylsilane. IR spectra (KBr) were recorded on
a FTIR Spectrum BX-II spectrophotometer. The elec-
tronic spectra were recorded in DMSO on Shimadzu UV
mini-1240 spectrophotometer. EPR spectra of the com-
plexes were recorded as polycrystalline sample and in the
DMF solution, at liquid nitrogen temperature for Co(II)
and at room temperature for Mn(II) and Cu(II) com-
plexes on E4-EPR spectrometer using the DPPH as the g-
marker.
1
of stability of fragments (Fig. 2). The H NMR spectrum
of the ligand (L) in CDCl3 does not gives any signal corre-
sponding to primary amine and alcoholic protons. It shows
a multiplet at 8.58 ppm corresponding to amide HN–CO,
4H protons [6] and does not show any signal corresponding
to primary amine and alcoholic protons. A multiplet signal
corresponding to methylene proton CO–CH2, 8H that are
adjacent to the nitrogen atom appeared at 3.45 ppm. NMR
spectrum also shows a singlet at 2.33 ppm corresponding to
CO–CH2–S, 8H that is close to sulphur atom [7]. The data
are summarized in the table given below:
1H NMR data (chemical shift in ppm)
CO–CH2
CO–NH
CO–CH2–S
3.45
8.58
2.33
Fig. 2. Electron impact mass spectra of the ligand (L).

S. Chandra, L.K. Gupta / Spectrochimica Acta Part A 60 (2004) 2767–2774
2769
Table 1
Molar conductance and elemental analysis data of the complexes
Complex
MW calculated
Molar conductance
Colour
mp (◦C)
Yield (%)
Elemental analysis data found
(calculated) (%)
(ꢀ−1 cm2 mol−1
)
C
H
N
Metal
[Mn(L)Cl2]
506
559
510
563
510
563
515
568
09
11
Light brown
Light brown
Shiny pink
Dark pink
280
288
69
71
60
61
65
66
74
77
23.62
(23.71)
21.56
(21.47)
23.62
(23.53)
21.20
(21.31)
23.64
(23.53)
21.19
(21.31)
23.51
(23.30)
21.20
2.44
(2.37)
2.22
(2.15)
2.29
(2.35)
2.19
(2.13)
2.47
(2.35)
2.08
(2.13)
2.41
(2.33)
2.17
11.00
(11.07)
14.93
(15.03)
10.92
(10.98)
14.99
(14.92)
11.06
(10.98)
15.00
(14.92)
10.92
(10.87)
14.88
10.80
(10.87)
9.77
(9.84)
11.50
(11.57)
10.59
(10.48)
11.65
(11.57)
10.51
(10.48)
12.32
(12.43)
11.38
C
10H12MnN4O4S4Cl2
[Mn(L)(NO3)2]
10H12MnN6O10S4
C
[Co(L)Cl2]
08
290
C10H12CoN4O4S4Cl2
[Co(L)(NO3)2]
C10H12CoN6O10S4
[Ni(L)]Cl2
07
295
237
225
12
Brick red
>300
>300
291
C
10H12NiN4O4S4Cl2
[Ni(L)](NO3)2
C10H12NiN6O10S4
[Cu(L)Cl2]
Shiny orange
Nilgiri blue
Royal blue
C
10H12CuN4O4S4Cl2
[Cu(L)(NO3)2]
10H12CuN6O10S4
10
286
C
(21.13)
(2.11)
(14.79)
(11.27)
IR spectrum of the ligand does not exhibit any band cor-
trogen of –NH group [N4], which is further supported by
the appearance of a medium intensity band in the range
∼465–483 cm−1 attributed to [ν(M–N)].
responding for the free primary diamine and hydroxyl group
[8]. Four new bands appear in the spectrum of the free ligand
in the regions 1620, 1590, 1248 and 780 cm−1 assignable to
=
amide I [ν(C O)], amide II [ν(C–N) + δ(N–H)], amide III
3.3. IR bands due to anions
=
[δ(N–H)] and amide IV [δ(C O)] bands, respectively [9,10].
Bands at ∼795 and 1478 cm−1 may be due to the thioamides
IR spectra of nitrate complexes display three (N–O)
stretching bands, at ∼1412–1464 cm−1 (ν5), 1307–1315
cm−1 (ν1) and 1005–1044 cm−1 (ν2). The separation of
I and II, respectively. A sharp band observed ∼3278 cm−1
,
may be assigned to [ν(N–H)] of the secondary amino group
[11].
two highest frequency bands (ν5–ν1), ∆ is 103–130 cm−1
.
Suggesting that both the nitrate groups are coordinated to
the central metal ion [12] in unidentate manner.
However, the IR spectrum of Ni(II) nitrate complex
displays a sharp and strong band at 1379 cm−1 which
suggests that the uncoordinated behavior of nitrate group
[12].
3.2. Complexes
On the basis of elemental analysis, the complexes were
assigned to possess the composition shown in Table 1.
The molar conductance measurements of the complexes
in DMSO correspond to be nonelectrolyte nature for
Mn(II), Co(II) and Cu(II) while 1:2 electrolytes for Ni(II)
complexes. Thus, these complexes may be formulated as
[M(L)X2] and [Ni(L)]X2 (where M: Mn(II), Co(II), and
Cu(II) and X: Cl− and NO3−]. On complex formation the
shifting toward lower side of [␯(N–H)] band and the band
of amides II and III, suggest the coordination through ni-
4. Manganese(II) complexes
Manganese(II) complexes show magnetic moment at
room temperature in the range 5.86–5.94 BM corre-
sponding to five unpaired electrons. Electronic spectra
Table 2
Magnetic moment and electronic spectral data of the complexes
Complex
µeff. BM
λmax (cm−1
)
ε (l mol−1 cm−1
)
[Mn(L)Cl2]
[Mn(L)(NO3)2]
[Co(L)Cl2]
[Co(L)(NO3)2]
[Ni(L)]Cl2
[Ni(L)](NO3)2
[Cu(L)Cl2]
5.94
5.86
4.96
5.02
Diamagnetic
Diamagnetic
1.98
17898, 22966, 27126, 36319
18310, 22776, 27434, 38172
10363, 14362, 18622, 35676
10373, 14815, 18742, 37126
14092, 20980, 24228
29, 37, 63, 125
32, 35, 65, 127
66, 75, 84, 142
67, 78, 87, 147
56, 95, 132
13816, 20762, 23876
10996, 18622, 27397
53, 91, 129
53, 59, 153
[Cu(L)(NO3)2]
2.01
11780, 18792, 27397
56, 62, 153

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S. Chandra, L.K. Gupta / Spectrochimica Acta Part A 60 (2004) 2767–2774
Fig. 3. Electronic spectra of the complexes: (A) [Mn(L)Cl2]; (B) [Mn(L)(NO3)2]; (C) [Co(L)Cl2]; (D) [Co(L)(NO3)2]; (E) [Ni(L)Cl2]; and (F)
[Ni(L)(NO3)2].
of Mn(II) complexes, Fig. 3(A–B), exhibit four weak
intensity absorption bands in the range 17,898–18,310 (ε =
29–32 l mol−1 cm−1), 22,779–22,966 (ε = 35–37 l mol−1
The parameter B and C were calculated from the second
and third transitions because these transitions are free from
the crystal field splitting and depend on B and C parameters
[9,10].The calculated values of the ligand field parameters
are given in Table 3.
EPR spectra were recorded at room temperature as poly-
crystalline sample and in solution of DMF Fig. 5(A–D).
The polycrystalline spectra were isotropic and exhibit the
‘g’ value in the range 1.9998–2.0178, (Table 3). In DMSO
cm−1), 27,126–27,434 (ε
=
63–65 mol−1 cm−1), and
36,319–38,172 cm−1 (ε = 137–141 l mol−1 cm−1), Table 2.
6
These bands may be assigned to the transitions: A1g
→
→
4T1g (4G), A1g → Eg, A1g (4G) (10B + 5C), A1g
6
4
4
6
4Eg (4D) (17B + 5C) and A1g → T1g (4P) (7B + 7C),
6
4
respectively.

S. Chandra, L.K. Gupta / Spectrochimica Acta Part A 60 (2004) 2767–2774
2771
Table 3
The electronic spectra of all the cobalt(II) com-
plexes Fig. 3(C–D), display absorption in the region
10,363–10,373 (ε = 66–67 mol−1 cm−1), 14,362–14,815
(ε = 75–78 l mol−1 cm−1), 18,622–18,742 (ε = 84–87 l
mol−1 cm−1) and 35,676–37,126 cm−1 (ε = 142–147 l
mol−1 cm−1). These bands may be assigned to the tran-
Ligand field parameters of the complexes
Complex
Dq
B
C
β
LFSE
ν2/ν1
(cm−1
)
(cm−1
)
(cm−1
)
(kJ mol−1
)
[Mn(L)Cl2]
1790
605
609
700
701
742
728
3383
3337
–
–
–
–
0.77
0.78
0.63 123.81
0.63 123.93
0.71 202.01
0.70 198.14
–
–
1.28
1.24
1.39
1.43
1.49
1.50
[Mn(L)(NO3)2] 1831
[Co(L)Cl2] 1295
[Co(L)(NO3)2] 1297
[Ni(L)]Cl2 1409
[Ni(L)](NO3)2 1382
4
4
4
sitions: T1g(F) → T2g(F) (ν1), T1g
→
4A2g (ν2) and
4T1g(F) → T1g(P) (ν3), respectively [13]. It is difficult to
give the assignments for the fourth band and it may be due
to charge transfer. The position of electronic spectral bands
indicates that these complexes have distorted octahedral
geometry [9,10,12], Fig. 4.
4
The d7 system has the ground state term 4F in an
octahedral crystal field is split into three states. Since
these states are connected by spin-orbit coupling, the spin
lattice-relaxation times are short, making EPR measure-
ments possible only at very low temperature. That is why
EPR spectra of cobalt(II) complexes were recorded as poly-
crystalline sample Fig. 5(E-F) and in DMF solution at liquid
nitrogen temperature (LNT). The g-values were found to be
almost same in both cases in polycrystalline sample as well
as in the solution, (Table 3), it indicates the same geometry.
Table 4
EPR spectral data of the complexes
Complexes
EPR spectral data at room temperature
(at LNT for Co(II))
g
g
giso
G
A◦
||
⊥
[Mn(L)Cl2]
[Mn(L)(NO3)2]
[Co(L)Cl2]
[Co(L)(NO3)2]
[Cu(L)Cl2]
[Cu(L)(NO3)2]
–
–
–
–
1.9998
2.0178
2.1886
2.1735
2.1091
2.1283
–
–
–
–
109.65
112.82
2.7018
2.7458
2.1722
2.2086
1.9320
1.8874
2.0776
2.0882
–
–
–
–
2.2190
2.3650
6. Nickel(II) complexes
solution Mn(II) complexes show EPR spectra containing the
six lines arising due to the hyperfine interaction between the
unpaired electron with the 55Mn nuclear (1 = 5/2). The nu-
clear magnetic quantum number M1, corresponding to these
lines are −5/2, −3/2, −1/2, +1/2, +3/2 and +5/2 from low
to the high field (Table 4).
At room temperature these complexes show the diamag-
netic behavior, indicating the square-planar environment
around the Ni(II) ion, Fig. 4.
The electronic spectra of the Ni(II) complexes ex-
hibit three absorption bands, Fig. 3(E–F) in the range
13,816–14,092 (ε = 53–56l mol−1 cm−1), 20,762–20,980
(ε = 91–95 l mol−1 cm−1), and 23,876–24,228 cm−1 (ε =
129–132 l mol−1 cm−1). Corresponding to square planner
geometry Fig. 4(B). These bands may be assigned to the
5. Cobalt(II) complexes
At room temperature the magnetic moment mea-
surements of cobalt(II) complexes lie in the range
4.96–5.02 BM corresponding to three unpaired electrons,
Table 2.
1
1
three spin allowed transitions: A1g(D) → A2g(G) (ν1),
1A1g(D) → B2g(G) (ν2) and A1g(D) → 1Eg(G) (ν3),
1
1
respectively [13].
Fig. 4. Suggested structure of the complexes (where M: Mn(II), Co(II), and Cu(II) and X: Cl− and NO3−).

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S. Chandra, L.K. Gupta / Spectrochimica Acta Part A 60 (2004) 2767–2774
7. Copper(II) complexes
27,397 cm−1 (ε = 155 l mol−1 cm−1) (ν3), corresponding
to the following transitions [9,13]: 2B1g → A1g (dx2−y2
→
2
2
2
2
2
The magnetic moment of the Cu(II) complexes at room
temperature lie in the range 1.98–2.01 BM corresponding to
one unpaired electron.
dz2 ) ν1, B1g → B2g (dx2−y2 → dzy) ν2 and B1g → B2g
(dx2−y2 → dzy, dyz) ν3, respectively.
Room temperature EPR spectra of Cu(II) complexes were
recorded as polycrystalline sample Fig. 5(G–H) and in the
solution of the DMF, on X-band at frequency 9.5 GHz under
the magnetic field strength 3200 G. Polycrystalline spectra
Electronic spectra of copper(II) complexes display bands
in the range 10,996–11,780 (ε = 53–56 l mol−1 cm−1
)
(ν1), 18,622–18,792 (ε = 59–62 l mol−1 cm−1) (ν2) and
Fig. 5. EPR spectra of the complexes: (A) [Mn(L)Cl2] as polycrystalline sample; (B) [Mn(L)(NO3)2] as polycrystalline sample; (C) [Mn(L)Cl2] in DMF
solution; (D) [Mn(L)(NO3)2] in DMF solution; (E) [Co(L)Cl2] as polycrystalline sample; (F) [Co(L)(NO3)2] as polycrystalline sample; (G) [Cu(L)Cl2]
as polycrystalline sample; and (H) [Cu(L)(NO3)2] as polycrystalline sample.

S. Chandra, L.K. Gupta / Spectrochimica Acta Part A 60 (2004) 2767–2774
2773
Fig. 5. (Continued ).
exhibit a single broad signal [14]. No band correspond-
ing to ꢁMs = 2 transitions was observed in the spec-
trum suggesting Cu–Cu interaction [14]. The absence of
above transition can be explained by assuming the interac-
tion between two paramagnetic centers is negligible [15].
where B (free ion) for Mn(II) is 786, for Ni(II) is 1041 and
for Co(II) is 1120 cm−1 [9,10]. The values of β lie in the
range of 0.63–0.78. These values indicate the appreciable
covalent character of metal ligand ‘␴’ bond.
The analysis of spectra give g = 2.1722–2.2086, g
=
||
||
⊥
2.0776–2.0882. The observed g values for the complexes
9. Antimicrobial screening
are less than 2.3 in agreement with the covalent character of
the metal ligand bond [15]. The trend g > g > 2.0023
||
⊥
The ligand and its transition metal complexes were eval-
uated against different species of bacteria and fungi [17,18].
observed for the complexes indicate that the unpaired elec-
tron is localized in dx2−y2 orbital of the Cu(II) ion and the
spectral figures are characteristic of axial symmetry. Tetrag-
onally elongated structure are thus confirmed for the Cu(II)
complexes.
9.1. Antibacterial screening
The antibacterial action of the ligand and the complexes
of Mn(II), Co(II), Ni(II) and Cu(II) was checked by the
disc diffusion technique. This was done on Sarcina lutea
(gram-positive) and Escherichia coli (gram-negative) bacte-
ria at 25 ◦C. The disc of Whatmann no. 4 filter paper having
the diameter 6.00 mm were soaked in the solution of com-
pounds in DMSO (1.0 mg cm−1). After drying it was placed
on nutrient agar plates. The inhibition areas were observed
after 48 h. DMSO was used as a control and Gentamycin as
a standard drug.
G = (g − 2)/(g − 2), which measure the exchange in-
||
⊥
teraction between the metal centers in a polycrystalline solid
has been calculated. According to Hathaway and Billing
[16] if G > 4, the exchange interaction is negligible but
G < 4 indicates considerable exchange interaction in the
solid complexes. In the complexes, reported in this paper,
the ‘G’ value are in the range 2.2190–2.3650 <4 indicating
the exchange interaction in solid complex.
The bacterial growth inhibition capacity of the complexes
follow the order Cu(II) > Ni(II) > Mn(II) > Co(II), given in
Fig. 6(A).
8. Ligand field parameters
Various ligand field parameters were calculated for the
complexes and are listed in Table 3. The values of Dq in
Co(II) complexes were calculated from transition energy ra-
tio diagram using the ν3/ν2 ratio [13]. Our results are in
agreement with the complexes reported earlier [9,10,14].
The Nephelauxetic parameter β was readily obtained by us-
ing the relation:
9.2. Antifungal screening
The antifungal activity of the ligand and its com-
plexes was checked, by the agar plate technique for the
Aspergillus-niger and Aspergillus-glaucus fungi. The com-
pounds were directly mixed to the medium in different
concentrations. The fungus was placed on the medium with
the help of the inoculum needle. The pettridishes were
B (complex)
β =
B (free ion)

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S. Chandra, L.K. Gupta / Spectrochimica Acta Part A 60 (2004) 2767–2774
where A is the diameter of fungal colony in control plate
and B the diameter of fungal colony in test plate.
The complexes show fungal inhibition in the following
order: Co < Mn < Ni < Cu. Copper(II) complexes exhibits
noble antifungal activity against both the species Fig. 6(B).
Acknowledgements
We are thankful to the Principal, Zakir Husain College for
providing research facilities, RSIC, IIT Mumbai for record-
ing EPR spectra and University Grant Commission, New
Delhi, for financial assistance.
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Fig. 6. Biological screening of the ligand and its complexes: (A) antibac-
terial screening and (B) antifungal screening.
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wrapped in polythene sheets, containing some drops of
EtOH and put in incubator at 30 3 ◦C for 70–90 h. The
growth of fungus was measured by the recording the diam-
eter of fungal colony. The following relation calculated the
fungal growth inhibition:
(A − B)
Fungal growth inhibition (%) =
× 100
A